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Based on kernel version 4.15. Page generated on 2018-01-29 10:01 EST.

1	Documentation for /proc/sys/vm/*	kernel version 2.6.29
2		(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
3		(c) 2008         Peter W. Morreale <pmorreale@novell.com>
5	For general info and legal blurb, please look in README.
7	==============================================================
9	This file contains the documentation for the sysctl files in
10	/proc/sys/vm and is valid for Linux kernel version 2.6.29.
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.
16	Default values and initialization routines for most of these
17	files can be found in mm/swap.c.
19	Currently, these files are in /proc/sys/vm:
21	- admin_reserve_kbytes
22	- block_dump
23	- compact_memory
24	- compact_unevictable_allowed
25	- dirty_background_bytes
26	- dirty_background_ratio
27	- dirty_bytes
28	- dirty_expire_centisecs
29	- dirty_ratio
30	- dirty_writeback_centisecs
31	- drop_caches
32	- extfrag_threshold
33	- hugepages_treat_as_movable
34	- hugetlb_shm_group
35	- laptop_mode
36	- legacy_va_layout
37	- lowmem_reserve_ratio
38	- max_map_count
39	- memory_failure_early_kill
40	- memory_failure_recovery
41	- min_free_kbytes
42	- min_slab_ratio
43	- min_unmapped_ratio
44	- mmap_min_addr
45	- mmap_rnd_bits
46	- mmap_rnd_compat_bits
47	- nr_hugepages
48	- nr_overcommit_hugepages
49	- nr_trim_pages         (only if CONFIG_MMU=n)
50	- numa_zonelist_order
51	- oom_dump_tasks
52	- oom_kill_allocating_task
53	- overcommit_kbytes
54	- overcommit_memory
55	- overcommit_ratio
56	- page-cluster
57	- panic_on_oom
58	- percpu_pagelist_fraction
59	- stat_interval
60	- stat_refresh
61	- numa_stat
62	- swappiness
63	- user_reserve_kbytes
64	- vfs_cache_pressure
65	- watermark_scale_factor
66	- zone_reclaim_mode
68	==============================================================
70	admin_reserve_kbytes
72	The amount of free memory in the system that should be reserved for users
73	with the capability cap_sys_admin.
75	admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
77	That should provide enough for the admin to log in and kill a process,
78	if necessary, under the default overcommit 'guess' mode.
80	Systems running under overcommit 'never' should increase this to account
81	for the full Virtual Memory Size of programs used to recover. Otherwise,
82	root may not be able to log in to recover the system.
84	How do you calculate a minimum useful reserve?
86	sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
88	For overcommit 'guess', we can sum resident set sizes (RSS).
89	On x86_64 this is about 8MB.
91	For overcommit 'never', we can take the max of their virtual sizes (VSZ)
92	and add the sum of their RSS.
93	On x86_64 this is about 128MB.
95	Changing this takes effect whenever an application requests memory.
97	==============================================================
99	block_dump
101	block_dump enables block I/O debugging when set to a nonzero value. More
102	information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
104	==============================================================
106	compact_memory
108	Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
109	all zones are compacted such that free memory is available in contiguous
110	blocks where possible. This can be important for example in the allocation of
111	huge pages although processes will also directly compact memory as required.
113	==============================================================
115	compact_unevictable_allowed
117	Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
118	allowed to examine the unevictable lru (mlocked pages) for pages to compact.
119	This should be used on systems where stalls for minor page faults are an
120	acceptable trade for large contiguous free memory.  Set to 0 to prevent
121	compaction from moving pages that are unevictable.  Default value is 1.
123	==============================================================
125	dirty_background_bytes
127	Contains the amount of dirty memory at which the background kernel
128	flusher threads will start writeback.
130	Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
131	one of them may be specified at a time. When one sysctl is written it is
132	immediately taken into account to evaluate the dirty memory limits and the
133	other appears as 0 when read.
135	==============================================================
137	dirty_background_ratio
139	Contains, as a percentage of total available memory that contains free pages
140	and reclaimable pages, the number of pages at which the background kernel
141	flusher threads will start writing out dirty data.
143	The total available memory is not equal to total system memory.
145	==============================================================
147	dirty_bytes
149	Contains the amount of dirty memory at which a process generating disk writes
150	will itself start writeback.
152	Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
153	specified at a time. When one sysctl is written it is immediately taken into
154	account to evaluate the dirty memory limits and the other appears as 0 when
155	read.
157	Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
158	value lower than this limit will be ignored and the old configuration will be
159	retained.
161	==============================================================
163	dirty_expire_centisecs
165	This tunable is used to define when dirty data is old enough to be eligible
166	for writeout by the kernel flusher threads.  It is expressed in 100'ths
167	of a second.  Data which has been dirty in-memory for longer than this
168	interval will be written out next time a flusher thread wakes up.
170	==============================================================
172	dirty_ratio
174	Contains, as a percentage of total available memory that contains free pages
175	and reclaimable pages, the number of pages at which a process which is
176	generating disk writes will itself start writing out dirty data.
178	The total available memory is not equal to total system memory.
180	==============================================================
182	dirty_writeback_centisecs
184	The kernel flusher threads will periodically wake up and write `old' data
185	out to disk.  This tunable expresses the interval between those wakeups, in
186	100'ths of a second.
188	Setting this to zero disables periodic writeback altogether.
190	==============================================================
192	drop_caches
194	Writing to this will cause the kernel to drop clean caches, as well as
195	reclaimable slab objects like dentries and inodes.  Once dropped, their
196	memory becomes free.
198	To free pagecache:
199		echo 1 > /proc/sys/vm/drop_caches
200	To free reclaimable slab objects (includes dentries and inodes):
201		echo 2 > /proc/sys/vm/drop_caches
202	To free slab objects and pagecache:
203		echo 3 > /proc/sys/vm/drop_caches
205	This is a non-destructive operation and will not free any dirty objects.
206	To increase the number of objects freed by this operation, the user may run
207	`sync' prior to writing to /proc/sys/vm/drop_caches.  This will minimize the
208	number of dirty objects on the system and create more candidates to be
209	dropped.
211	This file is not a means to control the growth of the various kernel caches
212	(inodes, dentries, pagecache, etc...)  These objects are automatically
213	reclaimed by the kernel when memory is needed elsewhere on the system.
215	Use of this file can cause performance problems.  Since it discards cached
216	objects, it may cost a significant amount of I/O and CPU to recreate the
217	dropped objects, especially if they were under heavy use.  Because of this,
218	use outside of a testing or debugging environment is not recommended.
220	You may see informational messages in your kernel log when this file is
221	used:
223		cat (1234): drop_caches: 3
225	These are informational only.  They do not mean that anything is wrong
226	with your system.  To disable them, echo 4 (bit 3) into drop_caches.
228	==============================================================
230	extfrag_threshold
232	This parameter affects whether the kernel will compact memory or direct
233	reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
234	debugfs shows what the fragmentation index for each order is in each zone in
235	the system. Values tending towards 0 imply allocations would fail due to lack
236	of memory, values towards 1000 imply failures are due to fragmentation and -1
237	implies that the allocation will succeed as long as watermarks are met.
239	The kernel will not compact memory in a zone if the
240	fragmentation index is <= extfrag_threshold. The default value is 500.
242	==============================================================
244	highmem_is_dirtyable
246	Available only for systems with CONFIG_HIGHMEM enabled (32b systems).
248	This parameter controls whether the high memory is considered for dirty
249	writers throttling.  This is not the case by default which means that
250	only the amount of memory directly visible/usable by the kernel can
251	be dirtied. As a result, on systems with a large amount of memory and
252	lowmem basically depleted writers might be throttled too early and
253	streaming writes can get very slow.
255	Changing the value to non zero would allow more memory to be dirtied
256	and thus allow writers to write more data which can be flushed to the
257	storage more effectively. Note this also comes with a risk of pre-mature
258	OOM killer because some writers (e.g. direct block device writes) can
259	only use the low memory and they can fill it up with dirty data without
260	any throttling.
262	==============================================================
264	hugepages_treat_as_movable
266	This parameter controls whether we can allocate hugepages from ZONE_MOVABLE
267	or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE.
268	ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified,
269	so this parameter has no effect if used without kernelcore=.
271	Hugepage migration is now available in some situations which depend on the
272	architecture and/or the hugepage size. If a hugepage supports migration,
273	allocation from ZONE_MOVABLE is always enabled for the hugepage regardless
274	of the value of this parameter.
275	IOW, this parameter affects only non-migratable hugepages.
277	Assuming that hugepages are not migratable in your system, one usecase of
278	this parameter is that users can make hugepage pool more extensible by
279	enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE
280	page reclaim/migration/compaction work more and you can get contiguous
281	memory more likely. Note that using ZONE_MOVABLE for non-migratable
282	hugepages can do harm to other features like memory hotremove (because
283	memory hotremove expects that memory blocks on ZONE_MOVABLE are always
284	removable,) so it's a trade-off responsible for the users.
286	==============================================================
288	hugetlb_shm_group
290	hugetlb_shm_group contains group id that is allowed to create SysV
291	shared memory segment using hugetlb page.
293	==============================================================
295	laptop_mode
297	laptop_mode is a knob that controls "laptop mode". All the things that are
298	controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
300	==============================================================
302	legacy_va_layout
304	If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
305	will use the legacy (2.4) layout for all processes.
307	==============================================================
309	lowmem_reserve_ratio
311	For some specialised workloads on highmem machines it is dangerous for
312	the kernel to allow process memory to be allocated from the "lowmem"
313	zone.  This is because that memory could then be pinned via the mlock()
314	system call, or by unavailability of swapspace.
316	And on large highmem machines this lack of reclaimable lowmem memory
317	can be fatal.
319	So the Linux page allocator has a mechanism which prevents allocations
320	which _could_ use highmem from using too much lowmem.  This means that
321	a certain amount of lowmem is defended from the possibility of being
322	captured into pinned user memory.
324	(The same argument applies to the old 16 megabyte ISA DMA region.  This
325	mechanism will also defend that region from allocations which could use
326	highmem or lowmem).
328	The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
329	in defending these lower zones.
331	If you have a machine which uses highmem or ISA DMA and your
332	applications are using mlock(), or if you are running with no swap then
333	you probably should change the lowmem_reserve_ratio setting.
335	The lowmem_reserve_ratio is an array. You can see them by reading this file.
336	-
337	% cat /proc/sys/vm/lowmem_reserve_ratio
338	256     256     32
339	-
340	Note: # of this elements is one fewer than number of zones. Because the highest
341	      zone's value is not necessary for following calculation.
343	But, these values are not used directly. The kernel calculates # of protection
344	pages for each zones from them. These are shown as array of protection pages
345	in /proc/zoneinfo like followings. (This is an example of x86-64 box).
346	Each zone has an array of protection pages like this.
348	-
349	Node 0, zone      DMA
350	  pages free     1355
351	        min      3
352	        low      3
353	        high     4
354		:
355		:
356	    numa_other   0
357	        protection: (0, 2004, 2004, 2004)
358		^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
359	  pagesets
360	    cpu: 0 pcp: 0
361	        :
362	-
363	These protections are added to score to judge whether this zone should be used
364	for page allocation or should be reclaimed.
366	In this example, if normal pages (index=2) are required to this DMA zone and
367	watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
368	not be used because pages_free(1355) is smaller than watermark + protection[2]
369	(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
370	normal page requirement. If requirement is DMA zone(index=0), protection[0]
371	(=0) is used.
373	zone[i]'s protection[j] is calculated by following expression.
375	(i < j):
376	  zone[i]->protection[j]
377	  = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
378	    / lowmem_reserve_ratio[i];
379	(i = j):
380	   (should not be protected. = 0;
381	(i > j):
382	   (not necessary, but looks 0)
384	The default values of lowmem_reserve_ratio[i] are
385	    256 (if zone[i] means DMA or DMA32 zone)
386	    32  (others).
387	As above expression, they are reciprocal number of ratio.
388	256 means 1/256. # of protection pages becomes about "0.39%" of total managed
389	pages of higher zones on the node.
391	If you would like to protect more pages, smaller values are effective.
392	The minimum value is 1 (1/1 -> 100%).
394	==============================================================
396	max_map_count:
398	This file contains the maximum number of memory map areas a process
399	may have. Memory map areas are used as a side-effect of calling
400	malloc, directly by mmap, mprotect, and madvise, and also when loading
401	shared libraries.
403	While most applications need less than a thousand maps, certain
404	programs, particularly malloc debuggers, may consume lots of them,
405	e.g., up to one or two maps per allocation.
407	The default value is 65536.
409	=============================================================
411	memory_failure_early_kill:
413	Control how to kill processes when uncorrected memory error (typically
414	a 2bit error in a memory module) is detected in the background by hardware
415	that cannot be handled by the kernel. In some cases (like the page
416	still having a valid copy on disk) the kernel will handle the failure
417	transparently without affecting any applications. But if there is
418	no other uptodate copy of the data it will kill to prevent any data
419	corruptions from propagating.
421	1: Kill all processes that have the corrupted and not reloadable page mapped
422	as soon as the corruption is detected.  Note this is not supported
423	for a few types of pages, like kernel internally allocated data or
424	the swap cache, but works for the majority of user pages.
426	0: Only unmap the corrupted page from all processes and only kill a process
427	who tries to access it.
429	The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
430	handle this if they want to.
432	This is only active on architectures/platforms with advanced machine
433	check handling and depends on the hardware capabilities.
435	Applications can override this setting individually with the PR_MCE_KILL prctl
437	==============================================================
439	memory_failure_recovery
441	Enable memory failure recovery (when supported by the platform)
443	1: Attempt recovery.
445	0: Always panic on a memory failure.
447	==============================================================
449	min_free_kbytes:
451	This is used to force the Linux VM to keep a minimum number
452	of kilobytes free.  The VM uses this number to compute a
453	watermark[WMARK_MIN] value for each lowmem zone in the system.
454	Each lowmem zone gets a number of reserved free pages based
455	proportionally on its size.
457	Some minimal amount of memory is needed to satisfy PF_MEMALLOC
458	allocations; if you set this to lower than 1024KB, your system will
459	become subtly broken, and prone to deadlock under high loads.
461	Setting this too high will OOM your machine instantly.
463	=============================================================
465	min_slab_ratio:
467	This is available only on NUMA kernels.
469	A percentage of the total pages in each zone.  On Zone reclaim
470	(fallback from the local zone occurs) slabs will be reclaimed if more
471	than this percentage of pages in a zone are reclaimable slab pages.
472	This insures that the slab growth stays under control even in NUMA
473	systems that rarely perform global reclaim.
475	The default is 5 percent.
477	Note that slab reclaim is triggered in a per zone / node fashion.
478	The process of reclaiming slab memory is currently not node specific
479	and may not be fast.
481	=============================================================
483	min_unmapped_ratio:
485	This is available only on NUMA kernels.
487	This is a percentage of the total pages in each zone. Zone reclaim will
488	only occur if more than this percentage of pages are in a state that
489	zone_reclaim_mode allows to be reclaimed.
491	If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
492	against all file-backed unmapped pages including swapcache pages and tmpfs
493	files. Otherwise, only unmapped pages backed by normal files but not tmpfs
494	files and similar are considered.
496	The default is 1 percent.
498	==============================================================
500	mmap_min_addr
502	This file indicates the amount of address space  which a user process will
503	be restricted from mmapping.  Since kernel null dereference bugs could
504	accidentally operate based on the information in the first couple of pages
505	of memory userspace processes should not be allowed to write to them.  By
506	default this value is set to 0 and no protections will be enforced by the
507	security module.  Setting this value to something like 64k will allow the
508	vast majority of applications to work correctly and provide defense in depth
509	against future potential kernel bugs.
511	==============================================================
513	mmap_rnd_bits:
515	This value can be used to select the number of bits to use to
516	determine the random offset to the base address of vma regions
517	resulting from mmap allocations on architectures which support
518	tuning address space randomization.  This value will be bounded
519	by the architecture's minimum and maximum supported values.
521	This value can be changed after boot using the
522	/proc/sys/vm/mmap_rnd_bits tunable
524	==============================================================
526	mmap_rnd_compat_bits:
528	This value can be used to select the number of bits to use to
529	determine the random offset to the base address of vma regions
530	resulting from mmap allocations for applications run in
531	compatibility mode on architectures which support tuning address
532	space randomization.  This value will be bounded by the
533	architecture's minimum and maximum supported values.
535	This value can be changed after boot using the
536	/proc/sys/vm/mmap_rnd_compat_bits tunable
538	==============================================================
540	nr_hugepages
542	Change the minimum size of the hugepage pool.
544	See Documentation/vm/hugetlbpage.txt
546	==============================================================
548	nr_overcommit_hugepages
550	Change the maximum size of the hugepage pool. The maximum is
551	nr_hugepages + nr_overcommit_hugepages.
553	See Documentation/vm/hugetlbpage.txt
555	==============================================================
557	nr_trim_pages
559	This is available only on NOMMU kernels.
561	This value adjusts the excess page trimming behaviour of power-of-2 aligned
562	NOMMU mmap allocations.
564	A value of 0 disables trimming of allocations entirely, while a value of 1
565	trims excess pages aggressively. Any value >= 1 acts as the watermark where
566	trimming of allocations is initiated.
568	The default value is 1.
570	See Documentation/nommu-mmap.txt for more information.
572	==============================================================
574	numa_zonelist_order
576	This sysctl is only for NUMA and it is deprecated. Anything but
577	Node order will fail!
579	'where the memory is allocated from' is controlled by zonelists.
580	(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
581	 you may be able to read ZONE_DMA as ZONE_DMA32...)
583	In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
585	This means that a memory allocation request for GFP_KERNEL will
586	get memory from ZONE_DMA only when ZONE_NORMAL is not available.
588	In NUMA case, you can think of following 2 types of order.
589	Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
591	(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
592	(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
594	Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
595	will be used before ZONE_NORMAL exhaustion. This increases possibility of
596	out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
598	Type(B) cannot offer the best locality but is more robust against OOM of
599	the DMA zone.
601	Type(A) is called as "Node" order. Type (B) is "Zone" order.
603	"Node order" orders the zonelists by node, then by zone within each node.
604	Specify "[Nn]ode" for node order
606	"Zone Order" orders the zonelists by zone type, then by node within each
607	zone.  Specify "[Zz]one" for zone order.
609	Specify "[Dd]efault" to request automatic configuration.
611	On 32-bit, the Normal zone needs to be preserved for allocations accessible
612	by the kernel, so "zone" order will be selected.
614	On 64-bit, devices that require DMA32/DMA are relatively rare, so "node"
615	order will be selected.
617	Default order is recommended unless this is causing problems for your
618	system/application.
620	==============================================================
622	oom_dump_tasks
624	Enables a system-wide task dump (excluding kernel threads) to be produced
625	when the kernel performs an OOM-killing and includes such information as
626	pid, uid, tgid, vm size, rss, pgtables_bytes, swapents, oom_score_adj
627	score, and name.  This is helpful to determine why the OOM killer was
628	invoked, to identify the rogue task that caused it, and to determine why
629	the OOM killer chose the task it did to kill.
631	If this is set to zero, this information is suppressed.  On very
632	large systems with thousands of tasks it may not be feasible to dump
633	the memory state information for each one.  Such systems should not
634	be forced to incur a performance penalty in OOM conditions when the
635	information may not be desired.
637	If this is set to non-zero, this information is shown whenever the
638	OOM killer actually kills a memory-hogging task.
640	The default value is 1 (enabled).
642	==============================================================
644	oom_kill_allocating_task
646	This enables or disables killing the OOM-triggering task in
647	out-of-memory situations.
649	If this is set to zero, the OOM killer will scan through the entire
650	tasklist and select a task based on heuristics to kill.  This normally
651	selects a rogue memory-hogging task that frees up a large amount of
652	memory when killed.
654	If this is set to non-zero, the OOM killer simply kills the task that
655	triggered the out-of-memory condition.  This avoids the expensive
656	tasklist scan.
658	If panic_on_oom is selected, it takes precedence over whatever value
659	is used in oom_kill_allocating_task.
661	The default value is 0.
663	==============================================================
665	overcommit_kbytes:
667	When overcommit_memory is set to 2, the committed address space is not
668	permitted to exceed swap plus this amount of physical RAM. See below.
670	Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
671	of them may be specified at a time. Setting one disables the other (which
672	then appears as 0 when read).
674	==============================================================
676	overcommit_memory:
678	This value contains a flag that enables memory overcommitment.
680	When this flag is 0, the kernel attempts to estimate the amount
681	of free memory left when userspace requests more memory.
683	When this flag is 1, the kernel pretends there is always enough
684	memory until it actually runs out.
686	When this flag is 2, the kernel uses a "never overcommit"
687	policy that attempts to prevent any overcommit of memory.
688	Note that user_reserve_kbytes affects this policy.
690	This feature can be very useful because there are a lot of
691	programs that malloc() huge amounts of memory "just-in-case"
692	and don't use much of it.
694	The default value is 0.
696	See Documentation/vm/overcommit-accounting and
697	mm/mmap.c::__vm_enough_memory() for more information.
699	==============================================================
701	overcommit_ratio:
703	When overcommit_memory is set to 2, the committed address
704	space is not permitted to exceed swap plus this percentage
705	of physical RAM.  See above.
707	==============================================================
709	page-cluster
711	page-cluster controls the number of pages up to which consecutive pages
712	are read in from swap in a single attempt. This is the swap counterpart
713	to page cache readahead.
714	The mentioned consecutivity is not in terms of virtual/physical addresses,
715	but consecutive on swap space - that means they were swapped out together.
717	It is a logarithmic value - setting it to zero means "1 page", setting
718	it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
719	Zero disables swap readahead completely.
721	The default value is three (eight pages at a time).  There may be some
722	small benefits in tuning this to a different value if your workload is
723	swap-intensive.
725	Lower values mean lower latencies for initial faults, but at the same time
726	extra faults and I/O delays for following faults if they would have been part of
727	that consecutive pages readahead would have brought in.
729	=============================================================
731	panic_on_oom
733	This enables or disables panic on out-of-memory feature.
735	If this is set to 0, the kernel will kill some rogue process,
736	called oom_killer.  Usually, oom_killer can kill rogue processes and
737	system will survive.
739	If this is set to 1, the kernel panics when out-of-memory happens.
740	However, if a process limits using nodes by mempolicy/cpusets,
741	and those nodes become memory exhaustion status, one process
742	may be killed by oom-killer. No panic occurs in this case.
743	Because other nodes' memory may be free. This means system total status
744	may be not fatal yet.
746	If this is set to 2, the kernel panics compulsorily even on the
747	above-mentioned. Even oom happens under memory cgroup, the whole
748	system panics.
750	The default value is 0.
751	1 and 2 are for failover of clustering. Please select either
752	according to your policy of failover.
753	panic_on_oom=2+kdump gives you very strong tool to investigate
754	why oom happens. You can get snapshot.
756	=============================================================
758	percpu_pagelist_fraction
760	This is the fraction of pages at most (high mark pcp->high) in each zone that
761	are allocated for each per cpu page list.  The min value for this is 8.  It
762	means that we don't allow more than 1/8th of pages in each zone to be
763	allocated in any single per_cpu_pagelist.  This entry only changes the value
764	of hot per cpu pagelists.  User can specify a number like 100 to allocate
765	1/100th of each zone to each per cpu page list.
767	The batch value of each per cpu pagelist is also updated as a result.  It is
768	set to pcp->high/4.  The upper limit of batch is (PAGE_SHIFT * 8)
770	The initial value is zero.  Kernel does not use this value at boot time to set
771	the high water marks for each per cpu page list.  If the user writes '0' to this
772	sysctl, it will revert to this default behavior.
774	==============================================================
776	stat_interval
778	The time interval between which vm statistics are updated.  The default
779	is 1 second.
781	==============================================================
783	stat_refresh
785	Any read or write (by root only) flushes all the per-cpu vm statistics
786	into their global totals, for more accurate reports when testing
787	e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
789	As a side-effect, it also checks for negative totals (elsewhere reported
790	as 0) and "fails" with EINVAL if any are found, with a warning in dmesg.
791	(At time of writing, a few stats are known sometimes to be found negative,
792	with no ill effects: errors and warnings on these stats are suppressed.)
794	==============================================================
796	numa_stat
798	This interface allows runtime configuration of numa statistics.
800	When page allocation performance becomes a bottleneck and you can tolerate
801	some possible tool breakage and decreased numa counter precision, you can
802	do:
803		echo 0 > /proc/sys/vm/numa_stat
805	When page allocation performance is not a bottleneck and you want all
806	tooling to work, you can do:
807		echo 1 > /proc/sys/vm/numa_stat
809	==============================================================
811	swappiness
813	This control is used to define how aggressive the kernel will swap
814	memory pages.  Higher values will increase aggressiveness, lower values
815	decrease the amount of swap.  A value of 0 instructs the kernel not to
816	initiate swap until the amount of free and file-backed pages is less
817	than the high water mark in a zone.
819	The default value is 60.
821	==============================================================
823	- user_reserve_kbytes
825	When overcommit_memory is set to 2, "never overcommit" mode, reserve
826	min(3% of current process size, user_reserve_kbytes) of free memory.
827	This is intended to prevent a user from starting a single memory hogging
828	process, such that they cannot recover (kill the hog).
830	user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
832	If this is reduced to zero, then the user will be allowed to allocate
833	all free memory with a single process, minus admin_reserve_kbytes.
834	Any subsequent attempts to execute a command will result in
835	"fork: Cannot allocate memory".
837	Changing this takes effect whenever an application requests memory.
839	==============================================================
841	vfs_cache_pressure
842	------------------
844	This percentage value controls the tendency of the kernel to reclaim
845	the memory which is used for caching of directory and inode objects.
847	At the default value of vfs_cache_pressure=100 the kernel will attempt to
848	reclaim dentries and inodes at a "fair" rate with respect to pagecache and
849	swapcache reclaim.  Decreasing vfs_cache_pressure causes the kernel to prefer
850	to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
851	never reclaim dentries and inodes due to memory pressure and this can easily
852	lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
853	causes the kernel to prefer to reclaim dentries and inodes.
855	Increasing vfs_cache_pressure significantly beyond 100 may have negative
856	performance impact. Reclaim code needs to take various locks to find freeable
857	directory and inode objects. With vfs_cache_pressure=1000, it will look for
858	ten times more freeable objects than there are.
860	=============================================================
862	watermark_scale_factor:
864	This factor controls the aggressiveness of kswapd. It defines the
865	amount of memory left in a node/system before kswapd is woken up and
866	how much memory needs to be free before kswapd goes back to sleep.
868	The unit is in fractions of 10,000. The default value of 10 means the
869	distances between watermarks are 0.1% of the available memory in the
870	node/system. The maximum value is 1000, or 10% of memory.
872	A high rate of threads entering direct reclaim (allocstall) or kswapd
873	going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate
874	that the number of free pages kswapd maintains for latency reasons is
875	too small for the allocation bursts occurring in the system. This knob
876	can then be used to tune kswapd aggressiveness accordingly.
878	==============================================================
880	zone_reclaim_mode:
882	Zone_reclaim_mode allows someone to set more or less aggressive approaches to
883	reclaim memory when a zone runs out of memory. If it is set to zero then no
884	zone reclaim occurs. Allocations will be satisfied from other zones / nodes
885	in the system.
887	This is value ORed together of
889	1	= Zone reclaim on
890	2	= Zone reclaim writes dirty pages out
891	4	= Zone reclaim swaps pages
893	zone_reclaim_mode is disabled by default.  For file servers or workloads
894	that benefit from having their data cached, zone_reclaim_mode should be
895	left disabled as the caching effect is likely to be more important than
896	data locality.
898	zone_reclaim may be enabled if it's known that the workload is partitioned
899	such that each partition fits within a NUMA node and that accessing remote
900	memory would cause a measurable performance reduction.  The page allocator
901	will then reclaim easily reusable pages (those page cache pages that are
902	currently not used) before allocating off node pages.
904	Allowing zone reclaim to write out pages stops processes that are
905	writing large amounts of data from dirtying pages on other nodes. Zone
906	reclaim will write out dirty pages if a zone fills up and so effectively
907	throttle the process. This may decrease the performance of a single process
908	since it cannot use all of system memory to buffer the outgoing writes
909	anymore but it preserve the memory on other nodes so that the performance
910	of other processes running on other nodes will not be affected.
912	Allowing regular swap effectively restricts allocations to the local
913	node unless explicitly overridden by memory policies or cpuset
914	configurations.
916	============ End of Document =================================
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