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db0fb184 | 1 | Documentation for /proc/sys/vm/* kernel version 2.6.29 |
1da177e4 | 2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> |
db0fb184 | 3 | (c) 2008 Peter W. Morreale <pmorreale@novell.com> |
1da177e4 LT |
4 | |
5 | For general info and legal blurb, please look in README. | |
6 | ||
7 | ============================================================== | |
8 | ||
9 | This file contains the documentation for the sysctl files in | |
db0fb184 | 10 | /proc/sys/vm and is valid for Linux kernel version 2.6.29. |
1da177e4 LT |
11 | |
12 | The files in this directory can be used to tune the operation | |
13 | of the virtual memory (VM) subsystem of the Linux kernel and | |
14 | the writeout of dirty data to disk. | |
15 | ||
16 | Default values and initialization routines for most of these | |
17 | files can be found in mm/swap.c. | |
18 | ||
19 | Currently, these files are in /proc/sys/vm: | |
db0fb184 | 20 | |
4eeab4f5 | 21 | - admin_reserve_kbytes |
db0fb184 | 22 | - block_dump |
76ab0f53 | 23 | - compact_memory |
db0fb184 | 24 | - dirty_background_bytes |
1da177e4 | 25 | - dirty_background_ratio |
db0fb184 | 26 | - dirty_bytes |
1da177e4 | 27 | - dirty_expire_centisecs |
db0fb184 | 28 | - dirty_ratio |
1da177e4 | 29 | - dirty_writeback_centisecs |
db0fb184 | 30 | - drop_caches |
5e771905 | 31 | - extfrag_threshold |
6fa3eb70 | 32 | - extra_free_kbytes |
db0fb184 PM |
33 | - hugepages_treat_as_movable |
34 | - hugetlb_shm_group | |
35 | - laptop_mode | |
36 | - legacy_va_layout | |
37 | - lowmem_reserve_ratio | |
1da177e4 | 38 | - max_map_count |
6a46079c AK |
39 | - memory_failure_early_kill |
40 | - memory_failure_recovery | |
1da177e4 | 41 | - min_free_kbytes |
0ff38490 | 42 | - min_slab_ratio |
db0fb184 PM |
43 | - min_unmapped_ratio |
44 | - mmap_min_addr | |
d5dbac87 NA |
45 | - nr_hugepages |
46 | - nr_overcommit_hugepages | |
db0fb184 PM |
47 | - nr_trim_pages (only if CONFIG_MMU=n) |
48 | - numa_zonelist_order | |
49 | - oom_dump_tasks | |
50 | - oom_kill_allocating_task | |
51 | - overcommit_memory | |
52 | - overcommit_ratio | |
53 | - page-cluster | |
54 | - panic_on_oom | |
55 | - percpu_pagelist_fraction | |
56 | - stat_interval | |
57 | - swappiness | |
c9b1d098 | 58 | - user_reserve_kbytes |
db0fb184 PM |
59 | - vfs_cache_pressure |
60 | - zone_reclaim_mode | |
61 | ||
1da177e4 LT |
62 | ============================================================== |
63 | ||
4eeab4f5 AS |
64 | admin_reserve_kbytes |
65 | ||
66 | The amount of free memory in the system that should be reserved for users | |
67 | with the capability cap_sys_admin. | |
68 | ||
69 | admin_reserve_kbytes defaults to min(3% of free pages, 8MB) | |
70 | ||
71 | That should provide enough for the admin to log in and kill a process, | |
72 | if necessary, under the default overcommit 'guess' mode. | |
73 | ||
74 | Systems running under overcommit 'never' should increase this to account | |
75 | for the full Virtual Memory Size of programs used to recover. Otherwise, | |
76 | root may not be able to log in to recover the system. | |
77 | ||
78 | How do you calculate a minimum useful reserve? | |
79 | ||
80 | sshd or login + bash (or some other shell) + top (or ps, kill, etc.) | |
81 | ||
82 | For overcommit 'guess', we can sum resident set sizes (RSS). | |
83 | On x86_64 this is about 8MB. | |
84 | ||
85 | For overcommit 'never', we can take the max of their virtual sizes (VSZ) | |
86 | and add the sum of their RSS. | |
87 | On x86_64 this is about 128MB. | |
88 | ||
89 | Changing this takes effect whenever an application requests memory. | |
90 | ||
91 | ============================================================== | |
92 | ||
db0fb184 | 93 | block_dump |
1da177e4 | 94 | |
db0fb184 PM |
95 | block_dump enables block I/O debugging when set to a nonzero value. More |
96 | information on block I/O debugging is in Documentation/laptops/laptop-mode.txt. | |
1da177e4 LT |
97 | |
98 | ============================================================== | |
99 | ||
76ab0f53 MG |
100 | compact_memory |
101 | ||
102 | Available only when CONFIG_COMPACTION is set. When 1 is written to the file, | |
103 | all zones are compacted such that free memory is available in contiguous | |
104 | blocks where possible. This can be important for example in the allocation of | |
105 | huge pages although processes will also directly compact memory as required. | |
106 | ||
107 | ============================================================== | |
108 | ||
db0fb184 | 109 | dirty_background_bytes |
1da177e4 | 110 | |
6601fac8 AB |
111 | Contains the amount of dirty memory at which the background kernel |
112 | flusher threads will start writeback. | |
1da177e4 | 113 | |
abffc020 AR |
114 | Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only |
115 | one of them may be specified at a time. When one sysctl is written it is | |
116 | immediately taken into account to evaluate the dirty memory limits and the | |
117 | other appears as 0 when read. | |
1da177e4 | 118 | |
db0fb184 | 119 | ============================================================== |
1da177e4 | 120 | |
db0fb184 | 121 | dirty_background_ratio |
1da177e4 | 122 | |
db0fb184 | 123 | Contains, as a percentage of total system memory, the number of pages at which |
6601fac8 | 124 | the background kernel flusher threads will start writing out dirty data. |
1da177e4 | 125 | |
db0fb184 | 126 | ============================================================== |
1da177e4 | 127 | |
db0fb184 PM |
128 | dirty_bytes |
129 | ||
130 | Contains the amount of dirty memory at which a process generating disk writes | |
131 | will itself start writeback. | |
132 | ||
abffc020 AR |
133 | Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be |
134 | specified at a time. When one sysctl is written it is immediately taken into | |
135 | account to evaluate the dirty memory limits and the other appears as 0 when | |
136 | read. | |
1da177e4 | 137 | |
9e4a5bda AR |
138 | Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any |
139 | value lower than this limit will be ignored and the old configuration will be | |
140 | retained. | |
141 | ||
1da177e4 LT |
142 | ============================================================== |
143 | ||
db0fb184 | 144 | dirty_expire_centisecs |
1da177e4 | 145 | |
db0fb184 | 146 | This tunable is used to define when dirty data is old enough to be eligible |
6601fac8 AB |
147 | for writeout by the kernel flusher threads. It is expressed in 100'ths |
148 | of a second. Data which has been dirty in-memory for longer than this | |
149 | interval will be written out next time a flusher thread wakes up. | |
db0fb184 PM |
150 | |
151 | ============================================================== | |
152 | ||
153 | dirty_ratio | |
154 | ||
155 | Contains, as a percentage of total system memory, the number of pages at which | |
156 | a process which is generating disk writes will itself start writing out dirty | |
157 | data. | |
1da177e4 LT |
158 | |
159 | ============================================================== | |
160 | ||
db0fb184 | 161 | dirty_writeback_centisecs |
1da177e4 | 162 | |
6601fac8 | 163 | The kernel flusher threads will periodically wake up and write `old' data |
db0fb184 PM |
164 | out to disk. This tunable expresses the interval between those wakeups, in |
165 | 100'ths of a second. | |
1da177e4 | 166 | |
db0fb184 | 167 | Setting this to zero disables periodic writeback altogether. |
1da177e4 LT |
168 | |
169 | ============================================================== | |
170 | ||
db0fb184 | 171 | drop_caches |
1da177e4 | 172 | |
db0fb184 PM |
173 | Writing to this will cause the kernel to drop clean caches, dentries and |
174 | inodes from memory, causing that memory to become free. | |
1da177e4 | 175 | |
db0fb184 PM |
176 | To free pagecache: |
177 | echo 1 > /proc/sys/vm/drop_caches | |
178 | To free dentries and inodes: | |
179 | echo 2 > /proc/sys/vm/drop_caches | |
180 | To free pagecache, dentries and inodes: | |
181 | echo 3 > /proc/sys/vm/drop_caches | |
1da177e4 | 182 | |
db0fb184 PM |
183 | As this is a non-destructive operation and dirty objects are not freeable, the |
184 | user should run `sync' first. | |
1da177e4 LT |
185 | |
186 | ============================================================== | |
187 | ||
5e771905 MG |
188 | extfrag_threshold |
189 | ||
190 | This parameter affects whether the kernel will compact memory or direct | |
191 | reclaim to satisfy a high-order allocation. /proc/extfrag_index shows what | |
192 | the fragmentation index for each order is in each zone in the system. Values | |
193 | tending towards 0 imply allocations would fail due to lack of memory, | |
194 | values towards 1000 imply failures are due to fragmentation and -1 implies | |
195 | that the allocation will succeed as long as watermarks are met. | |
196 | ||
197 | The kernel will not compact memory in a zone if the | |
198 | fragmentation index is <= extfrag_threshold. The default value is 500. | |
199 | ||
200 | ============================================================== | |
201 | ||
6fa3eb70 S |
202 | extra_free_kbytes |
203 | ||
204 | This parameter tells the VM to keep extra free memory between the threshold | |
205 | where background reclaim (kswapd) kicks in, and the threshold where direct | |
206 | reclaim (by allocating processes) kicks in. | |
207 | ||
208 | This is useful for workloads that require low latency memory allocations | |
209 | and have a bounded burstiness in memory allocations, for example a | |
210 | realtime application that receives and transmits network traffic | |
211 | (causing in-kernel memory allocations) with a maximum total message burst | |
212 | size of 200MB may need 200MB of extra free memory to avoid direct reclaim | |
213 | related latencies. | |
214 | ||
215 | ============================================================== | |
216 | ||
db0fb184 | 217 | hugepages_treat_as_movable |
1da177e4 | 218 | |
db0fb184 PM |
219 | This parameter is only useful when kernelcore= is specified at boot time to |
220 | create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages | |
221 | are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero | |
222 | value written to hugepages_treat_as_movable allows huge pages to be allocated | |
223 | from ZONE_MOVABLE. | |
8ad4b1fb | 224 | |
db0fb184 PM |
225 | Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge |
226 | pages pool can easily grow or shrink within. Assuming that applications are | |
227 | not running that mlock() a lot of memory, it is likely the huge pages pool | |
228 | can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value | |
229 | into nr_hugepages and triggering page reclaim. | |
24950898 | 230 | |
8ad4b1fb RS |
231 | ============================================================== |
232 | ||
db0fb184 | 233 | hugetlb_shm_group |
8ad4b1fb | 234 | |
db0fb184 PM |
235 | hugetlb_shm_group contains group id that is allowed to create SysV |
236 | shared memory segment using hugetlb page. | |
8ad4b1fb | 237 | |
db0fb184 | 238 | ============================================================== |
8ad4b1fb | 239 | |
db0fb184 | 240 | laptop_mode |
1743660b | 241 | |
db0fb184 PM |
242 | laptop_mode is a knob that controls "laptop mode". All the things that are |
243 | controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt. | |
1743660b | 244 | |
db0fb184 | 245 | ============================================================== |
1743660b | 246 | |
db0fb184 | 247 | legacy_va_layout |
1b2ffb78 | 248 | |
2174efb6 | 249 | If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel |
db0fb184 | 250 | will use the legacy (2.4) layout for all processes. |
1b2ffb78 | 251 | |
db0fb184 | 252 | ============================================================== |
1b2ffb78 | 253 | |
db0fb184 PM |
254 | lowmem_reserve_ratio |
255 | ||
256 | For some specialised workloads on highmem machines it is dangerous for | |
257 | the kernel to allow process memory to be allocated from the "lowmem" | |
258 | zone. This is because that memory could then be pinned via the mlock() | |
259 | system call, or by unavailability of swapspace. | |
260 | ||
261 | And on large highmem machines this lack of reclaimable lowmem memory | |
262 | can be fatal. | |
263 | ||
264 | So the Linux page allocator has a mechanism which prevents allocations | |
265 | which _could_ use highmem from using too much lowmem. This means that | |
266 | a certain amount of lowmem is defended from the possibility of being | |
267 | captured into pinned user memory. | |
268 | ||
269 | (The same argument applies to the old 16 megabyte ISA DMA region. This | |
270 | mechanism will also defend that region from allocations which could use | |
271 | highmem or lowmem). | |
272 | ||
273 | The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is | |
274 | in defending these lower zones. | |
275 | ||
276 | If you have a machine which uses highmem or ISA DMA and your | |
277 | applications are using mlock(), or if you are running with no swap then | |
278 | you probably should change the lowmem_reserve_ratio setting. | |
279 | ||
280 | The lowmem_reserve_ratio is an array. You can see them by reading this file. | |
281 | - | |
282 | % cat /proc/sys/vm/lowmem_reserve_ratio | |
283 | 256 256 32 | |
284 | - | |
285 | Note: # of this elements is one fewer than number of zones. Because the highest | |
286 | zone's value is not necessary for following calculation. | |
287 | ||
288 | But, these values are not used directly. The kernel calculates # of protection | |
289 | pages for each zones from them. These are shown as array of protection pages | |
290 | in /proc/zoneinfo like followings. (This is an example of x86-64 box). | |
291 | Each zone has an array of protection pages like this. | |
292 | ||
293 | - | |
294 | Node 0, zone DMA | |
295 | pages free 1355 | |
296 | min 3 | |
297 | low 3 | |
298 | high 4 | |
299 | : | |
300 | : | |
301 | numa_other 0 | |
302 | protection: (0, 2004, 2004, 2004) | |
303 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
304 | pagesets | |
305 | cpu: 0 pcp: 0 | |
306 | : | |
307 | - | |
308 | These protections are added to score to judge whether this zone should be used | |
309 | for page allocation or should be reclaimed. | |
310 | ||
311 | In this example, if normal pages (index=2) are required to this DMA zone and | |
41858966 MG |
312 | watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should |
313 | not be used because pages_free(1355) is smaller than watermark + protection[2] | |
db0fb184 PM |
314 | (4 + 2004 = 2008). If this protection value is 0, this zone would be used for |
315 | normal page requirement. If requirement is DMA zone(index=0), protection[0] | |
316 | (=0) is used. | |
317 | ||
318 | zone[i]'s protection[j] is calculated by following expression. | |
319 | ||
320 | (i < j): | |
321 | zone[i]->protection[j] | |
322 | = (total sums of present_pages from zone[i+1] to zone[j] on the node) | |
323 | / lowmem_reserve_ratio[i]; | |
324 | (i = j): | |
325 | (should not be protected. = 0; | |
326 | (i > j): | |
327 | (not necessary, but looks 0) | |
328 | ||
329 | The default values of lowmem_reserve_ratio[i] are | |
330 | 256 (if zone[i] means DMA or DMA32 zone) | |
331 | 32 (others). | |
332 | As above expression, they are reciprocal number of ratio. | |
333 | 256 means 1/256. # of protection pages becomes about "0.39%" of total present | |
334 | pages of higher zones on the node. | |
335 | ||
336 | If you would like to protect more pages, smaller values are effective. | |
337 | The minimum value is 1 (1/1 -> 100%). | |
1b2ffb78 | 338 | |
db0fb184 | 339 | ============================================================== |
1b2ffb78 | 340 | |
db0fb184 | 341 | max_map_count: |
1743660b | 342 | |
db0fb184 PM |
343 | This file contains the maximum number of memory map areas a process |
344 | may have. Memory map areas are used as a side-effect of calling | |
345 | malloc, directly by mmap and mprotect, and also when loading shared | |
346 | libraries. | |
1743660b | 347 | |
db0fb184 PM |
348 | While most applications need less than a thousand maps, certain |
349 | programs, particularly malloc debuggers, may consume lots of them, | |
350 | e.g., up to one or two maps per allocation. | |
fadd8fbd | 351 | |
db0fb184 | 352 | The default value is 65536. |
9614634f | 353 | |
6a46079c AK |
354 | ============================================================= |
355 | ||
356 | memory_failure_early_kill: | |
357 | ||
358 | Control how to kill processes when uncorrected memory error (typically | |
359 | a 2bit error in a memory module) is detected in the background by hardware | |
360 | that cannot be handled by the kernel. In some cases (like the page | |
361 | still having a valid copy on disk) the kernel will handle the failure | |
362 | transparently without affecting any applications. But if there is | |
363 | no other uptodate copy of the data it will kill to prevent any data | |
364 | corruptions from propagating. | |
365 | ||
366 | 1: Kill all processes that have the corrupted and not reloadable page mapped | |
367 | as soon as the corruption is detected. Note this is not supported | |
368 | for a few types of pages, like kernel internally allocated data or | |
369 | the swap cache, but works for the majority of user pages. | |
370 | ||
371 | 0: Only unmap the corrupted page from all processes and only kill a process | |
372 | who tries to access it. | |
373 | ||
374 | The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can | |
375 | handle this if they want to. | |
376 | ||
377 | This is only active on architectures/platforms with advanced machine | |
378 | check handling and depends on the hardware capabilities. | |
379 | ||
380 | Applications can override this setting individually with the PR_MCE_KILL prctl | |
381 | ||
382 | ============================================================== | |
383 | ||
384 | memory_failure_recovery | |
385 | ||
386 | Enable memory failure recovery (when supported by the platform) | |
387 | ||
388 | 1: Attempt recovery. | |
389 | ||
390 | 0: Always panic on a memory failure. | |
391 | ||
db0fb184 | 392 | ============================================================== |
9614634f | 393 | |
db0fb184 | 394 | min_free_kbytes: |
9614634f | 395 | |
db0fb184 | 396 | This is used to force the Linux VM to keep a minimum number |
41858966 MG |
397 | of kilobytes free. The VM uses this number to compute a |
398 | watermark[WMARK_MIN] value for each lowmem zone in the system. | |
399 | Each lowmem zone gets a number of reserved free pages based | |
400 | proportionally on its size. | |
db0fb184 PM |
401 | |
402 | Some minimal amount of memory is needed to satisfy PF_MEMALLOC | |
403 | allocations; if you set this to lower than 1024KB, your system will | |
404 | become subtly broken, and prone to deadlock under high loads. | |
405 | ||
406 | Setting this too high will OOM your machine instantly. | |
9614634f CL |
407 | |
408 | ============================================================= | |
409 | ||
0ff38490 CL |
410 | min_slab_ratio: |
411 | ||
412 | This is available only on NUMA kernels. | |
413 | ||
414 | A percentage of the total pages in each zone. On Zone reclaim | |
415 | (fallback from the local zone occurs) slabs will be reclaimed if more | |
416 | than this percentage of pages in a zone are reclaimable slab pages. | |
417 | This insures that the slab growth stays under control even in NUMA | |
418 | systems that rarely perform global reclaim. | |
419 | ||
420 | The default is 5 percent. | |
421 | ||
422 | Note that slab reclaim is triggered in a per zone / node fashion. | |
423 | The process of reclaiming slab memory is currently not node specific | |
424 | and may not be fast. | |
425 | ||
426 | ============================================================= | |
427 | ||
db0fb184 | 428 | min_unmapped_ratio: |
fadd8fbd | 429 | |
db0fb184 | 430 | This is available only on NUMA kernels. |
fadd8fbd | 431 | |
90afa5de MG |
432 | This is a percentage of the total pages in each zone. Zone reclaim will |
433 | only occur if more than this percentage of pages are in a state that | |
434 | zone_reclaim_mode allows to be reclaimed. | |
435 | ||
436 | If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared | |
437 | against all file-backed unmapped pages including swapcache pages and tmpfs | |
438 | files. Otherwise, only unmapped pages backed by normal files but not tmpfs | |
439 | files and similar are considered. | |
2b744c01 | 440 | |
db0fb184 | 441 | The default is 1 percent. |
fadd8fbd | 442 | |
db0fb184 | 443 | ============================================================== |
2b744c01 | 444 | |
db0fb184 | 445 | mmap_min_addr |
ed032189 | 446 | |
db0fb184 | 447 | This file indicates the amount of address space which a user process will |
af901ca1 | 448 | be restricted from mmapping. Since kernel null dereference bugs could |
db0fb184 PM |
449 | accidentally operate based on the information in the first couple of pages |
450 | of memory userspace processes should not be allowed to write to them. By | |
451 | default this value is set to 0 and no protections will be enforced by the | |
452 | security module. Setting this value to something like 64k will allow the | |
453 | vast majority of applications to work correctly and provide defense in depth | |
454 | against future potential kernel bugs. | |
fe071d7e | 455 | |
db0fb184 | 456 | ============================================================== |
fef1bdd6 | 457 | |
db0fb184 | 458 | nr_hugepages |
fef1bdd6 | 459 | |
db0fb184 | 460 | Change the minimum size of the hugepage pool. |
fef1bdd6 | 461 | |
db0fb184 | 462 | See Documentation/vm/hugetlbpage.txt |
fef1bdd6 | 463 | |
db0fb184 | 464 | ============================================================== |
fef1bdd6 | 465 | |
db0fb184 | 466 | nr_overcommit_hugepages |
fef1bdd6 | 467 | |
db0fb184 PM |
468 | Change the maximum size of the hugepage pool. The maximum is |
469 | nr_hugepages + nr_overcommit_hugepages. | |
fe071d7e | 470 | |
db0fb184 | 471 | See Documentation/vm/hugetlbpage.txt |
fe071d7e | 472 | |
db0fb184 | 473 | ============================================================== |
fe071d7e | 474 | |
db0fb184 | 475 | nr_trim_pages |
ed032189 | 476 | |
db0fb184 PM |
477 | This is available only on NOMMU kernels. |
478 | ||
479 | This value adjusts the excess page trimming behaviour of power-of-2 aligned | |
480 | NOMMU mmap allocations. | |
481 | ||
482 | A value of 0 disables trimming of allocations entirely, while a value of 1 | |
483 | trims excess pages aggressively. Any value >= 1 acts as the watermark where | |
484 | trimming of allocations is initiated. | |
485 | ||
486 | The default value is 1. | |
487 | ||
488 | See Documentation/nommu-mmap.txt for more information. | |
ed032189 | 489 | |
f0c0b2b8 KH |
490 | ============================================================== |
491 | ||
492 | numa_zonelist_order | |
493 | ||
494 | This sysctl is only for NUMA. | |
495 | 'where the memory is allocated from' is controlled by zonelists. | |
496 | (This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation. | |
497 | you may be able to read ZONE_DMA as ZONE_DMA32...) | |
498 | ||
499 | In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following. | |
500 | ZONE_NORMAL -> ZONE_DMA | |
501 | This means that a memory allocation request for GFP_KERNEL will | |
502 | get memory from ZONE_DMA only when ZONE_NORMAL is not available. | |
503 | ||
504 | In NUMA case, you can think of following 2 types of order. | |
505 | Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL | |
506 | ||
507 | (A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL | |
508 | (B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA. | |
509 | ||
510 | Type(A) offers the best locality for processes on Node(0), but ZONE_DMA | |
511 | will be used before ZONE_NORMAL exhaustion. This increases possibility of | |
512 | out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small. | |
513 | ||
514 | Type(B) cannot offer the best locality but is more robust against OOM of | |
515 | the DMA zone. | |
516 | ||
517 | Type(A) is called as "Node" order. Type (B) is "Zone" order. | |
518 | ||
519 | "Node order" orders the zonelists by node, then by zone within each node. | |
5a3016a6 | 520 | Specify "[Nn]ode" for node order |
f0c0b2b8 KH |
521 | |
522 | "Zone Order" orders the zonelists by zone type, then by node within each | |
5a3016a6 | 523 | zone. Specify "[Zz]one" for zone order. |
f0c0b2b8 KH |
524 | |
525 | Specify "[Dd]efault" to request automatic configuration. Autoconfiguration | |
526 | will select "node" order in following case. | |
527 | (1) if the DMA zone does not exist or | |
528 | (2) if the DMA zone comprises greater than 50% of the available memory or | |
529 | (3) if any node's DMA zone comprises greater than 60% of its local memory and | |
530 | the amount of local memory is big enough. | |
531 | ||
532 | Otherwise, "zone" order will be selected. Default order is recommended unless | |
533 | this is causing problems for your system/application. | |
d5dbac87 NA |
534 | |
535 | ============================================================== | |
536 | ||
db0fb184 | 537 | oom_dump_tasks |
d5dbac87 | 538 | |
db0fb184 PM |
539 | Enables a system-wide task dump (excluding kernel threads) to be |
540 | produced when the kernel performs an OOM-killing and includes such | |
de34d965 DR |
541 | information as pid, uid, tgid, vm size, rss, nr_ptes, swapents, |
542 | oom_score_adj score, and name. This is helpful to determine why the | |
543 | OOM killer was invoked, to identify the rogue task that caused it, | |
544 | and to determine why the OOM killer chose the task it did to kill. | |
d5dbac87 | 545 | |
db0fb184 PM |
546 | If this is set to zero, this information is suppressed. On very |
547 | large systems with thousands of tasks it may not be feasible to dump | |
548 | the memory state information for each one. Such systems should not | |
549 | be forced to incur a performance penalty in OOM conditions when the | |
550 | information may not be desired. | |
551 | ||
552 | If this is set to non-zero, this information is shown whenever the | |
553 | OOM killer actually kills a memory-hogging task. | |
554 | ||
ad915c43 | 555 | The default value is 1 (enabled). |
d5dbac87 NA |
556 | |
557 | ============================================================== | |
558 | ||
db0fb184 | 559 | oom_kill_allocating_task |
d5dbac87 | 560 | |
db0fb184 PM |
561 | This enables or disables killing the OOM-triggering task in |
562 | out-of-memory situations. | |
d5dbac87 | 563 | |
db0fb184 PM |
564 | If this is set to zero, the OOM killer will scan through the entire |
565 | tasklist and select a task based on heuristics to kill. This normally | |
566 | selects a rogue memory-hogging task that frees up a large amount of | |
567 | memory when killed. | |
568 | ||
569 | If this is set to non-zero, the OOM killer simply kills the task that | |
570 | triggered the out-of-memory condition. This avoids the expensive | |
571 | tasklist scan. | |
572 | ||
573 | If panic_on_oom is selected, it takes precedence over whatever value | |
574 | is used in oom_kill_allocating_task. | |
575 | ||
576 | The default value is 0. | |
dd8632a1 PM |
577 | |
578 | ============================================================== | |
579 | ||
db0fb184 | 580 | overcommit_memory: |
dd8632a1 | 581 | |
db0fb184 | 582 | This value contains a flag that enables memory overcommitment. |
dd8632a1 | 583 | |
db0fb184 PM |
584 | When this flag is 0, the kernel attempts to estimate the amount |
585 | of free memory left when userspace requests more memory. | |
dd8632a1 | 586 | |
db0fb184 PM |
587 | When this flag is 1, the kernel pretends there is always enough |
588 | memory until it actually runs out. | |
dd8632a1 | 589 | |
db0fb184 PM |
590 | When this flag is 2, the kernel uses a "never overcommit" |
591 | policy that attempts to prevent any overcommit of memory. | |
c9b1d098 | 592 | Note that user_reserve_kbytes affects this policy. |
dd8632a1 | 593 | |
db0fb184 PM |
594 | This feature can be very useful because there are a lot of |
595 | programs that malloc() huge amounts of memory "just-in-case" | |
596 | and don't use much of it. | |
597 | ||
598 | The default value is 0. | |
599 | ||
600 | See Documentation/vm/overcommit-accounting and | |
601 | security/commoncap.c::cap_vm_enough_memory() for more information. | |
602 | ||
603 | ============================================================== | |
604 | ||
605 | overcommit_ratio: | |
606 | ||
607 | When overcommit_memory is set to 2, the committed address | |
608 | space is not permitted to exceed swap plus this percentage | |
609 | of physical RAM. See above. | |
610 | ||
611 | ============================================================== | |
612 | ||
613 | page-cluster | |
614 | ||
df858fa8 CE |
615 | page-cluster controls the number of pages up to which consecutive pages |
616 | are read in from swap in a single attempt. This is the swap counterpart | |
617 | to page cache readahead. | |
618 | The mentioned consecutivity is not in terms of virtual/physical addresses, | |
619 | but consecutive on swap space - that means they were swapped out together. | |
db0fb184 PM |
620 | |
621 | It is a logarithmic value - setting it to zero means "1 page", setting | |
622 | it to 1 means "2 pages", setting it to 2 means "4 pages", etc. | |
df858fa8 | 623 | Zero disables swap readahead completely. |
db0fb184 PM |
624 | |
625 | The default value is three (eight pages at a time). There may be some | |
626 | small benefits in tuning this to a different value if your workload is | |
627 | swap-intensive. | |
628 | ||
df858fa8 CE |
629 | Lower values mean lower latencies for initial faults, but at the same time |
630 | extra faults and I/O delays for following faults if they would have been part of | |
631 | that consecutive pages readahead would have brought in. | |
632 | ||
db0fb184 PM |
633 | ============================================================= |
634 | ||
635 | panic_on_oom | |
636 | ||
637 | This enables or disables panic on out-of-memory feature. | |
638 | ||
639 | If this is set to 0, the kernel will kill some rogue process, | |
640 | called oom_killer. Usually, oom_killer can kill rogue processes and | |
641 | system will survive. | |
642 | ||
643 | If this is set to 1, the kernel panics when out-of-memory happens. | |
644 | However, if a process limits using nodes by mempolicy/cpusets, | |
645 | and those nodes become memory exhaustion status, one process | |
646 | may be killed by oom-killer. No panic occurs in this case. | |
647 | Because other nodes' memory may be free. This means system total status | |
648 | may be not fatal yet. | |
649 | ||
650 | If this is set to 2, the kernel panics compulsorily even on the | |
daaf1e68 KH |
651 | above-mentioned. Even oom happens under memory cgroup, the whole |
652 | system panics. | |
db0fb184 PM |
653 | |
654 | The default value is 0. | |
655 | 1 and 2 are for failover of clustering. Please select either | |
656 | according to your policy of failover. | |
daaf1e68 KH |
657 | panic_on_oom=2+kdump gives you very strong tool to investigate |
658 | why oom happens. You can get snapshot. | |
db0fb184 PM |
659 | |
660 | ============================================================= | |
661 | ||
662 | percpu_pagelist_fraction | |
663 | ||
664 | This is the fraction of pages at most (high mark pcp->high) in each zone that | |
665 | are allocated for each per cpu page list. The min value for this is 8. It | |
666 | means that we don't allow more than 1/8th of pages in each zone to be | |
667 | allocated in any single per_cpu_pagelist. This entry only changes the value | |
668 | of hot per cpu pagelists. User can specify a number like 100 to allocate | |
669 | 1/100th of each zone to each per cpu page list. | |
670 | ||
671 | The batch value of each per cpu pagelist is also updated as a result. It is | |
672 | set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8) | |
673 | ||
674 | The initial value is zero. Kernel does not use this value at boot time to set | |
675 | the high water marks for each per cpu page list. | |
676 | ||
677 | ============================================================== | |
678 | ||
679 | stat_interval | |
680 | ||
681 | The time interval between which vm statistics are updated. The default | |
682 | is 1 second. | |
683 | ||
684 | ============================================================== | |
685 | ||
686 | swappiness | |
687 | ||
688 | This control is used to define how aggressive the kernel will swap | |
689 | memory pages. Higher values will increase agressiveness, lower values | |
19f59460 | 690 | decrease the amount of swap. |
db0fb184 PM |
691 | |
692 | The default value is 60. | |
693 | ||
694 | ============================================================== | |
695 | ||
c9b1d098 AS |
696 | - user_reserve_kbytes |
697 | ||
698 | When overcommit_memory is set to 2, "never overommit" mode, reserve | |
699 | min(3% of current process size, user_reserve_kbytes) of free memory. | |
700 | This is intended to prevent a user from starting a single memory hogging | |
701 | process, such that they cannot recover (kill the hog). | |
702 | ||
703 | user_reserve_kbytes defaults to min(3% of the current process size, 128MB). | |
704 | ||
705 | If this is reduced to zero, then the user will be allowed to allocate | |
706 | all free memory with a single process, minus admin_reserve_kbytes. | |
707 | Any subsequent attempts to execute a command will result in | |
708 | "fork: Cannot allocate memory". | |
709 | ||
710 | Changing this takes effect whenever an application requests memory. | |
711 | ||
712 | ============================================================== | |
713 | ||
db0fb184 PM |
714 | vfs_cache_pressure |
715 | ------------------ | |
716 | ||
717 | Controls the tendency of the kernel to reclaim the memory which is used for | |
718 | caching of directory and inode objects. | |
719 | ||
720 | At the default value of vfs_cache_pressure=100 the kernel will attempt to | |
721 | reclaim dentries and inodes at a "fair" rate with respect to pagecache and | |
722 | swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer | |
55c37a84 JK |
723 | to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will |
724 | never reclaim dentries and inodes due to memory pressure and this can easily | |
725 | lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 | |
db0fb184 PM |
726 | causes the kernel to prefer to reclaim dentries and inodes. |
727 | ||
728 | ============================================================== | |
729 | ||
730 | zone_reclaim_mode: | |
731 | ||
732 | Zone_reclaim_mode allows someone to set more or less aggressive approaches to | |
733 | reclaim memory when a zone runs out of memory. If it is set to zero then no | |
734 | zone reclaim occurs. Allocations will be satisfied from other zones / nodes | |
735 | in the system. | |
736 | ||
737 | This is value ORed together of | |
738 | ||
739 | 1 = Zone reclaim on | |
740 | 2 = Zone reclaim writes dirty pages out | |
741 | 4 = Zone reclaim swaps pages | |
742 | ||
743 | zone_reclaim_mode is set during bootup to 1 if it is determined that pages | |
744 | from remote zones will cause a measurable performance reduction. The | |
745 | page allocator will then reclaim easily reusable pages (those page | |
746 | cache pages that are currently not used) before allocating off node pages. | |
747 | ||
748 | It may be beneficial to switch off zone reclaim if the system is | |
749 | used for a file server and all of memory should be used for caching files | |
750 | from disk. In that case the caching effect is more important than | |
751 | data locality. | |
752 | ||
753 | Allowing zone reclaim to write out pages stops processes that are | |
754 | writing large amounts of data from dirtying pages on other nodes. Zone | |
755 | reclaim will write out dirty pages if a zone fills up and so effectively | |
756 | throttle the process. This may decrease the performance of a single process | |
757 | since it cannot use all of system memory to buffer the outgoing writes | |
758 | anymore but it preserve the memory on other nodes so that the performance | |
759 | of other processes running on other nodes will not be affected. | |
760 | ||
761 | Allowing regular swap effectively restricts allocations to the local | |
762 | node unless explicitly overridden by memory policies or cpuset | |
763 | configurations. | |
764 | ||
765 | ============ End of Document ================================= |