mm: export a function to get vm committed memory

It will be useful to be able to access global memory commitment from
device drivers.  On the Hyper-V platform, the host has a policy engine to
balance the available physical memory amongst all competing virtual
machines hosted on a given node.  This policy engine is driven by a number
of metrics including the memory commitment reported by the guests.  The
balloon driver for Linux on Hyper-V will use this function to retrieve
guest memory commitment.  This function is also used in Xen self
ballooning code.

[akpm@linux-foundation.org: coding-style tweak]
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/xen/xen-selfballoon.c b/drivers/xen/xen-selfballoon.c
index 7d041cb6da2662fada88101835b94d1aed63b9bc..2552d3e0a70f2759597c54b8218e17248412337c 100644 (file)
--- a/drivers/xen/xen-selfballoon.c
+++ b/drivers/xen/xen-selfballoon.c
@@ -222,7 +222,7 @@ static void selfballoon_process(struct work_struct *work)
        if (xen_selfballooning_enabled) {
                cur_pages = totalram_pages;
                tgt_pages = cur_pages; /* default is no change */
-               goal_pages = percpu_counter_read_positive(&vm_committed_as) +
+               goal_pages = vm_memory_committed() +
                                totalreserve_pages +
                                MB2PAGES(selfballoon_reserved_mb);
 #ifdef CONFIG_FRONTSWAP

diff --git a/include/linux/mman.h b/include/linux/mman.h
index d09dde1e57fb43e2f5be170d31e8fceb8c41a389..9aa863da287fedf383f3c507c287aa220cbd6a86 100644 (file)
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -11,6 +11,8 @@ extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
 extern struct percpu_counter vm_committed_as;
 
+unsigned long vm_memory_committed(void);
+
 static inline void vm_acct_memory(long pages)
 {
        percpu_counter_add(&vm_committed_as, pages);

diff --git a/mm/mmap.c b/mm/mmap.c
index 2d942353d681a8b4f08155eebdcfb20b088093e7..b064822be82e4acb1117a44ec3c0fdee903783c3 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -88,6 +88,20 @@ int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
  */
 struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp;
 
+/*
+ * The global memory commitment made in the system can be a metric
+ * that can be used to drive ballooning decisions when Linux is hosted
+ * as a guest. On Hyper-V, the host implements a policy engine for dynamically
+ * balancing memory across competing virtual machines that are hosted.
+ * Several metrics drive this policy engine including the guest reported
+ * memory commitment.
+ */
+unsigned long vm_memory_committed(void)
+{
+       return percpu_counter_read_positive(&vm_committed_as);
+}
+EXPORT_SYMBOL_GPL(vm_memory_committed);
+
 /*
  * Check that a process has enough memory to allocate a new virtual
  * mapping. 0 means there is enough memory for the allocation to

diff --git a/mm/nommu.c b/mm/nommu.c
index 45131b41bcdbaf4fdfd6c411a6d0aef526ed0883..79c3cac87afa1d1f96fc9397f50bb370980e0a84 100644 (file)
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -66,6 +66,21 @@ int heap_stack_gap = 0;
 
 atomic_long_t mmap_pages_allocated;
 
+/*
+ * The global memory commitment made in the system can be a metric
+ * that can be used to drive ballooning decisions when Linux is hosted
+ * as a guest. On Hyper-V, the host implements a policy engine for dynamically
+ * balancing memory across competing virtual machines that are hosted.
+ * Several metrics drive this policy engine including the guest reported
+ * memory commitment.
+ */
+unsigned long vm_memory_committed(void)
+{
+       return percpu_counter_read_positive(&vm_committed_as);
+}
+
+EXPORT_SYMBOL_GPL(vm_memory_committed);
+
 EXPORT_SYMBOL(mem_map);
 EXPORT_SYMBOL(num_physpages);