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141 lines
4.8 KiB
Plaintext
141 lines
4.8 KiB
Plaintext
Documentation for /proc/sys/vm/* kernel version 2.2.10
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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For general info and legal blurb, please look in README.
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==============================================================
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This file contains the documentation for the sysctl files in
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/proc/sys/vm and is valid for Linux kernel version 2.2.
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The files in this directory can be used to tune the operation
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of the virtual memory (VM) subsystem of the Linux kernel and
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the writeout of dirty data to disk.
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Default values and initialization routines for most of these
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files can be found in mm/swap.c.
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Currently, these files are in /proc/sys/vm:
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- overcommit_memory
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- page-cluster
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- dirty_ratio
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- dirty_background_ratio
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- dirty_expire_centisecs
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- dirty_writeback_centisecs
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- max_map_count
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- min_free_kbytes
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- laptop_mode
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- block_dump
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- drop-caches
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- zone_reclaim_mode
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==============================================================
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dirty_ratio, dirty_background_ratio, dirty_expire_centisecs,
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dirty_writeback_centisecs, vfs_cache_pressure, laptop_mode,
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block_dump, swap_token_timeout, drop-caches:
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See Documentation/filesystems/proc.txt
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==============================================================
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overcommit_memory:
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This value contains a flag that enables memory overcommitment.
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When this flag is 0, the kernel attempts to estimate the amount
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of free memory left when userspace requests more memory.
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When this flag is 1, the kernel pretends there is always enough
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memory until it actually runs out.
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When this flag is 2, the kernel uses a "never overcommit"
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policy that attempts to prevent any overcommit of memory.
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This feature can be very useful because there are a lot of
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programs that malloc() huge amounts of memory "just-in-case"
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and don't use much of it.
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The default value is 0.
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See Documentation/vm/overcommit-accounting and
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security/commoncap.c::cap_vm_enough_memory() for more information.
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==============================================================
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overcommit_ratio:
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When overcommit_memory is set to 2, the committed address
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space is not permitted to exceed swap plus this percentage
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of physical RAM. See above.
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==============================================================
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page-cluster:
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The Linux VM subsystem avoids excessive disk seeks by reading
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multiple pages on a page fault. The number of pages it reads
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is dependent on the amount of memory in your machine.
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The number of pages the kernel reads in at once is equal to
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2 ^ page-cluster. Values above 2 ^ 5 don't make much sense
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for swap because we only cluster swap data in 32-page groups.
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==============================================================
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max_map_count:
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This file contains the maximum number of memory map areas a process
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may have. Memory map areas are used as a side-effect of calling
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malloc, directly by mmap and mprotect, and also when loading shared
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libraries.
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While most applications need less than a thousand maps, certain
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programs, particularly malloc debuggers, may consume lots of them,
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e.g., up to one or two maps per allocation.
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The default value is 65536.
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==============================================================
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min_free_kbytes:
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This is used to force the Linux VM to keep a minimum number
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of kilobytes free. The VM uses this number to compute a pages_min
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value for each lowmem zone in the system. Each lowmem zone gets
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a number of reserved free pages based proportionally on its size.
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==============================================================
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percpu_pagelist_fraction
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This is the fraction of pages at most (high mark pcp->high) in each zone that
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are allocated for each per cpu page list. The min value for this is 8. It
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means that we don't allow more than 1/8th of pages in each zone to be
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allocated in any single per_cpu_pagelist. This entry only changes the value
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of hot per cpu pagelists. User can specify a number like 100 to allocate
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1/100th of each zone to each per cpu page list.
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The batch value of each per cpu pagelist is also updated as a result. It is
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set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
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The initial value is zero. Kernel does not use this value at boot time to set
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the high water marks for each per cpu page list.
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===============================================================
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zone_reclaim_mode:
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This is set during bootup to 1 if it is determined that pages from
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remote zones will cause a significant performance reduction. The
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page allocator will then reclaim easily reusable pages (those page
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cache pages that are currently not used) before going off node.
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The user can override this setting. It may be beneficial to switch
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off zone reclaim if the system is used for a file server and all
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of memory should be used for caching files from disk.
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It may be beneficial to switch this on if one wants to do zone
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reclaim regardless of the numa distances in the system.
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