CGROUPS
-------
-Written by Paul Menage <menage@google.com> based on Documentation/cpusets.txt
+Written by Paul Menage <menage@google.com> based on
+Documentation/cgroups/cpusets.txt
Original copyright statements from cpusets.txt:
Portions Copyright (C) 2004 BULL SA.
tracking. The intention is that other subsystems hook into the generic
cgroup support to provide new attributes for cgroups, such as
accounting/limiting the resources which processes in a cgroup can
-access. For example, cpusets (see Documentation/cpusets.txt) allows
+access. For example, cpusets (see Documentation/cgroups/cpusets.txt) allows
you to associate a set of CPUs and a set of memory nodes with the
tasks in each cgroup.
--- /dev/null
+CPU Accounting Controller
+-------------------------
+
+The CPU accounting controller is used to group tasks using cgroups and
+account the CPU usage of these groups of tasks.
+
+The CPU accounting controller supports multi-hierarchy groups. An accounting
+group accumulates the CPU usage of all of its child groups and the tasks
+directly present in its group.
+
+Accounting groups can be created by first mounting the cgroup filesystem.
+
+# mkdir /cgroups
+# mount -t cgroup -ocpuacct none /cgroups
+
+With the above step, the initial or the parent accounting group
+becomes visible at /cgroups. At bootup, this group includes all the
+tasks in the system. /cgroups/tasks lists the tasks in this cgroup.
+/cgroups/cpuacct.usage gives the CPU time (in nanoseconds) obtained by
+this group which is essentially the CPU time obtained by all the tasks
+in the system.
+
+New accounting groups can be created under the parent group /cgroups.
+
+# cd /cgroups
+# mkdir g1
+# echo $$ > g1
+
+The above steps create a new group g1 and move the current shell
+process (bash) into it. CPU time consumed by this bash and its children
+can be obtained from g1/cpuacct.usage and the same is accumulated in
+/cgroups/cpuacct.usage also.
--- /dev/null
+ CPUSETS
+ -------
+
+Copyright (C) 2004 BULL SA.
+Written by Simon.Derr@bull.net
+
+Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
+Modified by Paul Jackson <pj@sgi.com>
+Modified by Christoph Lameter <clameter@sgi.com>
+Modified by Paul Menage <menage@google.com>
+Modified by Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
+
+CONTENTS:
+=========
+
+1. Cpusets
+ 1.1 What are cpusets ?
+ 1.2 Why are cpusets needed ?
+ 1.3 How are cpusets implemented ?
+ 1.4 What are exclusive cpusets ?
+ 1.5 What is memory_pressure ?
+ 1.6 What is memory spread ?
+ 1.7 What is sched_load_balance ?
+ 1.8 What is sched_relax_domain_level ?
+ 1.9 How do I use cpusets ?
+2. Usage Examples and Syntax
+ 2.1 Basic Usage
+ 2.2 Adding/removing cpus
+ 2.3 Setting flags
+ 2.4 Attaching processes
+3. Questions
+4. Contact
+
+1. Cpusets
+==========
+
+1.1 What are cpusets ?
+----------------------
+
+Cpusets provide a mechanism for assigning a set of CPUs and Memory
+Nodes to a set of tasks. In this document "Memory Node" refers to
+an on-line node that contains memory.
+
+Cpusets constrain the CPU and Memory placement of tasks to only
+the resources within a tasks current cpuset. They form a nested
+hierarchy visible in a virtual file system. These are the essential
+hooks, beyond what is already present, required to manage dynamic
+job placement on large systems.
+
+Cpusets use the generic cgroup subsystem described in
+Documentation/cgroups/cgroups.txt.
+
+Requests by a task, using the sched_setaffinity(2) system call to
+include CPUs in its CPU affinity mask, and using the mbind(2) and
+set_mempolicy(2) system calls to include Memory Nodes in its memory
+policy, are both filtered through that tasks cpuset, filtering out any
+CPUs or Memory Nodes not in that cpuset. The scheduler will not
+schedule a task on a CPU that is not allowed in its cpus_allowed
+vector, and the kernel page allocator will not allocate a page on a
+node that is not allowed in the requesting tasks mems_allowed vector.
+
+User level code may create and destroy cpusets by name in the cgroup
+virtual file system, manage the attributes and permissions of these
+cpusets and which CPUs and Memory Nodes are assigned to each cpuset,
+specify and query to which cpuset a task is assigned, and list the
+task pids assigned to a cpuset.
+
+
+1.2 Why are cpusets needed ?
+----------------------------
+
+The management of large computer systems, with many processors (CPUs),
+complex memory cache hierarchies and multiple Memory Nodes having
+non-uniform access times (NUMA) presents additional challenges for
+the efficient scheduling and memory placement of processes.
+
+Frequently more modest sized systems can be operated with adequate
+efficiency just by letting the operating system automatically share
+the available CPU and Memory resources amongst the requesting tasks.
+
+But larger systems, which benefit more from careful processor and
+memory placement to reduce memory access times and contention,
+and which typically represent a larger investment for the customer,
+can benefit from explicitly placing jobs on properly sized subsets of
+the system.
+
+This can be especially valuable on:
+
+ * Web Servers running multiple instances of the same web application,
+ * Servers running different applications (for instance, a web server
+ and a database), or
+ * NUMA systems running large HPC applications with demanding
+ performance characteristics.
+
+These subsets, or "soft partitions" must be able to be dynamically
+adjusted, as the job mix changes, without impacting other concurrently
+executing jobs. The location of the running jobs pages may also be moved
+when the memory locations are changed.
+
+The kernel cpuset patch provides the minimum essential kernel
+mechanisms required to efficiently implement such subsets. It
+leverages existing CPU and Memory Placement facilities in the Linux
+kernel to avoid any additional impact on the critical scheduler or
+memory allocator code.
+
+
+1.3 How are cpusets implemented ?
+---------------------------------
+
+Cpusets provide a Linux kernel mechanism to constrain which CPUs and
+Memory Nodes are used by a process or set of processes.
+
+The Linux kernel already has a pair of mechanisms to specify on which
+CPUs a task may be scheduled (sched_setaffinity) and on which Memory
+Nodes it may obtain memory (mbind, set_mempolicy).
+
+Cpusets extends these two mechanisms as follows:
+
+ - Cpusets are sets of allowed CPUs and Memory Nodes, known to the
+ kernel.
+ - Each task in the system is attached to a cpuset, via a pointer
+ in the task structure to a reference counted cgroup structure.
+ - Calls to sched_setaffinity are filtered to just those CPUs
+ allowed in that tasks cpuset.
+ - Calls to mbind and set_mempolicy are filtered to just
+ those Memory Nodes allowed in that tasks cpuset.
+ - The root cpuset contains all the systems CPUs and Memory
+ Nodes.
+ - For any cpuset, one can define child cpusets containing a subset
+ of the parents CPU and Memory Node resources.
+ - The hierarchy of cpusets can be mounted at /dev/cpuset, for
+ browsing and manipulation from user space.
+ - A cpuset may be marked exclusive, which ensures that no other
+ cpuset (except direct ancestors and descendents) may contain
+ any overlapping CPUs or Memory Nodes.
+ - You can list all the tasks (by pid) attached to any cpuset.
+
+The implementation of cpusets requires a few, simple hooks
+into the rest of the kernel, none in performance critical paths:
+
+ - in init/main.c, to initialize the root cpuset at system boot.
+ - in fork and exit, to attach and detach a task from its cpuset.
+ - in sched_setaffinity, to mask the requested CPUs by what's
+ allowed in that tasks cpuset.
+ - in sched.c migrate_all_tasks(), to keep migrating tasks within
+ the CPUs allowed by their cpuset, if possible.
+ - in the mbind and set_mempolicy system calls, to mask the requested
+ Memory Nodes by what's allowed in that tasks cpuset.
+ - in page_alloc.c, to restrict memory to allowed nodes.
+ - in vmscan.c, to restrict page recovery to the current cpuset.
+
+You should mount the "cgroup" filesystem type in order to enable
+browsing and modifying the cpusets presently known to the kernel. No
+new system calls are added for cpusets - all support for querying and
+modifying cpusets is via this cpuset file system.
+
+The /proc/<pid>/status file for each task has four added lines,
+displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
+and mems_allowed (on which Memory Nodes it may obtain memory),
+in the two formats seen in the following example:
+
+ Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
+ Cpus_allowed_list: 0-127
+ Mems_allowed: ffffffff,ffffffff
+ Mems_allowed_list: 0-63
+
+Each cpuset is represented by a directory in the cgroup file system
+containing (on top of the standard cgroup files) the following
+files describing that cpuset:
+
+ - cpus: list of CPUs in that cpuset
+ - mems: list of Memory Nodes in that cpuset
+ - memory_migrate flag: if set, move pages to cpusets nodes
+ - cpu_exclusive flag: is cpu placement exclusive?
+ - mem_exclusive flag: is memory placement exclusive?
+ - mem_hardwall flag: is memory allocation hardwalled
+ - memory_pressure: measure of how much paging pressure in cpuset
+
+In addition, the root cpuset only has the following file:
+ - memory_pressure_enabled flag: compute memory_pressure?
+
+New cpusets are created using the mkdir system call or shell
+command. The properties of a cpuset, such as its flags, allowed
+CPUs and Memory Nodes, and attached tasks, are modified by writing
+to the appropriate file in that cpusets directory, as listed above.
+
+The named hierarchical structure of nested cpusets allows partitioning
+a large system into nested, dynamically changeable, "soft-partitions".
+
+The attachment of each task, automatically inherited at fork by any
+children of that task, to a cpuset allows organizing the work load
+on a system into related sets of tasks such that each set is constrained
+to using the CPUs and Memory Nodes of a particular cpuset. A task
+may be re-attached to any other cpuset, if allowed by the permissions
+on the necessary cpuset file system directories.
+
+Such management of a system "in the large" integrates smoothly with
+the detailed placement done on individual tasks and memory regions
+using the sched_setaffinity, mbind and set_mempolicy system calls.
+
+The following rules apply to each cpuset:
+
+ - Its CPUs and Memory Nodes must be a subset of its parents.
+ - It can't be marked exclusive unless its parent is.
+ - If its cpu or memory is exclusive, they may not overlap any sibling.
+
+These rules, and the natural hierarchy of cpusets, enable efficient
+enforcement of the exclusive guarantee, without having to scan all
+cpusets every time any of them change to ensure nothing overlaps a
+exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
+to represent the cpuset hierarchy provides for a familiar permission
+and name space for cpusets, with a minimum of additional kernel code.
+
+The cpus and mems files in the root (top_cpuset) cpuset are
+read-only. The cpus file automatically tracks the value of
+cpu_online_map using a CPU hotplug notifier, and the mems file
+automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,
+nodes with memory--using the cpuset_track_online_nodes() hook.
+
+
+1.4 What are exclusive cpusets ?
+--------------------------------
+
+If a cpuset is cpu or mem exclusive, no other cpuset, other than
+a direct ancestor or descendent, may share any of the same CPUs or
+Memory Nodes.
+
+A cpuset that is mem_exclusive *or* mem_hardwall is "hardwalled",
+i.e. it restricts kernel allocations for page, buffer and other data
+commonly shared by the kernel across multiple users. All cpusets,
+whether hardwalled or not, restrict allocations of memory for user
+space. This enables configuring a system so that several independent
+jobs can share common kernel data, such as file system pages, while
+isolating each job's user allocation in its own cpuset. To do this,
+construct a large mem_exclusive cpuset to hold all the jobs, and
+construct child, non-mem_exclusive cpusets for each individual job.
+Only a small amount of typical kernel memory, such as requests from
+interrupt handlers, is allowed to be taken outside even a
+mem_exclusive cpuset.
+
+
+1.5 What is memory_pressure ?
+-----------------------------
+The memory_pressure of a cpuset provides a simple per-cpuset metric
+of the rate that the tasks in a cpuset are attempting to free up in
+use memory on the nodes of the cpuset to satisfy additional memory
+requests.
+
+This enables batch managers monitoring jobs running in dedicated
+cpusets to efficiently detect what level of memory pressure that job
+is causing.
+
+This is useful both on tightly managed systems running a wide mix of
+submitted jobs, which may choose to terminate or re-prioritize jobs that
+are trying to use more memory than allowed on the nodes assigned them,
+and with tightly coupled, long running, massively parallel scientific
+computing jobs that will dramatically fail to meet required performance
+goals if they start to use more memory than allowed to them.
+
+This mechanism provides a very economical way for the batch manager
+to monitor a cpuset for signs of memory pressure. It's up to the
+batch manager or other user code to decide what to do about it and
+take action.
+
+==> Unless this feature is enabled by writing "1" to the special file
+ /dev/cpuset/memory_pressure_enabled, the hook in the rebalance
+ code of __alloc_pages() for this metric reduces to simply noticing
+ that the cpuset_memory_pressure_enabled flag is zero. So only
+ systems that enable this feature will compute the metric.
+
+Why a per-cpuset, running average:
+
+ Because this meter is per-cpuset, rather than per-task or mm,
+ the system load imposed by a batch scheduler monitoring this
+ metric is sharply reduced on large systems, because a scan of
+ the tasklist can be avoided on each set of queries.
+
+ Because this meter is a running average, instead of an accumulating
+ counter, a batch scheduler can detect memory pressure with a
+ single read, instead of having to read and accumulate results
+ for a period of time.
+
+ Because this meter is per-cpuset rather than per-task or mm,
+ the batch scheduler can obtain the key information, memory
+ pressure in a cpuset, with a single read, rather than having to
+ query and accumulate results over all the (dynamically changing)
+ set of tasks in the cpuset.
+
+A per-cpuset simple digital filter (requires a spinlock and 3 words
+of data per-cpuset) is kept, and updated by any task attached to that
+cpuset, if it enters the synchronous (direct) page reclaim code.
+
+A per-cpuset file provides an integer number representing the recent
+(half-life of 10 seconds) rate of direct page reclaims caused by
+the tasks in the cpuset, in units of reclaims attempted per second,
+times 1000.
+
+
+1.6 What is memory spread ?
+---------------------------
+There are two boolean flag files per cpuset that control where the
+kernel allocates pages for the file system buffers and related in
+kernel data structures. They are called 'memory_spread_page' and
+'memory_spread_slab'.
+
+If the per-cpuset boolean flag file 'memory_spread_page' is set, then
+the kernel will spread the file system buffers (page cache) evenly
+over all the nodes that the faulting task is allowed to use, instead
+of preferring to put those pages on the node where the task is running.
+
+If the per-cpuset boolean flag file 'memory_spread_slab' is set,
+then the kernel will spread some file system related slab caches,
+such as for inodes and dentries evenly over all the nodes that the
+faulting task is allowed to use, instead of preferring to put those
+pages on the node where the task is running.
+
+The setting of these flags does not affect anonymous data segment or
+stack segment pages of a task.
+
+By default, both kinds of memory spreading are off, and memory
+pages are allocated on the node local to where the task is running,
+except perhaps as modified by the tasks NUMA mempolicy or cpuset
+configuration, so long as sufficient free memory pages are available.
+
+When new cpusets are created, they inherit the memory spread settings
+of their parent.
+
+Setting memory spreading causes allocations for the affected page
+or slab caches to ignore the tasks NUMA mempolicy and be spread
+instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
+mempolicies will not notice any change in these calls as a result of
+their containing tasks memory spread settings. If memory spreading
+is turned off, then the currently specified NUMA mempolicy once again
+applies to memory page allocations.
+
+Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
+files. By default they contain "0", meaning that the feature is off
+for that cpuset. If a "1" is written to that file, then that turns
+the named feature on.
+
+The implementation is simple.
+
+Setting the flag 'memory_spread_page' turns on a per-process flag
+PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
+joins that cpuset. The page allocation calls for the page cache
+is modified to perform an inline check for this PF_SPREAD_PAGE task
+flag, and if set, a call to a new routine cpuset_mem_spread_node()
+returns the node to prefer for the allocation.
+
+Similarly, setting 'memory_spread_slab' turns on the flag
+PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
+pages from the node returned by cpuset_mem_spread_node().
+
+The cpuset_mem_spread_node() routine is also simple. It uses the
+value of a per-task rotor cpuset_mem_spread_rotor to select the next
+node in the current tasks mems_allowed to prefer for the allocation.
+
+This memory placement policy is also known (in other contexts) as
+round-robin or interleave.
+
+This policy can provide substantial improvements for jobs that need
+to place thread local data on the corresponding node, but that need
+to access large file system data sets that need to be spread across
+the several nodes in the jobs cpuset in order to fit. Without this
+policy, especially for jobs that might have one thread reading in the
+data set, the memory allocation across the nodes in the jobs cpuset
+can become very uneven.
+
+1.7 What is sched_load_balance ?
+--------------------------------
+
+The kernel scheduler (kernel/sched.c) automatically load balances
+tasks. If one CPU is underutilized, kernel code running on that
+CPU will look for tasks on other more overloaded CPUs and move those
+tasks to itself, within the constraints of such placement mechanisms
+as cpusets and sched_setaffinity.
+
+The algorithmic cost of load balancing and its impact on key shared
+kernel data structures such as the task list increases more than
+linearly with the number of CPUs being balanced. So the scheduler
+has support to partition the systems CPUs into a number of sched
+domains such that it only load balances within each sched domain.
+Each sched domain covers some subset of the CPUs in the system;
+no two sched domains overlap; some CPUs might not be in any sched
+domain and hence won't be load balanced.
+
+Put simply, it costs less to balance between two smaller sched domains
+than one big one, but doing so means that overloads in one of the
+two domains won't be load balanced to the other one.
+
+By default, there is one sched domain covering all CPUs, except those
+marked isolated using the kernel boot time "isolcpus=" argument.
+
+This default load balancing across all CPUs is not well suited for
+the following two situations:
+ 1) On large systems, load balancing across many CPUs is expensive.
+ If the system is managed using cpusets to place independent jobs
+ on separate sets of CPUs, full load balancing is unnecessary.
+ 2) Systems supporting realtime on some CPUs need to minimize
+ system overhead on those CPUs, including avoiding task load
+ balancing if that is not needed.
+
+When the per-cpuset flag "sched_load_balance" is enabled (the default
+setting), it requests that all the CPUs in that cpusets allowed 'cpus'
+be contained in a single sched domain, ensuring that load balancing
+can move a task (not otherwised pinned, as by sched_setaffinity)
+from any CPU in that cpuset to any other.
+
+When the per-cpuset flag "sched_load_balance" is disabled, then the
+scheduler will avoid load balancing across the CPUs in that cpuset,
+--except-- in so far as is necessary because some overlapping cpuset
+has "sched_load_balance" enabled.
+
+So, for example, if the top cpuset has the flag "sched_load_balance"
+enabled, then the scheduler will have one sched domain covering all
+CPUs, and the setting of the "sched_load_balance" flag in any other
+cpusets won't matter, as we're already fully load balancing.
+
+Therefore in the above two situations, the top cpuset flag
+"sched_load_balance" should be disabled, and only some of the smaller,
+child cpusets have this flag enabled.
+
+When doing this, you don't usually want to leave any unpinned tasks in
+the top cpuset that might use non-trivial amounts of CPU, as such tasks
+may be artificially constrained to some subset of CPUs, depending on
+the particulars of this flag setting in descendent cpusets. Even if
+such a task could use spare CPU cycles in some other CPUs, the kernel
+scheduler might not consider the possibility of load balancing that
+task to that underused CPU.
+
+Of course, tasks pinned to a particular CPU can be left in a cpuset
+that disables "sched_load_balance" as those tasks aren't going anywhere
+else anyway.
+
+There is an impedance mismatch here, between cpusets and sched domains.
+Cpusets are hierarchical and nest. Sched domains are flat; they don't
+overlap and each CPU is in at most one sched domain.
+
+It is necessary for sched domains to be flat because load balancing
+across partially overlapping sets of CPUs would risk unstable dynamics
+that would be beyond our understanding. So if each of two partially
+overlapping cpusets enables the flag 'sched_load_balance', then we
+form a single sched domain that is a superset of both. We won't move
+a task to a CPU outside it cpuset, but the scheduler load balancing
+code might waste some compute cycles considering that possibility.
+
+This mismatch is why there is not a simple one-to-one relation
+between which cpusets have the flag "sched_load_balance" enabled,
+and the sched domain configuration. If a cpuset enables the flag, it
+will get balancing across all its CPUs, but if it disables the flag,
+it will only be assured of no load balancing if no other overlapping
+cpuset enables the flag.
+
+If two cpusets have partially overlapping 'cpus' allowed, and only
+one of them has this flag enabled, then the other may find its
+tasks only partially load balanced, just on the overlapping CPUs.
+This is just the general case of the top_cpuset example given a few
+paragraphs above. In the general case, as in the top cpuset case,
+don't leave tasks that might use non-trivial amounts of CPU in
+such partially load balanced cpusets, as they may be artificially
+constrained to some subset of the CPUs allowed to them, for lack of
+load balancing to the other CPUs.
+
+1.7.1 sched_load_balance implementation details.
+------------------------------------------------
+
+The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
+to most cpuset flags.) When enabled for a cpuset, the kernel will
+ensure that it can load balance across all the CPUs in that cpuset
+(makes sure that all the CPUs in the cpus_allowed of that cpuset are
+in the same sched domain.)
+
+If two overlapping cpusets both have 'sched_load_balance' enabled,
+then they will be (must be) both in the same sched domain.
+
+If, as is the default, the top cpuset has 'sched_load_balance' enabled,
+then by the above that means there is a single sched domain covering
+the whole system, regardless of any other cpuset settings.
+
+The kernel commits to user space that it will avoid load balancing
+where it can. It will pick as fine a granularity partition of sched
+domains as it can while still providing load balancing for any set
+of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
+
+The internal kernel cpuset to scheduler interface passes from the
+cpuset code to the scheduler code a partition of the load balanced
+CPUs in the system. This partition is a set of subsets (represented
+as an array of cpumask_t) of CPUs, pairwise disjoint, that cover all
+the CPUs that must be load balanced.
+
+Whenever the 'sched_load_balance' flag changes, or CPUs come or go
+from a cpuset with this flag enabled, or a cpuset with this flag
+enabled is removed, the cpuset code builds a new such partition and
+passes it to the scheduler sched domain setup code, to have the sched
+domains rebuilt as necessary.
+
+This partition exactly defines what sched domains the scheduler should
+setup - one sched domain for each element (cpumask_t) in the partition.
+
+The scheduler remembers the currently active sched domain partitions.
+When the scheduler routine partition_sched_domains() is invoked from
+the cpuset code to update these sched domains, it compares the new
+partition requested with the current, and updates its sched domains,
+removing the old and adding the new, for each change.
+
+
+1.8 What is sched_relax_domain_level ?
+--------------------------------------
+
+In sched domain, the scheduler migrates tasks in 2 ways; periodic load
+balance on tick, and at time of some schedule events.
+
+When a task is woken up, scheduler try to move the task on idle CPU.
+For example, if a task A running on CPU X activates another task B
+on the same CPU X, and if CPU Y is X's sibling and performing idle,
+then scheduler migrate task B to CPU Y so that task B can start on
+CPU Y without waiting task A on CPU X.
+
+And if a CPU run out of tasks in its runqueue, the CPU try to pull
+extra tasks from other busy CPUs to help them before it is going to
+be idle.
+
+Of course it takes some searching cost to find movable tasks and/or
+idle CPUs, the scheduler might not search all CPUs in the domain
+everytime. In fact, in some architectures, the searching ranges on
+events are limited in the same socket or node where the CPU locates,
+while the load balance on tick searchs all.
+
+For example, assume CPU Z is relatively far from CPU X. Even if CPU Z
+is idle while CPU X and the siblings are busy, scheduler can't migrate
+woken task B from X to Z since it is out of its searching range.
+As the result, task B on CPU X need to wait task A or wait load balance
+on the next tick. For some applications in special situation, waiting
+1 tick may be too long.
+
+The 'sched_relax_domain_level' file allows you to request changing
+this searching range as you like. This file takes int value which
+indicates size of searching range in levels ideally as follows,
+otherwise initial value -1 that indicates the cpuset has no request.
+
+ -1 : no request. use system default or follow request of others.
+ 0 : no search.
+ 1 : search siblings (hyperthreads in a core).
+ 2 : search cores in a package.
+ 3 : search cpus in a node [= system wide on non-NUMA system]
+ ( 4 : search nodes in a chunk of node [on NUMA system] )
+ ( 5 : search system wide [on NUMA system] )
+
+The system default is architecture dependent. The system default
+can be changed using the relax_domain_level= boot parameter.
+
+This file is per-cpuset and affect the sched domain where the cpuset
+belongs to. Therefore if the flag 'sched_load_balance' of a cpuset
+is disabled, then 'sched_relax_domain_level' have no effect since
+there is no sched domain belonging the cpuset.
+
+If multiple cpusets are overlapping and hence they form a single sched
+domain, the largest value among those is used. Be careful, if one
+requests 0 and others are -1 then 0 is used.
+
+Note that modifying this file will have both good and bad effects,
+and whether it is acceptable or not will be depend on your situation.
+Don't modify this file if you are not sure.
+
+If your situation is:
+ - The migration costs between each cpu can be assumed considerably
+ small(for you) due to your special application's behavior or
+ special hardware support for CPU cache etc.
+ - The searching cost doesn't have impact(for you) or you can make
+ the searching cost enough small by managing cpuset to compact etc.
+ - The latency is required even it sacrifices cache hit rate etc.
+then increasing 'sched_relax_domain_level' would benefit you.
+
+
+1.9 How do I use cpusets ?
+--------------------------
+
+In order to minimize the impact of cpusets on critical kernel
+code, such as the scheduler, and due to the fact that the kernel
+does not support one task updating the memory placement of another
+task directly, the impact on a task of changing its cpuset CPU
+or Memory Node placement, or of changing to which cpuset a task
+is attached, is subtle.
+
+If a cpuset has its Memory Nodes modified, then for each task attached
+to that cpuset, the next time that the kernel attempts to allocate
+a page of memory for that task, the kernel will notice the change
+in the tasks cpuset, and update its per-task memory placement to
+remain within the new cpusets memory placement. If the task was using
+mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
+its new cpuset, then the task will continue to use whatever subset
+of MPOL_BIND nodes are still allowed in the new cpuset. If the task
+was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
+in the new cpuset, then the task will be essentially treated as if it
+was MPOL_BIND bound to the new cpuset (even though its numa placement,
+as queried by get_mempolicy(), doesn't change). If a task is moved
+from one cpuset to another, then the kernel will adjust the tasks
+memory placement, as above, the next time that the kernel attempts
+to allocate a page of memory for that task.
+
+If a cpuset has its 'cpus' modified, then each task in that cpuset
+will have its allowed CPU placement changed immediately. Similarly,
+if a tasks pid is written to a cpusets 'tasks' file, in either its
+current cpuset or another cpuset, then its allowed CPU placement is
+changed immediately. If such a task had been bound to some subset
+of its cpuset using the sched_setaffinity() call, the task will be
+allowed to run on any CPU allowed in its new cpuset, negating the
+affect of the prior sched_setaffinity() call.
+
+In summary, the memory placement of a task whose cpuset is changed is
+updated by the kernel, on the next allocation of a page for that task,
+but the processor placement is not updated, until that tasks pid is
+rewritten to the 'tasks' file of its cpuset. This is done to avoid
+impacting the scheduler code in the kernel with a check for changes
+in a tasks processor placement.
+
+Normally, once a page is allocated (given a physical page
+of main memory) then that page stays on whatever node it
+was allocated, so long as it remains allocated, even if the
+cpusets memory placement policy 'mems' subsequently changes.
+If the cpuset flag file 'memory_migrate' is set true, then when
+tasks are attached to that cpuset, any pages that task had
+allocated to it on nodes in its previous cpuset are migrated
+to the tasks new cpuset. The relative placement of the page within
+the cpuset is preserved during these migration operations if possible.
+For example if the page was on the second valid node of the prior cpuset
+then the page will be placed on the second valid node of the new cpuset.
+
+Also if 'memory_migrate' is set true, then if that cpusets
+'mems' file is modified, pages allocated to tasks in that
+cpuset, that were on nodes in the previous setting of 'mems',
+will be moved to nodes in the new setting of 'mems.'
+Pages that were not in the tasks prior cpuset, or in the cpusets
+prior 'mems' setting, will not be moved.
+
+There is an exception to the above. If hotplug functionality is used
+to remove all the CPUs that are currently assigned to a cpuset,
+then all the tasks in that cpuset will be moved to the nearest ancestor
+with non-empty cpus. But the moving of some (or all) tasks might fail if
+cpuset is bound with another cgroup subsystem which has some restrictions
+on task attaching. In this failing case, those tasks will stay
+in the original cpuset, and the kernel will automatically update
+their cpus_allowed to allow all online CPUs. When memory hotplug
+functionality for removing Memory Nodes is available, a similar exception
+is expected to apply there as well. In general, the kernel prefers to
+violate cpuset placement, over starving a task that has had all
+its allowed CPUs or Memory Nodes taken offline.
+
+There is a second exception to the above. GFP_ATOMIC requests are
+kernel internal allocations that must be satisfied, immediately.
+The kernel may drop some request, in rare cases even panic, if a
+GFP_ATOMIC alloc fails. If the request cannot be satisfied within
+the current tasks cpuset, then we relax the cpuset, and look for
+memory anywhere we can find it. It's better to violate the cpuset
+than stress the kernel.
+
+To start a new job that is to be contained within a cpuset, the steps are:
+
+ 1) mkdir /dev/cpuset
+ 2) mount -t cgroup -ocpuset cpuset /dev/cpuset
+ 3) Create the new cpuset by doing mkdir's and write's (or echo's) in
+ the /dev/cpuset virtual file system.
+ 4) Start a task that will be the "founding father" of the new job.
+ 5) Attach that task to the new cpuset by writing its pid to the
+ /dev/cpuset tasks file for that cpuset.
+ 6) fork, exec or clone the job tasks from this founding father task.
+
+For example, the following sequence of commands will setup a cpuset
+named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
+and then start a subshell 'sh' in that cpuset:
+
+ mount -t cgroup -ocpuset cpuset /dev/cpuset
+ cd /dev/cpuset
+ mkdir Charlie
+ cd Charlie
+ /bin/echo 2-3 > cpus
+ /bin/echo 1 > mems
+ /bin/echo $$ > tasks
+ sh
+ # The subshell 'sh' is now running in cpuset Charlie
+ # The next line should display '/Charlie'
+ cat /proc/self/cpuset
+
+In the future, a C library interface to cpusets will likely be
+available. For now, the only way to query or modify cpusets is
+via the cpuset file system, using the various cd, mkdir, echo, cat,
+rmdir commands from the shell, or their equivalent from C.
+
+The sched_setaffinity calls can also be done at the shell prompt using
+SGI's runon or Robert Love's taskset. The mbind and set_mempolicy
+calls can be done at the shell prompt using the numactl command
+(part of Andi Kleen's numa package).
+
+2. Usage Examples and Syntax
+============================
+
+2.1 Basic Usage
+---------------
+
+Creating, modifying, using the cpusets can be done through the cpuset
+virtual filesystem.
+
+To mount it, type:
+# mount -t cgroup -o cpuset cpuset /dev/cpuset
+
+Then under /dev/cpuset you can find a tree that corresponds to the
+tree of the cpusets in the system. For instance, /dev/cpuset
+is the cpuset that holds the whole system.
+
+If you want to create a new cpuset under /dev/cpuset:
+# cd /dev/cpuset
+# mkdir my_cpuset
+
+Now you want to do something with this cpuset.
+# cd my_cpuset
+
+In this directory you can find several files:
+# ls
+cpu_exclusive memory_migrate mems tasks
+cpus memory_pressure notify_on_release
+mem_exclusive memory_spread_page sched_load_balance
+mem_hardwall memory_spread_slab sched_relax_domain_level
+
+Reading them will give you information about the state of this cpuset:
+the CPUs and Memory Nodes it can use, the processes that are using
+it, its properties. By writing to these files you can manipulate
+the cpuset.
+
+Set some flags:
+# /bin/echo 1 > cpu_exclusive
+
+Add some cpus:
+# /bin/echo 0-7 > cpus
+
+Add some mems:
+# /bin/echo 0-7 > mems
+
+Now attach your shell to this cpuset:
+# /bin/echo $$ > tasks
+
+You can also create cpusets inside your cpuset by using mkdir in this
+directory.
+# mkdir my_sub_cs
+
+To remove a cpuset, just use rmdir:
+# rmdir my_sub_cs
+This will fail if the cpuset is in use (has cpusets inside, or has
+processes attached).
+
+Note that for legacy reasons, the "cpuset" filesystem exists as a
+wrapper around the cgroup filesystem.
+
+The command
+
+mount -t cpuset X /dev/cpuset
+
+is equivalent to
+
+mount -t cgroup -ocpuset X /dev/cpuset
+echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent
+
+2.2 Adding/removing cpus
+------------------------
+
+This is the syntax to use when writing in the cpus or mems files
+in cpuset directories:
+
+# /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
+# /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
+
+2.3 Setting flags
+-----------------
+
+The syntax is very simple:
+
+# /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
+# /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
+
+2.4 Attaching processes
+-----------------------
+
+# /bin/echo PID > tasks
+
+Note that it is PID, not PIDs. You can only attach ONE task at a time.
+If you have several tasks to attach, you have to do it one after another:
+
+# /bin/echo PID1 > tasks
+# /bin/echo PID2 > tasks
+ ...
+# /bin/echo PIDn > tasks
+
+
+3. Questions
+============
+
+Q: what's up with this '/bin/echo' ?
+A: bash's builtin 'echo' command does not check calls to write() against
+ errors. If you use it in the cpuset file system, you won't be
+ able to tell whether a command succeeded or failed.
+
+Q: When I attach processes, only the first of the line gets really attached !
+A: We can only return one error code per call to write(). So you should also
+ put only ONE pid.
+
+4. Contact
+==========
+
+Web: http://www.bullopensource.org/cpuset
--- /dev/null
+Device Whitelist Controller
+
+1. Description:
+
+Implement a cgroup to track and enforce open and mknod restrictions
+on device files. A device cgroup associates a device access
+whitelist with each cgroup. A whitelist entry has 4 fields.
+'type' is a (all), c (char), or b (block). 'all' means it applies
+to all types and all major and minor numbers. Major and minor are
+either an integer or * for all. Access is a composition of r
+(read), w (write), and m (mknod).
+
+The root device cgroup starts with rwm to 'all'. A child device
+cgroup gets a copy of the parent. Administrators can then remove
+devices from the whitelist or add new entries. A child cgroup can
+never receive a device access which is denied by its parent. However
+when a device access is removed from a parent it will not also be
+removed from the child(ren).
+
+2. User Interface
+
+An entry is added using devices.allow, and removed using
+devices.deny. For instance
+
+ echo 'c 1:3 mr' > /cgroups/1/devices.allow
+
+allows cgroup 1 to read and mknod the device usually known as
+/dev/null. Doing
+
+ echo a > /cgroups/1/devices.deny
+
+will remove the default 'a *:* rwm' entry. Doing
+
+ echo a > /cgroups/1/devices.allow
+
+will add the 'a *:* rwm' entry to the whitelist.
+
+3. Security
+
+Any task can move itself between cgroups. This clearly won't
+suffice, but we can decide the best way to adequately restrict
+movement as people get some experience with this. We may just want
+to require CAP_SYS_ADMIN, which at least is a separate bit from
+CAP_MKNOD. We may want to just refuse moving to a cgroup which
+isn't a descendent of the current one. Or we may want to use
+CAP_MAC_ADMIN, since we really are trying to lock down root.
+
+CAP_SYS_ADMIN is needed to modify the whitelist or move another
+task to a new cgroup. (Again we'll probably want to change that).
+
+A cgroup may not be granted more permissions than the cgroup's
+parent has.
--- /dev/null
+Memory Resource Controller(Memcg) Implementation Memo.
+Last Updated: 2008/12/15
+Base Kernel Version: based on 2.6.28-rc8-mm.
+
+Because VM is getting complex (one of reasons is memcg...), memcg's behavior
+is complex. This is a document for memcg's internal behavior.
+Please note that implementation details can be changed.
+
+(*) Topics on API should be in Documentation/cgroups/memory.txt)
+
+0. How to record usage ?
+ 2 objects are used.
+
+ page_cgroup ....an object per page.
+ Allocated at boot or memory hotplug. Freed at memory hot removal.
+
+ swap_cgroup ... an entry per swp_entry.
+ Allocated at swapon(). Freed at swapoff().
+
+ The page_cgroup has USED bit and double count against a page_cgroup never
+ occurs. swap_cgroup is used only when a charged page is swapped-out.
+
+1. Charge
+
+ a page/swp_entry may be charged (usage += PAGE_SIZE) at
+
+ mem_cgroup_newpage_charge()
+ Called at new page fault and Copy-On-Write.
+
+ mem_cgroup_try_charge_swapin()
+ Called at do_swap_page() (page fault on swap entry) and swapoff.
+ Followed by charge-commit-cancel protocol. (With swap accounting)
+ At commit, a charge recorded in swap_cgroup is removed.
+
+ mem_cgroup_cache_charge()
+ Called at add_to_page_cache()
+
+ mem_cgroup_cache_charge_swapin()
+ Called at shmem's swapin.
+
+ mem_cgroup_prepare_migration()
+ Called before migration. "extra" charge is done and followed by
+ charge-commit-cancel protocol.
+ At commit, charge against oldpage or newpage will be committed.
+
+2. Uncharge
+ a page/swp_entry may be uncharged (usage -= PAGE_SIZE) by
+
+ mem_cgroup_uncharge_page()
+ Called when an anonymous page is fully unmapped. I.e., mapcount goes
+ to 0. If the page is SwapCache, uncharge is delayed until
+ mem_cgroup_uncharge_swapcache().
+
+ mem_cgroup_uncharge_cache_page()
+ Called when a page-cache is deleted from radix-tree. If the page is
+ SwapCache, uncharge is delayed until mem_cgroup_uncharge_swapcache().
+
+ mem_cgroup_uncharge_swapcache()
+ Called when SwapCache is removed from radix-tree. The charge itself
+ is moved to swap_cgroup. (If mem+swap controller is disabled, no
+ charge to swap occurs.)
+
+ mem_cgroup_uncharge_swap()
+ Called when swp_entry's refcnt goes down to 0. A charge against swap
+ disappears.
+
+ mem_cgroup_end_migration(old, new)
+ At success of migration old is uncharged (if necessary), a charge
+ to new page is committed. At failure, charge to old page is committed.
+
+3. charge-commit-cancel
+ In some case, we can't know this "charge" is valid or not at charging
+ (because of races).
+ To handle such case, there are charge-commit-cancel functions.
+ mem_cgroup_try_charge_XXX
+ mem_cgroup_commit_charge_XXX
+ mem_cgroup_cancel_charge_XXX
+ these are used in swap-in and migration.
+
+ At try_charge(), there are no flags to say "this page is charged".
+ at this point, usage += PAGE_SIZE.
+
+ At commit(), the function checks the page should be charged or not
+ and set flags or avoid charging.(usage -= PAGE_SIZE)
+
+ At cancel(), simply usage -= PAGE_SIZE.
+
+Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y.
+
+4. Anonymous
+ Anonymous page is newly allocated at
+ - page fault into MAP_ANONYMOUS mapping.
+ - Copy-On-Write.
+ It is charged right after it's allocated before doing any page table
+ related operations. Of course, it's uncharged when another page is used
+ for the fault address.
+
+ At freeing anonymous page (by exit() or munmap()), zap_pte() is called
+ and pages for ptes are freed one by one.(see mm/memory.c). Uncharges
+ are done at page_remove_rmap() when page_mapcount() goes down to 0.
+
+ Another page freeing is by page-reclaim (vmscan.c) and anonymous
+ pages are swapped out. In this case, the page is marked as
+ PageSwapCache(). uncharge() routine doesn't uncharge the page marked
+ as SwapCache(). It's delayed until __delete_from_swap_cache().
+
+ 4.1 Swap-in.
+ At swap-in, the page is taken from swap-cache. There are 2 cases.
+
+ (a) If the SwapCache is newly allocated and read, it has no charges.
+ (b) If the SwapCache has been mapped by processes, it has been
+ charged already.
+
+ This swap-in is one of the most complicated work. In do_swap_page(),
+ following events occur when pte is unchanged.
+
+ (1) the page (SwapCache) is looked up.
+ (2) lock_page()
+ (3) try_charge_swapin()
+ (4) reuse_swap_page() (may call delete_swap_cache())
+ (5) commit_charge_swapin()
+ (6) swap_free().
+
+ Considering following situation for example.
+
+ (A) The page has not been charged before (2) and reuse_swap_page()
+ doesn't call delete_from_swap_cache().
+ (B) The page has not been charged before (2) and reuse_swap_page()
+ calls delete_from_swap_cache().
+ (C) The page has been charged before (2) and reuse_swap_page() doesn't
+ call delete_from_swap_cache().
+ (D) The page has been charged before (2) and reuse_swap_page() calls
+ delete_from_swap_cache().
+
+ memory.usage/memsw.usage changes to this page/swp_entry will be
+ Case (A) (B) (C) (D)
+ Event
+ Before (2) 0/ 1 0/ 1 1/ 1 1/ 1
+ ===========================================
+ (3) +1/+1 +1/+1 +1/+1 +1/+1
+ (4) - 0/ 0 - -1/ 0
+ (5) 0/-1 0/ 0 -1/-1 0/ 0
+ (6) - 0/-1 - 0/-1
+ ===========================================
+ Result 1/ 1 1/ 1 1/ 1 1/ 1
+
+ In any cases, charges to this page should be 1/ 1.
+
+ 4.2 Swap-out.
+ At swap-out, typical state transition is below.
+
+ (a) add to swap cache. (marked as SwapCache)
+ swp_entry's refcnt += 1.
+ (b) fully unmapped.
+ swp_entry's refcnt += # of ptes.
+ (c) write back to swap.
+ (d) delete from swap cache. (remove from SwapCache)
+ swp_entry's refcnt -= 1.
+
+
+ At (b), the page is marked as SwapCache and not uncharged.
+ At (d), the page is removed from SwapCache and a charge in page_cgroup
+ is moved to swap_cgroup.
+
+ Finally, at task exit,
+ (e) zap_pte() is called and swp_entry's refcnt -=1 -> 0.
+ Here, a charge in swap_cgroup disappears.
+
+5. Page Cache
+ Page Cache is charged at
+ - add_to_page_cache_locked().
+
+ uncharged at
+ - __remove_from_page_cache().
+
+ The logic is very clear. (About migration, see below)
+ Note: __remove_from_page_cache() is called by remove_from_page_cache()
+ and __remove_mapping().
+
+6. Shmem(tmpfs) Page Cache
+ Memcg's charge/uncharge have special handlers of shmem. The best way
+ to understand shmem's page state transition is to read mm/shmem.c.
+ But brief explanation of the behavior of memcg around shmem will be
+ helpful to understand the logic.
+
+ Shmem's page (just leaf page, not direct/indirect block) can be on
+ - radix-tree of shmem's inode.
+ - SwapCache.
+ - Both on radix-tree and SwapCache. This happens at swap-in
+ and swap-out,
+
+ It's charged when...
+ - A new page is added to shmem's radix-tree.
+ - A swp page is read. (move a charge from swap_cgroup to page_cgroup)
+ It's uncharged when
+ - A page is removed from radix-tree and not SwapCache.
+ - When SwapCache is removed, a charge is moved to swap_cgroup.
+ - When swp_entry's refcnt goes down to 0, a charge in swap_cgroup
+ disappears.
+
+7. Page Migration
+ One of the most complicated functions is page-migration-handler.
+ Memcg has 2 routines. Assume that we are migrating a page's contents
+ from OLDPAGE to NEWPAGE.
+
+ Usual migration logic is..
+ (a) remove the page from LRU.
+ (b) allocate NEWPAGE (migration target)
+ (c) lock by lock_page().
+ (d) unmap all mappings.
+ (e-1) If necessary, replace entry in radix-tree.
+ (e-2) move contents of a page.
+ (f) map all mappings again.
+ (g) pushback the page to LRU.
+ (-) OLDPAGE will be freed.
+
+ Before (g), memcg should complete all necessary charge/uncharge to
+ NEWPAGE/OLDPAGE.
+
+ The point is....
+ - If OLDPAGE is anonymous, all charges will be dropped at (d) because
+ try_to_unmap() drops all mapcount and the page will not be
+ SwapCache.
+
+ - If OLDPAGE is SwapCache, charges will be kept at (g) because
+ __delete_from_swap_cache() isn't called at (e-1)
+
+ - If OLDPAGE is page-cache, charges will be kept at (g) because
+ remove_from_swap_cache() isn't called at (e-1)
+
+ memcg provides following hooks.
+
+ - mem_cgroup_prepare_migration(OLDPAGE)
+ Called after (b) to account a charge (usage += PAGE_SIZE) against
+ memcg which OLDPAGE belongs to.
+
+ - mem_cgroup_end_migration(OLDPAGE, NEWPAGE)
+ Called after (f) before (g).
+ If OLDPAGE is used, commit OLDPAGE again. If OLDPAGE is already
+ charged, a charge by prepare_migration() is automatically canceled.
+ If NEWPAGE is used, commit NEWPAGE and uncharge OLDPAGE.
+
+ But zap_pte() (by exit or munmap) can be called while migration,
+ we have to check if OLDPAGE/NEWPAGE is a valid page after commit().
+
+8. LRU
+ Each memcg has its own private LRU. Now, it's handling is under global
+ VM's control (means that it's handled under global zone->lru_lock).
+ Almost all routines around memcg's LRU is called by global LRU's
+ list management functions under zone->lru_lock().
+
+ A special function is mem_cgroup_isolate_pages(). This scans
+ memcg's private LRU and call __isolate_lru_page() to extract a page
+ from LRU.
+ (By __isolate_lru_page(), the page is removed from both of global and
+ private LRU.)
+
+
+9. Typical Tests.
+
+ Tests for racy cases.
+
+ 9.1 Small limit to memcg.
+ When you do test to do racy case, it's good test to set memcg's limit
+ to be very small rather than GB. Many races found in the test under
+ xKB or xxMB limits.
+ (Memory behavior under GB and Memory behavior under MB shows very
+ different situation.)
+
+ 9.2 Shmem
+ Historically, memcg's shmem handling was poor and we saw some amount
+ of troubles here. This is because shmem is page-cache but can be
+ SwapCache. Test with shmem/tmpfs is always good test.
+
+ 9.3 Migration
+ For NUMA, migration is an another special case. To do easy test, cpuset
+ is useful. Following is a sample script to do migration.
+
+ mount -t cgroup -o cpuset none /opt/cpuset
+
+ mkdir /opt/cpuset/01
+ echo 1 > /opt/cpuset/01/cpuset.cpus
+ echo 0 > /opt/cpuset/01/cpuset.mems
+ echo 1 > /opt/cpuset/01/cpuset.memory_migrate
+ mkdir /opt/cpuset/02
+ echo 1 > /opt/cpuset/02/cpuset.cpus
+ echo 1 > /opt/cpuset/02/cpuset.mems
+ echo 1 > /opt/cpuset/02/cpuset.memory_migrate
+
+ In above set, when you moves a task from 01 to 02, page migration to
+ node 0 to node 1 will occur. Following is a script to migrate all
+ under cpuset.
+ --
+ move_task()
+ {
+ for pid in $1
+ do
+ /bin/echo $pid >$2/tasks 2>/dev/null
+ echo -n $pid
+ echo -n " "
+ done
+ echo END
+ }
+
+ G1_TASK=`cat ${G1}/tasks`
+ G2_TASK=`cat ${G2}/tasks`
+ move_task "${G1_TASK}" ${G2} &
+ --
+ 9.4 Memory hotplug.
+ memory hotplug test is one of good test.
+ to offline memory, do following.
+ # echo offline > /sys/devices/system/memory/memoryXXX/state
+ (XXX is the place of memory)
+ This is an easy way to test page migration, too.
+
+ 9.5 mkdir/rmdir
+ When using hierarchy, mkdir/rmdir test should be done.
+ Use tests like the following.
+
+ echo 1 >/opt/cgroup/01/memory/use_hierarchy
+ mkdir /opt/cgroup/01/child_a
+ mkdir /opt/cgroup/01/child_b
+
+ set limit to 01.
+ add limit to 01/child_b
+ run jobs under child_a and child_b
+
+ create/delete following groups at random while jobs are running.
+ /opt/cgroup/01/child_a/child_aa
+ /opt/cgroup/01/child_b/child_bb
+ /opt/cgroup/01/child_c
+
+ running new jobs in new group is also good.
+
+ 9.6 Mount with other subsystems.
+ Mounting with other subsystems is a good test because there is a
+ race and lock dependency with other cgroup subsystems.
+
+ example)
+ # mount -t cgroup none /cgroup -t cpuset,memory,cpu,devices
+
+ and do task move, mkdir, rmdir etc...under this.
--- /dev/null
+Memory Resource Controller
+
+NOTE: The Memory Resource Controller has been generically been referred
+to as the memory controller in this document. Do not confuse memory controller
+used here with the memory controller that is used in hardware.
+
+Salient features
+
+a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages
+b. The infrastructure allows easy addition of other types of memory to control
+c. Provides *zero overhead* for non memory controller users
+d. Provides a double LRU: global memory pressure causes reclaim from the
+ global LRU; a cgroup on hitting a limit, reclaims from the per
+ cgroup LRU
+
+NOTE: Swap Cache (unmapped) is not accounted now.
+
+Benefits and Purpose of the memory controller
+
+The memory controller isolates the memory behaviour of a group of tasks
+from the rest of the system. The article on LWN [12] mentions some probable
+uses of the memory controller. The memory controller can be used to
+
+a. Isolate an application or a group of applications
+ Memory hungry applications can be isolated and limited to a smaller
+ amount of memory.
+b. Create a cgroup with limited amount of memory, this can be used
+ as a good alternative to booting with mem=XXXX.
+c. Virtualization solutions can control the amount of memory they want
+ to assign to a virtual machine instance.
+d. A CD/DVD burner could control the amount of memory used by the
+ rest of the system to ensure that burning does not fail due to lack
+ of available memory.
+e. There are several other use cases, find one or use the controller just
+ for fun (to learn and hack on the VM subsystem).
+
+1. History
+
+The memory controller has a long history. A request for comments for the memory
+controller was posted by Balbir Singh [1]. At the time the RFC was posted
+there were several implementations for memory control. The goal of the
+RFC was to build consensus and agreement for the minimal features required
+for memory control. The first RSS controller was posted by Balbir Singh[2]
+in Feb 2007. Pavel Emelianov [3][4][5] has since posted three versions of the
+RSS controller. At OLS, at the resource management BoF, everyone suggested
+that we handle both page cache and RSS together. Another request was raised
+to allow user space handling of OOM. The current memory controller is
+at version 6; it combines both mapped (RSS) and unmapped Page
+Cache Control [11].
+
+2. Memory Control
+
+Memory is a unique resource in the sense that it is present in a limited
+amount. If a task requires a lot of CPU processing, the task can spread
+its processing over a period of hours, days, months or years, but with
+memory, the same physical memory needs to be reused to accomplish the task.
+
+The memory controller implementation has been divided into phases. These
+are:
+
+1. Memory controller
+2. mlock(2) controller
+3. Kernel user memory accounting and slab control
+4. user mappings length controller
+
+The memory controller is the first controller developed.
+
+2.1. Design
+
+The core of the design is a counter called the res_counter. The res_counter
+tracks the current memory usage and limit of the group of processes associated
+with the controller. Each cgroup has a memory controller specific data
+structure (mem_cgroup) associated with it.
+
+2.2. Accounting
+
+ +--------------------+
+ | mem_cgroup |
+ | (res_counter) |
+ +--------------------+
+ / ^ \
+ / | \
+ +---------------+ | +---------------+
+ | mm_struct | |.... | mm_struct |
+ | | | | |
+ +---------------+ | +---------------+
+ |
+ + --------------+
+ |
+ +---------------+ +------+--------+
+ | page +----------> page_cgroup|
+ | | | |
+ +---------------+ +---------------+
+
+ (Figure 1: Hierarchy of Accounting)
+
+
+Figure 1 shows the important aspects of the controller
+
+1. Accounting happens per cgroup
+2. Each mm_struct knows about which cgroup it belongs to
+3. Each page has a pointer to the page_cgroup, which in turn knows the
+ cgroup it belongs to
+
+The accounting is done as follows: mem_cgroup_charge() is invoked to setup
+the necessary data structures and check if the cgroup that is being charged
+is over its limit. If it is then reclaim is invoked on the cgroup.
+More details can be found in the reclaim section of this document.
+If everything goes well, a page meta-data-structure called page_cgroup is
+allocated and associated with the page. This routine also adds the page to
+the per cgroup LRU.
+
+2.2.1 Accounting details
+
+All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
+(some pages which never be reclaimable and will not be on global LRU
+ are not accounted. we just accounts pages under usual vm management.)
+
+RSS pages are accounted at page_fault unless they've already been accounted
+for earlier. A file page will be accounted for as Page Cache when it's
+inserted into inode (radix-tree). While it's mapped into the page tables of
+processes, duplicate accounting is carefully avoided.
+
+A RSS page is unaccounted when it's fully unmapped. A PageCache page is
+unaccounted when it's removed from radix-tree.
+
+At page migration, accounting information is kept.
+
+Note: we just account pages-on-lru because our purpose is to control amount
+of used pages. not-on-lru pages are tend to be out-of-control from vm view.
+
+2.3 Shared Page Accounting
+
+Shared pages are accounted on the basis of the first touch approach. The
+cgroup that first touches a page is accounted for the page. The principle
+behind this approach is that a cgroup that aggressively uses a shared
+page will eventually get charged for it (once it is uncharged from
+the cgroup that brought it in -- this will happen on memory pressure).
+
+Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used..
+When you do swapoff and make swapped-out pages of shmem(tmpfs) to
+be backed into memory in force, charges for pages are accounted against the
+caller of swapoff rather than the users of shmem.
+
+
+2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP)
+Swap Extension allows you to record charge for swap. A swapped-in page is
+charged back to original page allocator if possible.
+
+When swap is accounted, following files are added.
+ - memory.memsw.usage_in_bytes.
+ - memory.memsw.limit_in_bytes.
+
+usage of mem+swap is limited by memsw.limit_in_bytes.
+
+Note: why 'mem+swap' rather than swap.
+The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
+to move account from memory to swap...there is no change in usage of
+mem+swap.
+
+In other words, when we want to limit the usage of swap without affecting
+global LRU, mem+swap limit is better than just limiting swap from OS point
+of view.
+
+2.5 Reclaim
+
+Each cgroup maintains a per cgroup LRU that consists of an active
+and inactive list. When a cgroup goes over its limit, we first try
+to reclaim memory from the cgroup so as to make space for the new
+pages that the cgroup has touched. If the reclaim is unsuccessful,
+an OOM routine is invoked to select and kill the bulkiest task in the
+cgroup.
+
+The reclaim algorithm has not been modified for cgroups, except that
+pages that are selected for reclaiming come from the per cgroup LRU
+list.
+
+2. Locking
+
+The memory controller uses the following hierarchy
+
+1. zone->lru_lock is used for selecting pages to be isolated
+2. mem->per_zone->lru_lock protects the per cgroup LRU (per zone)
+3. lock_page_cgroup() is used to protect page->page_cgroup
+
+3. User Interface
+
+0. Configuration
+
+a. Enable CONFIG_CGROUPS
+b. Enable CONFIG_RESOURCE_COUNTERS
+c. Enable CONFIG_CGROUP_MEM_RES_CTLR
+
+1. Prepare the cgroups
+# mkdir -p /cgroups
+# mount -t cgroup none /cgroups -o memory
+
+2. Make the new group and move bash into it
+# mkdir /cgroups/0
+# echo $$ > /cgroups/0/tasks
+
+Since now we're in the 0 cgroup,
+We can alter the memory limit:
+# echo 4M > /cgroups/0/memory.limit_in_bytes
+
+NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
+mega or gigabytes.
+
+# cat /cgroups/0/memory.limit_in_bytes
+4194304
+
+NOTE: The interface has now changed to display the usage in bytes
+instead of pages
+
+We can check the usage:
+# cat /cgroups/0/memory.usage_in_bytes
+1216512
+
+A successful write to this file does not guarantee a successful set of
+this limit to the value written into the file. This can be due to a
+number of factors, such as rounding up to page boundaries or the total
+availability of memory on the system. The user is required to re-read
+this file after a write to guarantee the value committed by the kernel.
+
+# echo 1 > memory.limit_in_bytes
+# cat memory.limit_in_bytes
+4096
+
+The memory.failcnt field gives the number of times that the cgroup limit was
+exceeded.
+
+The memory.stat file gives accounting information. Now, the number of
+caches, RSS and Active pages/Inactive pages are shown.
+
+4. Testing
+
+Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11].
+Apart from that v6 has been tested with several applications and regular
+daily use. The controller has also been tested on the PPC64, x86_64 and
+UML platforms.
+
+4.1 Troubleshooting
+
+Sometimes a user might find that the application under a cgroup is
+terminated. There are several causes for this:
+
+1. The cgroup limit is too low (just too low to do anything useful)
+2. The user is using anonymous memory and swap is turned off or too low
+
+A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of
+some of the pages cached in the cgroup (page cache pages).
+
+4.2 Task migration
+
+When a task migrates from one cgroup to another, it's charge is not
+carried forward. The pages allocated from the original cgroup still
+remain charged to it, the charge is dropped when the page is freed or
+reclaimed.
+
+4.3 Removing a cgroup
+
+A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
+cgroup might have some charge associated with it, even though all
+tasks have migrated away from it.
+Such charges are freed(at default) or moved to its parent. When moved,
+both of RSS and CACHES are moved to parent.
+If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also.
+
+Charges recorded in swap information is not updated at removal of cgroup.
+Recorded information is discarded and a cgroup which uses swap (swapcache)
+will be charged as a new owner of it.
+
+
+5. Misc. interfaces.
+
+5.1 force_empty
+ memory.force_empty interface is provided to make cgroup's memory usage empty.
+ You can use this interface only when the cgroup has no tasks.
+ When writing anything to this
+
+ # echo 0 > memory.force_empty
+
+ Almost all pages tracked by this memcg will be unmapped and freed. Some of
+ pages cannot be freed because it's locked or in-use. Such pages are moved
+ to parent and this cgroup will be empty. But this may return -EBUSY in
+ some too busy case.
+
+ Typical use case of this interface is that calling this before rmdir().
+ Because rmdir() moves all pages to parent, some out-of-use page caches can be
+ moved to the parent. If you want to avoid that, force_empty will be useful.
+
+5.2 stat file
+ memory.stat file includes following statistics (now)
+ cache - # of pages from page-cache and shmem.
+ rss - # of pages from anonymous memory.
+ pgpgin - # of event of charging
+ pgpgout - # of event of uncharging
+ active_anon - # of pages on active lru of anon, shmem.
+ inactive_anon - # of pages on active lru of anon, shmem
+ active_file - # of pages on active lru of file-cache
+ inactive_file - # of pages on inactive lru of file cache
+ unevictable - # of pages cannot be reclaimed.(mlocked etc)
+
+ Below is depend on CONFIG_DEBUG_VM.
+ inactive_ratio - VM inernal parameter. (see mm/page_alloc.c)
+ recent_rotated_anon - VM internal parameter. (see mm/vmscan.c)
+ recent_rotated_file - VM internal parameter. (see mm/vmscan.c)
+ recent_scanned_anon - VM internal parameter. (see mm/vmscan.c)
+ recent_scanned_file - VM internal parameter. (see mm/vmscan.c)
+
+ Memo:
+ recent_rotated means recent frequency of lru rotation.
+ recent_scanned means recent # of scans to lru.
+ showing for better debug please see the code for meanings.
+
+
+5.3 swappiness
+ Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
+
+ Following cgroup's swapiness can't be changed.
+ - root cgroup (uses /proc/sys/vm/swappiness).
+ - a cgroup which uses hierarchy and it has child cgroup.
+ - a cgroup which uses hierarchy and not the root of hierarchy.
+
+
+6. Hierarchy support
+
+The memory controller supports a deep hierarchy and hierarchical accounting.
+The hierarchy is created by creating the appropriate cgroups in the
+cgroup filesystem. Consider for example, the following cgroup filesystem
+hierarchy
+
+ root
+ / | \
+ / | \
+ a b c
+ | \
+ | \
+ d e
+
+In the diagram above, with hierarchical accounting enabled, all memory
+usage of e, is accounted to its ancestors up until the root (i.e, c and root),
+that has memory.use_hierarchy enabled. If one of the ancestors goes over its
+limit, the reclaim algorithm reclaims from the tasks in the ancestor and the
+children of the ancestor.
+
+6.1 Enabling hierarchical accounting and reclaim
+
+The memory controller by default disables the hierarchy feature. Support
+can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup
+
+# echo 1 > memory.use_hierarchy
+
+The feature can be disabled by
+
+# echo 0 > memory.use_hierarchy
+
+NOTE1: Enabling/disabling will fail if the cgroup already has other
+cgroups created below it.
+
+NOTE2: This feature can be enabled/disabled per subtree.
+
+7. TODO
+
+1. Add support for accounting huge pages (as a separate controller)
+2. Make per-cgroup scanner reclaim not-shared pages first
+3. Teach controller to account for shared-pages
+4. Start reclamation in the background when the limit is
+ not yet hit but the usage is getting closer
+
+Summary
+
+Overall, the memory controller has been a stable controller and has been
+commented and discussed quite extensively in the community.
+
+References
+
+1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
+2. Singh, Balbir. Memory Controller (RSS Control),
+ http://lwn.net/Articles/222762/
+3. Emelianov, Pavel. Resource controllers based on process cgroups
+ http://lkml.org/lkml/2007/3/6/198
+4. Emelianov, Pavel. RSS controller based on process cgroups (v2)
+ http://lkml.org/lkml/2007/4/9/78
+5. Emelianov, Pavel. RSS controller based on process cgroups (v3)
+ http://lkml.org/lkml/2007/5/30/244
+6. Menage, Paul. Control Groups v10, http://lwn.net/Articles/236032/
+7. Vaidyanathan, Srinivasan, Control Groups: Pagecache accounting and control
+ subsystem (v3), http://lwn.net/Articles/235534/
+8. Singh, Balbir. RSS controller v2 test results (lmbench),
+ http://lkml.org/lkml/2007/5/17/232
+9. Singh, Balbir. RSS controller v2 AIM9 results
+ http://lkml.org/lkml/2007/5/18/1
+10. Singh, Balbir. Memory controller v6 test results,
+ http://lkml.org/lkml/2007/8/19/36
+11. Singh, Balbir. Memory controller introduction (v6),
+ http://lkml.org/lkml/2007/8/17/69
+12. Corbet, Jonathan, Controlling memory use in cgroups,
+ http://lwn.net/Articles/243795/
--- /dev/null
+
+ The Resource Counter
+
+The resource counter, declared at include/linux/res_counter.h,
+is supposed to facilitate the resource management by controllers
+by providing common stuff for accounting.
+
+This "stuff" includes the res_counter structure and routines
+to work with it.
+
+
+
+1. Crucial parts of the res_counter structure
+
+ a. unsigned long long usage
+
+ The usage value shows the amount of a resource that is consumed
+ by a group at a given time. The units of measurement should be
+ determined by the controller that uses this counter. E.g. it can
+ be bytes, items or any other unit the controller operates on.
+
+ b. unsigned long long max_usage
+
+ The maximal value of the usage over time.
+
+ This value is useful when gathering statistical information about
+ the particular group, as it shows the actual resource requirements
+ for a particular group, not just some usage snapshot.
+
+ c. unsigned long long limit
+
+ The maximal allowed amount of resource to consume by the group. In
+ case the group requests for more resources, so that the usage value
+ would exceed the limit, the resource allocation is rejected (see
+ the next section).
+
+ d. unsigned long long failcnt
+
+ The failcnt stands for "failures counter". This is the number of
+ resource allocation attempts that failed.
+
+ c. spinlock_t lock
+
+ Protects changes of the above values.
+
+
+
+2. Basic accounting routines
+
+ a. void res_counter_init(struct res_counter *rc)
+
+ Initializes the resource counter. As usual, should be the first
+ routine called for a new counter.
+
+ b. int res_counter_charge[_locked]
+ (struct res_counter *rc, unsigned long val)
+
+ When a resource is about to be allocated it has to be accounted
+ with the appropriate resource counter (controller should determine
+ which one to use on its own). This operation is called "charging".
+
+ This is not very important which operation - resource allocation
+ or charging - is performed first, but
+ * if the allocation is performed first, this may create a
+ temporary resource over-usage by the time resource counter is
+ charged;
+ * if the charging is performed first, then it should be uncharged
+ on error path (if the one is called).
+
+ c. void res_counter_uncharge[_locked]
+ (struct res_counter *rc, unsigned long val)
+
+ When a resource is released (freed) it should be de-accounted
+ from the resource counter it was accounted to. This is called
+ "uncharging".
+
+ The _locked routines imply that the res_counter->lock is taken.
+
+
+ 2.1 Other accounting routines
+
+ There are more routines that may help you with common needs, like
+ checking whether the limit is reached or resetting the max_usage
+ value. They are all declared in include/linux/res_counter.h.
+
+
+
+3. Analyzing the resource counter registrations
+
+ a. If the failcnt value constantly grows, this means that the counter's
+ limit is too tight. Either the group is misbehaving and consumes too
+ many resources, or the configuration is not suitable for the group
+ and the limit should be increased.
+
+ b. The max_usage value can be used to quickly tune the group. One may
+ set the limits to maximal values and either load the container with
+ a common pattern or leave one for a while. After this the max_usage
+ value shows the amount of memory the container would require during
+ its common activity.
+
+ Setting the limit a bit above this value gives a pretty good
+ configuration that works in most of the cases.
+
+ c. If the max_usage is much less than the limit, but the failcnt value
+ is growing, then the group tries to allocate a big chunk of resource
+ at once.
+
+ d. If the max_usage is much less than the limit, but the failcnt value
+ is 0, then this group is given too high limit, that it does not
+ require. It is better to lower the limit a bit leaving more resource
+ for other groups.
+
+
+
+4. Communication with the control groups subsystem (cgroups)
+
+All the resource controllers that are using cgroups and resource counters
+should provide files (in the cgroup filesystem) to work with the resource
+counter fields. They are recommended to adhere to the following rules:
+
+ a. File names
+
+ Field name File name
+ ---------------------------------------------------
+ usage usage_in_<unit_of_measurement>
+ max_usage max_usage_in_<unit_of_measurement>
+ limit limit_in_<unit_of_measurement>
+ failcnt failcnt
+ lock no file :)
+
+ b. Reading from file should show the corresponding field value in the
+ appropriate format.
+
+ c. Writing to file
+
+ Field Expected behavior
+ ----------------------------------
+ usage prohibited
+ max_usage reset to usage
+ limit set the limit
+ failcnt reset to zero
+
+
+
+5. Usage example
+
+ a. Declare a task group (take a look at cgroups subsystem for this) and
+ fold a res_counter into it
+
+ struct my_group {
+ struct res_counter res;
+
+ <other fields>
+ }
+
+ b. Put hooks in resource allocation/release paths
+
+ int alloc_something(...)
+ {
+ if (res_counter_charge(res_counter_ptr, amount) < 0)
+ return -ENOMEM;
+
+ <allocate the resource and return to the caller>
+ }
+
+ void release_something(...)
+ {
+ res_counter_uncharge(res_counter_ptr, amount);
+
+ <release the resource>
+ }
+
+ In order to keep the usage value self-consistent, both the
+ "res_counter_ptr" and the "amount" in release_something() should be
+ the same as they were in the alloc_something() when the releasing
+ resource was allocated.
+
+ c. Provide the way to read res_counter values and set them (the cgroups
+ still can help with it).
+
+ c. Compile and run :)
+++ /dev/null
-CPU Accounting Controller
--------------------------
-
-The CPU accounting controller is used to group tasks using cgroups and
-account the CPU usage of these groups of tasks.
-
-The CPU accounting controller supports multi-hierarchy groups. An accounting
-group accumulates the CPU usage of all of its child groups and the tasks
-directly present in its group.
-
-Accounting groups can be created by first mounting the cgroup filesystem.
-
-# mkdir /cgroups
-# mount -t cgroup -ocpuacct none /cgroups
-
-With the above step, the initial or the parent accounting group
-becomes visible at /cgroups. At bootup, this group includes all the
-tasks in the system. /cgroups/tasks lists the tasks in this cgroup.
-/cgroups/cpuacct.usage gives the CPU time (in nanoseconds) obtained by
-this group which is essentially the CPU time obtained by all the tasks
-in the system.
-
-New accounting groups can be created under the parent group /cgroups.
-
-# cd /cgroups
-# mkdir g1
-# echo $$ > g1
-
-The above steps create a new group g1 and move the current shell
-process (bash) into it. CPU time consumed by this bash and its children
-can be obtained from g1/cpuacct.usage and the same is accumulated in
-/cgroups/cpuacct.usage also.
+++ /dev/null
-Device Whitelist Controller
-
-1. Description:
-
-Implement a cgroup to track and enforce open and mknod restrictions
-on device files. A device cgroup associates a device access
-whitelist with each cgroup. A whitelist entry has 4 fields.
-'type' is a (all), c (char), or b (block). 'all' means it applies
-to all types and all major and minor numbers. Major and minor are
-either an integer or * for all. Access is a composition of r
-(read), w (write), and m (mknod).
-
-The root device cgroup starts with rwm to 'all'. A child device
-cgroup gets a copy of the parent. Administrators can then remove
-devices from the whitelist or add new entries. A child cgroup can
-never receive a device access which is denied by its parent. However
-when a device access is removed from a parent it will not also be
-removed from the child(ren).
-
-2. User Interface
-
-An entry is added using devices.allow, and removed using
-devices.deny. For instance
-
- echo 'c 1:3 mr' > /cgroups/1/devices.allow
-
-allows cgroup 1 to read and mknod the device usually known as
-/dev/null. Doing
-
- echo a > /cgroups/1/devices.deny
-
-will remove the default 'a *:* rwm' entry. Doing
-
- echo a > /cgroups/1/devices.allow
-
-will add the 'a *:* rwm' entry to the whitelist.
-
-3. Security
-
-Any task can move itself between cgroups. This clearly won't
-suffice, but we can decide the best way to adequately restrict
-movement as people get some experience with this. We may just want
-to require CAP_SYS_ADMIN, which at least is a separate bit from
-CAP_MKNOD. We may want to just refuse moving to a cgroup which
-isn't a descendent of the current one. Or we may want to use
-CAP_MAC_ADMIN, since we really are trying to lock down root.
-
-CAP_SYS_ADMIN is needed to modify the whitelist or move another
-task to a new cgroup. (Again we'll probably want to change that).
-
-A cgroup may not be granted more permissions than the cgroup's
-parent has.
+++ /dev/null
-Memory Resource Controller(Memcg) Implementation Memo.
-Last Updated: 2008/12/15
-Base Kernel Version: based on 2.6.28-rc8-mm.
-
-Because VM is getting complex (one of reasons is memcg...), memcg's behavior
-is complex. This is a document for memcg's internal behavior.
-Please note that implementation details can be changed.
-
-(*) Topics on API should be in Documentation/controllers/memory.txt)
-
-0. How to record usage ?
- 2 objects are used.
-
- page_cgroup ....an object per page.
- Allocated at boot or memory hotplug. Freed at memory hot removal.
-
- swap_cgroup ... an entry per swp_entry.
- Allocated at swapon(). Freed at swapoff().
-
- The page_cgroup has USED bit and double count against a page_cgroup never
- occurs. swap_cgroup is used only when a charged page is swapped-out.
-
-1. Charge
-
- a page/swp_entry may be charged (usage += PAGE_SIZE) at
-
- mem_cgroup_newpage_charge()
- Called at new page fault and Copy-On-Write.
-
- mem_cgroup_try_charge_swapin()
- Called at do_swap_page() (page fault on swap entry) and swapoff.
- Followed by charge-commit-cancel protocol. (With swap accounting)
- At commit, a charge recorded in swap_cgroup is removed.
-
- mem_cgroup_cache_charge()
- Called at add_to_page_cache()
-
- mem_cgroup_cache_charge_swapin()
- Called at shmem's swapin.
-
- mem_cgroup_prepare_migration()
- Called before migration. "extra" charge is done and followed by
- charge-commit-cancel protocol.
- At commit, charge against oldpage or newpage will be committed.
-
-2. Uncharge
- a page/swp_entry may be uncharged (usage -= PAGE_SIZE) by
-
- mem_cgroup_uncharge_page()
- Called when an anonymous page is fully unmapped. I.e., mapcount goes
- to 0. If the page is SwapCache, uncharge is delayed until
- mem_cgroup_uncharge_swapcache().
-
- mem_cgroup_uncharge_cache_page()
- Called when a page-cache is deleted from radix-tree. If the page is
- SwapCache, uncharge is delayed until mem_cgroup_uncharge_swapcache().
-
- mem_cgroup_uncharge_swapcache()
- Called when SwapCache is removed from radix-tree. The charge itself
- is moved to swap_cgroup. (If mem+swap controller is disabled, no
- charge to swap occurs.)
-
- mem_cgroup_uncharge_swap()
- Called when swp_entry's refcnt goes down to 0. A charge against swap
- disappears.
-
- mem_cgroup_end_migration(old, new)
- At success of migration old is uncharged (if necessary), a charge
- to new page is committed. At failure, charge to old page is committed.
-
-3. charge-commit-cancel
- In some case, we can't know this "charge" is valid or not at charging
- (because of races).
- To handle such case, there are charge-commit-cancel functions.
- mem_cgroup_try_charge_XXX
- mem_cgroup_commit_charge_XXX
- mem_cgroup_cancel_charge_XXX
- these are used in swap-in and migration.
-
- At try_charge(), there are no flags to say "this page is charged".
- at this point, usage += PAGE_SIZE.
-
- At commit(), the function checks the page should be charged or not
- and set flags or avoid charging.(usage -= PAGE_SIZE)
-
- At cancel(), simply usage -= PAGE_SIZE.
-
-Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y.
-
-4. Anonymous
- Anonymous page is newly allocated at
- - page fault into MAP_ANONYMOUS mapping.
- - Copy-On-Write.
- It is charged right after it's allocated before doing any page table
- related operations. Of course, it's uncharged when another page is used
- for the fault address.
-
- At freeing anonymous page (by exit() or munmap()), zap_pte() is called
- and pages for ptes are freed one by one.(see mm/memory.c). Uncharges
- are done at page_remove_rmap() when page_mapcount() goes down to 0.
-
- Another page freeing is by page-reclaim (vmscan.c) and anonymous
- pages are swapped out. In this case, the page is marked as
- PageSwapCache(). uncharge() routine doesn't uncharge the page marked
- as SwapCache(). It's delayed until __delete_from_swap_cache().
-
- 4.1 Swap-in.
- At swap-in, the page is taken from swap-cache. There are 2 cases.
-
- (a) If the SwapCache is newly allocated and read, it has no charges.
- (b) If the SwapCache has been mapped by processes, it has been
- charged already.
-
- This swap-in is one of the most complicated work. In do_swap_page(),
- following events occur when pte is unchanged.
-
- (1) the page (SwapCache) is looked up.
- (2) lock_page()
- (3) try_charge_swapin()
- (4) reuse_swap_page() (may call delete_swap_cache())
- (5) commit_charge_swapin()
- (6) swap_free().
-
- Considering following situation for example.
-
- (A) The page has not been charged before (2) and reuse_swap_page()
- doesn't call delete_from_swap_cache().
- (B) The page has not been charged before (2) and reuse_swap_page()
- calls delete_from_swap_cache().
- (C) The page has been charged before (2) and reuse_swap_page() doesn't
- call delete_from_swap_cache().
- (D) The page has been charged before (2) and reuse_swap_page() calls
- delete_from_swap_cache().
-
- memory.usage/memsw.usage changes to this page/swp_entry will be
- Case (A) (B) (C) (D)
- Event
- Before (2) 0/ 1 0/ 1 1/ 1 1/ 1
- ===========================================
- (3) +1/+1 +1/+1 +1/+1 +1/+1
- (4) - 0/ 0 - -1/ 0
- (5) 0/-1 0/ 0 -1/-1 0/ 0
- (6) - 0/-1 - 0/-1
- ===========================================
- Result 1/ 1 1/ 1 1/ 1 1/ 1
-
- In any cases, charges to this page should be 1/ 1.
-
- 4.2 Swap-out.
- At swap-out, typical state transition is below.
-
- (a) add to swap cache. (marked as SwapCache)
- swp_entry's refcnt += 1.
- (b) fully unmapped.
- swp_entry's refcnt += # of ptes.
- (c) write back to swap.
- (d) delete from swap cache. (remove from SwapCache)
- swp_entry's refcnt -= 1.
-
-
- At (b), the page is marked as SwapCache and not uncharged.
- At (d), the page is removed from SwapCache and a charge in page_cgroup
- is moved to swap_cgroup.
-
- Finally, at task exit,
- (e) zap_pte() is called and swp_entry's refcnt -=1 -> 0.
- Here, a charge in swap_cgroup disappears.
-
-5. Page Cache
- Page Cache is charged at
- - add_to_page_cache_locked().
-
- uncharged at
- - __remove_from_page_cache().
-
- The logic is very clear. (About migration, see below)
- Note: __remove_from_page_cache() is called by remove_from_page_cache()
- and __remove_mapping().
-
-6. Shmem(tmpfs) Page Cache
- Memcg's charge/uncharge have special handlers of shmem. The best way
- to understand shmem's page state transition is to read mm/shmem.c.
- But brief explanation of the behavior of memcg around shmem will be
- helpful to understand the logic.
-
- Shmem's page (just leaf page, not direct/indirect block) can be on
- - radix-tree of shmem's inode.
- - SwapCache.
- - Both on radix-tree and SwapCache. This happens at swap-in
- and swap-out,
-
- It's charged when...
- - A new page is added to shmem's radix-tree.
- - A swp page is read. (move a charge from swap_cgroup to page_cgroup)
- It's uncharged when
- - A page is removed from radix-tree and not SwapCache.
- - When SwapCache is removed, a charge is moved to swap_cgroup.
- - When swp_entry's refcnt goes down to 0, a charge in swap_cgroup
- disappears.
-
-7. Page Migration
- One of the most complicated functions is page-migration-handler.
- Memcg has 2 routines. Assume that we are migrating a page's contents
- from OLDPAGE to NEWPAGE.
-
- Usual migration logic is..
- (a) remove the page from LRU.
- (b) allocate NEWPAGE (migration target)
- (c) lock by lock_page().
- (d) unmap all mappings.
- (e-1) If necessary, replace entry in radix-tree.
- (e-2) move contents of a page.
- (f) map all mappings again.
- (g) pushback the page to LRU.
- (-) OLDPAGE will be freed.
-
- Before (g), memcg should complete all necessary charge/uncharge to
- NEWPAGE/OLDPAGE.
-
- The point is....
- - If OLDPAGE is anonymous, all charges will be dropped at (d) because
- try_to_unmap() drops all mapcount and the page will not be
- SwapCache.
-
- - If OLDPAGE is SwapCache, charges will be kept at (g) because
- __delete_from_swap_cache() isn't called at (e-1)
-
- - If OLDPAGE is page-cache, charges will be kept at (g) because
- remove_from_swap_cache() isn't called at (e-1)
-
- memcg provides following hooks.
-
- - mem_cgroup_prepare_migration(OLDPAGE)
- Called after (b) to account a charge (usage += PAGE_SIZE) against
- memcg which OLDPAGE belongs to.
-
- - mem_cgroup_end_migration(OLDPAGE, NEWPAGE)
- Called after (f) before (g).
- If OLDPAGE is used, commit OLDPAGE again. If OLDPAGE is already
- charged, a charge by prepare_migration() is automatically canceled.
- If NEWPAGE is used, commit NEWPAGE and uncharge OLDPAGE.
-
- But zap_pte() (by exit or munmap) can be called while migration,
- we have to check if OLDPAGE/NEWPAGE is a valid page after commit().
-
-8. LRU
- Each memcg has its own private LRU. Now, it's handling is under global
- VM's control (means that it's handled under global zone->lru_lock).
- Almost all routines around memcg's LRU is called by global LRU's
- list management functions under zone->lru_lock().
-
- A special function is mem_cgroup_isolate_pages(). This scans
- memcg's private LRU and call __isolate_lru_page() to extract a page
- from LRU.
- (By __isolate_lru_page(), the page is removed from both of global and
- private LRU.)
-
-
-9. Typical Tests.
-
- Tests for racy cases.
-
- 9.1 Small limit to memcg.
- When you do test to do racy case, it's good test to set memcg's limit
- to be very small rather than GB. Many races found in the test under
- xKB or xxMB limits.
- (Memory behavior under GB and Memory behavior under MB shows very
- different situation.)
-
- 9.2 Shmem
- Historically, memcg's shmem handling was poor and we saw some amount
- of troubles here. This is because shmem is page-cache but can be
- SwapCache. Test with shmem/tmpfs is always good test.
-
- 9.3 Migration
- For NUMA, migration is an another special case. To do easy test, cpuset
- is useful. Following is a sample script to do migration.
-
- mount -t cgroup -o cpuset none /opt/cpuset
-
- mkdir /opt/cpuset/01
- echo 1 > /opt/cpuset/01/cpuset.cpus
- echo 0 > /opt/cpuset/01/cpuset.mems
- echo 1 > /opt/cpuset/01/cpuset.memory_migrate
- mkdir /opt/cpuset/02
- echo 1 > /opt/cpuset/02/cpuset.cpus
- echo 1 > /opt/cpuset/02/cpuset.mems
- echo 1 > /opt/cpuset/02/cpuset.memory_migrate
-
- In above set, when you moves a task from 01 to 02, page migration to
- node 0 to node 1 will occur. Following is a script to migrate all
- under cpuset.
- --
- move_task()
- {
- for pid in $1
- do
- /bin/echo $pid >$2/tasks 2>/dev/null
- echo -n $pid
- echo -n " "
- done
- echo END
- }
-
- G1_TASK=`cat ${G1}/tasks`
- G2_TASK=`cat ${G2}/tasks`
- move_task "${G1_TASK}" ${G2} &
- --
- 9.4 Memory hotplug.
- memory hotplug test is one of good test.
- to offline memory, do following.
- # echo offline > /sys/devices/system/memory/memoryXXX/state
- (XXX is the place of memory)
- This is an easy way to test page migration, too.
-
- 9.5 mkdir/rmdir
- When using hierarchy, mkdir/rmdir test should be done.
- Use tests like the following.
-
- echo 1 >/opt/cgroup/01/memory/use_hierarchy
- mkdir /opt/cgroup/01/child_a
- mkdir /opt/cgroup/01/child_b
-
- set limit to 01.
- add limit to 01/child_b
- run jobs under child_a and child_b
-
- create/delete following groups at random while jobs are running.
- /opt/cgroup/01/child_a/child_aa
- /opt/cgroup/01/child_b/child_bb
- /opt/cgroup/01/child_c
-
- running new jobs in new group is also good.
-
- 9.6 Mount with other subsystems.
- Mounting with other subsystems is a good test because there is a
- race and lock dependency with other cgroup subsystems.
-
- example)
- # mount -t cgroup none /cgroup -t cpuset,memory,cpu,devices
-
- and do task move, mkdir, rmdir etc...under this.
+++ /dev/null
-Memory Resource Controller
-
-NOTE: The Memory Resource Controller has been generically been referred
-to as the memory controller in this document. Do not confuse memory controller
-used here with the memory controller that is used in hardware.
-
-Salient features
-
-a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages
-b. The infrastructure allows easy addition of other types of memory to control
-c. Provides *zero overhead* for non memory controller users
-d. Provides a double LRU: global memory pressure causes reclaim from the
- global LRU; a cgroup on hitting a limit, reclaims from the per
- cgroup LRU
-
-NOTE: Swap Cache (unmapped) is not accounted now.
-
-Benefits and Purpose of the memory controller
-
-The memory controller isolates the memory behaviour of a group of tasks
-from the rest of the system. The article on LWN [12] mentions some probable
-uses of the memory controller. The memory controller can be used to
-
-a. Isolate an application or a group of applications
- Memory hungry applications can be isolated and limited to a smaller
- amount of memory.
-b. Create a cgroup with limited amount of memory, this can be used
- as a good alternative to booting with mem=XXXX.
-c. Virtualization solutions can control the amount of memory they want
- to assign to a virtual machine instance.
-d. A CD/DVD burner could control the amount of memory used by the
- rest of the system to ensure that burning does not fail due to lack
- of available memory.
-e. There are several other use cases, find one or use the controller just
- for fun (to learn and hack on the VM subsystem).
-
-1. History
-
-The memory controller has a long history. A request for comments for the memory
-controller was posted by Balbir Singh [1]. At the time the RFC was posted
-there were several implementations for memory control. The goal of the
-RFC was to build consensus and agreement for the minimal features required
-for memory control. The first RSS controller was posted by Balbir Singh[2]
-in Feb 2007. Pavel Emelianov [3][4][5] has since posted three versions of the
-RSS controller. At OLS, at the resource management BoF, everyone suggested
-that we handle both page cache and RSS together. Another request was raised
-to allow user space handling of OOM. The current memory controller is
-at version 6; it combines both mapped (RSS) and unmapped Page
-Cache Control [11].
-
-2. Memory Control
-
-Memory is a unique resource in the sense that it is present in a limited
-amount. If a task requires a lot of CPU processing, the task can spread
-its processing over a period of hours, days, months or years, but with
-memory, the same physical memory needs to be reused to accomplish the task.
-
-The memory controller implementation has been divided into phases. These
-are:
-
-1. Memory controller
-2. mlock(2) controller
-3. Kernel user memory accounting and slab control
-4. user mappings length controller
-
-The memory controller is the first controller developed.
-
-2.1. Design
-
-The core of the design is a counter called the res_counter. The res_counter
-tracks the current memory usage and limit of the group of processes associated
-with the controller. Each cgroup has a memory controller specific data
-structure (mem_cgroup) associated with it.
-
-2.2. Accounting
-
- +--------------------+
- | mem_cgroup |
- | (res_counter) |
- +--------------------+
- / ^ \
- / | \
- +---------------+ | +---------------+
- | mm_struct | |.... | mm_struct |
- | | | | |
- +---------------+ | +---------------+
- |
- + --------------+
- |
- +---------------+ +------+--------+
- | page +----------> page_cgroup|
- | | | |
- +---------------+ +---------------+
-
- (Figure 1: Hierarchy of Accounting)
-
-
-Figure 1 shows the important aspects of the controller
-
-1. Accounting happens per cgroup
-2. Each mm_struct knows about which cgroup it belongs to
-3. Each page has a pointer to the page_cgroup, which in turn knows the
- cgroup it belongs to
-
-The accounting is done as follows: mem_cgroup_charge() is invoked to setup
-the necessary data structures and check if the cgroup that is being charged
-is over its limit. If it is then reclaim is invoked on the cgroup.
-More details can be found in the reclaim section of this document.
-If everything goes well, a page meta-data-structure called page_cgroup is
-allocated and associated with the page. This routine also adds the page to
-the per cgroup LRU.
-
-2.2.1 Accounting details
-
-All mapped anon pages (RSS) and cache pages (Page Cache) are accounted.
-(some pages which never be reclaimable and will not be on global LRU
- are not accounted. we just accounts pages under usual vm management.)
-
-RSS pages are accounted at page_fault unless they've already been accounted
-for earlier. A file page will be accounted for as Page Cache when it's
-inserted into inode (radix-tree). While it's mapped into the page tables of
-processes, duplicate accounting is carefully avoided.
-
-A RSS page is unaccounted when it's fully unmapped. A PageCache page is
-unaccounted when it's removed from radix-tree.
-
-At page migration, accounting information is kept.
-
-Note: we just account pages-on-lru because our purpose is to control amount
-of used pages. not-on-lru pages are tend to be out-of-control from vm view.
-
-2.3 Shared Page Accounting
-
-Shared pages are accounted on the basis of the first touch approach. The
-cgroup that first touches a page is accounted for the page. The principle
-behind this approach is that a cgroup that aggressively uses a shared
-page will eventually get charged for it (once it is uncharged from
-the cgroup that brought it in -- this will happen on memory pressure).
-
-Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used..
-When you do swapoff and make swapped-out pages of shmem(tmpfs) to
-be backed into memory in force, charges for pages are accounted against the
-caller of swapoff rather than the users of shmem.
-
-
-2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP)
-Swap Extension allows you to record charge for swap. A swapped-in page is
-charged back to original page allocator if possible.
-
-When swap is accounted, following files are added.
- - memory.memsw.usage_in_bytes.
- - memory.memsw.limit_in_bytes.
-
-usage of mem+swap is limited by memsw.limit_in_bytes.
-
-Note: why 'mem+swap' rather than swap.
-The global LRU(kswapd) can swap out arbitrary pages. Swap-out means
-to move account from memory to swap...there is no change in usage of
-mem+swap.
-
-In other words, when we want to limit the usage of swap without affecting
-global LRU, mem+swap limit is better than just limiting swap from OS point
-of view.
-
-2.5 Reclaim
-
-Each cgroup maintains a per cgroup LRU that consists of an active
-and inactive list. When a cgroup goes over its limit, we first try
-to reclaim memory from the cgroup so as to make space for the new
-pages that the cgroup has touched. If the reclaim is unsuccessful,
-an OOM routine is invoked to select and kill the bulkiest task in the
-cgroup.
-
-The reclaim algorithm has not been modified for cgroups, except that
-pages that are selected for reclaiming come from the per cgroup LRU
-list.
-
-2. Locking
-
-The memory controller uses the following hierarchy
-
-1. zone->lru_lock is used for selecting pages to be isolated
-2. mem->per_zone->lru_lock protects the per cgroup LRU (per zone)
-3. lock_page_cgroup() is used to protect page->page_cgroup
-
-3. User Interface
-
-0. Configuration
-
-a. Enable CONFIG_CGROUPS
-b. Enable CONFIG_RESOURCE_COUNTERS
-c. Enable CONFIG_CGROUP_MEM_RES_CTLR
-
-1. Prepare the cgroups
-# mkdir -p /cgroups
-# mount -t cgroup none /cgroups -o memory
-
-2. Make the new group and move bash into it
-# mkdir /cgroups/0
-# echo $$ > /cgroups/0/tasks
-
-Since now we're in the 0 cgroup,
-We can alter the memory limit:
-# echo 4M > /cgroups/0/memory.limit_in_bytes
-
-NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
-mega or gigabytes.
-
-# cat /cgroups/0/memory.limit_in_bytes
-4194304
-
-NOTE: The interface has now changed to display the usage in bytes
-instead of pages
-
-We can check the usage:
-# cat /cgroups/0/memory.usage_in_bytes
-1216512
-
-A successful write to this file does not guarantee a successful set of
-this limit to the value written into the file. This can be due to a
-number of factors, such as rounding up to page boundaries or the total
-availability of memory on the system. The user is required to re-read
-this file after a write to guarantee the value committed by the kernel.
-
-# echo 1 > memory.limit_in_bytes
-# cat memory.limit_in_bytes
-4096
-
-The memory.failcnt field gives the number of times that the cgroup limit was
-exceeded.
-
-The memory.stat file gives accounting information. Now, the number of
-caches, RSS and Active pages/Inactive pages are shown.
-
-4. Testing
-
-Balbir posted lmbench, AIM9, LTP and vmmstress results [10] and [11].
-Apart from that v6 has been tested with several applications and regular
-daily use. The controller has also been tested on the PPC64, x86_64 and
-UML platforms.
-
-4.1 Troubleshooting
-
-Sometimes a user might find that the application under a cgroup is
-terminated. There are several causes for this:
-
-1. The cgroup limit is too low (just too low to do anything useful)
-2. The user is using anonymous memory and swap is turned off or too low
-
-A sync followed by echo 1 > /proc/sys/vm/drop_caches will help get rid of
-some of the pages cached in the cgroup (page cache pages).
-
-4.2 Task migration
-
-When a task migrates from one cgroup to another, it's charge is not
-carried forward. The pages allocated from the original cgroup still
-remain charged to it, the charge is dropped when the page is freed or
-reclaimed.
-
-4.3 Removing a cgroup
-
-A cgroup can be removed by rmdir, but as discussed in sections 4.1 and 4.2, a
-cgroup might have some charge associated with it, even though all
-tasks have migrated away from it.
-Such charges are freed(at default) or moved to its parent. When moved,
-both of RSS and CACHES are moved to parent.
-If both of them are busy, rmdir() returns -EBUSY. See 5.1 Also.
-
-Charges recorded in swap information is not updated at removal of cgroup.
-Recorded information is discarded and a cgroup which uses swap (swapcache)
-will be charged as a new owner of it.
-
-
-5. Misc. interfaces.
-
-5.1 force_empty
- memory.force_empty interface is provided to make cgroup's memory usage empty.
- You can use this interface only when the cgroup has no tasks.
- When writing anything to this
-
- # echo 0 > memory.force_empty
-
- Almost all pages tracked by this memcg will be unmapped and freed. Some of
- pages cannot be freed because it's locked or in-use. Such pages are moved
- to parent and this cgroup will be empty. But this may return -EBUSY in
- some too busy case.
-
- Typical use case of this interface is that calling this before rmdir().
- Because rmdir() moves all pages to parent, some out-of-use page caches can be
- moved to the parent. If you want to avoid that, force_empty will be useful.
-
-5.2 stat file
- memory.stat file includes following statistics (now)
- cache - # of pages from page-cache and shmem.
- rss - # of pages from anonymous memory.
- pgpgin - # of event of charging
- pgpgout - # of event of uncharging
- active_anon - # of pages on active lru of anon, shmem.
- inactive_anon - # of pages on active lru of anon, shmem
- active_file - # of pages on active lru of file-cache
- inactive_file - # of pages on inactive lru of file cache
- unevictable - # of pages cannot be reclaimed.(mlocked etc)
-
- Below is depend on CONFIG_DEBUG_VM.
- inactive_ratio - VM inernal parameter. (see mm/page_alloc.c)
- recent_rotated_anon - VM internal parameter. (see mm/vmscan.c)
- recent_rotated_file - VM internal parameter. (see mm/vmscan.c)
- recent_scanned_anon - VM internal parameter. (see mm/vmscan.c)
- recent_scanned_file - VM internal parameter. (see mm/vmscan.c)
-
- Memo:
- recent_rotated means recent frequency of lru rotation.
- recent_scanned means recent # of scans to lru.
- showing for better debug please see the code for meanings.
-
-
-5.3 swappiness
- Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
-
- Following cgroup's swapiness can't be changed.
- - root cgroup (uses /proc/sys/vm/swappiness).
- - a cgroup which uses hierarchy and it has child cgroup.
- - a cgroup which uses hierarchy and not the root of hierarchy.
-
-
-6. Hierarchy support
-
-The memory controller supports a deep hierarchy and hierarchical accounting.
-The hierarchy is created by creating the appropriate cgroups in the
-cgroup filesystem. Consider for example, the following cgroup filesystem
-hierarchy
-
- root
- / | \
- / | \
- a b c
- | \
- | \
- d e
-
-In the diagram above, with hierarchical accounting enabled, all memory
-usage of e, is accounted to its ancestors up until the root (i.e, c and root),
-that has memory.use_hierarchy enabled. If one of the ancestors goes over its
-limit, the reclaim algorithm reclaims from the tasks in the ancestor and the
-children of the ancestor.
-
-6.1 Enabling hierarchical accounting and reclaim
-
-The memory controller by default disables the hierarchy feature. Support
-can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup
-
-# echo 1 > memory.use_hierarchy
-
-The feature can be disabled by
-
-# echo 0 > memory.use_hierarchy
-
-NOTE1: Enabling/disabling will fail if the cgroup already has other
-cgroups created below it.
-
-NOTE2: This feature can be enabled/disabled per subtree.
-
-7. TODO
-
-1. Add support for accounting huge pages (as a separate controller)
-2. Make per-cgroup scanner reclaim not-shared pages first
-3. Teach controller to account for shared-pages
-4. Start reclamation in the background when the limit is
- not yet hit but the usage is getting closer
-
-Summary
-
-Overall, the memory controller has been a stable controller and has been
-commented and discussed quite extensively in the community.
-
-References
-
-1. Singh, Balbir. RFC: Memory Controller, http://lwn.net/Articles/206697/
-2. Singh, Balbir. Memory Controller (RSS Control),
- http://lwn.net/Articles/222762/
-3. Emelianov, Pavel. Resource controllers based on process cgroups
- http://lkml.org/lkml/2007/3/6/198
-4. Emelianov, Pavel. RSS controller based on process cgroups (v2)
- http://lkml.org/lkml/2007/4/9/78
-5. Emelianov, Pavel. RSS controller based on process cgroups (v3)
- http://lkml.org/lkml/2007/5/30/244
-6. Menage, Paul. Control Groups v10, http://lwn.net/Articles/236032/
-7. Vaidyanathan, Srinivasan, Control Groups: Pagecache accounting and control
- subsystem (v3), http://lwn.net/Articles/235534/
-8. Singh, Balbir. RSS controller v2 test results (lmbench),
- http://lkml.org/lkml/2007/5/17/232
-9. Singh, Balbir. RSS controller v2 AIM9 results
- http://lkml.org/lkml/2007/5/18/1
-10. Singh, Balbir. Memory controller v6 test results,
- http://lkml.org/lkml/2007/8/19/36
-11. Singh, Balbir. Memory controller introduction (v6),
- http://lkml.org/lkml/2007/8/17/69
-12. Corbet, Jonathan, Controlling memory use in cgroups,
- http://lwn.net/Articles/243795/
+++ /dev/null
-
- The Resource Counter
-
-The resource counter, declared at include/linux/res_counter.h,
-is supposed to facilitate the resource management by controllers
-by providing common stuff for accounting.
-
-This "stuff" includes the res_counter structure and routines
-to work with it.
-
-
-
-1. Crucial parts of the res_counter structure
-
- a. unsigned long long usage
-
- The usage value shows the amount of a resource that is consumed
- by a group at a given time. The units of measurement should be
- determined by the controller that uses this counter. E.g. it can
- be bytes, items or any other unit the controller operates on.
-
- b. unsigned long long max_usage
-
- The maximal value of the usage over time.
-
- This value is useful when gathering statistical information about
- the particular group, as it shows the actual resource requirements
- for a particular group, not just some usage snapshot.
-
- c. unsigned long long limit
-
- The maximal allowed amount of resource to consume by the group. In
- case the group requests for more resources, so that the usage value
- would exceed the limit, the resource allocation is rejected (see
- the next section).
-
- d. unsigned long long failcnt
-
- The failcnt stands for "failures counter". This is the number of
- resource allocation attempts that failed.
-
- c. spinlock_t lock
-
- Protects changes of the above values.
-
-
-
-2. Basic accounting routines
-
- a. void res_counter_init(struct res_counter *rc)
-
- Initializes the resource counter. As usual, should be the first
- routine called for a new counter.
-
- b. int res_counter_charge[_locked]
- (struct res_counter *rc, unsigned long val)
-
- When a resource is about to be allocated it has to be accounted
- with the appropriate resource counter (controller should determine
- which one to use on its own). This operation is called "charging".
-
- This is not very important which operation - resource allocation
- or charging - is performed first, but
- * if the allocation is performed first, this may create a
- temporary resource over-usage by the time resource counter is
- charged;
- * if the charging is performed first, then it should be uncharged
- on error path (if the one is called).
-
- c. void res_counter_uncharge[_locked]
- (struct res_counter *rc, unsigned long val)
-
- When a resource is released (freed) it should be de-accounted
- from the resource counter it was accounted to. This is called
- "uncharging".
-
- The _locked routines imply that the res_counter->lock is taken.
-
-
- 2.1 Other accounting routines
-
- There are more routines that may help you with common needs, like
- checking whether the limit is reached or resetting the max_usage
- value. They are all declared in include/linux/res_counter.h.
-
-
-
-3. Analyzing the resource counter registrations
-
- a. If the failcnt value constantly grows, this means that the counter's
- limit is too tight. Either the group is misbehaving and consumes too
- many resources, or the configuration is not suitable for the group
- and the limit should be increased.
-
- b. The max_usage value can be used to quickly tune the group. One may
- set the limits to maximal values and either load the container with
- a common pattern or leave one for a while. After this the max_usage
- value shows the amount of memory the container would require during
- its common activity.
-
- Setting the limit a bit above this value gives a pretty good
- configuration that works in most of the cases.
-
- c. If the max_usage is much less than the limit, but the failcnt value
- is growing, then the group tries to allocate a big chunk of resource
- at once.
-
- d. If the max_usage is much less than the limit, but the failcnt value
- is 0, then this group is given too high limit, that it does not
- require. It is better to lower the limit a bit leaving more resource
- for other groups.
-
-
-
-4. Communication with the control groups subsystem (cgroups)
-
-All the resource controllers that are using cgroups and resource counters
-should provide files (in the cgroup filesystem) to work with the resource
-counter fields. They are recommended to adhere to the following rules:
-
- a. File names
-
- Field name File name
- ---------------------------------------------------
- usage usage_in_<unit_of_measurement>
- max_usage max_usage_in_<unit_of_measurement>
- limit limit_in_<unit_of_measurement>
- failcnt failcnt
- lock no file :)
-
- b. Reading from file should show the corresponding field value in the
- appropriate format.
-
- c. Writing to file
-
- Field Expected behavior
- ----------------------------------
- usage prohibited
- max_usage reset to usage
- limit set the limit
- failcnt reset to zero
-
-
-
-5. Usage example
-
- a. Declare a task group (take a look at cgroups subsystem for this) and
- fold a res_counter into it
-
- struct my_group {
- struct res_counter res;
-
- <other fields>
- }
-
- b. Put hooks in resource allocation/release paths
-
- int alloc_something(...)
- {
- if (res_counter_charge(res_counter_ptr, amount) < 0)
- return -ENOMEM;
-
- <allocate the resource and return to the caller>
- }
-
- void release_something(...)
- {
- res_counter_uncharge(res_counter_ptr, amount);
-
- <release the resource>
- }
-
- In order to keep the usage value self-consistent, both the
- "res_counter_ptr" and the "amount" in release_something() should be
- the same as they were in the alloc_something() when the releasing
- resource was allocated.
-
- c. Provide the way to read res_counter values and set them (the cgroups
- still can help with it).
-
- c. Compile and run :)
+++ /dev/null
- CPUSETS
- -------
-
-Copyright (C) 2004 BULL SA.
-Written by Simon.Derr@bull.net
-
-Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
-Modified by Paul Jackson <pj@sgi.com>
-Modified by Christoph Lameter <clameter@sgi.com>
-Modified by Paul Menage <menage@google.com>
-Modified by Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
-
-CONTENTS:
-=========
-
-1. Cpusets
- 1.1 What are cpusets ?
- 1.2 Why are cpusets needed ?
- 1.3 How are cpusets implemented ?
- 1.4 What are exclusive cpusets ?
- 1.5 What is memory_pressure ?
- 1.6 What is memory spread ?
- 1.7 What is sched_load_balance ?
- 1.8 What is sched_relax_domain_level ?
- 1.9 How do I use cpusets ?
-2. Usage Examples and Syntax
- 2.1 Basic Usage
- 2.2 Adding/removing cpus
- 2.3 Setting flags
- 2.4 Attaching processes
-3. Questions
-4. Contact
-
-1. Cpusets
-==========
-
-1.1 What are cpusets ?
-----------------------
-
-Cpusets provide a mechanism for assigning a set of CPUs and Memory
-Nodes to a set of tasks. In this document "Memory Node" refers to
-an on-line node that contains memory.
-
-Cpusets constrain the CPU and Memory placement of tasks to only
-the resources within a tasks current cpuset. They form a nested
-hierarchy visible in a virtual file system. These are the essential
-hooks, beyond what is already present, required to manage dynamic
-job placement on large systems.
-
-Cpusets use the generic cgroup subsystem described in
-Documentation/cgroups/cgroups.txt.
-
-Requests by a task, using the sched_setaffinity(2) system call to
-include CPUs in its CPU affinity mask, and using the mbind(2) and
-set_mempolicy(2) system calls to include Memory Nodes in its memory
-policy, are both filtered through that tasks cpuset, filtering out any
-CPUs or Memory Nodes not in that cpuset. The scheduler will not
-schedule a task on a CPU that is not allowed in its cpus_allowed
-vector, and the kernel page allocator will not allocate a page on a
-node that is not allowed in the requesting tasks mems_allowed vector.
-
-User level code may create and destroy cpusets by name in the cgroup
-virtual file system, manage the attributes and permissions of these
-cpusets and which CPUs and Memory Nodes are assigned to each cpuset,
-specify and query to which cpuset a task is assigned, and list the
-task pids assigned to a cpuset.
-
-
-1.2 Why are cpusets needed ?
-----------------------------
-
-The management of large computer systems, with many processors (CPUs),
-complex memory cache hierarchies and multiple Memory Nodes having
-non-uniform access times (NUMA) presents additional challenges for
-the efficient scheduling and memory placement of processes.
-
-Frequently more modest sized systems can be operated with adequate
-efficiency just by letting the operating system automatically share
-the available CPU and Memory resources amongst the requesting tasks.
-
-But larger systems, which benefit more from careful processor and
-memory placement to reduce memory access times and contention,
-and which typically represent a larger investment for the customer,
-can benefit from explicitly placing jobs on properly sized subsets of
-the system.
-
-This can be especially valuable on:
-
- * Web Servers running multiple instances of the same web application,
- * Servers running different applications (for instance, a web server
- and a database), or
- * NUMA systems running large HPC applications with demanding
- performance characteristics.
-
-These subsets, or "soft partitions" must be able to be dynamically
-adjusted, as the job mix changes, without impacting other concurrently
-executing jobs. The location of the running jobs pages may also be moved
-when the memory locations are changed.
-
-The kernel cpuset patch provides the minimum essential kernel
-mechanisms required to efficiently implement such subsets. It
-leverages existing CPU and Memory Placement facilities in the Linux
-kernel to avoid any additional impact on the critical scheduler or
-memory allocator code.
-
-
-1.3 How are cpusets implemented ?
----------------------------------
-
-Cpusets provide a Linux kernel mechanism to constrain which CPUs and
-Memory Nodes are used by a process or set of processes.
-
-The Linux kernel already has a pair of mechanisms to specify on which
-CPUs a task may be scheduled (sched_setaffinity) and on which Memory
-Nodes it may obtain memory (mbind, set_mempolicy).
-
-Cpusets extends these two mechanisms as follows:
-
- - Cpusets are sets of allowed CPUs and Memory Nodes, known to the
- kernel.
- - Each task in the system is attached to a cpuset, via a pointer
- in the task structure to a reference counted cgroup structure.
- - Calls to sched_setaffinity are filtered to just those CPUs
- allowed in that tasks cpuset.
- - Calls to mbind and set_mempolicy are filtered to just
- those Memory Nodes allowed in that tasks cpuset.
- - The root cpuset contains all the systems CPUs and Memory
- Nodes.
- - For any cpuset, one can define child cpusets containing a subset
- of the parents CPU and Memory Node resources.
- - The hierarchy of cpusets can be mounted at /dev/cpuset, for
- browsing and manipulation from user space.
- - A cpuset may be marked exclusive, which ensures that no other
- cpuset (except direct ancestors and descendents) may contain
- any overlapping CPUs or Memory Nodes.
- - You can list all the tasks (by pid) attached to any cpuset.
-
-The implementation of cpusets requires a few, simple hooks
-into the rest of the kernel, none in performance critical paths:
-
- - in init/main.c, to initialize the root cpuset at system boot.
- - in fork and exit, to attach and detach a task from its cpuset.
- - in sched_setaffinity, to mask the requested CPUs by what's
- allowed in that tasks cpuset.
- - in sched.c migrate_all_tasks(), to keep migrating tasks within
- the CPUs allowed by their cpuset, if possible.
- - in the mbind and set_mempolicy system calls, to mask the requested
- Memory Nodes by what's allowed in that tasks cpuset.
- - in page_alloc.c, to restrict memory to allowed nodes.
- - in vmscan.c, to restrict page recovery to the current cpuset.
-
-You should mount the "cgroup" filesystem type in order to enable
-browsing and modifying the cpusets presently known to the kernel. No
-new system calls are added for cpusets - all support for querying and
-modifying cpusets is via this cpuset file system.
-
-The /proc/<pid>/status file for each task has four added lines,
-displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
-and mems_allowed (on which Memory Nodes it may obtain memory),
-in the two formats seen in the following example:
-
- Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
- Cpus_allowed_list: 0-127
- Mems_allowed: ffffffff,ffffffff
- Mems_allowed_list: 0-63
-
-Each cpuset is represented by a directory in the cgroup file system
-containing (on top of the standard cgroup files) the following
-files describing that cpuset:
-
- - cpus: list of CPUs in that cpuset
- - mems: list of Memory Nodes in that cpuset
- - memory_migrate flag: if set, move pages to cpusets nodes
- - cpu_exclusive flag: is cpu placement exclusive?
- - mem_exclusive flag: is memory placement exclusive?
- - mem_hardwall flag: is memory allocation hardwalled
- - memory_pressure: measure of how much paging pressure in cpuset
-
-In addition, the root cpuset only has the following file:
- - memory_pressure_enabled flag: compute memory_pressure?
-
-New cpusets are created using the mkdir system call or shell
-command. The properties of a cpuset, such as its flags, allowed
-CPUs and Memory Nodes, and attached tasks, are modified by writing
-to the appropriate file in that cpusets directory, as listed above.
-
-The named hierarchical structure of nested cpusets allows partitioning
-a large system into nested, dynamically changeable, "soft-partitions".
-
-The attachment of each task, automatically inherited at fork by any
-children of that task, to a cpuset allows organizing the work load
-on a system into related sets of tasks such that each set is constrained
-to using the CPUs and Memory Nodes of a particular cpuset. A task
-may be re-attached to any other cpuset, if allowed by the permissions
-on the necessary cpuset file system directories.
-
-Such management of a system "in the large" integrates smoothly with
-the detailed placement done on individual tasks and memory regions
-using the sched_setaffinity, mbind and set_mempolicy system calls.
-
-The following rules apply to each cpuset:
-
- - Its CPUs and Memory Nodes must be a subset of its parents.
- - It can't be marked exclusive unless its parent is.
- - If its cpu or memory is exclusive, they may not overlap any sibling.
-
-These rules, and the natural hierarchy of cpusets, enable efficient
-enforcement of the exclusive guarantee, without having to scan all
-cpusets every time any of them change to ensure nothing overlaps a
-exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
-to represent the cpuset hierarchy provides for a familiar permission
-and name space for cpusets, with a minimum of additional kernel code.
-
-The cpus and mems files in the root (top_cpuset) cpuset are
-read-only. The cpus file automatically tracks the value of
-cpu_online_map using a CPU hotplug notifier, and the mems file
-automatically tracks the value of node_states[N_HIGH_MEMORY]--i.e.,
-nodes with memory--using the cpuset_track_online_nodes() hook.
-
-
-1.4 What are exclusive cpusets ?
---------------------------------
-
-If a cpuset is cpu or mem exclusive, no other cpuset, other than
-a direct ancestor or descendent, may share any of the same CPUs or
-Memory Nodes.
-
-A cpuset that is mem_exclusive *or* mem_hardwall is "hardwalled",
-i.e. it restricts kernel allocations for page, buffer and other data
-commonly shared by the kernel across multiple users. All cpusets,
-whether hardwalled or not, restrict allocations of memory for user
-space. This enables configuring a system so that several independent
-jobs can share common kernel data, such as file system pages, while
-isolating each job's user allocation in its own cpuset. To do this,
-construct a large mem_exclusive cpuset to hold all the jobs, and
-construct child, non-mem_exclusive cpusets for each individual job.
-Only a small amount of typical kernel memory, such as requests from
-interrupt handlers, is allowed to be taken outside even a
-mem_exclusive cpuset.
-
-
-1.5 What is memory_pressure ?
------------------------------
-The memory_pressure of a cpuset provides a simple per-cpuset metric
-of the rate that the tasks in a cpuset are attempting to free up in
-use memory on the nodes of the cpuset to satisfy additional memory
-requests.
-
-This enables batch managers monitoring jobs running in dedicated
-cpusets to efficiently detect what level of memory pressure that job
-is causing.
-
-This is useful both on tightly managed systems running a wide mix of
-submitted jobs, which may choose to terminate or re-prioritize jobs that
-are trying to use more memory than allowed on the nodes assigned them,
-and with tightly coupled, long running, massively parallel scientific
-computing jobs that will dramatically fail to meet required performance
-goals if they start to use more memory than allowed to them.
-
-This mechanism provides a very economical way for the batch manager
-to monitor a cpuset for signs of memory pressure. It's up to the
-batch manager or other user code to decide what to do about it and
-take action.
-
-==> Unless this feature is enabled by writing "1" to the special file
- /dev/cpuset/memory_pressure_enabled, the hook in the rebalance
- code of __alloc_pages() for this metric reduces to simply noticing
- that the cpuset_memory_pressure_enabled flag is zero. So only
- systems that enable this feature will compute the metric.
-
-Why a per-cpuset, running average:
-
- Because this meter is per-cpuset, rather than per-task or mm,
- the system load imposed by a batch scheduler monitoring this
- metric is sharply reduced on large systems, because a scan of
- the tasklist can be avoided on each set of queries.
-
- Because this meter is a running average, instead of an accumulating
- counter, a batch scheduler can detect memory pressure with a
- single read, instead of having to read and accumulate results
- for a period of time.
-
- Because this meter is per-cpuset rather than per-task or mm,
- the batch scheduler can obtain the key information, memory
- pressure in a cpuset, with a single read, rather than having to
- query and accumulate results over all the (dynamically changing)
- set of tasks in the cpuset.
-
-A per-cpuset simple digital filter (requires a spinlock and 3 words
-of data per-cpuset) is kept, and updated by any task attached to that
-cpuset, if it enters the synchronous (direct) page reclaim code.
-
-A per-cpuset file provides an integer number representing the recent
-(half-life of 10 seconds) rate of direct page reclaims caused by
-the tasks in the cpuset, in units of reclaims attempted per second,
-times 1000.
-
-
-1.6 What is memory spread ?
----------------------------
-There are two boolean flag files per cpuset that control where the
-kernel allocates pages for the file system buffers and related in
-kernel data structures. They are called 'memory_spread_page' and
-'memory_spread_slab'.
-
-If the per-cpuset boolean flag file 'memory_spread_page' is set, then
-the kernel will spread the file system buffers (page cache) evenly
-over all the nodes that the faulting task is allowed to use, instead
-of preferring to put those pages on the node where the task is running.
-
-If the per-cpuset boolean flag file 'memory_spread_slab' is set,
-then the kernel will spread some file system related slab caches,
-such as for inodes and dentries evenly over all the nodes that the
-faulting task is allowed to use, instead of preferring to put those
-pages on the node where the task is running.
-
-The setting of these flags does not affect anonymous data segment or
-stack segment pages of a task.
-
-By default, both kinds of memory spreading are off, and memory
-pages are allocated on the node local to where the task is running,
-except perhaps as modified by the tasks NUMA mempolicy or cpuset
-configuration, so long as sufficient free memory pages are available.
-
-When new cpusets are created, they inherit the memory spread settings
-of their parent.
-
-Setting memory spreading causes allocations for the affected page
-or slab caches to ignore the tasks NUMA mempolicy and be spread
-instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
-mempolicies will not notice any change in these calls as a result of
-their containing tasks memory spread settings. If memory spreading
-is turned off, then the currently specified NUMA mempolicy once again
-applies to memory page allocations.
-
-Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
-files. By default they contain "0", meaning that the feature is off
-for that cpuset. If a "1" is written to that file, then that turns
-the named feature on.
-
-The implementation is simple.
-
-Setting the flag 'memory_spread_page' turns on a per-process flag
-PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
-joins that cpuset. The page allocation calls for the page cache
-is modified to perform an inline check for this PF_SPREAD_PAGE task
-flag, and if set, a call to a new routine cpuset_mem_spread_node()
-returns the node to prefer for the allocation.
-
-Similarly, setting 'memory_spread_slab' turns on the flag
-PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
-pages from the node returned by cpuset_mem_spread_node().
-
-The cpuset_mem_spread_node() routine is also simple. It uses the
-value of a per-task rotor cpuset_mem_spread_rotor to select the next
-node in the current tasks mems_allowed to prefer for the allocation.
-
-This memory placement policy is also known (in other contexts) as
-round-robin or interleave.
-
-This policy can provide substantial improvements for jobs that need
-to place thread local data on the corresponding node, but that need
-to access large file system data sets that need to be spread across
-the several nodes in the jobs cpuset in order to fit. Without this
-policy, especially for jobs that might have one thread reading in the
-data set, the memory allocation across the nodes in the jobs cpuset
-can become very uneven.
-
-1.7 What is sched_load_balance ?
---------------------------------
-
-The kernel scheduler (kernel/sched.c) automatically load balances
-tasks. If one CPU is underutilized, kernel code running on that
-CPU will look for tasks on other more overloaded CPUs and move those
-tasks to itself, within the constraints of such placement mechanisms
-as cpusets and sched_setaffinity.
-
-The algorithmic cost of load balancing and its impact on key shared
-kernel data structures such as the task list increases more than
-linearly with the number of CPUs being balanced. So the scheduler
-has support to partition the systems CPUs into a number of sched
-domains such that it only load balances within each sched domain.
-Each sched domain covers some subset of the CPUs in the system;
-no two sched domains overlap; some CPUs might not be in any sched
-domain and hence won't be load balanced.
-
-Put simply, it costs less to balance between two smaller sched domains
-than one big one, but doing so means that overloads in one of the
-two domains won't be load balanced to the other one.
-
-By default, there is one sched domain covering all CPUs, except those
-marked isolated using the kernel boot time "isolcpus=" argument.
-
-This default load balancing across all CPUs is not well suited for
-the following two situations:
- 1) On large systems, load balancing across many CPUs is expensive.
- If the system is managed using cpusets to place independent jobs
- on separate sets of CPUs, full load balancing is unnecessary.
- 2) Systems supporting realtime on some CPUs need to minimize
- system overhead on those CPUs, including avoiding task load
- balancing if that is not needed.
-
-When the per-cpuset flag "sched_load_balance" is enabled (the default
-setting), it requests that all the CPUs in that cpusets allowed 'cpus'
-be contained in a single sched domain, ensuring that load balancing
-can move a task (not otherwised pinned, as by sched_setaffinity)
-from any CPU in that cpuset to any other.
-
-When the per-cpuset flag "sched_load_balance" is disabled, then the
-scheduler will avoid load balancing across the CPUs in that cpuset,
---except-- in so far as is necessary because some overlapping cpuset
-has "sched_load_balance" enabled.
-
-So, for example, if the top cpuset has the flag "sched_load_balance"
-enabled, then the scheduler will have one sched domain covering all
-CPUs, and the setting of the "sched_load_balance" flag in any other
-cpusets won't matter, as we're already fully load balancing.
-
-Therefore in the above two situations, the top cpuset flag
-"sched_load_balance" should be disabled, and only some of the smaller,
-child cpusets have this flag enabled.
-
-When doing this, you don't usually want to leave any unpinned tasks in
-the top cpuset that might use non-trivial amounts of CPU, as such tasks
-may be artificially constrained to some subset of CPUs, depending on
-the particulars of this flag setting in descendent cpusets. Even if
-such a task could use spare CPU cycles in some other CPUs, the kernel
-scheduler might not consider the possibility of load balancing that
-task to that underused CPU.
-
-Of course, tasks pinned to a particular CPU can be left in a cpuset
-that disables "sched_load_balance" as those tasks aren't going anywhere
-else anyway.
-
-There is an impedance mismatch here, between cpusets and sched domains.
-Cpusets are hierarchical and nest. Sched domains are flat; they don't
-overlap and each CPU is in at most one sched domain.
-
-It is necessary for sched domains to be flat because load balancing
-across partially overlapping sets of CPUs would risk unstable dynamics
-that would be beyond our understanding. So if each of two partially
-overlapping cpusets enables the flag 'sched_load_balance', then we
-form a single sched domain that is a superset of both. We won't move
-a task to a CPU outside it cpuset, but the scheduler load balancing
-code might waste some compute cycles considering that possibility.
-
-This mismatch is why there is not a simple one-to-one relation
-between which cpusets have the flag "sched_load_balance" enabled,
-and the sched domain configuration. If a cpuset enables the flag, it
-will get balancing across all its CPUs, but if it disables the flag,
-it will only be assured of no load balancing if no other overlapping
-cpuset enables the flag.
-
-If two cpusets have partially overlapping 'cpus' allowed, and only
-one of them has this flag enabled, then the other may find its
-tasks only partially load balanced, just on the overlapping CPUs.
-This is just the general case of the top_cpuset example given a few
-paragraphs above. In the general case, as in the top cpuset case,
-don't leave tasks that might use non-trivial amounts of CPU in
-such partially load balanced cpusets, as they may be artificially
-constrained to some subset of the CPUs allowed to them, for lack of
-load balancing to the other CPUs.
-
-1.7.1 sched_load_balance implementation details.
-------------------------------------------------
-
-The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
-to most cpuset flags.) When enabled for a cpuset, the kernel will
-ensure that it can load balance across all the CPUs in that cpuset
-(makes sure that all the CPUs in the cpus_allowed of that cpuset are
-in the same sched domain.)
-
-If two overlapping cpusets both have 'sched_load_balance' enabled,
-then they will be (must be) both in the same sched domain.
-
-If, as is the default, the top cpuset has 'sched_load_balance' enabled,
-then by the above that means there is a single sched domain covering
-the whole system, regardless of any other cpuset settings.
-
-The kernel commits to user space that it will avoid load balancing
-where it can. It will pick as fine a granularity partition of sched
-domains as it can while still providing load balancing for any set
-of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
-
-The internal kernel cpuset to scheduler interface passes from the
-cpuset code to the scheduler code a partition of the load balanced
-CPUs in the system. This partition is a set of subsets (represented
-as an array of cpumask_t) of CPUs, pairwise disjoint, that cover all
-the CPUs that must be load balanced.
-
-Whenever the 'sched_load_balance' flag changes, or CPUs come or go
-from a cpuset with this flag enabled, or a cpuset with this flag
-enabled is removed, the cpuset code builds a new such partition and
-passes it to the scheduler sched domain setup code, to have the sched
-domains rebuilt as necessary.
-
-This partition exactly defines what sched domains the scheduler should
-setup - one sched domain for each element (cpumask_t) in the partition.
-
-The scheduler remembers the currently active sched domain partitions.
-When the scheduler routine partition_sched_domains() is invoked from
-the cpuset code to update these sched domains, it compares the new
-partition requested with the current, and updates its sched domains,
-removing the old and adding the new, for each change.
-
-
-1.8 What is sched_relax_domain_level ?
---------------------------------------
-
-In sched domain, the scheduler migrates tasks in 2 ways; periodic load
-balance on tick, and at time of some schedule events.
-
-When a task is woken up, scheduler try to move the task on idle CPU.
-For example, if a task A running on CPU X activates another task B
-on the same CPU X, and if CPU Y is X's sibling and performing idle,
-then scheduler migrate task B to CPU Y so that task B can start on
-CPU Y without waiting task A on CPU X.
-
-And if a CPU run out of tasks in its runqueue, the CPU try to pull
-extra tasks from other busy CPUs to help them before it is going to
-be idle.
-
-Of course it takes some searching cost to find movable tasks and/or
-idle CPUs, the scheduler might not search all CPUs in the domain
-everytime. In fact, in some architectures, the searching ranges on
-events are limited in the same socket or node where the CPU locates,
-while the load balance on tick searchs all.
-
-For example, assume CPU Z is relatively far from CPU X. Even if CPU Z
-is idle while CPU X and the siblings are busy, scheduler can't migrate
-woken task B from X to Z since it is out of its searching range.
-As the result, task B on CPU X need to wait task A or wait load balance
-on the next tick. For some applications in special situation, waiting
-1 tick may be too long.
-
-The 'sched_relax_domain_level' file allows you to request changing
-this searching range as you like. This file takes int value which
-indicates size of searching range in levels ideally as follows,
-otherwise initial value -1 that indicates the cpuset has no request.
-
- -1 : no request. use system default or follow request of others.
- 0 : no search.
- 1 : search siblings (hyperthreads in a core).
- 2 : search cores in a package.
- 3 : search cpus in a node [= system wide on non-NUMA system]
- ( 4 : search nodes in a chunk of node [on NUMA system] )
- ( 5 : search system wide [on NUMA system] )
-
-The system default is architecture dependent. The system default
-can be changed using the relax_domain_level= boot parameter.
-
-This file is per-cpuset and affect the sched domain where the cpuset
-belongs to. Therefore if the flag 'sched_load_balance' of a cpuset
-is disabled, then 'sched_relax_domain_level' have no effect since
-there is no sched domain belonging the cpuset.
-
-If multiple cpusets are overlapping and hence they form a single sched
-domain, the largest value among those is used. Be careful, if one
-requests 0 and others are -1 then 0 is used.
-
-Note that modifying this file will have both good and bad effects,
-and whether it is acceptable or not will be depend on your situation.
-Don't modify this file if you are not sure.
-
-If your situation is:
- - The migration costs between each cpu can be assumed considerably
- small(for you) due to your special application's behavior or
- special hardware support for CPU cache etc.
- - The searching cost doesn't have impact(for you) or you can make
- the searching cost enough small by managing cpuset to compact etc.
- - The latency is required even it sacrifices cache hit rate etc.
-then increasing 'sched_relax_domain_level' would benefit you.
-
-
-1.9 How do I use cpusets ?
---------------------------
-
-In order to minimize the impact of cpusets on critical kernel
-code, such as the scheduler, and due to the fact that the kernel
-does not support one task updating the memory placement of another
-task directly, the impact on a task of changing its cpuset CPU
-or Memory Node placement, or of changing to which cpuset a task
-is attached, is subtle.
-
-If a cpuset has its Memory Nodes modified, then for each task attached
-to that cpuset, the next time that the kernel attempts to allocate
-a page of memory for that task, the kernel will notice the change
-in the tasks cpuset, and update its per-task memory placement to
-remain within the new cpusets memory placement. If the task was using
-mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
-its new cpuset, then the task will continue to use whatever subset
-of MPOL_BIND nodes are still allowed in the new cpuset. If the task
-was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
-in the new cpuset, then the task will be essentially treated as if it
-was MPOL_BIND bound to the new cpuset (even though its numa placement,
-as queried by get_mempolicy(), doesn't change). If a task is moved
-from one cpuset to another, then the kernel will adjust the tasks
-memory placement, as above, the next time that the kernel attempts
-to allocate a page of memory for that task.
-
-If a cpuset has its 'cpus' modified, then each task in that cpuset
-will have its allowed CPU placement changed immediately. Similarly,
-if a tasks pid is written to a cpusets 'tasks' file, in either its
-current cpuset or another cpuset, then its allowed CPU placement is
-changed immediately. If such a task had been bound to some subset
-of its cpuset using the sched_setaffinity() call, the task will be
-allowed to run on any CPU allowed in its new cpuset, negating the
-affect of the prior sched_setaffinity() call.
-
-In summary, the memory placement of a task whose cpuset is changed is
-updated by the kernel, on the next allocation of a page for that task,
-but the processor placement is not updated, until that tasks pid is
-rewritten to the 'tasks' file of its cpuset. This is done to avoid
-impacting the scheduler code in the kernel with a check for changes
-in a tasks processor placement.
-
-Normally, once a page is allocated (given a physical page
-of main memory) then that page stays on whatever node it
-was allocated, so long as it remains allocated, even if the
-cpusets memory placement policy 'mems' subsequently changes.
-If the cpuset flag file 'memory_migrate' is set true, then when
-tasks are attached to that cpuset, any pages that task had
-allocated to it on nodes in its previous cpuset are migrated
-to the tasks new cpuset. The relative placement of the page within
-the cpuset is preserved during these migration operations if possible.
-For example if the page was on the second valid node of the prior cpuset
-then the page will be placed on the second valid node of the new cpuset.
-
-Also if 'memory_migrate' is set true, then if that cpusets
-'mems' file is modified, pages allocated to tasks in that
-cpuset, that were on nodes in the previous setting of 'mems',
-will be moved to nodes in the new setting of 'mems.'
-Pages that were not in the tasks prior cpuset, or in the cpusets
-prior 'mems' setting, will not be moved.
-
-There is an exception to the above. If hotplug functionality is used
-to remove all the CPUs that are currently assigned to a cpuset,
-then all the tasks in that cpuset will be moved to the nearest ancestor
-with non-empty cpus. But the moving of some (or all) tasks might fail if
-cpuset is bound with another cgroup subsystem which has some restrictions
-on task attaching. In this failing case, those tasks will stay
-in the original cpuset, and the kernel will automatically update
-their cpus_allowed to allow all online CPUs. When memory hotplug
-functionality for removing Memory Nodes is available, a similar exception
-is expected to apply there as well. In general, the kernel prefers to
-violate cpuset placement, over starving a task that has had all
-its allowed CPUs or Memory Nodes taken offline.
-
-There is a second exception to the above. GFP_ATOMIC requests are
-kernel internal allocations that must be satisfied, immediately.
-The kernel may drop some request, in rare cases even panic, if a
-GFP_ATOMIC alloc fails. If the request cannot be satisfied within
-the current tasks cpuset, then we relax the cpuset, and look for
-memory anywhere we can find it. It's better to violate the cpuset
-than stress the kernel.
-
-To start a new job that is to be contained within a cpuset, the steps are:
-
- 1) mkdir /dev/cpuset
- 2) mount -t cgroup -ocpuset cpuset /dev/cpuset
- 3) Create the new cpuset by doing mkdir's and write's (or echo's) in
- the /dev/cpuset virtual file system.
- 4) Start a task that will be the "founding father" of the new job.
- 5) Attach that task to the new cpuset by writing its pid to the
- /dev/cpuset tasks file for that cpuset.
- 6) fork, exec or clone the job tasks from this founding father task.
-
-For example, the following sequence of commands will setup a cpuset
-named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
-and then start a subshell 'sh' in that cpuset:
-
- mount -t cgroup -ocpuset cpuset /dev/cpuset
- cd /dev/cpuset
- mkdir Charlie
- cd Charlie
- /bin/echo 2-3 > cpus
- /bin/echo 1 > mems
- /bin/echo $$ > tasks
- sh
- # The subshell 'sh' is now running in cpuset Charlie
- # The next line should display '/Charlie'
- cat /proc/self/cpuset
-
-In the future, a C library interface to cpusets will likely be
-available. For now, the only way to query or modify cpusets is
-via the cpuset file system, using the various cd, mkdir, echo, cat,
-rmdir commands from the shell, or their equivalent from C.
-
-The sched_setaffinity calls can also be done at the shell prompt using
-SGI's runon or Robert Love's taskset. The mbind and set_mempolicy
-calls can be done at the shell prompt using the numactl command
-(part of Andi Kleen's numa package).
-
-2. Usage Examples and Syntax
-============================
-
-2.1 Basic Usage
----------------
-
-Creating, modifying, using the cpusets can be done through the cpuset
-virtual filesystem.
-
-To mount it, type:
-# mount -t cgroup -o cpuset cpuset /dev/cpuset
-
-Then under /dev/cpuset you can find a tree that corresponds to the
-tree of the cpusets in the system. For instance, /dev/cpuset
-is the cpuset that holds the whole system.
-
-If you want to create a new cpuset under /dev/cpuset:
-# cd /dev/cpuset
-# mkdir my_cpuset
-
-Now you want to do something with this cpuset.
-# cd my_cpuset
-
-In this directory you can find several files:
-# ls
-cpu_exclusive memory_migrate mems tasks
-cpus memory_pressure notify_on_release
-mem_exclusive memory_spread_page sched_load_balance
-mem_hardwall memory_spread_slab sched_relax_domain_level
-
-Reading them will give you information about the state of this cpuset:
-the CPUs and Memory Nodes it can use, the processes that are using
-it, its properties. By writing to these files you can manipulate
-the cpuset.
-
-Set some flags:
-# /bin/echo 1 > cpu_exclusive
-
-Add some cpus:
-# /bin/echo 0-7 > cpus
-
-Add some mems:
-# /bin/echo 0-7 > mems
-
-Now attach your shell to this cpuset:
-# /bin/echo $$ > tasks
-
-You can also create cpusets inside your cpuset by using mkdir in this
-directory.
-# mkdir my_sub_cs
-
-To remove a cpuset, just use rmdir:
-# rmdir my_sub_cs
-This will fail if the cpuset is in use (has cpusets inside, or has
-processes attached).
-
-Note that for legacy reasons, the "cpuset" filesystem exists as a
-wrapper around the cgroup filesystem.
-
-The command
-
-mount -t cpuset X /dev/cpuset
-
-is equivalent to
-
-mount -t cgroup -ocpuset X /dev/cpuset
-echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent
-
-2.2 Adding/removing cpus
-------------------------
-
-This is the syntax to use when writing in the cpus or mems files
-in cpuset directories:
-
-# /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
-# /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
-
-2.3 Setting flags
------------------
-
-The syntax is very simple:
-
-# /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
-# /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
-
-2.4 Attaching processes
------------------------
-
-# /bin/echo PID > tasks
-
-Note that it is PID, not PIDs. You can only attach ONE task at a time.
-If you have several tasks to attach, you have to do it one after another:
-
-# /bin/echo PID1 > tasks
-# /bin/echo PID2 > tasks
- ...
-# /bin/echo PIDn > tasks
-
-
-3. Questions
-============
-
-Q: what's up with this '/bin/echo' ?
-A: bash's builtin 'echo' command does not check calls to write() against
- errors. If you use it in the cpuset file system, you won't be
- able to tell whether a command succeeded or failed.
-
-Q: When I attach processes, only the first of the line gets really attached !
-A: We can only return one error code per call to write(). So you should also
- put only ONE pid.
-
-4. Contact
-==========
-
-Web: http://www.bullopensource.org/cpuset
This options needs CONFIG_CGROUPS to be defined, and lets the administrator
create arbitrary groups of tasks, using the "cgroup" pseudo filesystem. See
- Documentation/cgroups.txt for more information about this filesystem.
+ Documentation/cgroups/cgroups.txt for more information about this filesystem.
Only one of these options to group tasks can be chosen and not both.
*
* Author: Pavel Emelianov <xemul@openvz.org>
*
- * See Documentation/controllers/resource_counter.txt for more
+ * See Documentation/cgroups/resource_counter.txt for more
* info about what this counter is.
*/
This option allows you to create arbitrary task groups
using the "cgroup" pseudo filesystem and control
the cpu bandwidth allocated to each such task group.
- Refer to Documentation/cgroups.txt for more information
- on "cgroup" pseudo filesystem.
+ Refer to Documentation/cgroups/cgroups.txt for more
+ information on "cgroup" pseudo filesystem.
endchoice
use with process control subsystems such as Cpusets, CFS, memory
controls or device isolation.
See
- - Documentation/cpusets.txt (Cpusets)
- Documentation/scheduler/sched-design-CFS.txt (CFS)
- - Documentation/cgroups/ (features for grouping, isolation)
- - Documentation/controllers/ (features for resource control)
+ - Documentation/cgroups/ (features for grouping, isolation
+ and resource control)
Say N if unsure.
* load balancing domains (sched domains) as specified by that partial
* partition.
*
- * See "What is sched_load_balance" in Documentation/cpusets.txt
+ * See "What is sched_load_balance" in Documentation/cgroups/cpusets.txt
* for a background explanation of this.
*
* Does not return errors, on the theory that the callers of this
projects / GitHub / LineageOS / android_kernel_samsung_universal7580.git / commitdiff