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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
Peter W Morrealedb0fb182009-01-15 13:50:42 -080024- dirty_background_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -070025- dirty_background_ratio
Peter W Morrealedb0fb182009-01-15 13:50:42 -080026- dirty_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -070027- dirty_expire_centisecs
Peter W Morrealedb0fb182009-01-15 13:50:42 -080028- dirty_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -070029- dirty_writeback_centisecs
Peter W Morrealedb0fb182009-01-15 13:50:42 -080030- drop_caches
Mel Gorman5e771902010-05-24 14:32:31 -070031- extfrag_threshold
Peter W Morrealedb0fb182009-01-15 13:50:42 -080032- hugepages_treat_as_movable
33- hugetlb_shm_group
34- laptop_mode
35- legacy_va_layout
36- lowmem_reserve_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -070037- max_map_count
Andi Kleen6a460792009-09-16 11:50:15 +020038- memory_failure_early_kill
39- memory_failure_recovery
Linus Torvalds1da177e2005-04-16 15:20:36 -070040- min_free_kbytes
Christoph Lameter0ff38492006-09-25 23:31:52 -070041- min_slab_ratio
Peter W Morrealedb0fb182009-01-15 13:50:42 -080042- min_unmapped_ratio
43- mmap_min_addr
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -080044- nr_hugepages
45- nr_overcommit_hugepages
Peter W Morrealedb0fb182009-01-15 13:50:42 -080046- nr_trim_pages (only if CONFIG_MMU=n)
47- numa_zonelist_order
48- oom_dump_tasks
49- oom_kill_allocating_task
Jerome Marchand49f0ce52014-01-21 15:49:14 -080050- overcommit_kbytes
Peter W Morrealedb0fb182009-01-15 13:50:42 -080051- overcommit_memory
52- overcommit_ratio
53- page-cluster
54- panic_on_oom
55- percpu_pagelist_fraction
56- stat_interval
57- swappiness
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -070058- user_reserve_kbytes
Peter W Morrealedb0fb182009-01-15 13:50:42 -080059- vfs_cache_pressure
60- zone_reclaim_mode
61
Linus Torvalds1da177e2005-04-16 15:20:36 -070062==============================================================
63
Andrew Shewmaker4eeab4f2013-04-29 15:08:11 -070064admin_reserve_kbytes
65
66The amount of free memory in the system that should be reserved for users
67with the capability cap_sys_admin.
68
69admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
70
71That should provide enough for the admin to log in and kill a process,
72if necessary, under the default overcommit 'guess' mode.
73
74Systems running under overcommit 'never' should increase this to account
75for the full Virtual Memory Size of programs used to recover. Otherwise,
76root may not be able to log in to recover the system.
77
78How do you calculate a minimum useful reserve?
79
80sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
81
82For overcommit 'guess', we can sum resident set sizes (RSS).
83On x86_64 this is about 8MB.
84
85For overcommit 'never', we can take the max of their virtual sizes (VSZ)
86and add the sum of their RSS.
87On x86_64 this is about 128MB.
88
89Changing this takes effect whenever an application requests memory.
90
91==============================================================
92
Peter W Morrealedb0fb182009-01-15 13:50:42 -080093block_dump
Linus Torvalds1da177e2005-04-16 15:20:36 -070094
Peter W Morrealedb0fb182009-01-15 13:50:42 -080095block_dump enables block I/O debugging when set to a nonzero value. More
96information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
98==============================================================
99
Mel Gorman76ab0f52010-05-24 14:32:28 -0700100compact_memory
101
102Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
103all zones are compacted such that free memory is available in contiguous
104blocks where possible. This can be important for example in the allocation of
105huge pages although processes will also directly compact memory as required.
106
107==============================================================
108
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800109dirty_background_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300111Contains the amount of dirty memory at which the background kernel
112flusher threads will start writeback.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113
Andrea Righiabffc022010-10-27 15:33:31 -0700114Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
115one of them may be specified at a time. When one sysctl is written it is
116immediately taken into account to evaluate the dirty memory limits and the
117other appears as 0 when read.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700118
119==============================================================
120
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800121dirty_background_ratio
Linus Torvalds1da177e2005-04-16 15:20:36 -0700122
Zheng Liu715ea412013-11-12 15:08:30 -0800123Contains, as a percentage of total available memory that contains free pages
124and reclaimable pages, the number of pages at which the background kernel
125flusher threads will start writing out dirty data.
126
127The total avaiable memory is not equal to total system memory.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700128
129==============================================================
130
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800131dirty_bytes
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800133Contains the amount of dirty memory at which a process generating disk writes
134will itself start writeback.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700135
Andrea Righiabffc022010-10-27 15:33:31 -0700136Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
137specified at a time. When one sysctl is written it is immediately taken into
138account to evaluate the dirty memory limits and the other appears as 0 when
139read.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800140
Andrea Righi9e4a5bd2009-04-30 15:08:57 -0700141Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
142value lower than this limit will be ignored and the old configuration will be
143retained.
144
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800145==============================================================
146
147dirty_expire_centisecs
148
149This tunable is used to define when dirty data is old enough to be eligible
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300150for writeout by the kernel flusher threads. It is expressed in 100'ths
151of a second. Data which has been dirty in-memory for longer than this
152interval will be written out next time a flusher thread wakes up.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800153
154==============================================================
155
156dirty_ratio
157
Zheng Liu715ea412013-11-12 15:08:30 -0800158Contains, as a percentage of total available memory that contains free pages
159and reclaimable pages, the number of pages at which a process which is
160generating disk writes will itself start writing out dirty data.
161
162The total avaiable memory is not equal to total system memory.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800163
164==============================================================
165
166dirty_writeback_centisecs
167
Artem Bityutskiy6601fac2012-07-25 18:12:01 +0300168The kernel flusher threads will periodically wake up and write `old' data
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800169out to disk. This tunable expresses the interval between those wakeups, in
170100'ths of a second.
171
172Setting this to zero disables periodic writeback altogether.
173
174==============================================================
175
176drop_caches
177
Dave Hansen5509a5d2014-04-03 14:48:19 -0700178Writing to this will cause the kernel to drop clean caches, as well as
179reclaimable slab objects like dentries and inodes. Once dropped, their
180memory becomes free.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800181
182To free pagecache:
183 echo 1 > /proc/sys/vm/drop_caches
Dave Hansen5509a5d2014-04-03 14:48:19 -0700184To free reclaimable slab objects (includes dentries and inodes):
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800185 echo 2 > /proc/sys/vm/drop_caches
Dave Hansen5509a5d2014-04-03 14:48:19 -0700186To free slab objects and pagecache:
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800187 echo 3 > /proc/sys/vm/drop_caches
188
Dave Hansen5509a5d2014-04-03 14:48:19 -0700189This is a non-destructive operation and will not free any dirty objects.
190To increase the number of objects freed by this operation, the user may run
191`sync' prior to writing to /proc/sys/vm/drop_caches. This will minimize the
192number of dirty objects on the system and create more candidates to be
193dropped.
194
195This file is not a means to control the growth of the various kernel caches
196(inodes, dentries, pagecache, etc...) These objects are automatically
197reclaimed by the kernel when memory is needed elsewhere on the system.
198
199Use of this file can cause performance problems. Since it discards cached
200objects, it may cost a significant amount of I/O and CPU to recreate the
201dropped objects, especially if they were under heavy use. Because of this,
202use outside of a testing or debugging environment is not recommended.
203
204You may see informational messages in your kernel log when this file is
205used:
206
207 cat (1234): drop_caches: 3
208
209These are informational only. They do not mean that anything is wrong
210with your system. To disable them, echo 4 (bit 3) into drop_caches.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800211
212==============================================================
213
Mel Gorman5e771902010-05-24 14:32:31 -0700214extfrag_threshold
215
216This parameter affects whether the kernel will compact memory or direct
217reclaim to satisfy a high-order allocation. /proc/extfrag_index shows what
218the fragmentation index for each order is in each zone in the system. Values
219tending towards 0 imply allocations would fail due to lack of memory,
220values towards 1000 imply failures are due to fragmentation and -1 implies
221that the allocation will succeed as long as watermarks are met.
222
223The kernel will not compact memory in a zone if the
224fragmentation index is <= extfrag_threshold. The default value is 500.
225
226==============================================================
227
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800228hugepages_treat_as_movable
229
Naoya Horiguchi86cdb462013-09-11 14:22:13 -0700230This parameter controls whether we can allocate hugepages from ZONE_MOVABLE
231or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE.
232ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified,
233so this parameter has no effect if used without kernelcore=.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800234
Naoya Horiguchi86cdb462013-09-11 14:22:13 -0700235Hugepage migration is now available in some situations which depend on the
236architecture and/or the hugepage size. If a hugepage supports migration,
237allocation from ZONE_MOVABLE is always enabled for the hugepage regardless
238of the value of this parameter.
239IOW, this parameter affects only non-migratable hugepages.
240
241Assuming that hugepages are not migratable in your system, one usecase of
242this parameter is that users can make hugepage pool more extensible by
243enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE
244page reclaim/migration/compaction work more and you can get contiguous
245memory more likely. Note that using ZONE_MOVABLE for non-migratable
246hugepages can do harm to other features like memory hotremove (because
247memory hotremove expects that memory blocks on ZONE_MOVABLE are always
248removable,) so it's a trade-off responsible for the users.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800249
250==============================================================
251
252hugetlb_shm_group
253
254hugetlb_shm_group contains group id that is allowed to create SysV
255shared memory segment using hugetlb page.
256
257==============================================================
258
259laptop_mode
260
261laptop_mode is a knob that controls "laptop mode". All the things that are
262controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
263
264==============================================================
265
266legacy_va_layout
267
Kulikov Vasiliy2174efb2010-06-28 13:59:28 +0200268If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800269will use the legacy (2.4) layout for all processes.
270
271==============================================================
272
273lowmem_reserve_ratio
274
275For some specialised workloads on highmem machines it is dangerous for
276the kernel to allow process memory to be allocated from the "lowmem"
277zone. This is because that memory could then be pinned via the mlock()
278system call, or by unavailability of swapspace.
279
280And on large highmem machines this lack of reclaimable lowmem memory
281can be fatal.
282
283So the Linux page allocator has a mechanism which prevents allocations
284which _could_ use highmem from using too much lowmem. This means that
285a certain amount of lowmem is defended from the possibility of being
286captured into pinned user memory.
287
288(The same argument applies to the old 16 megabyte ISA DMA region. This
289mechanism will also defend that region from allocations which could use
290highmem or lowmem).
291
292The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
293in defending these lower zones.
294
295If you have a machine which uses highmem or ISA DMA and your
296applications are using mlock(), or if you are running with no swap then
297you probably should change the lowmem_reserve_ratio setting.
298
299The lowmem_reserve_ratio is an array. You can see them by reading this file.
300-
301% cat /proc/sys/vm/lowmem_reserve_ratio
302256 256 32
303-
304Note: # of this elements is one fewer than number of zones. Because the highest
305 zone's value is not necessary for following calculation.
306
307But, these values are not used directly. The kernel calculates # of protection
308pages for each zones from them. These are shown as array of protection pages
309in /proc/zoneinfo like followings. (This is an example of x86-64 box).
310Each zone has an array of protection pages like this.
311
312-
313Node 0, zone DMA
314 pages free 1355
315 min 3
316 low 3
317 high 4
318 :
319 :
320 numa_other 0
321 protection: (0, 2004, 2004, 2004)
322 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
323 pagesets
324 cpu: 0 pcp: 0
325 :
326-
327These protections are added to score to judge whether this zone should be used
328for page allocation or should be reclaimed.
329
330In this example, if normal pages (index=2) are required to this DMA zone and
Mel Gorman41858962009-06-16 15:32:12 -0700331watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
332not be used because pages_free(1355) is smaller than watermark + protection[2]
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800333(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
334normal page requirement. If requirement is DMA zone(index=0), protection[0]
335(=0) is used.
336
337zone[i]'s protection[j] is calculated by following expression.
338
339(i < j):
340 zone[i]->protection[j]
341 = (total sums of present_pages from zone[i+1] to zone[j] on the node)
342 / lowmem_reserve_ratio[i];
343(i = j):
344 (should not be protected. = 0;
345(i > j):
346 (not necessary, but looks 0)
347
348The default values of lowmem_reserve_ratio[i] are
349 256 (if zone[i] means DMA or DMA32 zone)
350 32 (others).
351As above expression, they are reciprocal number of ratio.
352256 means 1/256. # of protection pages becomes about "0.39%" of total present
353pages of higher zones on the node.
354
355If you would like to protect more pages, smaller values are effective.
356The minimum value is 1 (1/1 -> 100%).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700357
358==============================================================
359
360max_map_count:
361
362This file contains the maximum number of memory map areas a process
363may have. Memory map areas are used as a side-effect of calling
364malloc, directly by mmap and mprotect, and also when loading shared
365libraries.
366
367While most applications need less than a thousand maps, certain
368programs, particularly malloc debuggers, may consume lots of them,
369e.g., up to one or two maps per allocation.
370
371The default value is 65536.
372
Andi Kleen6a460792009-09-16 11:50:15 +0200373=============================================================
374
375memory_failure_early_kill:
376
377Control how to kill processes when uncorrected memory error (typically
378a 2bit error in a memory module) is detected in the background by hardware
379that cannot be handled by the kernel. In some cases (like the page
380still having a valid copy on disk) the kernel will handle the failure
381transparently without affecting any applications. But if there is
382no other uptodate copy of the data it will kill to prevent any data
383corruptions from propagating.
384
3851: Kill all processes that have the corrupted and not reloadable page mapped
386as soon as the corruption is detected. Note this is not supported
387for a few types of pages, like kernel internally allocated data or
388the swap cache, but works for the majority of user pages.
389
3900: Only unmap the corrupted page from all processes and only kill a process
391who tries to access it.
392
393The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
394handle this if they want to.
395
396This is only active on architectures/platforms with advanced machine
397check handling and depends on the hardware capabilities.
398
399Applications can override this setting individually with the PR_MCE_KILL prctl
400
401==============================================================
402
403memory_failure_recovery
404
405Enable memory failure recovery (when supported by the platform)
406
4071: Attempt recovery.
408
4090: Always panic on a memory failure.
410
Linus Torvalds1da177e2005-04-16 15:20:36 -0700411==============================================================
412
413min_free_kbytes:
414
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800415This is used to force the Linux VM to keep a minimum number
Mel Gorman41858962009-06-16 15:32:12 -0700416of kilobytes free. The VM uses this number to compute a
417watermark[WMARK_MIN] value for each lowmem zone in the system.
418Each lowmem zone gets a number of reserved free pages based
419proportionally on its size.
Rohit Seth8ad4b1f2006-01-08 01:00:40 -0800420
Matt LaPlanted9195882008-07-25 19:45:33 -0700421Some minimal amount of memory is needed to satisfy PF_MEMALLOC
Pavel Machek24950892007-10-16 23:31:28 -0700422allocations; if you set this to lower than 1024KB, your system will
423become subtly broken, and prone to deadlock under high loads.
424
425Setting this too high will OOM your machine instantly.
426
Christoph Lameter96146342006-07-03 00:24:13 -0700427=============================================================
428
Christoph Lameter0ff38492006-09-25 23:31:52 -0700429min_slab_ratio:
430
431This is available only on NUMA kernels.
432
433A percentage of the total pages in each zone. On Zone reclaim
434(fallback from the local zone occurs) slabs will be reclaimed if more
435than this percentage of pages in a zone are reclaimable slab pages.
436This insures that the slab growth stays under control even in NUMA
437systems that rarely perform global reclaim.
438
439The default is 5 percent.
440
441Note that slab reclaim is triggered in a per zone / node fashion.
442The process of reclaiming slab memory is currently not node specific
443and may not be fast.
444
445=============================================================
446
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800447min_unmapped_ratio:
KAMEZAWA Hiroyukifadd8fb2006-06-23 02:03:13 -0700448
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800449This is available only on NUMA kernels.
Yasunori Goto2b744c02007-05-06 14:49:59 -0700450
Mel Gorman90afa5d2009-06-16 15:33:20 -0700451This is a percentage of the total pages in each zone. Zone reclaim will
452only occur if more than this percentage of pages are in a state that
453zone_reclaim_mode allows to be reclaimed.
454
455If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
456against all file-backed unmapped pages including swapcache pages and tmpfs
457files. Otherwise, only unmapped pages backed by normal files but not tmpfs
458files and similar are considered.
Yasunori Goto2b744c02007-05-06 14:49:59 -0700459
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800460The default is 1 percent.
David Rientjesfe071d72007-10-16 23:25:56 -0700461
Eric Parised032182007-06-28 15:55:21 -0400462==============================================================
463
464mmap_min_addr
465
466This file indicates the amount of address space which a user process will
André Goddard Rosaaf901ca2009-11-14 13:09:05 -0200467be restricted from mmapping. Since kernel null dereference bugs could
Eric Parised032182007-06-28 15:55:21 -0400468accidentally operate based on the information in the first couple of pages
469of memory userspace processes should not be allowed to write to them. By
470default this value is set to 0 and no protections will be enforced by the
471security module. Setting this value to something like 64k will allow the
472vast majority of applications to work correctly and provide defense in depth
473against future potential kernel bugs.
474
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700475==============================================================
476
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800477nr_hugepages
478
479Change the minimum size of the hugepage pool.
480
481See Documentation/vm/hugetlbpage.txt
482
483==============================================================
484
485nr_overcommit_hugepages
486
487Change the maximum size of the hugepage pool. The maximum is
488nr_hugepages + nr_overcommit_hugepages.
489
490See Documentation/vm/hugetlbpage.txt
491
492==============================================================
493
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800494nr_trim_pages
495
496This is available only on NOMMU kernels.
497
498This value adjusts the excess page trimming behaviour of power-of-2 aligned
499NOMMU mmap allocations.
500
501A value of 0 disables trimming of allocations entirely, while a value of 1
502trims excess pages aggressively. Any value >= 1 acts as the watermark where
503trimming of allocations is initiated.
504
505The default value is 1.
506
507See Documentation/nommu-mmap.txt for more information.
508
509==============================================================
510
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700511numa_zonelist_order
512
513This sysctl is only for NUMA.
514'where the memory is allocated from' is controlled by zonelists.
515(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
516 you may be able to read ZONE_DMA as ZONE_DMA32...)
517
518In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
519ZONE_NORMAL -> ZONE_DMA
520This means that a memory allocation request for GFP_KERNEL will
521get memory from ZONE_DMA only when ZONE_NORMAL is not available.
522
523In NUMA case, you can think of following 2 types of order.
524Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
525
526(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
527(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
528
529Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
530will be used before ZONE_NORMAL exhaustion. This increases possibility of
531out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
532
533Type(B) cannot offer the best locality but is more robust against OOM of
534the DMA zone.
535
536Type(A) is called as "Node" order. Type (B) is "Zone" order.
537
538"Node order" orders the zonelists by node, then by zone within each node.
Paul Bolle5a3016a2011-04-06 11:09:55 +0200539Specify "[Nn]ode" for node order
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700540
541"Zone Order" orders the zonelists by zone type, then by node within each
Paul Bolle5a3016a2011-04-06 11:09:55 +0200542zone. Specify "[Zz]one" for zone order.
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700543
544Specify "[Dd]efault" to request automatic configuration. Autoconfiguration
545will select "node" order in following case.
546(1) if the DMA zone does not exist or
547(2) if the DMA zone comprises greater than 50% of the available memory or
Wanpeng Lif8f191f2013-07-08 16:00:16 -0700548(3) if any node's DMA zone comprises greater than 70% of its local memory and
KAMEZAWA Hiroyukif0c0b2b2007-07-15 23:38:01 -0700549 the amount of local memory is big enough.
550
551Otherwise, "zone" order will be selected. Default order is recommended unless
552this is causing problems for your system/application.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800553
554==============================================================
555
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800556oom_dump_tasks
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800557
Kirill A. Shutemovdc6c9a32015-02-11 15:26:50 -0800558Enables a system-wide task dump (excluding kernel threads) to be produced
559when the kernel performs an OOM-killing and includes such information as
560pid, uid, tgid, vm size, rss, nr_ptes, nr_pmds, swapents, oom_score_adj
561score, and name. This is helpful to determine why the OOM killer was
562invoked, to identify the rogue task that caused it, and to determine why
563the OOM killer chose the task it did to kill.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800564
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800565If this is set to zero, this information is suppressed. On very
566large systems with thousands of tasks it may not be feasible to dump
567the memory state information for each one. Such systems should not
568be forced to incur a performance penalty in OOM conditions when the
569information may not be desired.
570
571If this is set to non-zero, this information is shown whenever the
572OOM killer actually kills a memory-hogging task.
573
David Rientjesad915c42010-08-09 17:18:53 -0700574The default value is 1 (enabled).
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800575
576==============================================================
577
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800578oom_kill_allocating_task
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800579
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800580This enables or disables killing the OOM-triggering task in
581out-of-memory situations.
Nishanth Aravamudand5dbac82007-12-17 16:20:25 -0800582
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800583If this is set to zero, the OOM killer will scan through the entire
584tasklist and select a task based on heuristics to kill. This normally
585selects a rogue memory-hogging task that frees up a large amount of
586memory when killed.
587
588If this is set to non-zero, the OOM killer simply kills the task that
589triggered the out-of-memory condition. This avoids the expensive
590tasklist scan.
591
592If panic_on_oom is selected, it takes precedence over whatever value
593is used in oom_kill_allocating_task.
594
595The default value is 0.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000596
597==============================================================
598
Jerome Marchand49f0ce52014-01-21 15:49:14 -0800599overcommit_kbytes:
600
601When overcommit_memory is set to 2, the committed address space is not
602permitted to exceed swap plus this amount of physical RAM. See below.
603
604Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
605of them may be specified at a time. Setting one disables the other (which
606then appears as 0 when read).
607
608==============================================================
609
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800610overcommit_memory:
Paul Mundtdd8632a2009-01-08 12:04:47 +0000611
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800612This value contains a flag that enables memory overcommitment.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000613
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800614When this flag is 0, the kernel attempts to estimate the amount
615of free memory left when userspace requests more memory.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000616
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800617When this flag is 1, the kernel pretends there is always enough
618memory until it actually runs out.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000619
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800620When this flag is 2, the kernel uses a "never overcommit"
621policy that attempts to prevent any overcommit of memory.
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700622Note that user_reserve_kbytes affects this policy.
Paul Mundtdd8632a2009-01-08 12:04:47 +0000623
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800624This feature can be very useful because there are a lot of
625programs that malloc() huge amounts of memory "just-in-case"
626and don't use much of it.
627
628The default value is 0.
629
630See Documentation/vm/overcommit-accounting and
631security/commoncap.c::cap_vm_enough_memory() for more information.
632
633==============================================================
634
635overcommit_ratio:
636
637When overcommit_memory is set to 2, the committed address
638space is not permitted to exceed swap plus this percentage
639of physical RAM. See above.
640
641==============================================================
642
643page-cluster
644
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700645page-cluster controls the number of pages up to which consecutive pages
646are read in from swap in a single attempt. This is the swap counterpart
647to page cache readahead.
648The mentioned consecutivity is not in terms of virtual/physical addresses,
649but consecutive on swap space - that means they were swapped out together.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800650
651It is a logarithmic value - setting it to zero means "1 page", setting
652it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700653Zero disables swap readahead completely.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800654
655The default value is three (eight pages at a time). There may be some
656small benefits in tuning this to a different value if your workload is
657swap-intensive.
658
Christian Ehrhardtdf858fa2012-07-31 16:41:46 -0700659Lower values mean lower latencies for initial faults, but at the same time
660extra faults and I/O delays for following faults if they would have been part of
661that consecutive pages readahead would have brought in.
662
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800663=============================================================
664
665panic_on_oom
666
667This enables or disables panic on out-of-memory feature.
668
669If this is set to 0, the kernel will kill some rogue process,
670called oom_killer. Usually, oom_killer can kill rogue processes and
671system will survive.
672
673If this is set to 1, the kernel panics when out-of-memory happens.
674However, if a process limits using nodes by mempolicy/cpusets,
675and those nodes become memory exhaustion status, one process
676may be killed by oom-killer. No panic occurs in this case.
677Because other nodes' memory may be free. This means system total status
678may be not fatal yet.
679
680If this is set to 2, the kernel panics compulsorily even on the
KAMEZAWA Hiroyukidaaf1e62010-03-10 15:22:32 -0800681above-mentioned. Even oom happens under memory cgroup, the whole
682system panics.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800683
684The default value is 0.
6851 and 2 are for failover of clustering. Please select either
686according to your policy of failover.
KAMEZAWA Hiroyukidaaf1e62010-03-10 15:22:32 -0800687panic_on_oom=2+kdump gives you very strong tool to investigate
688why oom happens. You can get snapshot.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800689
690=============================================================
691
692percpu_pagelist_fraction
693
694This is the fraction of pages at most (high mark pcp->high) in each zone that
695are allocated for each per cpu page list. The min value for this is 8. It
696means that we don't allow more than 1/8th of pages in each zone to be
697allocated in any single per_cpu_pagelist. This entry only changes the value
698of hot per cpu pagelists. User can specify a number like 100 to allocate
6991/100th of each zone to each per cpu page list.
700
701The batch value of each per cpu pagelist is also updated as a result. It is
702set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
703
704The initial value is zero. Kernel does not use this value at boot time to set
David Rientjes7cd2b0a2014-06-23 13:22:04 -0700705the high water marks for each per cpu page list. If the user writes '0' to this
706sysctl, it will revert to this default behavior.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800707
708==============================================================
709
710stat_interval
711
712The time interval between which vm statistics are updated. The default
713is 1 second.
714
715==============================================================
716
717swappiness
718
719This control is used to define how aggressive the kernel will swap
720memory pages. Higher values will increase agressiveness, lower values
Aaron Tomlin8582cb92014-01-29 14:05:38 -0800721decrease the amount of swap. A value of 0 instructs the kernel not to
722initiate swap until the amount of free and file-backed pages is less
723than the high water mark in a zone.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800724
725The default value is 60.
726
727==============================================================
728
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700729- user_reserve_kbytes
730
Masanari Iida633708a2015-01-02 12:03:19 +0900731When overcommit_memory is set to 2, "never overcommit" mode, reserve
Andrew Shewmakerc9b1d092013-04-29 15:08:10 -0700732min(3% of current process size, user_reserve_kbytes) of free memory.
733This is intended to prevent a user from starting a single memory hogging
734process, such that they cannot recover (kill the hog).
735
736user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
737
738If this is reduced to zero, then the user will be allowed to allocate
739all free memory with a single process, minus admin_reserve_kbytes.
740Any subsequent attempts to execute a command will result in
741"fork: Cannot allocate memory".
742
743Changing this takes effect whenever an application requests memory.
744
745==============================================================
746
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800747vfs_cache_pressure
748------------------
749
Denys Vlasenko4a0da712014-06-04 16:11:03 -0700750This percentage value controls the tendency of the kernel to reclaim
751the memory which is used for caching of directory and inode objects.
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800752
753At the default value of vfs_cache_pressure=100 the kernel will attempt to
754reclaim dentries and inodes at a "fair" rate with respect to pagecache and
755swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
Jan Kara55c37a82009-09-21 17:01:40 -0700756to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
757never reclaim dentries and inodes due to memory pressure and this can easily
758lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800759causes the kernel to prefer to reclaim dentries and inodes.
760
Denys Vlasenko4a0da712014-06-04 16:11:03 -0700761Increasing vfs_cache_pressure significantly beyond 100 may have negative
762performance impact. Reclaim code needs to take various locks to find freeable
763directory and inode objects. With vfs_cache_pressure=1000, it will look for
764ten times more freeable objects than there are.
765
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800766==============================================================
767
768zone_reclaim_mode:
769
770Zone_reclaim_mode allows someone to set more or less aggressive approaches to
771reclaim memory when a zone runs out of memory. If it is set to zero then no
772zone reclaim occurs. Allocations will be satisfied from other zones / nodes
773in the system.
774
775This is value ORed together of
776
7771 = Zone reclaim on
7782 = Zone reclaim writes dirty pages out
7794 = Zone reclaim swaps pages
780
Mel Gorman4f9b16a2014-06-04 16:07:14 -0700781zone_reclaim_mode is disabled by default. For file servers or workloads
782that benefit from having their data cached, zone_reclaim_mode should be
783left disabled as the caching effect is likely to be more important than
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800784data locality.
785
Mel Gorman4f9b16a2014-06-04 16:07:14 -0700786zone_reclaim may be enabled if it's known that the workload is partitioned
787such that each partition fits within a NUMA node and that accessing remote
788memory would cause a measurable performance reduction. The page allocator
789will then reclaim easily reusable pages (those page cache pages that are
790currently not used) before allocating off node pages.
791
Peter W Morrealedb0fb182009-01-15 13:50:42 -0800792Allowing zone reclaim to write out pages stops processes that are
793writing large amounts of data from dirtying pages on other nodes. Zone
794reclaim will write out dirty pages if a zone fills up and so effectively
795throttle the process. This may decrease the performance of a single process
796since it cannot use all of system memory to buffer the outgoing writes
797anymore but it preserve the memory on other nodes so that the performance
798of other processes running on other nodes will not be affected.
799
800Allowing regular swap effectively restricts allocations to the local
801node unless explicitly overridden by memory policies or cpuset
802configurations.
803
804============ End of Document =================================