Root/
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 | - block_dump |
22 | - compact_memory |
23 | - dirty_background_bytes |
24 | - dirty_background_ratio |
25 | - dirty_bytes |
26 | - dirty_expire_centisecs |
27 | - dirty_ratio |
28 | - dirty_writeback_centisecs |
29 | - drop_caches |
30 | - extfrag_threshold |
31 | - hugepages_treat_as_movable |
32 | - hugetlb_shm_group |
33 | - laptop_mode |
34 | - legacy_va_layout |
35 | - lowmem_reserve_ratio |
36 | - max_map_count |
37 | - memory_failure_early_kill |
38 | - memory_failure_recovery |
39 | - min_free_kbytes |
40 | - min_slab_ratio |
41 | - min_unmapped_ratio |
42 | - mmap_min_addr |
43 | - nr_hugepages |
44 | - nr_overcommit_hugepages |
45 | - nr_pdflush_threads |
46 | - nr_trim_pages (only if CONFIG_MMU=n) |
47 | - numa_zonelist_order |
48 | - oom_dump_tasks |
49 | - oom_kill_allocating_task |
50 | - overcommit_memory |
51 | - overcommit_ratio |
52 | - page-cluster |
53 | - panic_on_oom |
54 | - percpu_pagelist_fraction |
55 | - stat_interval |
56 | - swappiness |
57 | - vfs_cache_pressure |
58 | - zone_reclaim_mode |
59 | |
60 | ============================================================== |
61 | |
62 | block_dump |
63 | |
64 | block_dump enables block I/O debugging when set to a nonzero value. More |
65 | information on block I/O debugging is in Documentation/laptops/laptop-mode.txt. |
66 | |
67 | ============================================================== |
68 | |
69 | compact_memory |
70 | |
71 | Available only when CONFIG_COMPACTION is set. When 1 is written to the file, |
72 | all zones are compacted such that free memory is available in contiguous |
73 | blocks where possible. This can be important for example in the allocation of |
74 | huge pages although processes will also directly compact memory as required. |
75 | |
76 | ============================================================== |
77 | |
78 | dirty_background_bytes |
79 | |
80 | Contains the amount of dirty memory at which the pdflush background writeback |
81 | daemon will start writeback. |
82 | |
83 | Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only |
84 | one of them may be specified at a time. When one sysctl is written it is |
85 | immediately taken into account to evaluate the dirty memory limits and the |
86 | other appears as 0 when read. |
87 | |
88 | ============================================================== |
89 | |
90 | dirty_background_ratio |
91 | |
92 | Contains, as a percentage of total system memory, the number of pages at which |
93 | the pdflush background writeback daemon will start writing out dirty data. |
94 | |
95 | ============================================================== |
96 | |
97 | dirty_bytes |
98 | |
99 | Contains the amount of dirty memory at which a process generating disk writes |
100 | will itself start writeback. |
101 | |
102 | Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be |
103 | specified at a time. When one sysctl is written it is immediately taken into |
104 | account to evaluate the dirty memory limits and the other appears as 0 when |
105 | read. |
106 | |
107 | Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any |
108 | value lower than this limit will be ignored and the old configuration will be |
109 | retained. |
110 | |
111 | ============================================================== |
112 | |
113 | dirty_expire_centisecs |
114 | |
115 | This tunable is used to define when dirty data is old enough to be eligible |
116 | for writeout by the pdflush daemons. It is expressed in 100'ths of a second. |
117 | Data which has been dirty in-memory for longer than this interval will be |
118 | written out next time a pdflush daemon wakes up. |
119 | |
120 | ============================================================== |
121 | |
122 | dirty_ratio |
123 | |
124 | Contains, as a percentage of total system memory, the number of pages at which |
125 | a process which is generating disk writes will itself start writing out dirty |
126 | data. |
127 | |
128 | ============================================================== |
129 | |
130 | dirty_writeback_centisecs |
131 | |
132 | The pdflush writeback daemons will periodically wake up and write `old' data |
133 | out to disk. This tunable expresses the interval between those wakeups, in |
134 | 100'ths of a second. |
135 | |
136 | Setting this to zero disables periodic writeback altogether. |
137 | |
138 | ============================================================== |
139 | |
140 | drop_caches |
141 | |
142 | Writing to this will cause the kernel to drop clean caches, dentries and |
143 | inodes from memory, causing that memory to become free. |
144 | |
145 | To free pagecache: |
146 | echo 1 > /proc/sys/vm/drop_caches |
147 | To free dentries and inodes: |
148 | echo 2 > /proc/sys/vm/drop_caches |
149 | To free pagecache, dentries and inodes: |
150 | echo 3 > /proc/sys/vm/drop_caches |
151 | |
152 | As this is a non-destructive operation and dirty objects are not freeable, the |
153 | user should run `sync' first. |
154 | |
155 | ============================================================== |
156 | |
157 | extfrag_threshold |
158 | |
159 | This parameter affects whether the kernel will compact memory or direct |
160 | reclaim to satisfy a high-order allocation. /proc/extfrag_index shows what |
161 | the fragmentation index for each order is in each zone in the system. Values |
162 | tending towards 0 imply allocations would fail due to lack of memory, |
163 | values towards 1000 imply failures are due to fragmentation and -1 implies |
164 | that the allocation will succeed as long as watermarks are met. |
165 | |
166 | The kernel will not compact memory in a zone if the |
167 | fragmentation index is <= extfrag_threshold. The default value is 500. |
168 | |
169 | ============================================================== |
170 | |
171 | hugepages_treat_as_movable |
172 | |
173 | This parameter is only useful when kernelcore= is specified at boot time to |
174 | create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages |
175 | are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero |
176 | value written to hugepages_treat_as_movable allows huge pages to be allocated |
177 | from ZONE_MOVABLE. |
178 | |
179 | Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge |
180 | pages pool can easily grow or shrink within. Assuming that applications are |
181 | not running that mlock() a lot of memory, it is likely the huge pages pool |
182 | can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value |
183 | into nr_hugepages and triggering page reclaim. |
184 | |
185 | ============================================================== |
186 | |
187 | hugetlb_shm_group |
188 | |
189 | hugetlb_shm_group contains group id that is allowed to create SysV |
190 | shared memory segment using hugetlb page. |
191 | |
192 | ============================================================== |
193 | |
194 | laptop_mode |
195 | |
196 | laptop_mode is a knob that controls "laptop mode". All the things that are |
197 | controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt. |
198 | |
199 | ============================================================== |
200 | |
201 | legacy_va_layout |
202 | |
203 | If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel |
204 | will use the legacy (2.4) layout for all processes. |
205 | |
206 | ============================================================== |
207 | |
208 | lowmem_reserve_ratio |
209 | |
210 | For some specialised workloads on highmem machines it is dangerous for |
211 | the kernel to allow process memory to be allocated from the "lowmem" |
212 | zone. This is because that memory could then be pinned via the mlock() |
213 | system call, or by unavailability of swapspace. |
214 | |
215 | And on large highmem machines this lack of reclaimable lowmem memory |
216 | can be fatal. |
217 | |
218 | So the Linux page allocator has a mechanism which prevents allocations |
219 | which _could_ use highmem from using too much lowmem. This means that |
220 | a certain amount of lowmem is defended from the possibility of being |
221 | captured into pinned user memory. |
222 | |
223 | (The same argument applies to the old 16 megabyte ISA DMA region. This |
224 | mechanism will also defend that region from allocations which could use |
225 | highmem or lowmem). |
226 | |
227 | The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is |
228 | in defending these lower zones. |
229 | |
230 | If you have a machine which uses highmem or ISA DMA and your |
231 | applications are using mlock(), or if you are running with no swap then |
232 | you probably should change the lowmem_reserve_ratio setting. |
233 | |
234 | The lowmem_reserve_ratio is an array. You can see them by reading this file. |
235 | - |
236 | % cat /proc/sys/vm/lowmem_reserve_ratio |
237 | 256 256 32 |
238 | - |
239 | Note: # of this elements is one fewer than number of zones. Because the highest |
240 | zone's value is not necessary for following calculation. |
241 | |
242 | But, these values are not used directly. The kernel calculates # of protection |
243 | pages for each zones from them. These are shown as array of protection pages |
244 | in /proc/zoneinfo like followings. (This is an example of x86-64 box). |
245 | Each zone has an array of protection pages like this. |
246 | |
247 | - |
248 | Node 0, zone DMA |
249 | pages free 1355 |
250 | min 3 |
251 | low 3 |
252 | high 4 |
253 | : |
254 | : |
255 | numa_other 0 |
256 | protection: (0, 2004, 2004, 2004) |
257 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
258 | pagesets |
259 | cpu: 0 pcp: 0 |
260 | : |
261 | - |
262 | These protections are added to score to judge whether this zone should be used |
263 | for page allocation or should be reclaimed. |
264 | |
265 | In this example, if normal pages (index=2) are required to this DMA zone and |
266 | watermark[WMARK_HIGH] is used for watermark, the kernel judges this zone should |
267 | not be used because pages_free(1355) is smaller than watermark + protection[2] |
268 | (4 + 2004 = 2008). If this protection value is 0, this zone would be used for |
269 | normal page requirement. If requirement is DMA zone(index=0), protection[0] |
270 | (=0) is used. |
271 | |
272 | zone[i]'s protection[j] is calculated by following expression. |
273 | |
274 | (i < j): |
275 | zone[i]->protection[j] |
276 | = (total sums of present_pages from zone[i+1] to zone[j] on the node) |
277 | / lowmem_reserve_ratio[i]; |
278 | (i = j): |
279 | (should not be protected. = 0; |
280 | (i > j): |
281 | (not necessary, but looks 0) |
282 | |
283 | The default values of lowmem_reserve_ratio[i] are |
284 | 256 (if zone[i] means DMA or DMA32 zone) |
285 | 32 (others). |
286 | As above expression, they are reciprocal number of ratio. |
287 | 256 means 1/256. # of protection pages becomes about "0.39%" of total present |
288 | pages of higher zones on the node. |
289 | |
290 | If you would like to protect more pages, smaller values are effective. |
291 | The minimum value is 1 (1/1 -> 100%). |
292 | |
293 | ============================================================== |
294 | |
295 | max_map_count: |
296 | |
297 | This file contains the maximum number of memory map areas a process |
298 | may have. Memory map areas are used as a side-effect of calling |
299 | malloc, directly by mmap and mprotect, and also when loading shared |
300 | libraries. |
301 | |
302 | While most applications need less than a thousand maps, certain |
303 | programs, particularly malloc debuggers, may consume lots of them, |
304 | e.g., up to one or two maps per allocation. |
305 | |
306 | The default value is 65536. |
307 | |
308 | ============================================================= |
309 | |
310 | memory_failure_early_kill: |
311 | |
312 | Control how to kill processes when uncorrected memory error (typically |
313 | a 2bit error in a memory module) is detected in the background by hardware |
314 | that cannot be handled by the kernel. In some cases (like the page |
315 | still having a valid copy on disk) the kernel will handle the failure |
316 | transparently without affecting any applications. But if there is |
317 | no other uptodate copy of the data it will kill to prevent any data |
318 | corruptions from propagating. |
319 | |
320 | 1: Kill all processes that have the corrupted and not reloadable page mapped |
321 | as soon as the corruption is detected. Note this is not supported |
322 | for a few types of pages, like kernel internally allocated data or |
323 | the swap cache, but works for the majority of user pages. |
324 | |
325 | 0: Only unmap the corrupted page from all processes and only kill a process |
326 | who tries to access it. |
327 | |
328 | The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can |
329 | handle this if they want to. |
330 | |
331 | This is only active on architectures/platforms with advanced machine |
332 | check handling and depends on the hardware capabilities. |
333 | |
334 | Applications can override this setting individually with the PR_MCE_KILL prctl |
335 | |
336 | ============================================================== |
337 | |
338 | memory_failure_recovery |
339 | |
340 | Enable memory failure recovery (when supported by the platform) |
341 | |
342 | 1: Attempt recovery. |
343 | |
344 | 0: Always panic on a memory failure. |
345 | |
346 | ============================================================== |
347 | |
348 | min_free_kbytes: |
349 | |
350 | This is used to force the Linux VM to keep a minimum number |
351 | of kilobytes free. The VM uses this number to compute a |
352 | watermark[WMARK_MIN] value for each lowmem zone in the system. |
353 | Each lowmem zone gets a number of reserved free pages based |
354 | proportionally on its size. |
355 | |
356 | Some minimal amount of memory is needed to satisfy PF_MEMALLOC |
357 | allocations; if you set this to lower than 1024KB, your system will |
358 | become subtly broken, and prone to deadlock under high loads. |
359 | |
360 | Setting this too high will OOM your machine instantly. |
361 | |
362 | ============================================================= |
363 | |
364 | min_slab_ratio: |
365 | |
366 | This is available only on NUMA kernels. |
367 | |
368 | A percentage of the total pages in each zone. On Zone reclaim |
369 | (fallback from the local zone occurs) slabs will be reclaimed if more |
370 | than this percentage of pages in a zone are reclaimable slab pages. |
371 | This insures that the slab growth stays under control even in NUMA |
372 | systems that rarely perform global reclaim. |
373 | |
374 | The default is 5 percent. |
375 | |
376 | Note that slab reclaim is triggered in a per zone / node fashion. |
377 | The process of reclaiming slab memory is currently not node specific |
378 | and may not be fast. |
379 | |
380 | ============================================================= |
381 | |
382 | min_unmapped_ratio: |
383 | |
384 | This is available only on NUMA kernels. |
385 | |
386 | This is a percentage of the total pages in each zone. Zone reclaim will |
387 | only occur if more than this percentage of pages are in a state that |
388 | zone_reclaim_mode allows to be reclaimed. |
389 | |
390 | If zone_reclaim_mode has the value 4 OR'd, then the percentage is compared |
391 | against all file-backed unmapped pages including swapcache pages and tmpfs |
392 | files. Otherwise, only unmapped pages backed by normal files but not tmpfs |
393 | files and similar are considered. |
394 | |
395 | The default is 1 percent. |
396 | |
397 | ============================================================== |
398 | |
399 | mmap_min_addr |
400 | |
401 | This file indicates the amount of address space which a user process will |
402 | be restricted from mmapping. Since kernel null dereference bugs could |
403 | accidentally operate based on the information in the first couple of pages |
404 | of memory userspace processes should not be allowed to write to them. By |
405 | default this value is set to 0 and no protections will be enforced by the |
406 | security module. Setting this value to something like 64k will allow the |
407 | vast majority of applications to work correctly and provide defense in depth |
408 | against future potential kernel bugs. |
409 | |
410 | ============================================================== |
411 | |
412 | nr_hugepages |
413 | |
414 | Change the minimum size of the hugepage pool. |
415 | |
416 | See Documentation/vm/hugetlbpage.txt |
417 | |
418 | ============================================================== |
419 | |
420 | nr_overcommit_hugepages |
421 | |
422 | Change the maximum size of the hugepage pool. The maximum is |
423 | nr_hugepages + nr_overcommit_hugepages. |
424 | |
425 | See Documentation/vm/hugetlbpage.txt |
426 | |
427 | ============================================================== |
428 | |
429 | nr_pdflush_threads |
430 | |
431 | The current number of pdflush threads. This value is read-only. |
432 | The value changes according to the number of dirty pages in the system. |
433 | |
434 | When necessary, additional pdflush threads are created, one per second, up to |
435 | nr_pdflush_threads_max. |
436 | |
437 | ============================================================== |
438 | |
439 | nr_trim_pages |
440 | |
441 | This is available only on NOMMU kernels. |
442 | |
443 | This value adjusts the excess page trimming behaviour of power-of-2 aligned |
444 | NOMMU mmap allocations. |
445 | |
446 | A value of 0 disables trimming of allocations entirely, while a value of 1 |
447 | trims excess pages aggressively. Any value >= 1 acts as the watermark where |
448 | trimming of allocations is initiated. |
449 | |
450 | The default value is 1. |
451 | |
452 | See Documentation/nommu-mmap.txt for more information. |
453 | |
454 | ============================================================== |
455 | |
456 | numa_zonelist_order |
457 | |
458 | This sysctl is only for NUMA. |
459 | 'where the memory is allocated from' is controlled by zonelists. |
460 | (This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation. |
461 | you may be able to read ZONE_DMA as ZONE_DMA32...) |
462 | |
463 | In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following. |
464 | ZONE_NORMAL -> ZONE_DMA |
465 | This means that a memory allocation request for GFP_KERNEL will |
466 | get memory from ZONE_DMA only when ZONE_NORMAL is not available. |
467 | |
468 | In NUMA case, you can think of following 2 types of order. |
469 | Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL |
470 | |
471 | (A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL |
472 | (B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA. |
473 | |
474 | Type(A) offers the best locality for processes on Node(0), but ZONE_DMA |
475 | will be used before ZONE_NORMAL exhaustion. This increases possibility of |
476 | out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small. |
477 | |
478 | Type(B) cannot offer the best locality but is more robust against OOM of |
479 | the DMA zone. |
480 | |
481 | Type(A) is called as "Node" order. Type (B) is "Zone" order. |
482 | |
483 | "Node order" orders the zonelists by node, then by zone within each node. |
484 | Specify "[Nn]ode" for zone order |
485 | |
486 | "Zone Order" orders the zonelists by zone type, then by node within each |
487 | zone. Specify "[Zz]one"for zode order. |
488 | |
489 | Specify "[Dd]efault" to request automatic configuration. Autoconfiguration |
490 | will select "node" order in following case. |
491 | (1) if the DMA zone does not exist or |
492 | (2) if the DMA zone comprises greater than 50% of the available memory or |
493 | (3) if any node's DMA zone comprises greater than 60% of its local memory and |
494 | the amount of local memory is big enough. |
495 | |
496 | Otherwise, "zone" order will be selected. Default order is recommended unless |
497 | this is causing problems for your system/application. |
498 | |
499 | ============================================================== |
500 | |
501 | oom_dump_tasks |
502 | |
503 | Enables a system-wide task dump (excluding kernel threads) to be |
504 | produced when the kernel performs an OOM-killing and includes such |
505 | information as pid, uid, tgid, vm size, rss, cpu, oom_adj score, and |
506 | name. This is helpful to determine why the OOM killer was invoked |
507 | and to identify the rogue task that caused it. |
508 | |
509 | If this is set to zero, this information is suppressed. On very |
510 | large systems with thousands of tasks it may not be feasible to dump |
511 | the memory state information for each one. Such systems should not |
512 | be forced to incur a performance penalty in OOM conditions when the |
513 | information may not be desired. |
514 | |
515 | If this is set to non-zero, this information is shown whenever the |
516 | OOM killer actually kills a memory-hogging task. |
517 | |
518 | The default value is 1 (enabled). |
519 | |
520 | ============================================================== |
521 | |
522 | oom_kill_allocating_task |
523 | |
524 | This enables or disables killing the OOM-triggering task in |
525 | out-of-memory situations. |
526 | |
527 | If this is set to zero, the OOM killer will scan through the entire |
528 | tasklist and select a task based on heuristics to kill. This normally |
529 | selects a rogue memory-hogging task that frees up a large amount of |
530 | memory when killed. |
531 | |
532 | If this is set to non-zero, the OOM killer simply kills the task that |
533 | triggered the out-of-memory condition. This avoids the expensive |
534 | tasklist scan. |
535 | |
536 | If panic_on_oom is selected, it takes precedence over whatever value |
537 | is used in oom_kill_allocating_task. |
538 | |
539 | The default value is 0. |
540 | |
541 | ============================================================== |
542 | |
543 | overcommit_memory: |
544 | |
545 | This value contains a flag that enables memory overcommitment. |
546 | |
547 | When this flag is 0, the kernel attempts to estimate the amount |
548 | of free memory left when userspace requests more memory. |
549 | |
550 | When this flag is 1, the kernel pretends there is always enough |
551 | memory until it actually runs out. |
552 | |
553 | When this flag is 2, the kernel uses a "never overcommit" |
554 | policy that attempts to prevent any overcommit of memory. |
555 | |
556 | This feature can be very useful because there are a lot of |
557 | programs that malloc() huge amounts of memory "just-in-case" |
558 | and don't use much of it. |
559 | |
560 | The default value is 0. |
561 | |
562 | See Documentation/vm/overcommit-accounting and |
563 | security/commoncap.c::cap_vm_enough_memory() for more information. |
564 | |
565 | ============================================================== |
566 | |
567 | overcommit_ratio: |
568 | |
569 | When overcommit_memory is set to 2, the committed address |
570 | space is not permitted to exceed swap plus this percentage |
571 | of physical RAM. See above. |
572 | |
573 | ============================================================== |
574 | |
575 | page-cluster |
576 | |
577 | page-cluster controls the number of pages which are written to swap in |
578 | a single attempt. The swap I/O size. |
579 | |
580 | It is a logarithmic value - setting it to zero means "1 page", setting |
581 | it to 1 means "2 pages", setting it to 2 means "4 pages", etc. |
582 | |
583 | The default value is three (eight pages at a time). There may be some |
584 | small benefits in tuning this to a different value if your workload is |
585 | swap-intensive. |
586 | |
587 | ============================================================= |
588 | |
589 | panic_on_oom |
590 | |
591 | This enables or disables panic on out-of-memory feature. |
592 | |
593 | If this is set to 0, the kernel will kill some rogue process, |
594 | called oom_killer. Usually, oom_killer can kill rogue processes and |
595 | system will survive. |
596 | |
597 | If this is set to 1, the kernel panics when out-of-memory happens. |
598 | However, if a process limits using nodes by mempolicy/cpusets, |
599 | and those nodes become memory exhaustion status, one process |
600 | may be killed by oom-killer. No panic occurs in this case. |
601 | Because other nodes' memory may be free. This means system total status |
602 | may be not fatal yet. |
603 | |
604 | If this is set to 2, the kernel panics compulsorily even on the |
605 | above-mentioned. Even oom happens under memory cgroup, the whole |
606 | system panics. |
607 | |
608 | The default value is 0. |
609 | 1 and 2 are for failover of clustering. Please select either |
610 | according to your policy of failover. |
611 | panic_on_oom=2+kdump gives you very strong tool to investigate |
612 | why oom happens. You can get snapshot. |
613 | |
614 | ============================================================= |
615 | |
616 | percpu_pagelist_fraction |
617 | |
618 | This is the fraction of pages at most (high mark pcp->high) in each zone that |
619 | are allocated for each per cpu page list. The min value for this is 8. It |
620 | means that we don't allow more than 1/8th of pages in each zone to be |
621 | allocated in any single per_cpu_pagelist. This entry only changes the value |
622 | of hot per cpu pagelists. User can specify a number like 100 to allocate |
623 | 1/100th of each zone to each per cpu page list. |
624 | |
625 | The batch value of each per cpu pagelist is also updated as a result. It is |
626 | set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8) |
627 | |
628 | The initial value is zero. Kernel does not use this value at boot time to set |
629 | the high water marks for each per cpu page list. |
630 | |
631 | ============================================================== |
632 | |
633 | stat_interval |
634 | |
635 | The time interval between which vm statistics are updated. The default |
636 | is 1 second. |
637 | |
638 | ============================================================== |
639 | |
640 | swappiness |
641 | |
642 | This control is used to define how aggressive the kernel will swap |
643 | memory pages. Higher values will increase agressiveness, lower values |
644 | decrease the amount of swap. |
645 | |
646 | The default value is 60. |
647 | |
648 | ============================================================== |
649 | |
650 | vfs_cache_pressure |
651 | ------------------ |
652 | |
653 | Controls the tendency of the kernel to reclaim the memory which is used for |
654 | caching of directory and inode objects. |
655 | |
656 | At the default value of vfs_cache_pressure=100 the kernel will attempt to |
657 | reclaim dentries and inodes at a "fair" rate with respect to pagecache and |
658 | swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer |
659 | to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will |
660 | never reclaim dentries and inodes due to memory pressure and this can easily |
661 | lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 |
662 | causes the kernel to prefer to reclaim dentries and inodes. |
663 | |
664 | ============================================================== |
665 | |
666 | zone_reclaim_mode: |
667 | |
668 | Zone_reclaim_mode allows someone to set more or less aggressive approaches to |
669 | reclaim memory when a zone runs out of memory. If it is set to zero then no |
670 | zone reclaim occurs. Allocations will be satisfied from other zones / nodes |
671 | in the system. |
672 | |
673 | This is value ORed together of |
674 | |
675 | 1 = Zone reclaim on |
676 | 2 = Zone reclaim writes dirty pages out |
677 | 4 = Zone reclaim swaps pages |
678 | |
679 | zone_reclaim_mode is set during bootup to 1 if it is determined that pages |
680 | from remote zones will cause a measurable performance reduction. The |
681 | page allocator will then reclaim easily reusable pages (those page |
682 | cache pages that are currently not used) before allocating off node pages. |
683 | |
684 | It may be beneficial to switch off zone reclaim if the system is |
685 | used for a file server and all of memory should be used for caching files |
686 | from disk. In that case the caching effect is more important than |
687 | data locality. |
688 | |
689 | Allowing zone reclaim to write out pages stops processes that are |
690 | writing large amounts of data from dirtying pages on other nodes. Zone |
691 | reclaim will write out dirty pages if a zone fills up and so effectively |
692 | throttle the process. This may decrease the performance of a single process |
693 | since it cannot use all of system memory to buffer the outgoing writes |
694 | anymore but it preserve the memory on other nodes so that the performance |
695 | of other processes running on other nodes will not be affected. |
696 | |
697 | Allowing regular swap effectively restricts allocations to the local |
698 | node unless explicitly overridden by memory policies or cpuset |
699 | configurations. |
700 | |
701 | ============ End of Document ================================= |
702 |
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