view Documentation/sysctl/vm.txt @ 524:7f8b544237bf

netfront: Allow netfront in domain 0.

This is useful if your physical network device is in a utility domain.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 3e8752eb6d9c
line source
1 Documentation for /proc/sys/vm/* kernel version 2.2.10
2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
4 For general info and legal blurb, please look in README.
6 ==============================================================
8 This file contains the documentation for the sysctl files in
9 /proc/sys/vm and is valid for Linux kernel version 2.2.
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.
15 Default values and initialization routines for most of these
16 files can be found in mm/swap.c.
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
29 - drop-caches
30 - zone_reclaim_mode
31 - min_unmapped_ratio
32 - min_slab_ratio
33 - panic_on_oom
35 ==============================================================
37 dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,
38 dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,
39 block_dump, swap_token_timeout, drop-caches:
41 See Documentation/filesystems/proc.txt
43 ==============================================================
45 overcommit_memory:
47 This value contains a flag that enables memory overcommitment.
49 When this flag is 0, the kernel attempts to estimate the amount
50 of free memory left when userspace requests more memory.
52 When this flag is 1, the kernel pretends there is always enough
53 memory until it actually runs out.
55 When this flag is 2, the kernel uses a "never overcommit"
56 policy that attempts to prevent any overcommit of memory.
58 This feature can be very useful because there are a lot of
59 programs that malloc() huge amounts of memory "just-in-case"
60 and don't use much of it.
62 The default value is 0.
64 See Documentation/vm/overcommit-accounting and
65 security/commoncap.c::cap_vm_enough_memory() for more information.
67 ==============================================================
69 overcommit_ratio:
71 When overcommit_memory is set to 2, the committed address
72 space is not permitted to exceed swap plus this percentage
73 of physical RAM. See above.
75 ==============================================================
77 page-cluster:
79 The Linux VM subsystem avoids excessive disk seeks by reading
80 multiple pages on a page fault. The number of pages it reads
81 is dependent on the amount of memory in your machine.
83 The number of pages the kernel reads in at once is equal to
84 2 ^ page-cluster. Values above 2 ^ 5 don't make much sense
85 for swap because we only cluster swap data in 32-page groups.
87 ==============================================================
89 max_map_count:
91 This file contains the maximum number of memory map areas a process
92 may have. Memory map areas are used as a side-effect of calling
93 malloc, directly by mmap and mprotect, and also when loading shared
94 libraries.
96 While most applications need less than a thousand maps, certain
97 programs, particularly malloc debuggers, may consume lots of them,
98 e.g., up to one or two maps per allocation.
100 The default value is 65536.
102 ==============================================================
104 min_free_kbytes:
106 This is used to force the Linux VM to keep a minimum number
107 of kilobytes free. The VM uses this number to compute a pages_min
108 value for each lowmem zone in the system. Each lowmem zone gets
109 a number of reserved free pages based proportionally on its size.
111 ==============================================================
113 percpu_pagelist_fraction
115 This is the fraction of pages at most (high mark pcp->high) in each zone that
116 are allocated for each per cpu page list. The min value for this is 8. It
117 means that we don't allow more than 1/8th of pages in each zone to be
118 allocated in any single per_cpu_pagelist. This entry only changes the value
119 of hot per cpu pagelists. User can specify a number like 100 to allocate
120 1/100th of each zone to each per cpu page list.
122 The batch value of each per cpu pagelist is also updated as a result. It is
123 set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
125 The initial value is zero. Kernel does not use this value at boot time to set
126 the high water marks for each per cpu page list.
128 ===============================================================
130 zone_reclaim_mode:
132 Zone_reclaim_mode allows to set more or less agressive approaches to
133 reclaim memory when a zone runs out of memory. If it is set to zero then no
134 zone reclaim occurs. Allocations will be satisfied from other zones / nodes
135 in the system.
137 This is value ORed together of
139 1 = Zone reclaim on
140 2 = Zone reclaim writes dirty pages out
141 4 = Zone reclaim swaps pages
143 zone_reclaim_mode is set during bootup to 1 if it is determined that pages
144 from remote zones will cause a measurable performance reduction. The
145 page allocator will then reclaim easily reusable pages (those page
146 cache pages that are currently not used) before allocating off node pages.
148 It may be beneficial to switch off zone reclaim if the system is
149 used for a file server and all of memory should be used for caching files
150 from disk. In that case the caching effect is more important than
151 data locality.
153 Allowing zone reclaim to write out pages stops processes that are
154 writing large amounts of data from dirtying pages on other nodes. Zone
155 reclaim will write out dirty pages if a zone fills up and so effectively
156 throttle the process. This may decrease the performance of a single process
157 since it cannot use all of system memory to buffer the outgoing writes
158 anymore but it preserve the memory on other nodes so that the performance
159 of other processes running on other nodes will not be affected.
161 Allowing regular swap effectively restricts allocations to the local
162 node unless explicitly overridden by memory policies or cpuset
163 configurations.
165 =============================================================
167 min_unmapped_ratio:
169 This is available only on NUMA kernels.
171 A percentage of the total pages in each zone. Zone reclaim will only
172 occur if more than this percentage of pages are file backed and unmapped.
173 This is to insure that a minimal amount of local pages is still available for
174 file I/O even if the node is overallocated.
176 The default is 1 percent.
178 =============================================================
180 min_slab_ratio:
182 This is available only on NUMA kernels.
184 A percentage of the total pages in each zone. On Zone reclaim
185 (fallback from the local zone occurs) slabs will be reclaimed if more
186 than this percentage of pages in a zone are reclaimable slab pages.
187 This insures that the slab growth stays under control even in NUMA
188 systems that rarely perform global reclaim.
190 The default is 5 percent.
192 Note that slab reclaim is triggered in a per zone / node fashion.
193 The process of reclaiming slab memory is currently not node specific
194 and may not be fast.
196 =============================================================
198 panic_on_oom
200 This enables or disables panic on out-of-memory feature. If this is set to 1,
201 the kernel panics when out-of-memory happens. If this is set to 0, the kernel
202 will kill some rogue process, called oom_killer. Usually, oom_killer can kill
203 rogue processes and system will survive. If you want to panic the system
204 rather than killing rogue processes, set this to 1.
206 The default value is 0.