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1 | Documentation for /proc/sys/vm/* kernel version 2.2.10 |
2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> | |
3 | ||
4 | For general info and legal blurb, please look in README. | |
5 | ||
6 | ============================================================== | |
7 | ||
8 | This file contains the documentation for the sysctl files in | |
9 | /proc/sys/vm and is valid for Linux kernel version 2.2. | |
10 | ||
11 | The files in this directory can be used to tune the operation | |
12 | of the virtual memory (VM) subsystem of the Linux kernel and | |
13 | the writeout of dirty data to disk. | |
14 | ||
15 | Default values and initialization routines for most of these | |
16 | files can be found in mm/swap.c. | |
17 | ||
18 | Currently, these files are in /proc/sys/vm: | |
19 | - overcommit_memory | |
20 | - page-cluster | |
21 | - dirty_ratio | |
22 | - dirty_background_ratio | |
23 | - dirty_expire_centisecs | |
24 | - dirty_writeback_centisecs | |
25 | - max_map_count | |
26 | - min_free_kbytes | |
27 | - laptop_mode | |
28 | - block_dump | |
9d0243bc | 29 | - drop-caches |
1743660b | 30 | - zone_reclaim_mode |
9614634f | 31 | - min_unmapped_ratio |
0ff38490 | 32 | - min_slab_ratio |
fadd8fbd | 33 | - panic_on_oom |
fe071d7e | 34 | - oom_kill_allocating_task |
ed032189 | 35 | - mmap_min_address |
f0c0b2b8 | 36 | - numa_zonelist_order |
d5dbac87 NA |
37 | - nr_hugepages |
38 | - nr_overcommit_hugepages | |
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39 | |
40 | ============================================================== | |
41 | ||
42 | dirty_ratio, dirty_background_ratio, dirty_expire_centisecs, | |
43 | dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode, | |
ed7ed365 MG |
44 | block_dump, swap_token_timeout, drop-caches, |
45 | hugepages_treat_as_movable: | |
1da177e4 LT |
46 | |
47 | See Documentation/filesystems/proc.txt | |
48 | ||
49 | ============================================================== | |
50 | ||
51 | overcommit_memory: | |
52 | ||
53 | This value contains a flag that enables memory overcommitment. | |
54 | ||
55 | When this flag is 0, the kernel attempts to estimate the amount | |
56 | of free memory left when userspace requests more memory. | |
57 | ||
58 | When this flag is 1, the kernel pretends there is always enough | |
59 | memory until it actually runs out. | |
60 | ||
61 | When this flag is 2, the kernel uses a "never overcommit" | |
62 | policy that attempts to prevent any overcommit of memory. | |
63 | ||
64 | This feature can be very useful because there are a lot of | |
65 | programs that malloc() huge amounts of memory "just-in-case" | |
66 | and don't use much of it. | |
67 | ||
68 | The default value is 0. | |
69 | ||
70 | See Documentation/vm/overcommit-accounting and | |
71 | security/commoncap.c::cap_vm_enough_memory() for more information. | |
72 | ||
73 | ============================================================== | |
74 | ||
75 | overcommit_ratio: | |
76 | ||
77 | When overcommit_memory is set to 2, the committed address | |
78 | space is not permitted to exceed swap plus this percentage | |
79 | of physical RAM. See above. | |
80 | ||
81 | ============================================================== | |
82 | ||
83 | page-cluster: | |
84 | ||
85 | The Linux VM subsystem avoids excessive disk seeks by reading | |
86 | multiple pages on a page fault. The number of pages it reads | |
87 | is dependent on the amount of memory in your machine. | |
88 | ||
89 | The number of pages the kernel reads in at once is equal to | |
90 | 2 ^ page-cluster. Values above 2 ^ 5 don't make much sense | |
91 | for swap because we only cluster swap data in 32-page groups. | |
92 | ||
93 | ============================================================== | |
94 | ||
95 | max_map_count: | |
96 | ||
97 | This file contains the maximum number of memory map areas a process | |
98 | may have. Memory map areas are used as a side-effect of calling | |
99 | malloc, directly by mmap and mprotect, and also when loading shared | |
100 | libraries. | |
101 | ||
102 | While most applications need less than a thousand maps, certain | |
103 | programs, particularly malloc debuggers, may consume lots of them, | |
104 | e.g., up to one or two maps per allocation. | |
105 | ||
106 | The default value is 65536. | |
107 | ||
108 | ============================================================== | |
109 | ||
110 | min_free_kbytes: | |
111 | ||
112 | This is used to force the Linux VM to keep a minimum number | |
113 | of kilobytes free. The VM uses this number to compute a pages_min | |
114 | value for each lowmem zone in the system. Each lowmem zone gets | |
115 | a number of reserved free pages based proportionally on its size. | |
8ad4b1fb | 116 | |
24950898 PM |
117 | Some minimal ammount of memory is needed to satisfy PF_MEMALLOC |
118 | allocations; if you set this to lower than 1024KB, your system will | |
119 | become subtly broken, and prone to deadlock under high loads. | |
120 | ||
121 | Setting this too high will OOM your machine instantly. | |
122 | ||
8ad4b1fb RS |
123 | ============================================================== |
124 | ||
125 | percpu_pagelist_fraction | |
126 | ||
127 | This is the fraction of pages at most (high mark pcp->high) in each zone that | |
128 | are allocated for each per cpu page list. The min value for this is 8. It | |
129 | means that we don't allow more than 1/8th of pages in each zone to be | |
130 | allocated in any single per_cpu_pagelist. This entry only changes the value | |
131 | of hot per cpu pagelists. User can specify a number like 100 to allocate | |
132 | 1/100th of each zone to each per cpu page list. | |
133 | ||
134 | The batch value of each per cpu pagelist is also updated as a result. It is | |
135 | set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8) | |
136 | ||
137 | The initial value is zero. Kernel does not use this value at boot time to set | |
138 | the high water marks for each per cpu page list. | |
1743660b CL |
139 | |
140 | =============================================================== | |
141 | ||
142 | zone_reclaim_mode: | |
143 | ||
5d3f083d | 144 | Zone_reclaim_mode allows someone to set more or less aggressive approaches to |
1b2ffb78 CL |
145 | reclaim memory when a zone runs out of memory. If it is set to zero then no |
146 | zone reclaim occurs. Allocations will be satisfied from other zones / nodes | |
147 | in the system. | |
148 | ||
149 | This is value ORed together of | |
150 | ||
151 | 1 = Zone reclaim on | |
152 | 2 = Zone reclaim writes dirty pages out | |
153 | 4 = Zone reclaim swaps pages | |
154 | ||
155 | zone_reclaim_mode is set during bootup to 1 if it is determined that pages | |
156 | from remote zones will cause a measurable performance reduction. The | |
1743660b | 157 | page allocator will then reclaim easily reusable pages (those page |
1b2ffb78 CL |
158 | cache pages that are currently not used) before allocating off node pages. |
159 | ||
160 | It may be beneficial to switch off zone reclaim if the system is | |
161 | used for a file server and all of memory should be used for caching files | |
162 | from disk. In that case the caching effect is more important than | |
163 | data locality. | |
164 | ||
165 | Allowing zone reclaim to write out pages stops processes that are | |
166 | writing large amounts of data from dirtying pages on other nodes. Zone | |
167 | reclaim will write out dirty pages if a zone fills up and so effectively | |
168 | throttle the process. This may decrease the performance of a single process | |
169 | since it cannot use all of system memory to buffer the outgoing writes | |
170 | anymore but it preserve the memory on other nodes so that the performance | |
171 | of other processes running on other nodes will not be affected. | |
1743660b | 172 | |
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173 | Allowing regular swap effectively restricts allocations to the local |
174 | node unless explicitly overridden by memory policies or cpuset | |
175 | configurations. | |
1743660b | 176 | |
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177 | ============================================================= |
178 | ||
9614634f CL |
179 | min_unmapped_ratio: |
180 | ||
181 | This is available only on NUMA kernels. | |
182 | ||
0ff38490 | 183 | A percentage of the total pages in each zone. Zone reclaim will only |
9614634f CL |
184 | occur if more than this percentage of pages are file backed and unmapped. |
185 | This is to insure that a minimal amount of local pages is still available for | |
186 | file I/O even if the node is overallocated. | |
187 | ||
188 | The default is 1 percent. | |
189 | ||
190 | ============================================================= | |
191 | ||
0ff38490 CL |
192 | min_slab_ratio: |
193 | ||
194 | This is available only on NUMA kernels. | |
195 | ||
196 | A percentage of the total pages in each zone. On Zone reclaim | |
197 | (fallback from the local zone occurs) slabs will be reclaimed if more | |
198 | than this percentage of pages in a zone are reclaimable slab pages. | |
199 | This insures that the slab growth stays under control even in NUMA | |
200 | systems that rarely perform global reclaim. | |
201 | ||
202 | The default is 5 percent. | |
203 | ||
204 | Note that slab reclaim is triggered in a per zone / node fashion. | |
205 | The process of reclaiming slab memory is currently not node specific | |
206 | and may not be fast. | |
207 | ||
208 | ============================================================= | |
209 | ||
fadd8fbd KH |
210 | panic_on_oom |
211 | ||
2b744c01 | 212 | This enables or disables panic on out-of-memory feature. |
fadd8fbd | 213 | |
2b744c01 YG |
214 | If this is set to 0, the kernel will kill some rogue process, |
215 | called oom_killer. Usually, oom_killer can kill rogue processes and | |
216 | system will survive. | |
217 | ||
218 | If this is set to 1, the kernel panics when out-of-memory happens. | |
219 | However, if a process limits using nodes by mempolicy/cpusets, | |
220 | and those nodes become memory exhaustion status, one process | |
221 | may be killed by oom-killer. No panic occurs in this case. | |
222 | Because other nodes' memory may be free. This means system total status | |
223 | may be not fatal yet. | |
fadd8fbd | 224 | |
2b744c01 YG |
225 | If this is set to 2, the kernel panics compulsorily even on the |
226 | above-mentioned. | |
227 | ||
228 | The default value is 0. | |
229 | 1 and 2 are for failover of clustering. Please select either | |
230 | according to your policy of failover. | |
ed032189 | 231 | |
fe071d7e DR |
232 | ============================================================= |
233 | ||
234 | oom_kill_allocating_task | |
235 | ||
236 | This enables or disables killing the OOM-triggering task in | |
237 | out-of-memory situations. | |
238 | ||
239 | If this is set to zero, the OOM killer will scan through the entire | |
240 | tasklist and select a task based on heuristics to kill. This normally | |
241 | selects a rogue memory-hogging task that frees up a large amount of | |
242 | memory when killed. | |
243 | ||
244 | If this is set to non-zero, the OOM killer simply kills the task that | |
245 | triggered the out-of-memory condition. This avoids the expensive | |
246 | tasklist scan. | |
247 | ||
248 | If panic_on_oom is selected, it takes precedence over whatever value | |
249 | is used in oom_kill_allocating_task. | |
250 | ||
251 | The default value is 0. | |
252 | ||
ed032189 EP |
253 | ============================================================== |
254 | ||
255 | mmap_min_addr | |
256 | ||
257 | This file indicates the amount of address space which a user process will | |
258 | be restricted from mmaping. Since kernel null dereference bugs could | |
259 | accidentally operate based on the information in the first couple of pages | |
260 | of memory userspace processes should not be allowed to write to them. By | |
261 | default this value is set to 0 and no protections will be enforced by the | |
262 | security module. Setting this value to something like 64k will allow the | |
263 | vast majority of applications to work correctly and provide defense in depth | |
264 | against future potential kernel bugs. | |
265 | ||
f0c0b2b8 KH |
266 | ============================================================== |
267 | ||
268 | numa_zonelist_order | |
269 | ||
270 | This sysctl is only for NUMA. | |
271 | 'where the memory is allocated from' is controlled by zonelists. | |
272 | (This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation. | |
273 | you may be able to read ZONE_DMA as ZONE_DMA32...) | |
274 | ||
275 | In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following. | |
276 | ZONE_NORMAL -> ZONE_DMA | |
277 | This means that a memory allocation request for GFP_KERNEL will | |
278 | get memory from ZONE_DMA only when ZONE_NORMAL is not available. | |
279 | ||
280 | In NUMA case, you can think of following 2 types of order. | |
281 | Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL | |
282 | ||
283 | (A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL | |
284 | (B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA. | |
285 | ||
286 | Type(A) offers the best locality for processes on Node(0), but ZONE_DMA | |
287 | will be used before ZONE_NORMAL exhaustion. This increases possibility of | |
288 | out-of-memory(OOM) of ZONE_DMA because ZONE_DMA is tend to be small. | |
289 | ||
290 | Type(B) cannot offer the best locality but is more robust against OOM of | |
291 | the DMA zone. | |
292 | ||
293 | Type(A) is called as "Node" order. Type (B) is "Zone" order. | |
294 | ||
295 | "Node order" orders the zonelists by node, then by zone within each node. | |
296 | Specify "[Nn]ode" for zone order | |
297 | ||
298 | "Zone Order" orders the zonelists by zone type, then by node within each | |
299 | zone. Specify "[Zz]one"for zode order. | |
300 | ||
301 | Specify "[Dd]efault" to request automatic configuration. Autoconfiguration | |
302 | will select "node" order in following case. | |
303 | (1) if the DMA zone does not exist or | |
304 | (2) if the DMA zone comprises greater than 50% of the available memory or | |
305 | (3) if any node's DMA zone comprises greater than 60% of its local memory and | |
306 | the amount of local memory is big enough. | |
307 | ||
308 | Otherwise, "zone" order will be selected. Default order is recommended unless | |
309 | this is causing problems for your system/application. | |
d5dbac87 NA |
310 | |
311 | ============================================================== | |
312 | ||
313 | nr_hugepages | |
314 | ||
315 | Change the minimum size of the hugepage pool. | |
316 | ||
317 | See Documentation/vm/hugetlbpage.txt | |
318 | ||
319 | ============================================================== | |
320 | ||
321 | nr_overcommit_hugepages | |
322 | ||
323 | Change the maximum size of the hugepage pool. The maximum is | |
324 | nr_hugepages + nr_overcommit_hugepages. | |
325 | ||
326 | See Documentation/vm/hugetlbpage.txt |