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Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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>
4	
5	For general info and legal blurb, please look in README.
6	
7	==============================================================
8	
9	This file contains the documentation for the sysctl files in
10	/proc/sys/vm and is valid for Linux kernel version 2.6.29.
11	
12	The files in this directory can be used to tune the operation
13	of the virtual memory (VM) subsystem of the Linux kernel and
14	the writeout of dirty data to disk.
15	
16	Default values and initialization routines for most of these
17	files can be found in mm/swap.c.
18	
19	Currently, these files are in /proc/sys/vm:
20	
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	- hugetlb_shm_group
34	- laptop_mode
35	- legacy_va_layout
36	- lowmem_reserve_ratio
37	- max_map_count
38	- memory_failure_early_kill
39	- memory_failure_recovery
40	- min_free_kbytes
41	- min_slab_ratio
42	- min_unmapped_ratio
43	- mmap_min_addr
44	- mmap_rnd_bits
45	- mmap_rnd_compat_bits
46	- nr_hugepages
47	- nr_overcommit_hugepages
48	- nr_trim_pages         (only if CONFIG_MMU=n)
49	- numa_zonelist_order
50	- oom_dump_tasks
51	- oom_kill_allocating_task
52	- overcommit_kbytes
53	- overcommit_memory
54	- overcommit_ratio
55	- page-cluster
56	- panic_on_oom
57	- percpu_pagelist_fraction
58	- stat_interval
59	- stat_refresh
60	- numa_stat
61	- swappiness
62	- user_reserve_kbytes
63	- vfs_cache_pressure
64	- watermark_scale_factor
65	- zone_reclaim_mode
66	
67	==============================================================
68	
69	admin_reserve_kbytes
70	
71	The amount of free memory in the system that should be reserved for users
72	with the capability cap_sys_admin.
73	
74	admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
75	
76	That should provide enough for the admin to log in and kill a process,
77	if necessary, under the default overcommit 'guess' mode.
78	
79	Systems running under overcommit 'never' should increase this to account
80	for the full Virtual Memory Size of programs used to recover. Otherwise,
81	root may not be able to log in to recover the system.
82	
83	How do you calculate a minimum useful reserve?
84	
85	sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
86	
87	For overcommit 'guess', we can sum resident set sizes (RSS).
88	On x86_64 this is about 8MB.
89	
90	For overcommit 'never', we can take the max of their virtual sizes (VSZ)
91	and add the sum of their RSS.
92	On x86_64 this is about 128MB.
93	
94	Changing this takes effect whenever an application requests memory.
95	
96	==============================================================
97	
98	block_dump
99	
100	block_dump enables block I/O debugging when set to a nonzero value. More
101	information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
102	
103	==============================================================
104	
105	compact_memory
106	
107	Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
108	all zones are compacted such that free memory is available in contiguous
109	blocks where possible. This can be important for example in the allocation of
110	huge pages although processes will also directly compact memory as required.
111	
112	==============================================================
113	
114	compact_unevictable_allowed
115	
116	Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
117	allowed to examine the unevictable lru (mlocked pages) for pages to compact.
118	This should be used on systems where stalls for minor page faults are an
119	acceptable trade for large contiguous free memory.  Set to 0 to prevent
120	compaction from moving pages that are unevictable.  Default value is 1.
121	
122	==============================================================
123	
124	dirty_background_bytes
125	
126	Contains the amount of dirty memory at which the background kernel
127	flusher threads will start writeback.
128	
129	Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
130	one of them may be specified at a time. When one sysctl is written it is
131	immediately taken into account to evaluate the dirty memory limits and the
132	other appears as 0 when read.
133	
134	==============================================================
135	
136	dirty_background_ratio
137	
138	Contains, as a percentage of total available memory that contains free pages
139	and reclaimable pages, the number of pages at which the background kernel
140	flusher threads will start writing out dirty data.
141	
142	The total available memory is not equal to total system memory.
143	
144	==============================================================
145	
146	dirty_bytes
147	
148	Contains the amount of dirty memory at which a process generating disk writes
149	will itself start writeback.
150	
151	Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
152	specified at a time. When one sysctl is written it is immediately taken into
153	account to evaluate the dirty memory limits and the other appears as 0 when
154	read.
155	
156	Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
157	value lower than this limit will be ignored and the old configuration will be
158	retained.
159	
160	==============================================================
161	
162	dirty_expire_centisecs
163	
164	This tunable is used to define when dirty data is old enough to be eligible
165	for writeout by the kernel flusher threads.  It is expressed in 100'ths
166	of a second.  Data which has been dirty in-memory for longer than this
167	interval will be written out next time a flusher thread wakes up.
168	
169	==============================================================
170	
171	dirty_ratio
172	
173	Contains, as a percentage of total available memory that contains free pages
174	and reclaimable pages, the number of pages at which a process which is
175	generating disk writes will itself start writing out dirty data.
176	
177	The total available memory is not equal to total system memory.
178	
179	==============================================================
180	
181	dirty_writeback_centisecs
182	
183	The kernel flusher threads will periodically wake up and write `old' data
184	out to disk.  This tunable expresses the interval between those wakeups, in
185	100'ths of a second.
186	
187	Setting this to zero disables periodic writeback altogether.
188	
189	==============================================================
190	
191	drop_caches
192	
193	Writing to this will cause the kernel to drop clean caches, as well as
194	reclaimable slab objects like dentries and inodes.  Once dropped, their
195	memory becomes free.
196	
197	To free pagecache:
198		echo 1 > /proc/sys/vm/drop_caches
199	To free reclaimable slab objects (includes dentries and inodes):
200		echo 2 > /proc/sys/vm/drop_caches
201	To free slab objects and pagecache:
202		echo 3 > /proc/sys/vm/drop_caches
203	
204	This is a non-destructive operation and will not free any dirty objects.
205	To increase the number of objects freed by this operation, the user may run
206	`sync' prior to writing to /proc/sys/vm/drop_caches.  This will minimize the
207	number of dirty objects on the system and create more candidates to be
208	dropped.
209	
210	This file is not a means to control the growth of the various kernel caches
211	(inodes, dentries, pagecache, etc...)  These objects are automatically
212	reclaimed by the kernel when memory is needed elsewhere on the system.
213	
214	Use of this file can cause performance problems.  Since it discards cached
215	objects, it may cost a significant amount of I/O and CPU to recreate the
216	dropped objects, especially if they were under heavy use.  Because of this,
217	use outside of a testing or debugging environment is not recommended.
218	
219	You may see informational messages in your kernel log when this file is
220	used:
221	
222		cat (1234): drop_caches: 3
223	
224	These are informational only.  They do not mean that anything is wrong
225	with your system.  To disable them, echo 4 (bit 3) into drop_caches.
226	
227	==============================================================
228	
229	extfrag_threshold
230	
231	This parameter affects whether the kernel will compact memory or direct
232	reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
233	debugfs shows what the fragmentation index for each order is in each zone in
234	the system. Values tending towards 0 imply allocations would fail due to lack
235	of memory, values towards 1000 imply failures are due to fragmentation and -1
236	implies that the allocation will succeed as long as watermarks are met.
237	
238	The kernel will not compact memory in a zone if the
239	fragmentation index is <= extfrag_threshold. The default value is 500.
240	
241	==============================================================
242	
243	highmem_is_dirtyable
244	
245	Available only for systems with CONFIG_HIGHMEM enabled (32b systems).
246	
247	This parameter controls whether the high memory is considered for dirty
248	writers throttling.  This is not the case by default which means that
249	only the amount of memory directly visible/usable by the kernel can
250	be dirtied. As a result, on systems with a large amount of memory and
251	lowmem basically depleted writers might be throttled too early and
252	streaming writes can get very slow.
253	
254	Changing the value to non zero would allow more memory to be dirtied
255	and thus allow writers to write more data which can be flushed to the
256	storage more effectively. Note this also comes with a risk of pre-mature
257	OOM killer because some writers (e.g. direct block device writes) can
258	only use the low memory and they can fill it up with dirty data without
259	any throttling.
260	
261	==============================================================
262	
263	hugetlb_shm_group
264	
265	hugetlb_shm_group contains group id that is allowed to create SysV
266	shared memory segment using hugetlb page.
267	
268	==============================================================
269	
270	laptop_mode
271	
272	laptop_mode is a knob that controls "laptop mode". All the things that are
273	controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
274	
275	==============================================================
276	
277	legacy_va_layout
278	
279	If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
280	will use the legacy (2.4) layout for all processes.
281	
282	==============================================================
283	
284	lowmem_reserve_ratio
285	
286	For some specialised workloads on highmem machines it is dangerous for
287	the kernel to allow process memory to be allocated from the "lowmem"
288	zone.  This is because that memory could then be pinned via the mlock()
289	system call, or by unavailability of swapspace.
290	
291	And on large highmem machines this lack of reclaimable lowmem memory
292	can be fatal.
293	
294	So the Linux page allocator has a mechanism which prevents allocations
295	which _could_ use highmem from using too much lowmem.  This means that
296	a certain amount of lowmem is defended from the possibility of being
297	captured into pinned user memory.
298	
299	(The same argument applies to the old 16 megabyte ISA DMA region.  This
300	mechanism will also defend that region from allocations which could use
301	highmem or lowmem).
302	
303	The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
304	in defending these lower zones.
305	
306	If you have a machine which uses highmem or ISA DMA and your
307	applications are using mlock(), or if you are running with no swap then
308	you probably should change the lowmem_reserve_ratio setting.
309	
310	The lowmem_reserve_ratio is an array. You can see them by reading this file.
311	-
312	% cat /proc/sys/vm/lowmem_reserve_ratio
313	256     256     32
314	-
315	Note: # of this elements is one fewer than number of zones. Because the highest
316	      zone's value is not necessary for following calculation.
317	
318	But, these values are not used directly. The kernel calculates # of protection
319	pages for each zones from them. These are shown as array of protection pages
320	in /proc/zoneinfo like followings. (This is an example of x86-64 box).
321	Each zone has an array of protection pages like this.
322	
323	-
324	Node 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	-
338	These protections are added to score to judge whether this zone should be used
339	for page allocation or should be reclaimed.
340	
341	In this example, if normal pages (index=2) are required to this DMA zone and
342	watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
343	not be used because pages_free(1355) is smaller than watermark + protection[2]
344	(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
345	normal page requirement. If requirement is DMA zone(index=0), protection[0]
346	(=0) is used.
347	
348	zone[i]'s protection[j] is calculated by following expression.
349	
350	(i < j):
351	  zone[i]->protection[j]
352	  = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
353	    / lowmem_reserve_ratio[i];
354	(i = j):
355	   (should not be protected. = 0;
356	(i > j):
357	   (not necessary, but looks 0)
358	
359	The default values of lowmem_reserve_ratio[i] are
360	    256 (if zone[i] means DMA or DMA32 zone)
361	    32  (others).
362	As above expression, they are reciprocal number of ratio.
363	256 means 1/256. # of protection pages becomes about "0.39%" of total managed
364	pages of higher zones on the node.
365	
366	If you would like to protect more pages, smaller values are effective.
367	The minimum value is 1 (1/1 -> 100%).
368	
369	==============================================================
370	
371	max_map_count:
372	
373	This file contains the maximum number of memory map areas a process
374	may have. Memory map areas are used as a side-effect of calling
375	malloc, directly by mmap, mprotect, and madvise, and also when loading
376	shared libraries.
377	
378	While most applications need less than a thousand maps, certain
379	programs, particularly malloc debuggers, may consume lots of them,
380	e.g., up to one or two maps per allocation.
381	
382	The default value is 65536.
383	
384	=============================================================
385	
386	memory_failure_early_kill:
387	
388	Control how to kill processes when uncorrected memory error (typically
389	a 2bit error in a memory module) is detected in the background by hardware
390	that cannot be handled by the kernel. In some cases (like the page
391	still having a valid copy on disk) the kernel will handle the failure
392	transparently without affecting any applications. But if there is
393	no other uptodate copy of the data it will kill to prevent any data
394	corruptions from propagating.
395	
396	1: Kill all processes that have the corrupted and not reloadable page mapped
397	as soon as the corruption is detected.  Note this is not supported
398	for a few types of pages, like kernel internally allocated data or
399	the swap cache, but works for the majority of user pages.
400	
401	0: Only unmap the corrupted page from all processes and only kill a process
402	who tries to access it.
403	
404	The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
405	handle this if they want to.
406	
407	This is only active on architectures/platforms with advanced machine
408	check handling and depends on the hardware capabilities.
409	
410	Applications can override this setting individually with the PR_MCE_KILL prctl
411	
412	==============================================================
413	
414	memory_failure_recovery
415	
416	Enable memory failure recovery (when supported by the platform)
417	
418	1: Attempt recovery.
419	
420	0: Always panic on a memory failure.
421	
422	==============================================================
423	
424	min_free_kbytes:
425	
426	This is used to force the Linux VM to keep a minimum number
427	of kilobytes free.  The VM uses this number to compute a
428	watermark[WMARK_MIN] value for each lowmem zone in the system.
429	Each lowmem zone gets a number of reserved free pages based
430	proportionally on its size.
431	
432	Some minimal amount of memory is needed to satisfy PF_MEMALLOC
433	allocations; if you set this to lower than 1024KB, your system will
434	become subtly broken, and prone to deadlock under high loads.
435	
436	Setting this too high will OOM your machine instantly.
437	
438	=============================================================
439	
440	min_slab_ratio:
441	
442	This is available only on NUMA kernels.
443	
444	A percentage of the total pages in each zone.  On Zone reclaim
445	(fallback from the local zone occurs) slabs will be reclaimed if more
446	than this percentage of pages in a zone are reclaimable slab pages.
447	This insures that the slab growth stays under control even in NUMA
448	systems that rarely perform global reclaim.
449	
450	The default is 5 percent.
451	
452	Note that slab reclaim is triggered in a per zone / node fashion.
453	The process of reclaiming slab memory is currently not node specific
454	and may not be fast.
455	
456	=============================================================
457	
458	min_unmapped_ratio:
459	
460	This is available only on NUMA kernels.
461	
462	This is a percentage of the total pages in each zone. Zone reclaim will
463	only occur if more than this percentage of pages are in a state that
464	zone_reclaim_mode allows to be reclaimed.
465	
466	If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
467	against all file-backed unmapped pages including swapcache pages and tmpfs
468	files. Otherwise, only unmapped pages backed by normal files but not tmpfs
469	files and similar are considered.
470	
471	The default is 1 percent.
472	
473	==============================================================
474	
475	mmap_min_addr
476	
477	This file indicates the amount of address space  which a user process will
478	be restricted from mmapping.  Since kernel null dereference bugs could
479	accidentally operate based on the information in the first couple of pages
480	of memory userspace processes should not be allowed to write to them.  By
481	default this value is set to 0 and no protections will be enforced by the
482	security module.  Setting this value to something like 64k will allow the
483	vast majority of applications to work correctly and provide defense in depth
484	against future potential kernel bugs.
485	
486	==============================================================
487	
488	mmap_rnd_bits:
489	
490	This value can be used to select the number of bits to use to
491	determine the random offset to the base address of vma regions
492	resulting from mmap allocations on architectures which support
493	tuning address space randomization.  This value will be bounded
494	by the architecture's minimum and maximum supported values.
495	
496	This value can be changed after boot using the
497	/proc/sys/vm/mmap_rnd_bits tunable
498	
499	==============================================================
500	
501	mmap_rnd_compat_bits:
502	
503	This value can be used to select the number of bits to use to
504	determine the random offset to the base address of vma regions
505	resulting from mmap allocations for applications run in
506	compatibility mode on architectures which support tuning address
507	space randomization.  This value will be bounded by the
508	architecture's minimum and maximum supported values.
509	
510	This value can be changed after boot using the
511	/proc/sys/vm/mmap_rnd_compat_bits tunable
512	
513	==============================================================
514	
515	nr_hugepages
516	
517	Change the minimum size of the hugepage pool.
518	
519	See Documentation/vm/hugetlbpage.txt
520	
521	==============================================================
522	
523	nr_overcommit_hugepages
524	
525	Change the maximum size of the hugepage pool. The maximum is
526	nr_hugepages + nr_overcommit_hugepages.
527	
528	See Documentation/vm/hugetlbpage.txt
529	
530	==============================================================
531	
532	nr_trim_pages
533	
534	This is available only on NOMMU kernels.
535	
536	This value adjusts the excess page trimming behaviour of power-of-2 aligned
537	NOMMU mmap allocations.
538	
539	A value of 0 disables trimming of allocations entirely, while a value of 1
540	trims excess pages aggressively. Any value >= 1 acts as the watermark where
541	trimming of allocations is initiated.
542	
543	The default value is 1.
544	
545	See Documentation/nommu-mmap.txt for more information.
546	
547	==============================================================
548	
549	numa_zonelist_order
550	
551	This sysctl is only for NUMA and it is deprecated. Anything but
552	Node order will fail!
553	
554	'where the memory is allocated from' is controlled by zonelists.
555	(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
556	 you may be able to read ZONE_DMA as ZONE_DMA32...)
557	
558	In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
559	ZONE_NORMAL -> ZONE_DMA
560	This means that a memory allocation request for GFP_KERNEL will
561	get memory from ZONE_DMA only when ZONE_NORMAL is not available.
562	
563	In NUMA case, you can think of following 2 types of order.
564	Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
565	
566	(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
567	(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
568	
569	Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
570	will be used before ZONE_NORMAL exhaustion. This increases possibility of
571	out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
572	
573	Type(B) cannot offer the best locality but is more robust against OOM of
574	the DMA zone.
575	
576	Type(A) is called as "Node" order. Type (B) is "Zone" order.
577	
578	"Node order" orders the zonelists by node, then by zone within each node.
579	Specify "[Nn]ode" for node order
580	
581	"Zone Order" orders the zonelists by zone type, then by node within each
582	zone.  Specify "[Zz]one" for zone order.
583	
584	Specify "[Dd]efault" to request automatic configuration.
585	
586	On 32-bit, the Normal zone needs to be preserved for allocations accessible
587	by the kernel, so "zone" order will be selected.
588	
589	On 64-bit, devices that require DMA32/DMA are relatively rare, so "node"
590	order will be selected.
591	
592	Default order is recommended unless this is causing problems for your
593	system/application.
594	
595	==============================================================
596	
597	oom_dump_tasks
598	
599	Enables a system-wide task dump (excluding kernel threads) to be produced
600	when the kernel performs an OOM-killing and includes such information as
601	pid, uid, tgid, vm size, rss, pgtables_bytes, swapents, oom_score_adj
602	score, and name.  This is helpful to determine why the OOM killer was
603	invoked, to identify the rogue task that caused it, and to determine why
604	the OOM killer chose the task it did to kill.
605	
606	If this is set to zero, this information is suppressed.  On very
607	large systems with thousands of tasks it may not be feasible to dump
608	the memory state information for each one.  Such systems should not
609	be forced to incur a performance penalty in OOM conditions when the
610	information may not be desired.
611	
612	If this is set to non-zero, this information is shown whenever the
613	OOM killer actually kills a memory-hogging task.
614	
615	The default value is 1 (enabled).
616	
617	==============================================================
618	
619	oom_kill_allocating_task
620	
621	This enables or disables killing the OOM-triggering task in
622	out-of-memory situations.
623	
624	If this is set to zero, the OOM killer will scan through the entire
625	tasklist and select a task based on heuristics to kill.  This normally
626	selects a rogue memory-hogging task that frees up a large amount of
627	memory when killed.
628	
629	If this is set to non-zero, the OOM killer simply kills the task that
630	triggered the out-of-memory condition.  This avoids the expensive
631	tasklist scan.
632	
633	If panic_on_oom is selected, it takes precedence over whatever value
634	is used in oom_kill_allocating_task.
635	
636	The default value is 0.
637	
638	==============================================================
639	
640	overcommit_kbytes:
641	
642	When overcommit_memory is set to 2, the committed address space is not
643	permitted to exceed swap plus this amount of physical RAM. See below.
644	
645	Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
646	of them may be specified at a time. Setting one disables the other (which
647	then appears as 0 when read).
648	
649	==============================================================
650	
651	overcommit_memory:
652	
653	This value contains a flag that enables memory overcommitment.
654	
655	When this flag is 0, the kernel attempts to estimate the amount
656	of free memory left when userspace requests more memory.
657	
658	When this flag is 1, the kernel pretends there is always enough
659	memory until it actually runs out.
660	
661	When this flag is 2, the kernel uses a "never overcommit"
662	policy that attempts to prevent any overcommit of memory.
663	Note that user_reserve_kbytes affects this policy.
664	
665	This feature can be very useful because there are a lot of
666	programs that malloc() huge amounts of memory "just-in-case"
667	and don't use much of it.
668	
669	The default value is 0.
670	
671	See Documentation/vm/overcommit-accounting and
672	mm/mmap.c::__vm_enough_memory() for more information.
673	
674	==============================================================
675	
676	overcommit_ratio:
677	
678	When overcommit_memory is set to 2, the committed address
679	space is not permitted to exceed swap plus this percentage
680	of physical RAM.  See above.
681	
682	==============================================================
683	
684	page-cluster
685	
686	page-cluster controls the number of pages up to which consecutive pages
687	are read in from swap in a single attempt. This is the swap counterpart
688	to page cache readahead.
689	The mentioned consecutivity is not in terms of virtual/physical addresses,
690	but consecutive on swap space - that means they were swapped out together.
691	
692	It is a logarithmic value - setting it to zero means "1 page", setting
693	it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
694	Zero disables swap readahead completely.
695	
696	The default value is three (eight pages at a time).  There may be some
697	small benefits in tuning this to a different value if your workload is
698	swap-intensive.
699	
700	Lower values mean lower latencies for initial faults, but at the same time
701	extra faults and I/O delays for following faults if they would have been part of
702	that consecutive pages readahead would have brought in.
703	
704	=============================================================
705	
706	panic_on_oom
707	
708	This enables or disables panic on out-of-memory feature.
709	
710	If this is set to 0, the kernel will kill some rogue process,
711	called oom_killer.  Usually, oom_killer can kill rogue processes and
712	system will survive.
713	
714	If this is set to 1, the kernel panics when out-of-memory happens.
715	However, if a process limits using nodes by mempolicy/cpusets,
716	and those nodes become memory exhaustion status, one process
717	may be killed by oom-killer. No panic occurs in this case.
718	Because other nodes' memory may be free. This means system total status
719	may be not fatal yet.
720	
721	If this is set to 2, the kernel panics compulsorily even on the
722	above-mentioned. Even oom happens under memory cgroup, the whole
723	system panics.
724	
725	The default value is 0.
726	1 and 2 are for failover of clustering. Please select either
727	according to your policy of failover.
728	panic_on_oom=2+kdump gives you very strong tool to investigate
729	why oom happens. You can get snapshot.
730	
731	=============================================================
732	
733	percpu_pagelist_fraction
734	
735	This is the fraction of pages at most (high mark pcp->high) in each zone that
736	are allocated for each per cpu page list.  The min value for this is 8.  It
737	means that we don't allow more than 1/8th of pages in each zone to be
738	allocated in any single per_cpu_pagelist.  This entry only changes the value
739	of hot per cpu pagelists.  User can specify a number like 100 to allocate
740	1/100th of each zone to each per cpu page list.
741	
742	The batch value of each per cpu pagelist is also updated as a result.  It is
743	set to pcp->high/4.  The upper limit of batch is (PAGE_SHIFT * 8)
744	
745	The initial value is zero.  Kernel does not use this value at boot time to set
746	the high water marks for each per cpu page list.  If the user writes '0' to this
747	sysctl, it will revert to this default behavior.
748	
749	==============================================================
750	
751	stat_interval
752	
753	The time interval between which vm statistics are updated.  The default
754	is 1 second.
755	
756	==============================================================
757	
758	stat_refresh
759	
760	Any read or write (by root only) flushes all the per-cpu vm statistics
761	into their global totals, for more accurate reports when testing
762	e.g. cat /proc/sys/vm/stat_refresh /proc/meminfo
763	
764	As a side-effect, it also checks for negative totals (elsewhere reported
765	as 0) and "fails" with EINVAL if any are found, with a warning in dmesg.
766	(At time of writing, a few stats are known sometimes to be found negative,
767	with no ill effects: errors and warnings on these stats are suppressed.)
768	
769	==============================================================
770	
771	numa_stat
772	
773	This interface allows runtime configuration of numa statistics.
774	
775	When page allocation performance becomes a bottleneck and you can tolerate
776	some possible tool breakage and decreased numa counter precision, you can
777	do:
778		echo 0 > /proc/sys/vm/numa_stat
779	
780	When page allocation performance is not a bottleneck and you want all
781	tooling to work, you can do:
782		echo 1 > /proc/sys/vm/numa_stat
783	
784	==============================================================
785	
786	swappiness
787	
788	This control is used to define how aggressive the kernel will swap
789	memory pages.  Higher values will increase aggressiveness, lower values
790	decrease the amount of swap.  A value of 0 instructs the kernel not to
791	initiate swap until the amount of free and file-backed pages is less
792	than the high water mark in a zone.
793	
794	The default value is 60.
795	
796	==============================================================
797	
798	- user_reserve_kbytes
799	
800	When overcommit_memory is set to 2, "never overcommit" mode, reserve
801	min(3% of current process size, user_reserve_kbytes) of free memory.
802	This is intended to prevent a user from starting a single memory hogging
803	process, such that they cannot recover (kill the hog).
804	
805	user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
806	
807	If this is reduced to zero, then the user will be allowed to allocate
808	all free memory with a single process, minus admin_reserve_kbytes.
809	Any subsequent attempts to execute a command will result in
810	"fork: Cannot allocate memory".
811	
812	Changing this takes effect whenever an application requests memory.
813	
814	==============================================================
815	
816	vfs_cache_pressure
817	------------------
818	
819	This percentage value controls the tendency of the kernel to reclaim
820	the memory which is used for caching of directory and inode objects.
821	
822	At the default value of vfs_cache_pressure=100 the kernel will attempt to
823	reclaim dentries and inodes at a "fair" rate with respect to pagecache and
824	swapcache reclaim.  Decreasing vfs_cache_pressure causes the kernel to prefer
825	to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
826	never reclaim dentries and inodes due to memory pressure and this can easily
827	lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
828	causes the kernel to prefer to reclaim dentries and inodes.
829	
830	Increasing vfs_cache_pressure significantly beyond 100 may have negative
831	performance impact. Reclaim code needs to take various locks to find freeable
832	directory and inode objects. With vfs_cache_pressure=1000, it will look for
833	ten times more freeable objects than there are.
834	
835	=============================================================
836	
837	watermark_scale_factor:
838	
839	This factor controls the aggressiveness of kswapd. It defines the
840	amount of memory left in a node/system before kswapd is woken up and
841	how much memory needs to be free before kswapd goes back to sleep.
842	
843	The unit is in fractions of 10,000. The default value of 10 means the
844	distances between watermarks are 0.1% of the available memory in the
845	node/system. The maximum value is 1000, or 10% of memory.
846	
847	A high rate of threads entering direct reclaim (allocstall) or kswapd
848	going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate
849	that the number of free pages kswapd maintains for latency reasons is
850	too small for the allocation bursts occurring in the system. This knob
851	can then be used to tune kswapd aggressiveness accordingly.
852	
853	==============================================================
854	
855	zone_reclaim_mode:
856	
857	Zone_reclaim_mode allows someone to set more or less aggressive approaches to
858	reclaim memory when a zone runs out of memory. If it is set to zero then no
859	zone reclaim occurs. Allocations will be satisfied from other zones / nodes
860	in the system.
861	
862	This is value ORed together of
863	
864	1	= Zone reclaim on
865	2	= Zone reclaim writes dirty pages out
866	4	= Zone reclaim swaps pages
867	
868	zone_reclaim_mode is disabled by default.  For file servers or workloads
869	that benefit from having their data cached, zone_reclaim_mode should be
870	left disabled as the caching effect is likely to be more important than
871	data locality.
872	
873	zone_reclaim may be enabled if it's known that the workload is partitioned
874	such that each partition fits within a NUMA node and that accessing remote
875	memory would cause a measurable performance reduction.  The page allocator
876	will then reclaim easily reusable pages (those page cache pages that are
877	currently not used) before allocating off node pages.
878	
879	Allowing zone reclaim to write out pages stops processes that are
880	writing large amounts of data from dirtying pages on other nodes. Zone
881	reclaim will write out dirty pages if a zone fills up and so effectively
882	throttle the process. This may decrease the performance of a single process
883	since it cannot use all of system memory to buffer the outgoing writes
884	anymore but it preserve the memory on other nodes so that the performance
885	of other processes running on other nodes will not be affected.
886	
887	Allowing regular swap effectively restricts allocations to the local
888	node unless explicitly overridden by memory policies or cpuset
889	configurations.
890	
891	============ End of Document =================================
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