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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 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	- dirty_background_bytes
25	- dirty_background_ratio
26	- dirty_bytes
27	- dirty_expire_centisecs
28	- dirty_ratio
29	- dirty_writeback_centisecs
30	- drop_caches
31	- extfrag_threshold
32	- hugepages_treat_as_movable
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	- nr_hugepages
45	- nr_overcommit_hugepages
46	- nr_trim_pages         (only if CONFIG_MMU=n)
47	- numa_zonelist_order
48	- oom_dump_tasks
49	- oom_kill_allocating_task
50	- overcommit_kbytes
51	- overcommit_memory
52	- overcommit_ratio
53	- page-cluster
54	- panic_on_oom
55	- percpu_pagelist_fraction
56	- stat_interval
57	- swappiness
58	- user_reserve_kbytes
59	- vfs_cache_pressure
60	- zone_reclaim_mode
61	
62	==============================================================
63	
64	admin_reserve_kbytes
65	
66	The amount of free memory in the system that should be reserved for users
67	with the capability cap_sys_admin.
68	
69	admin_reserve_kbytes defaults to min(3% of free pages, 8MB)
70	
71	That should provide enough for the admin to log in and kill a process,
72	if necessary, under the default overcommit 'guess' mode.
73	
74	Systems running under overcommit 'never' should increase this to account
75	for the full Virtual Memory Size of programs used to recover. Otherwise,
76	root may not be able to log in to recover the system.
77	
78	How do you calculate a minimum useful reserve?
79	
80	sshd or login + bash (or some other shell) + top (or ps, kill, etc.)
81	
82	For overcommit 'guess', we can sum resident set sizes (RSS).
83	On x86_64 this is about 8MB.
84	
85	For overcommit 'never', we can take the max of their virtual sizes (VSZ)
86	and add the sum of their RSS.
87	On x86_64 this is about 128MB.
88	
89	Changing this takes effect whenever an application requests memory.
90	
91	==============================================================
92	
93	block_dump
94	
95	block_dump enables block I/O debugging when set to a nonzero value. More
96	information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
97	
98	==============================================================
99	
100	compact_memory
101	
102	Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
103	all zones are compacted such that free memory is available in contiguous
104	blocks where possible. This can be important for example in the allocation of
105	huge pages although processes will also directly compact memory as required.
106	
107	==============================================================
108	
109	dirty_background_bytes
110	
111	Contains the amount of dirty memory at which the background kernel
112	flusher threads will start writeback.
113	
114	Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
115	one of them may be specified at a time. When one sysctl is written it is
116	immediately taken into account to evaluate the dirty memory limits and the
117	other appears as 0 when read.
118	
119	==============================================================
120	
121	dirty_background_ratio
122	
123	Contains, as a percentage of total available memory that contains free pages
124	and reclaimable pages, the number of pages at which the background kernel
125	flusher threads will start writing out dirty data.
126	
127	The total avaiable memory is not equal to total system memory.
128	
129	==============================================================
130	
131	dirty_bytes
132	
133	Contains the amount of dirty memory at which a process generating disk writes
134	will itself start writeback.
135	
136	Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be
137	specified at a time. When one sysctl is written it is immediately taken into
138	account to evaluate the dirty memory limits and the other appears as 0 when
139	read.
140	
141	Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any
142	value lower than this limit will be ignored and the old configuration will be
143	retained.
144	
145	==============================================================
146	
147	dirty_expire_centisecs
148	
149	This tunable is used to define when dirty data is old enough to be eligible
150	for writeout by the kernel flusher threads.  It is expressed in 100'ths
151	of a second.  Data which has been dirty in-memory for longer than this
152	interval will be written out next time a flusher thread wakes up.
153	
154	==============================================================
155	
156	dirty_ratio
157	
158	Contains, as a percentage of total available memory that contains free pages
159	and reclaimable pages, the number of pages at which a process which is
160	generating disk writes will itself start writing out dirty data.
161	
162	The total avaiable memory is not equal to total system memory.
163	
164	==============================================================
165	
166	dirty_writeback_centisecs
167	
168	The kernel flusher threads will periodically wake up and write `old' data
169	out to disk.  This tunable expresses the interval between those wakeups, in
170	100'ths of a second.
171	
172	Setting this to zero disables periodic writeback altogether.
173	
174	==============================================================
175	
176	drop_caches
177	
178	Writing to this will cause the kernel to drop clean caches, as well as
179	reclaimable slab objects like dentries and inodes.  Once dropped, their
180	memory becomes free.
181	
182	To free pagecache:
183		echo 1 > /proc/sys/vm/drop_caches
184	To free reclaimable slab objects (includes dentries and inodes):
185		echo 2 > /proc/sys/vm/drop_caches
186	To free slab objects and pagecache:
187		echo 3 > /proc/sys/vm/drop_caches
188	
189	This is a non-destructive operation and will not free any dirty objects.
190	To 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
192	number of dirty objects on the system and create more candidates to be
193	dropped.
194	
195	This file is not a means to control the growth of the various kernel caches
196	(inodes, dentries, pagecache, etc...)  These objects are automatically
197	reclaimed by the kernel when memory is needed elsewhere on the system.
198	
199	Use of this file can cause performance problems.  Since it discards cached
200	objects, it may cost a significant amount of I/O and CPU to recreate the
201	dropped objects, especially if they were under heavy use.  Because of this,
202	use outside of a testing or debugging environment is not recommended.
203	
204	You may see informational messages in your kernel log when this file is
205	used:
206	
207		cat (1234): drop_caches: 3
208	
209	These are informational only.  They do not mean that anything is wrong
210	with your system.  To disable them, echo 4 (bit 3) into drop_caches.
211	
212	==============================================================
213	
214	extfrag_threshold
215	
216	This parameter affects whether the kernel will compact memory or direct
217	reclaim to satisfy a high-order allocation. /proc/extfrag_index shows what
218	the fragmentation index for each order is in each zone in the system. Values
219	tending towards 0 imply allocations would fail due to lack of memory,
220	values towards 1000 imply failures are due to fragmentation and -1 implies
221	that the allocation will succeed as long as watermarks are met.
222	
223	The kernel will not compact memory in a zone if the
224	fragmentation index is <= extfrag_threshold. The default value is 500.
225	
226	==============================================================
227	
228	hugepages_treat_as_movable
229	
230	This parameter controls whether we can allocate hugepages from ZONE_MOVABLE
231	or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE.
232	ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified,
233	so this parameter has no effect if used without kernelcore=.
234	
235	Hugepage migration is now available in some situations which depend on the
236	architecture and/or the hugepage size. If a hugepage supports migration,
237	allocation from ZONE_MOVABLE is always enabled for the hugepage regardless
238	of the value of this parameter.
239	IOW, this parameter affects only non-migratable hugepages.
240	
241	Assuming that hugepages are not migratable in your system, one usecase of
242	this parameter is that users can make hugepage pool more extensible by
243	enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE
244	page reclaim/migration/compaction work more and you can get contiguous
245	memory more likely. Note that using ZONE_MOVABLE for non-migratable
246	hugepages can do harm to other features like memory hotremove (because
247	memory hotremove expects that memory blocks on ZONE_MOVABLE are always
248	removable,) so it's a trade-off responsible for the users.
249	
250	==============================================================
251	
252	hugetlb_shm_group
253	
254	hugetlb_shm_group contains group id that is allowed to create SysV
255	shared memory segment using hugetlb page.
256	
257	==============================================================
258	
259	laptop_mode
260	
261	laptop_mode is a knob that controls "laptop mode". All the things that are
262	controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
263	
264	==============================================================
265	
266	legacy_va_layout
267	
268	If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
269	will use the legacy (2.4) layout for all processes.
270	
271	==============================================================
272	
273	lowmem_reserve_ratio
274	
275	For some specialised workloads on highmem machines it is dangerous for
276	the kernel to allow process memory to be allocated from the "lowmem"
277	zone.  This is because that memory could then be pinned via the mlock()
278	system call, or by unavailability of swapspace.
279	
280	And on large highmem machines this lack of reclaimable lowmem memory
281	can be fatal.
282	
283	So the Linux page allocator has a mechanism which prevents allocations
284	which _could_ use highmem from using too much lowmem.  This means that
285	a certain amount of lowmem is defended from the possibility of being
286	captured into pinned user memory.
287	
288	(The same argument applies to the old 16 megabyte ISA DMA region.  This
289	mechanism will also defend that region from allocations which could use
290	highmem or lowmem).
291	
292	The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
293	in defending these lower zones.
294	
295	If you have a machine which uses highmem or ISA DMA and your
296	applications are using mlock(), or if you are running with no swap then
297	you probably should change the lowmem_reserve_ratio setting.
298	
299	The lowmem_reserve_ratio is an array. You can see them by reading this file.
300	-
301	% cat /proc/sys/vm/lowmem_reserve_ratio
302	256     256     32
303	-
304	Note: # of this elements is one fewer than number of zones. Because the highest
305	      zone's value is not necessary for following calculation.
306	
307	But, these values are not used directly. The kernel calculates # of protection
308	pages for each zones from them. These are shown as array of protection pages
309	in /proc/zoneinfo like followings. (This is an example of x86-64 box).
310	Each zone has an array of protection pages like this.
311	
312	-
313	Node 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	-
327	These protections are added to score to judge whether this zone should be used
328	for page allocation or should be reclaimed.
329	
330	In this example, if normal pages (index=2) are required to this DMA zone and
331	watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should
332	not be used because pages_free(1355) is smaller than watermark + protection[2]
333	(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
334	normal page requirement. If requirement is DMA zone(index=0), protection[0]
335	(=0) is used.
336	
337	zone[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	
348	The default values of lowmem_reserve_ratio[i] are
349	    256 (if zone[i] means DMA or DMA32 zone)
350	    32  (others).
351	As above expression, they are reciprocal number of ratio.
352	256 means 1/256. # of protection pages becomes about "0.39%" of total present
353	pages of higher zones on the node.
354	
355	If you would like to protect more pages, smaller values are effective.
356	The minimum value is 1 (1/1 -> 100%).
357	
358	==============================================================
359	
360	max_map_count:
361	
362	This file contains the maximum number of memory map areas a process
363	may have. Memory map areas are used as a side-effect of calling
364	malloc, directly by mmap and mprotect, and also when loading shared
365	libraries.
366	
367	While most applications need less than a thousand maps, certain
368	programs, particularly malloc debuggers, may consume lots of them,
369	e.g., up to one or two maps per allocation.
370	
371	The default value is 65536.
372	
373	=============================================================
374	
375	memory_failure_early_kill:
376	
377	Control how to kill processes when uncorrected memory error (typically
378	a 2bit error in a memory module) is detected in the background by hardware
379	that cannot be handled by the kernel. In some cases (like the page
380	still having a valid copy on disk) the kernel will handle the failure
381	transparently without affecting any applications. But if there is
382	no other uptodate copy of the data it will kill to prevent any data
383	corruptions from propagating.
384	
385	1: Kill all processes that have the corrupted and not reloadable page mapped
386	as soon as the corruption is detected.  Note this is not supported
387	for a few types of pages, like kernel internally allocated data or
388	the swap cache, but works for the majority of user pages.
389	
390	0: Only unmap the corrupted page from all processes and only kill a process
391	who tries to access it.
392	
393	The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
394	handle this if they want to.
395	
396	This is only active on architectures/platforms with advanced machine
397	check handling and depends on the hardware capabilities.
398	
399	Applications can override this setting individually with the PR_MCE_KILL prctl
400	
401	==============================================================
402	
403	memory_failure_recovery
404	
405	Enable memory failure recovery (when supported by the platform)
406	
407	1: Attempt recovery.
408	
409	0: Always panic on a memory failure.
410	
411	==============================================================
412	
413	min_free_kbytes:
414	
415	This is used to force the Linux VM to keep a minimum number
416	of kilobytes free.  The VM uses this number to compute a
417	watermark[WMARK_MIN] value for each lowmem zone in the system.
418	Each lowmem zone gets a number of reserved free pages based
419	proportionally on its size.
420	
421	Some minimal amount of memory is needed to satisfy PF_MEMALLOC
422	allocations; if you set this to lower than 1024KB, your system will
423	become subtly broken, and prone to deadlock under high loads.
424	
425	Setting this too high will OOM your machine instantly.
426	
427	=============================================================
428	
429	min_slab_ratio:
430	
431	This is available only on NUMA kernels.
432	
433	A percentage of the total pages in each zone.  On Zone reclaim
434	(fallback from the local zone occurs) slabs will be reclaimed if more
435	than this percentage of pages in a zone are reclaimable slab pages.
436	This insures that the slab growth stays under control even in NUMA
437	systems that rarely perform global reclaim.
438	
439	The default is 5 percent.
440	
441	Note that slab reclaim is triggered in a per zone / node fashion.
442	The process of reclaiming slab memory is currently not node specific
443	and may not be fast.
444	
445	=============================================================
446	
447	min_unmapped_ratio:
448	
449	This is available only on NUMA kernels.
450	
451	This is a percentage of the total pages in each zone. Zone reclaim will
452	only occur if more than this percentage of pages are in a state that
453	zone_reclaim_mode allows to be reclaimed.
454	
455	If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared
456	against all file-backed unmapped pages including swapcache pages and tmpfs
457	files. Otherwise, only unmapped pages backed by normal files but not tmpfs
458	files and similar are considered.
459	
460	The default is 1 percent.
461	
462	==============================================================
463	
464	mmap_min_addr
465	
466	This file indicates the amount of address space  which a user process will
467	be restricted from mmapping.  Since kernel null dereference bugs could
468	accidentally operate based on the information in the first couple of pages
469	of memory userspace processes should not be allowed to write to them.  By
470	default this value is set to 0 and no protections will be enforced by the
471	security module.  Setting this value to something like 64k will allow the
472	vast majority of applications to work correctly and provide defense in depth
473	against future potential kernel bugs.
474	
475	==============================================================
476	
477	nr_hugepages
478	
479	Change the minimum size of the hugepage pool.
480	
481	See Documentation/vm/hugetlbpage.txt
482	
483	==============================================================
484	
485	nr_overcommit_hugepages
486	
487	Change the maximum size of the hugepage pool. The maximum is
488	nr_hugepages + nr_overcommit_hugepages.
489	
490	See Documentation/vm/hugetlbpage.txt
491	
492	==============================================================
493	
494	nr_trim_pages
495	
496	This is available only on NOMMU kernels.
497	
498	This value adjusts the excess page trimming behaviour of power-of-2 aligned
499	NOMMU mmap allocations.
500	
501	A value of 0 disables trimming of allocations entirely, while a value of 1
502	trims excess pages aggressively. Any value >= 1 acts as the watermark where
503	trimming of allocations is initiated.
504	
505	The default value is 1.
506	
507	See Documentation/nommu-mmap.txt for more information.
508	
509	==============================================================
510	
511	numa_zonelist_order
512	
513	This 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	
518	In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
519	ZONE_NORMAL -> ZONE_DMA
520	This means that a memory allocation request for GFP_KERNEL will
521	get memory from ZONE_DMA only when ZONE_NORMAL is not available.
522	
523	In NUMA case, you can think of following 2 types of order.
524	Assume 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	
529	Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
530	will be used before ZONE_NORMAL exhaustion. This increases possibility of
531	out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small.
532	
533	Type(B) cannot offer the best locality but is more robust against OOM of
534	the DMA zone.
535	
536	Type(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.
539	Specify "[Nn]ode" for node order
540	
541	"Zone Order" orders the zonelists by zone type, then by node within each
542	zone.  Specify "[Zz]one" for zone order.
543	
544	Specify "[Dd]efault" to request automatic configuration.  Autoconfiguration
545	will 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
548	(3) if any node's DMA zone comprises greater than 70% of its local memory and
549	    the amount of local memory is big enough.
550	
551	Otherwise, "zone" order will be selected. Default order is recommended unless
552	this is causing problems for your system/application.
553	
554	==============================================================
555	
556	oom_dump_tasks
557	
558	Enables a system-wide task dump (excluding kernel threads) to be
559	produced when the kernel performs an OOM-killing and includes such
560	information as pid, uid, tgid, vm size, rss, nr_ptes, swapents,
561	oom_score_adj score, and name.  This is helpful to determine why the
562	OOM killer was invoked, to identify the rogue task that caused it,
563	and to determine why the OOM killer chose the task it did to kill.
564	
565	If this is set to zero, this information is suppressed.  On very
566	large systems with thousands of tasks it may not be feasible to dump
567	the memory state information for each one.  Such systems should not
568	be forced to incur a performance penalty in OOM conditions when the
569	information may not be desired.
570	
571	If this is set to non-zero, this information is shown whenever the
572	OOM killer actually kills a memory-hogging task.
573	
574	The default value is 1 (enabled).
575	
576	==============================================================
577	
578	oom_kill_allocating_task
579	
580	This enables or disables killing the OOM-triggering task in
581	out-of-memory situations.
582	
583	If this is set to zero, the OOM killer will scan through the entire
584	tasklist and select a task based on heuristics to kill.  This normally
585	selects a rogue memory-hogging task that frees up a large amount of
586	memory when killed.
587	
588	If this is set to non-zero, the OOM killer simply kills the task that
589	triggered the out-of-memory condition.  This avoids the expensive
590	tasklist scan.
591	
592	If panic_on_oom is selected, it takes precedence over whatever value
593	is used in oom_kill_allocating_task.
594	
595	The default value is 0.
596	
597	==============================================================
598	
599	overcommit_kbytes:
600	
601	When overcommit_memory is set to 2, the committed address space is not
602	permitted to exceed swap plus this amount of physical RAM. See below.
603	
604	Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one
605	of them may be specified at a time. Setting one disables the other (which
606	then appears as 0 when read).
607	
608	==============================================================
609	
610	overcommit_memory:
611	
612	This value contains a flag that enables memory overcommitment.
613	
614	When this flag is 0, the kernel attempts to estimate the amount
615	of free memory left when userspace requests more memory.
616	
617	When this flag is 1, the kernel pretends there is always enough
618	memory until it actually runs out.
619	
620	When this flag is 2, the kernel uses a "never overcommit"
621	policy that attempts to prevent any overcommit of memory.
622	Note that user_reserve_kbytes affects this policy.
623	
624	This feature can be very useful because there are a lot of
625	programs that malloc() huge amounts of memory "just-in-case"
626	and don't use much of it.
627	
628	The default value is 0.
629	
630	See Documentation/vm/overcommit-accounting and
631	security/commoncap.c::cap_vm_enough_memory() for more information.
632	
633	==============================================================
634	
635	overcommit_ratio:
636	
637	When overcommit_memory is set to 2, the committed address
638	space is not permitted to exceed swap plus this percentage
639	of physical RAM.  See above.
640	
641	==============================================================
642	
643	page-cluster
644	
645	page-cluster controls the number of pages up to which consecutive pages
646	are read in from swap in a single attempt. This is the swap counterpart
647	to page cache readahead.
648	The mentioned consecutivity is not in terms of virtual/physical addresses,
649	but consecutive on swap space - that means they were swapped out together.
650	
651	It is a logarithmic value - setting it to zero means "1 page", setting
652	it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
653	Zero disables swap readahead completely.
654	
655	The default value is three (eight pages at a time).  There may be some
656	small benefits in tuning this to a different value if your workload is
657	swap-intensive.
658	
659	Lower values mean lower latencies for initial faults, but at the same time
660	extra faults and I/O delays for following faults if they would have been part of
661	that consecutive pages readahead would have brought in.
662	
663	=============================================================
664	
665	panic_on_oom
666	
667	This enables or disables panic on out-of-memory feature.
668	
669	If this is set to 0, the kernel will kill some rogue process,
670	called oom_killer.  Usually, oom_killer can kill rogue processes and
671	system will survive.
672	
673	If this is set to 1, the kernel panics when out-of-memory happens.
674	However, if a process limits using nodes by mempolicy/cpusets,
675	and those nodes become memory exhaustion status, one process
676	may be killed by oom-killer. No panic occurs in this case.
677	Because other nodes' memory may be free. This means system total status
678	may be not fatal yet.
679	
680	If this is set to 2, the kernel panics compulsorily even on the
681	above-mentioned. Even oom happens under memory cgroup, the whole
682	system panics.
683	
684	The default value is 0.
685	1 and 2 are for failover of clustering. Please select either
686	according to your policy of failover.
687	panic_on_oom=2+kdump gives you very strong tool to investigate
688	why oom happens. You can get snapshot.
689	
690	=============================================================
691	
692	percpu_pagelist_fraction
693	
694	This is the fraction of pages at most (high mark pcp->high) in each zone that
695	are allocated for each per cpu page list.  The min value for this is 8.  It
696	means that we don't allow more than 1/8th of pages in each zone to be
697	allocated in any single per_cpu_pagelist.  This entry only changes the value
698	of hot per cpu pagelists.  User can specify a number like 100 to allocate
699	1/100th of each zone to each per cpu page list.
700	
701	The batch value of each per cpu pagelist is also updated as a result.  It is
702	set to pcp->high/4.  The upper limit of batch is (PAGE_SHIFT * 8)
703	
704	The initial value is zero.  Kernel does not use this value at boot time to set
705	the high water marks for each per cpu page list.  If the user writes '0' to this
706	sysctl, it will revert to this default behavior.
707	
708	==============================================================
709	
710	stat_interval
711	
712	The time interval between which vm statistics are updated.  The default
713	is 1 second.
714	
715	==============================================================
716	
717	swappiness
718	
719	This control is used to define how aggressive the kernel will swap
720	memory pages.  Higher values will increase agressiveness, lower values
721	decrease the amount of swap.  A value of 0 instructs the kernel not to
722	initiate swap until the amount of free and file-backed pages is less
723	than the high water mark in a zone.
724	
725	The default value is 60.
726	
727	==============================================================
728	
729	- user_reserve_kbytes
730	
731	When overcommit_memory is set to 2, "never overommit" mode, reserve
732	min(3% of current process size, user_reserve_kbytes) of free memory.
733	This is intended to prevent a user from starting a single memory hogging
734	process, such that they cannot recover (kill the hog).
735	
736	user_reserve_kbytes defaults to min(3% of the current process size, 128MB).
737	
738	If this is reduced to zero, then the user will be allowed to allocate
739	all free memory with a single process, minus admin_reserve_kbytes.
740	Any subsequent attempts to execute a command will result in
741	"fork: Cannot allocate memory".
742	
743	Changing this takes effect whenever an application requests memory.
744	
745	==============================================================
746	
747	vfs_cache_pressure
748	------------------
749	
750	This percentage value controls the tendency of the kernel to reclaim
751	the memory which is used for caching of directory and inode objects.
752	
753	At the default value of vfs_cache_pressure=100 the kernel will attempt to
754	reclaim dentries and inodes at a "fair" rate with respect to pagecache and
755	swapcache reclaim.  Decreasing vfs_cache_pressure causes the kernel to prefer
756	to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will
757	never reclaim dentries and inodes due to memory pressure and this can easily
758	lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100
759	causes the kernel to prefer to reclaim dentries and inodes.
760	
761	Increasing vfs_cache_pressure significantly beyond 100 may have negative
762	performance impact. Reclaim code needs to take various locks to find freeable
763	directory and inode objects. With vfs_cache_pressure=1000, it will look for
764	ten times more freeable objects than there are.
765	
766	==============================================================
767	
768	zone_reclaim_mode:
769	
770	Zone_reclaim_mode allows someone to set more or less aggressive approaches to
771	reclaim memory when a zone runs out of memory. If it is set to zero then no
772	zone reclaim occurs. Allocations will be satisfied from other zones / nodes
773	in the system.
774	
775	This is value ORed together of
776	
777	1	= Zone reclaim on
778	2	= Zone reclaim writes dirty pages out
779	4	= Zone reclaim swaps pages
780	
781	zone_reclaim_mode is disabled by default.  For file servers or workloads
782	that benefit from having their data cached, zone_reclaim_mode should be
783	left disabled as the caching effect is likely to be more important than
784	data locality.
785	
786	zone_reclaim may be enabled if it's known that the workload is partitioned
787	such that each partition fits within a NUMA node and that accessing remote
788	memory would cause a measurable performance reduction.  The page allocator
789	will then reclaim easily reusable pages (those page cache pages that are
790	currently not used) before allocating off node pages.
791	
792	Allowing zone reclaim to write out pages stops processes that are
793	writing large amounts of data from dirtying pages on other nodes. Zone
794	reclaim will write out dirty pages if a zone fills up and so effectively
795	throttle the process. This may decrease the performance of a single process
796	since it cannot use all of system memory to buffer the outgoing writes
797	anymore but it preserve the memory on other nodes so that the performance
798	of other processes running on other nodes will not be affected.
799	
800	Allowing regular swap effectively restricts allocations to the local
801	node unless explicitly overridden by memory policies or cpuset
802	configurations.
803	
804	============ End of Document =================================
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