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Peter W Morrealedb0fb182009-01-15 13:50:42 -08001Documentation for /proc/sys/vm/* kernel version 2.6.29
Linus Torvalds1da177e2005-04-16 15:20:36 -07002 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
Peter W Morrealedb0fb182009-01-15 13:50:42 -08003 (c) 2008 Peter W. Morreale <pmorreale@novell.com>
Linus Torvalds1da177e2005-04-16 15:20:36 -07004
5For general info and legal blurb, please look in README.
6
7==============================================================
8
9This file contains the documentation for the sysctl files in
Peter W Morrealedb0fb182009-01-15 13:50:42 -080010/proc/sys/vm and is valid for Linux kernel version 2.6.29.
Linus Torvalds1da177e2005-04-16 15:20:36 -070011
12The files in this directory can be used to tune the operation
13of the virtual memory (VM) subsystem of the Linux kernel and
14the writeout of dirty data to disk.
15
16Default values and initialization routines for most of these
17files can be found in mm/swap.c.
18
19Currently, these files are in /proc/sys/vm:
Peter W Morrealedb0fb182009-01-15 13:50:42 -080020
Andrew Shewmaker4eeab4f2013-04-29 15:08:11 -070021- admin_reserve_kbytes
Peter W Morrealedb0fb182009-01-15 13:50:42 -080022- block_dump
Mel Gorman76ab0f52010-05-24 14:32:28 -070023- compact_memory
Eric B Munson5bbe3542015-04-15 16:13:20 -070024- compact_unevictable_allowed
Peter W Morrealedb0fb182009-01-15 13:50:42 -080025- dirty_background_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -070026- dirty_background_ratio
Peter W Morrealedb0fb182009-01-15 13:50:42 -080027- dirty_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -070028- dirty_expire_centisecs
Peter W Morrealedb0fb182009-01-15 13:50:42 -080029- dirty_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -070030- dirty_writeback_centisecs
Peter W Morrealedb0fb182009-01-15 13:50:42 -080031- drop_caches
Mel Gorman5e771902010-05-24 14:32:31 -070032- extfrag_threshold
Peter W Morrealedb0fb182009-01-15 13:50:42 -080033- hugepages_treat_as_movable
34- hugetlb_shm_group
35- laptop_mode
36- legacy_va_layout
37- lowmem_reserve_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -070038- max_map_count
Andi Kleen6a460792009-09-16 11:50:15 +020039- memory_failure_early_kill
40- memory_failure_recovery
Linus Torvalds1da177e2005-04-16 15:20:36 -070041- min_free_kbytes
Christoph Lameter0ff38492006-09-25 23:31:52 -070042- min_slab_ratio
Peter W Morrealedb0fb182009-01-15 13:50:42 -080043- min_unmapped_ratio
44- mmap_min_addr
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -080045- nr_hugepages
46- nr_overcommit_hugepages
Peter W Morrealedb0fb182009-01-15 13:50:42 -080047- nr_trim_pages (only if CONFIG_MMU=n)
48- numa_zonelist_order
49- oom_dump_tasks
50- oom_kill_allocating_task
Jerome Marchand49f0ce52014-01-21 15:49:14 -080051- overcommit_kbytes
Peter W Morrealedb0fb182009-01-15 13:50:42 -080052- overcommit_memory
53- overcommit_ratio
54- page-cluster
55- panic_on_oom
56- percpu_pagelist_fraction
57- stat_interval
58- swappiness
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -070059- user_reserve_kbytes
Peter W Morrealedb0fb182009-01-15 13:50:42 -080060- vfs_cache_pressure
61- zone_reclaim_mode
62
Linus Torvalds1da177e2005-04-16 15:20:36 -070063==============================================================
64
Andrew Shewmaker4eeab4f2013-04-29 15:08:11 -070065admin_reserve_kbytes
66
67The amount of free memory in the system that should be reserved for users
68with the capability cap_sys_admin.
69
70admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
71
72That should provide enough for the admin to log in and kill a process,
73if necessary, under the default overcommit 'guess' mode.
74
75Systems running under overcommit 'never' should increase this to account
76for the full Virtual Memory Size of programs used to recover. Otherwise,
77root may not be able to log in to recover the system.
78
79How do you calculate a minimum useful reserve?
80
81sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
82
83For overcommit 'guess', we can sum resident set sizes (RSS).
84On x86_64 this is about 8MB.
85
86For overcommit 'never', we can take the max of their virtual sizes (VSZ)
87and add the sum of their RSS.
88On x86_64 this is about 128MB.
89
90Changing this takes effect whenever an application requests memory.
91
92==============================================================
93
Peter W Morrealedb0fb182009-01-15 13:50:42 -080094block_dump
Linus Torvalds1da177e2005-04-16 15:20:36 -070095
Peter W Morrealedb0fb182009-01-15 13:50:42 -080096block_dump enables block I/O debugging when set to a nonzero value. More
97information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
Linus Torvalds1da177e2005-04-16 15:20:36 -070098
99==============================================================
100
Mel Gorman76ab0f52010-05-24 14:32:28 -0700101compact_memory
102
103Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
104all zones are compacted such that free memory is available in contiguous
105blocks where possible. This can be important for example in the allocation of
106huge pages although processes will also directly compact memory as required.
107
108==============================================================
109
Eric B Munson5bbe3542015-04-15 16:13:20 -0700110compact_unevictable_allowed
111
112Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
113allowed to examine the unevictable lru (mlocked pages) for pages to compact.
114This should be used on systems where stalls for minor page faults are an
115acceptable trade for large contiguous free memory. Set to 0 to prevent
116compaction from moving pages that are unevictable. Default value is 1.
117
118==============================================================
119
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800120dirty_background_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300122Contains the amount of dirty memory at which the background kernel
123flusher threads will start writeback.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124
Andrea Righiabffc022010-10-27 15:33:31 -0700125Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
126one of them may be specified at a time. When one sysctl is written it is
127immediately taken into account to evaluate the dirty memory limits and the
128other appears as 0 when read.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700129
130==============================================================
131
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800132dirty_background_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133
Zheng Liu715ea412013-11-12 15:08:30 -0800134Contains, as a percentage of total available memory that contains free pages
135and reclaimable pages, the number of pages at which the background kernel
136flusher threads will start writing out dirty data.
137
138The total avaiable memory is not equal to total system memory.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139
140==============================================================
141
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800142dirty_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700143
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800144Contains the amount of dirty memory at which a process generating disk writes
145will itself start writeback.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700146
Andrea Righiabffc022010-10-27 15:33:31 -0700147Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
148specified at a time. When one sysctl is written it is immediately taken into
149account to evaluate the dirty memory limits and the other appears as 0 when
150read.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800151
Andrea Righi9e4a5bd2009-04-30 15:08:57 -0700152Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
153value lower than this limit will be ignored and the old configuration will be
154retained.
155
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800156==============================================================
157
158dirty_expire_centisecs
159
160This tunable is used to define when dirty data is old enough to be eligible
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300161for writeout by the kernel flusher threads. It is expressed in 100'ths
162of a second. Data which has been dirty in-memory for longer than this
163interval will be written out next time a flusher thread wakes up.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800164
165==============================================================
166
167dirty_ratio
168
Zheng Liu715ea412013-11-12 15:08:30 -0800169Contains, as a percentage of total available memory that contains free pages
170and reclaimable pages, the number of pages at which a process which is
171generating disk writes will itself start writing out dirty data.
172
173The total avaiable memory is not equal to total system memory.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800174
175==============================================================
176
177dirty_writeback_centisecs
178
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300179The kernel flusher threads will periodically wake up and write `old' data
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800180out to disk. This tunable expresses the interval between those wakeups, in
181100'ths of a second.
182
183Setting this to zero disables periodic writeback altogether.
184
185==============================================================
186
187drop_caches
188
Dave Hansen5509a5d2014-04-03 14:48:19 -0700189Writing to this will cause the kernel to drop clean caches, as well as
190reclaimable slab objects like dentries and inodes. Once dropped, their
191memory becomes free.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800192
193To free pagecache:
194 echo 1 > /proc/sys/vm/drop_caches
Dave Hansen5509a5d2014-04-03 14:48:19 -0700195To free reclaimable slab objects (includes dentries and inodes):
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800196 echo 2 > /proc/sys/vm/drop_caches
Dave Hansen5509a5d2014-04-03 14:48:19 -0700197To free slab objects and pagecache:
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800198 echo 3 > /proc/sys/vm/drop_caches
199
Dave Hansen5509a5d2014-04-03 14:48:19 -0700200This is a non-destructive operation and will not free any dirty objects.
201To increase the number of objects freed by this operation, the user may run
202`sync' prior to writing to /proc/sys/vm/drop_caches. This will minimize the
203number of dirty objects on the system and create more candidates to be
204dropped.
205
206This file is not a means to control the growth of the various kernel caches
207(inodes, dentries, pagecache, etc...) These objects are automatically
208reclaimed by the kernel when memory is needed elsewhere on the system.
209
210Use of this file can cause performance problems. Since it discards cached
211objects, it may cost a significant amount of I/O and CPU to recreate the
212dropped objects, especially if they were under heavy use. Because of this,
213use outside of a testing or debugging environment is not recommended.
214
215You may see informational messages in your kernel log when this file is
216used:
217
218 cat (1234): drop_caches: 3
219
220These are informational only. They do not mean that anything is wrong
221with your system. To disable them, echo 4 (bit 3) into drop_caches.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800222
223==============================================================
224
Mel Gorman5e771902010-05-24 14:32:31 -0700225extfrag_threshold
226
227This parameter affects whether the kernel will compact memory or direct
Rabin Vincenta10726b2015-07-14 07:35:11 +0200228reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
229debugfs shows what the fragmentation index for each order is in each zone in
230the system. Values tending towards 0 imply allocations would fail due to lack
231of memory, values towards 1000 imply failures are due to fragmentation and -1
232implies that the allocation will succeed as long as watermarks are met.
Mel Gorman5e771902010-05-24 14:32:31 -0700233
234The kernel will not compact memory in a zone if the
235fragmentation index is <= extfrag_threshold. The default value is 500.
236
237==============================================================
238
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800239hugepages_treat_as_movable
240
Naoya Horiguchi86cdb462013-09-11 14:22:13 -0700241This parameter controls whether we can allocate hugepages from ZONE_MOVABLE
242or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE.
243ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified,
244so this parameter has no effect if used without kernelcore=.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800245
Naoya Horiguchi86cdb462013-09-11 14:22:13 -0700246Hugepage migration is now available in some situations which depend on the
247architecture and/or the hugepage size. If a hugepage supports migration,
248allocation from ZONE_MOVABLE is always enabled for the hugepage regardless
249of the value of this parameter.
250IOW, this parameter affects only non-migratable hugepages.
251
252Assuming that hugepages are not migratable in your system, one usecase of
253this parameter is that users can make hugepage pool more extensible by
254enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE
255page reclaim/migration/compaction work more and you can get contiguous
256memory more likely. Note that using ZONE_MOVABLE for non-migratable
257hugepages can do harm to other features like memory hotremove (because
258memory hotremove expects that memory blocks on ZONE_MOVABLE are always
259removable,) so it's a trade-off responsible for the users.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800260
261==============================================================
262
263hugetlb_shm_group
264
265hugetlb_shm_group contains group id that is allowed to create SysV
266shared memory segment using hugetlb page.
267
268==============================================================
269
270laptop_mode
271
272laptop_mode is a knob that controls "laptop mode". All the things that are
273controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
274
275==============================================================
276
277legacy_va_layout
278
Kulikov Vasiliy2174efb2010-06-28 13:59:28 +0200279If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800280will use the legacy (2.4) layout for all processes.
281
282==============================================================
283
284lowmem_reserve_ratio
285
286For some specialised workloads on highmem machines it is dangerous for
287the kernel to allow process memory to be allocated from the "lowmem"
288zone. This is because that memory could then be pinned via the mlock()
289system call, or by unavailability of swapspace.
290
291And on large highmem machines this lack of reclaimable lowmem memory
292can be fatal.
293
294So the Linux page allocator has a mechanism which prevents allocations
295which _could_ use highmem from using too much lowmem. This means that
296a certain amount of lowmem is defended from the possibility of being
297captured into pinned user memory.
298
299(The same argument applies to the old 16 megabyte ISA DMA region. This
300mechanism will also defend that region from allocations which could use
301highmem or lowmem).
302
303The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
304in defending these lower zones.
305
306If you have a machine which uses highmem or ISA DMA and your
307applications are using mlock(), or if you are running with no swap then
308you probably should change the lowmem_reserve_ratio setting.
309
310The lowmem_reserve_ratio is an array. You can see them by reading this file.
311-
312% cat /proc/sys/vm/lowmem_reserve_ratio
313256 256 32
314-
315Note: # of this elements is one fewer than number of zones. Because the highest
316 zone's value is not necessary for following calculation.
317
318But, these values are not used directly. The kernel calculates # of protection
319pages for each zones from them. These are shown as array of protection pages
320in /proc/zoneinfo like followings. (This is an example of x86-64 box).
321Each zone has an array of protection pages like this.
322
323-
324Node 0, zone DMA
325 pages free 1355
326 min 3
327 low 3
328 high 4
329 :
330 :
331 numa_other 0
332 protection: (0, 2004, 2004, 2004)
333 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
334 pagesets
335 cpu: 0 pcp: 0
336 :
337-
338These protections are added to score to judge whether this zone should be used
339for page allocation or should be reclaimed.
340
341In this example, if normal pages (index=2) are required to this DMA zone and
Mel Gorman41858962009-06-16 15:32:12 -0700342watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
343not be used because pages_free(1355) is smaller than watermark + protection[2]
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800344(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
345normal page requirement. If requirement is DMA zone(index=0), protection[0]
346(=0) is used.
347
348zone[i]'s protection[j] is calculated by following expression.
349
350(i < j):
351 zone[i]->protection[j]
Yaowei Bai013110a2015-09-08 15:04:10 -0700352 = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800353 / lowmem_reserve_ratio[i];
354(i = j):
355 (should not be protected. = 0;
356(i > j):
357 (not necessary, but looks 0)
358
359The default values of lowmem_reserve_ratio[i] are
360 256 (if zone[i] means DMA or DMA32 zone)
361 32 (others).
362As above expression, they are reciprocal number of ratio.
Yaowei Bai013110a2015-09-08 15:04:10 -0700363256 means 1/256. # of protection pages becomes about "0.39%" of total managed
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800364pages of higher zones on the node.
365
366If you would like to protect more pages, smaller values are effective.
367The minimum value is 1 (1/1 -> 100%).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700368
369==============================================================
370
371max_map_count:
372
373This file contains the maximum number of memory map areas a process
374may have. Memory map areas are used as a side-effect of calling
375malloc, directly by mmap and mprotect, and also when loading shared
376libraries.
377
378While most applications need less than a thousand maps, certain
379programs, particularly malloc debuggers, may consume lots of them,
380e.g., up to one or two maps per allocation.
381
382The default value is 65536.
383
Andi Kleen6a460792009-09-16 11:50:15 +0200384=============================================================
385
386memory_failure_early_kill:
387
388Control how to kill processes when uncorrected memory error (typically
389a 2bit error in a memory module) is detected in the background by hardware
390that cannot be handled by the kernel. In some cases (like the page
391still having a valid copy on disk) the kernel will handle the failure
392transparently without affecting any applications. But if there is
393no other uptodate copy of the data it will kill to prevent any data
394corruptions from propagating.
395
3961: Kill all processes that have the corrupted and not reloadable page mapped
397as soon as the corruption is detected. Note this is not supported
398for a few types of pages, like kernel internally allocated data or
399the swap cache, but works for the majority of user pages.
400
4010: Only unmap the corrupted page from all processes and only kill a process
402who tries to access it.
403
404The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
405handle this if they want to.
406
407This is only active on architectures/platforms with advanced machine
408check handling and depends on the hardware capabilities.
409
410Applications can override this setting individually with the PR_MCE_KILL prctl
411
412==============================================================
413
414memory_failure_recovery
415
416Enable memory failure recovery (when supported by the platform)
417
4181: Attempt recovery.
419
4200: Always panic on a memory failure.
421
Linus Torvalds1da177e2005-04-16 15:20:36 -0700422==============================================================
423
424min_free_kbytes:
425
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800426This is used to force the Linux VM to keep a minimum number
Mel Gorman41858962009-06-16 15:32:12 -0700427of kilobytes free. The VM uses this number to compute a
428watermark[WMARK_MIN] value for each lowmem zone in the system.
429Each lowmem zone gets a number of reserved free pages based
430proportionally on its size.
Rohit Seth8ad4b1f2006-01-08 01:00:40 -0800431
Matt LaPlanted9195882008-07-25 19:45:33 -0700432Some minimal amount of memory is needed to satisfy PF_MEMALLOC
Pavel Machek24950892007-10-16 23:31:28 -0700433allocations; if you set this to lower than 1024KB, your system will
434become subtly broken, and prone to deadlock under high loads.
435
436Setting this too high will OOM your machine instantly.
437
Christoph Lameter96146342006-07-03 00:24:13 -0700438=============================================================
439
Christoph Lameter0ff38492006-09-25 23:31:52 -0700440min_slab_ratio:
441
442This is available only on NUMA kernels.
443
444A percentage of the total pages in each zone. On Zone reclaim
445(fallback from the local zone occurs) slabs will be reclaimed if more
446than this percentage of pages in a zone are reclaimable slab pages.
447This insures that the slab growth stays under control even in NUMA
448systems that rarely perform global reclaim.
449
450The default is 5 percent.
451
452Note that slab reclaim is triggered in a per zone / node fashion.
453The process of reclaiming slab memory is currently not node specific
454and may not be fast.
455
456=============================================================
457
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800458min_unmapped_ratio:
KAMEZAWA Hiroyukifadd8fb2006-06-23 02:03:13 -0700459
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800460This is available only on NUMA kernels.
Yasunori Goto2b744c02007-05-06 14:49:59 -0700461
Mel Gorman90afa5d2009-06-16 15:33:20 -0700462This is a percentage of the total pages in each zone. Zone reclaim will
463only occur if more than this percentage of pages are in a state that
464zone_reclaim_mode allows to be reclaimed.
465
466If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
467against all file-backed unmapped pages including swapcache pages and tmpfs
468files. Otherwise, only unmapped pages backed by normal files but not tmpfs
469files and similar are considered.
Yasunori Goto2b744c02007-05-06 14:49:59 -0700470
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800471The default is 1 percent.
David Rientjesfe071d72007-10-16 23:25:56 -0700472
Eric Parised032182007-06-28 15:55:21 -0400473==============================================================
474
475mmap_min_addr
476
477This file indicates the amount of address space which a user process will
André Goddard Rosaaf901ca2009-11-14 13:09:05 -0200478be restricted from mmapping. Since kernel null dereference bugs could
Eric Parised032182007-06-28 15:55:21 -0400479accidentally operate based on the information in the first couple of pages
480of memory userspace processes should not be allowed to write to them. By
481default this value is set to 0 and no protections will be enforced by the
482security module. Setting this value to something like 64k will allow the
483vast majority of applications to work correctly and provide defense in depth
484against future potential kernel bugs.
485
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700486==============================================================
487
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800488nr_hugepages
489
490Change the minimum size of the hugepage pool.
491
492See Documentation/vm/hugetlbpage.txt
493
494==============================================================
495
496nr_overcommit_hugepages
497
498Change the maximum size of the hugepage pool. The maximum is
499nr_hugepages + nr_overcommit_hugepages.
500
501See Documentation/vm/hugetlbpage.txt
502
503==============================================================
504
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800505nr_trim_pages
506
507This is available only on NOMMU kernels.
508
509This value adjusts the excess page trimming behaviour of power-of-2 aligned
510NOMMU mmap allocations.
511
512A value of 0 disables trimming of allocations entirely, while a value of 1
513trims excess pages aggressively. Any value >= 1 acts as the watermark where
514trimming of allocations is initiated.
515
516The default value is 1.
517
518See Documentation/nommu-mmap.txt for more information.
519
520==============================================================
521
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700522numa_zonelist_order
523
524This sysctl is only for NUMA.
525'where the memory is allocated from' is controlled by zonelists.
526(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
527 you may be able to read ZONE_DMA as ZONE_DMA32...)
528
529In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
530ZONE_NORMAL -> ZONE_DMA
531This means that a memory allocation request for GFP_KERNEL will
532get memory from ZONE_DMA only when ZONE_NORMAL is not available.
533
534In NUMA case, you can think of following 2 types of order.
535Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
536
537(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
538(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
539
540Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
541will be used before ZONE_NORMAL exhaustion. This increases possibility of
542out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
543
544Type(B) cannot offer the best locality but is more robust against OOM of
545the DMA zone.
546
547Type(A) is called as "Node" order. Type (B) is "Zone" order.
548
549"Node order" orders the zonelists by node, then by zone within each node.
Paul Bolle5a3016a2011-04-06 11:09:55 +0200550Specify "[Nn]ode" for node order
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700551
552"Zone Order" orders the zonelists by zone type, then by node within each
Paul Bolle5a3016a2011-04-06 11:09:55 +0200553zone. Specify "[Zz]one" for zone order.
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700554
555Specify "[Dd]efault" to request automatic configuration. Autoconfiguration
556will select "node" order in following case.
557(1) if the DMA zone does not exist or
558(2) if the DMA zone comprises greater than 50% of the available memory or
Wanpeng Lif8f191f2013-07-08 16:00:16 -0700559(3) if any node's DMA zone comprises greater than 70% of its local memory and
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700560 the amount of local memory is big enough.
561
562Otherwise, "zone" order will be selected. Default order is recommended unless
563this is causing problems for your system/application.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800564
565==============================================================
566
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800567oom_dump_tasks
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800568
Kirill A. Shutemovdc6c9a32015-02-11 15:26:50 -0800569Enables a system-wide task dump (excluding kernel threads) to be produced
570when the kernel performs an OOM-killing and includes such information as
571pid, uid, tgid, vm size, rss, nr_ptes, nr_pmds, swapents, oom_score_adj
572score, and name. This is helpful to determine why the OOM killer was
573invoked, to identify the rogue task that caused it, and to determine why
574the OOM killer chose the task it did to kill.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800575
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800576If this is set to zero, this information is suppressed. On very
577large systems with thousands of tasks it may not be feasible to dump
578the memory state information for each one. Such systems should not
579be forced to incur a performance penalty in OOM conditions when the
580information may not be desired.
581
582If this is set to non-zero, this information is shown whenever the
583OOM killer actually kills a memory-hogging task.
584
David Rientjesad915c42010-08-09 17:18:53 -0700585The default value is 1 (enabled).
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800586
587==============================================================
588
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800589oom_kill_allocating_task
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800590
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800591This enables or disables killing the OOM-triggering task in
592out-of-memory situations.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800593
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800594If this is set to zero, the OOM killer will scan through the entire
595tasklist and select a task based on heuristics to kill. This normally
596selects a rogue memory-hogging task that frees up a large amount of
597memory when killed.
598
599If this is set to non-zero, the OOM killer simply kills the task that
600triggered the out-of-memory condition. This avoids the expensive
601tasklist scan.
602
603If panic_on_oom is selected, it takes precedence over whatever value
604is used in oom_kill_allocating_task.
605
606The default value is 0.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000607
608==============================================================
609
Jerome Marchand49f0ce52014-01-21 15:49:14 -0800610overcommit_kbytes:
611
612When overcommit_memory is set to 2, the committed address space is not
613permitted to exceed swap plus this amount of physical RAM. See below.
614
615Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
616of them may be specified at a time. Setting one disables the other (which
617then appears as 0 when read).
618
619==============================================================
620
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800621overcommit_memory:
Paul Mundtdd8632a2009-01-08 12:04:47 +0000622
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800623This value contains a flag that enables memory overcommitment.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000624
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800625When this flag is 0, the kernel attempts to estimate the amount
626of free memory left when userspace requests more memory.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000627
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800628When this flag is 1, the kernel pretends there is always enough
629memory until it actually runs out.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000630
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800631When this flag is 2, the kernel uses a "never overcommit"
632policy that attempts to prevent any overcommit of memory.
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700633Note that user_reserve_kbytes affects this policy.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000634
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800635This feature can be very useful because there are a lot of
636programs that malloc() huge amounts of memory "just-in-case"
637and don't use much of it.
638
639The default value is 0.
640
641See Documentation/vm/overcommit-accounting and
642security/commoncap.c::cap_vm_enough_memory() for more information.
643
644==============================================================
645
646overcommit_ratio:
647
648When overcommit_memory is set to 2, the committed address
649space is not permitted to exceed swap plus this percentage
650of physical RAM. See above.
651
652==============================================================
653
654page-cluster
655
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700656page-cluster controls the number of pages up to which consecutive pages
657are read in from swap in a single attempt. This is the swap counterpart
658to page cache readahead.
659The mentioned consecutivity is not in terms of virtual/physical addresses,
660but consecutive on swap space - that means they were swapped out together.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800661
662It is a logarithmic value - setting it to zero means "1 page", setting
663it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700664Zero disables swap readahead completely.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800665
666The default value is three (eight pages at a time). There may be some
667small benefits in tuning this to a different value if your workload is
668swap-intensive.
669
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700670Lower values mean lower latencies for initial faults, but at the same time
671extra faults and I/O delays for following faults if they would have been part of
672that consecutive pages readahead would have brought in.
673
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800674=============================================================
675
676panic_on_oom
677
678This enables or disables panic on out-of-memory feature.
679
680If this is set to 0, the kernel will kill some rogue process,
681called oom_killer. Usually, oom_killer can kill rogue processes and
682system will survive.
683
684If this is set to 1, the kernel panics when out-of-memory happens.
685However, if a process limits using nodes by mempolicy/cpusets,
686and those nodes become memory exhaustion status, one process
687may be killed by oom-killer. No panic occurs in this case.
688Because other nodes' memory may be free. This means system total status
689may be not fatal yet.
690
691If this is set to 2, the kernel panics compulsorily even on the
KAMEZAWA Hiroyukidaaf1e62010-03-10 15:22:32 -0800692above-mentioned. Even oom happens under memory cgroup, the whole
693system panics.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800694
695The default value is 0.
6961 and 2 are for failover of clustering. Please select either
697according to your policy of failover.
KAMEZAWA Hiroyukidaaf1e62010-03-10 15:22:32 -0800698panic_on_oom=2+kdump gives you very strong tool to investigate
699why oom happens. You can get snapshot.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800700
701=============================================================
702
703percpu_pagelist_fraction
704
705This is the fraction of pages at most (high mark pcp->high) in each zone that
706are allocated for each per cpu page list. The min value for this is 8. It
707means that we don't allow more than 1/8th of pages in each zone to be
708allocated in any single per_cpu_pagelist. This entry only changes the value
709of hot per cpu pagelists. User can specify a number like 100 to allocate
7101/100th of each zone to each per cpu page list.
711
712The batch value of each per cpu pagelist is also updated as a result. It is
713set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
714
715The initial value is zero. Kernel does not use this value at boot time to set
David Rientjes7cd2b0a2014-06-23 13:22:04 -0700716the high water marks for each per cpu page list. If the user writes '0' to this
717sysctl, it will revert to this default behavior.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800718
719==============================================================
720
721stat_interval
722
723The time interval between which vm statistics are updated. The default
724is 1 second.
725
726==============================================================
727
728swappiness
729
730This control is used to define how aggressive the kernel will swap
731memory pages. Higher values will increase agressiveness, lower values
Aaron Tomlin8582cb92014-01-29 14:05:38 -0800732decrease the amount of swap. A value of 0 instructs the kernel not to
733initiate swap until the amount of free and file-backed pages is less
734than the high water mark in a zone.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800735
736The default value is 60.
737
738==============================================================
739
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700740- user_reserve_kbytes
741
Masanari Iida633708a2015-01-02 12:03:19 +0900742When overcommit_memory is set to 2, "never overcommit" mode, reserve
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700743min(3% of current process size, user_reserve_kbytes) of free memory.
744This is intended to prevent a user from starting a single memory hogging
745process, such that they cannot recover (kill the hog).
746
747user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
748
749If this is reduced to zero, then the user will be allowed to allocate
750all free memory with a single process, minus admin_reserve_kbytes.
751Any subsequent attempts to execute a command will result in
752"fork: Cannot allocate memory".
753
754Changing this takes effect whenever an application requests memory.
755
756==============================================================
757
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800758vfs_cache_pressure
759------------------
760
Denys Vlasenko4a0da712014-06-04 16:11:03 -0700761This percentage value controls the tendency of the kernel to reclaim
762the memory which is used for caching of directory and inode objects.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800763
764At the default value of vfs_cache_pressure=100 the kernel will attempt to
765reclaim dentries and inodes at a "fair" rate with respect to pagecache and
766swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
Jan Kara55c37a82009-09-21 17:01:40 -0700767to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
768never reclaim dentries and inodes due to memory pressure and this can easily
769lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800770causes the kernel to prefer to reclaim dentries and inodes.
771
Denys Vlasenko4a0da712014-06-04 16:11:03 -0700772Increasing vfs_cache_pressure significantly beyond 100 may have negative
773performance impact. Reclaim code needs to take various locks to find freeable
774directory and inode objects. With vfs_cache_pressure=1000, it will look for
775ten times more freeable objects than there are.
776
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800777==============================================================
778
779zone_reclaim_mode:
780
781Zone_reclaim_mode allows someone to set more or less aggressive approaches to
782reclaim memory when a zone runs out of memory. If it is set to zero then no
783zone reclaim occurs. Allocations will be satisfied from other zones / nodes
784in the system.
785
786This is value ORed together of
787
7881 = Zone reclaim on
7892 = Zone reclaim writes dirty pages out
7904 = Zone reclaim swaps pages
791
Mel Gorman4f9b16a2014-06-04 16:07:14 -0700792zone_reclaim_mode is disabled by default. For file servers or workloads
793that benefit from having their data cached, zone_reclaim_mode should be
794left disabled as the caching effect is likely to be more important than
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800795data locality.
796
Mel Gorman4f9b16a2014-06-04 16:07:14 -0700797zone_reclaim may be enabled if it's known that the workload is partitioned
798such that each partition fits within a NUMA node and that accessing remote
799memory would cause a measurable performance reduction. The page allocator
800will then reclaim easily reusable pages (those page cache pages that are
801currently not used) before allocating off node pages.
802
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800803Allowing zone reclaim to write out pages stops processes that are
804writing large amounts of data from dirtying pages on other nodes. Zone
805reclaim will write out dirty pages if a zone fills up and so effectively
806throttle the process. This may decrease the performance of a single process
807since it cannot use all of system memory to buffer the outgoing writes
808anymore but it preserve the memory on other nodes so that the performance
809of other processes running on other nodes will not be affected.
810
811Allowing regular swap effectively restricts allocations to the local
812node unless explicitly overridden by memory policies or cpuset
813configurations.
814
815============ End of Document =================================