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@@ -1,12 +1,13 @@
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-Documentation for /proc/sys/vm/* kernel version 2.2.10
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+Documentation for /proc/sys/vm/* kernel version 2.6.29
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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+ (c) 2008 Peter W. Morreale <pmorreale@novell.com>
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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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+/proc/sys/vm and is valid for Linux kernel version 2.6.29.
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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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@@ -16,180 +17,274 @@ 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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+
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+- block_dump
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+- dirty_background_bytes
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- dirty_background_ratio
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+- dirty_bytes
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- dirty_expire_centisecs
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+- dirty_ratio
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- dirty_writeback_centisecs
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-- highmem_is_dirtyable (only if CONFIG_HIGHMEM set)
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+- drop_caches
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+- hugepages_treat_as_movable
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+- hugetlb_shm_group
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+- laptop_mode
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+- legacy_va_layout
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+- lowmem_reserve_ratio
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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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-- min_unmapped_ratio
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- min_slab_ratio
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-- panic_on_oom
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-- oom_dump_tasks
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-- oom_kill_allocating_task
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-- mmap_min_address
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-- numa_zonelist_order
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+- min_unmapped_ratio
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+- mmap_min_addr
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- nr_hugepages
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- nr_overcommit_hugepages
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-- nr_trim_pages (only if CONFIG_MMU=n)
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+- nr_pdflush_threads
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+- nr_trim_pages (only if CONFIG_MMU=n)
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+- numa_zonelist_order
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+- oom_dump_tasks
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+- oom_kill_allocating_task
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+- overcommit_memory
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+- overcommit_ratio
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+- page-cluster
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+- panic_on_oom
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+- percpu_pagelist_fraction
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+- stat_interval
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+- swappiness
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+- vfs_cache_pressure
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+- zone_reclaim_mode
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+
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==============================================================
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-dirty_bytes, dirty_ratio, dirty_background_bytes,
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-dirty_background_ratio, dirty_expire_centisecs,
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-dirty_writeback_centisecs, highmem_is_dirtyable,
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-vfs_cache_pressure, laptop_mode, block_dump, swap_token_timeout,
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-drop-caches, hugepages_treat_as_movable:
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+block_dump
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-See Documentation/filesystems/proc.txt
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+block_dump enables block I/O debugging when set to a nonzero value. More
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+information on block I/O debugging is in Documentation/laptops/laptop-mode.txt.
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==============================================================
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-overcommit_memory:
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+dirty_background_bytes
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-This value contains a flag that enables memory overcommitment.
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+Contains the amount of dirty memory at which the pdflush background writeback
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+daemon will start writeback.
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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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+If dirty_background_bytes is written, dirty_background_ratio becomes a function
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+of its value (dirty_background_bytes / the amount of dirtyable system 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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+==============================================================
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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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+dirty_background_ratio
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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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+Contains, as a percentage of total system memory, the number of pages at which
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+the pdflush background writeback daemon will start writing out dirty data.
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-The default value is 0.
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+==============================================================
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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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+dirty_bytes
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+
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+Contains the amount of dirty memory at which a process generating disk writes
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+will itself start writeback.
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+
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+If dirty_bytes is written, dirty_ratio becomes a function of its value
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+(dirty_bytes / the amount of dirtyable system memory).
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==============================================================
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-overcommit_ratio:
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+dirty_expire_centisecs
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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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+This tunable is used to define when dirty data is old enough to be eligible
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+for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
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+Data which has been dirty in-memory for longer than this interval will be
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+written out next time a pdflush daemon wakes up.
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+
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+==============================================================
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+
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+dirty_ratio
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+
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+Contains, as a percentage of total system memory, the number of pages at which
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+a process which is generating disk writes will itself start writing out dirty
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+data.
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==============================================================
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-page-cluster:
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+dirty_writeback_centisecs
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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 pdflush writeback daemons will periodically wake up and write `old' data
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+out to disk. This tunable expresses the interval between those wakeups, in
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+100'ths of a second.
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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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+Setting this to zero disables periodic writeback altogether.
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==============================================================
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-max_map_count:
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+drop_caches
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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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+Writing to this will cause the kernel to drop clean caches, dentries and
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+inodes from memory, causing that memory to become free.
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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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+To free pagecache:
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+ echo 1 > /proc/sys/vm/drop_caches
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+To free dentries and inodes:
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+ echo 2 > /proc/sys/vm/drop_caches
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+To free pagecache, dentries and inodes:
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+ echo 3 > /proc/sys/vm/drop_caches
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-The default value is 65536.
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+As this is a non-destructive operation and dirty objects are not freeable, the
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+user should run `sync' first.
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==============================================================
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-min_free_kbytes:
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+hugepages_treat_as_movable
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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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+This parameter is only useful when kernelcore= is specified at boot time to
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+create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
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+are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
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+value written to hugepages_treat_as_movable allows huge pages to be allocated
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+from ZONE_MOVABLE.
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-Some minimal amount of memory is needed to satisfy PF_MEMALLOC
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-allocations; if you set this to lower than 1024KB, your system will
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-become subtly broken, and prone to deadlock under high loads.
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-
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-Setting this too high will OOM your machine instantly.
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+Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
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+pages pool can easily grow or shrink within. Assuming that applications are
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+not running that mlock() a lot of memory, it is likely the huge pages pool
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+can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
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+into nr_hugepages and triggering page reclaim.
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==============================================================
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-percpu_pagelist_fraction
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+hugetlb_shm_group
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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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+hugetlb_shm_group contains group id that is allowed to create SysV
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+shared memory segment using hugetlb page.
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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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+==============================================================
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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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+laptop_mode
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-===============================================================
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+laptop_mode is a knob that controls "laptop mode". All the things that are
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+controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt.
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-zone_reclaim_mode:
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+==============================================================
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-Zone_reclaim_mode allows someone to set more or less aggressive approaches to
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-reclaim memory when a zone runs out of memory. If it is set to zero then no
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-zone reclaim occurs. Allocations will be satisfied from other zones / nodes
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-in the system.
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+legacy_va_layout
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-This is value ORed together of
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+If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
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+will use the legacy (2.4) layout for all processes.
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-1 = Zone reclaim on
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-2 = Zone reclaim writes dirty pages out
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-4 = Zone reclaim swaps pages
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+==============================================================
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-zone_reclaim_mode is set during bootup to 1 if it is determined that pages
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-from remote zones will cause a measurable 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 allocating off node pages.
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+lowmem_reserve_ratio
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+
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+For some specialised workloads on highmem machines it is dangerous for
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+the kernel to allow process memory to be allocated from the "lowmem"
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+zone. This is because that memory could then be pinned via the mlock()
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+system call, or by unavailability of swapspace.
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+
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+And on large highmem machines this lack of reclaimable lowmem memory
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+can be fatal.
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+
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+So the Linux page allocator has a mechanism which prevents allocations
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+which _could_ use highmem from using too much lowmem. This means that
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+a certain amount of lowmem is defended from the possibility of being
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+captured into pinned user memory.
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+
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+(The same argument applies to the old 16 megabyte ISA DMA region. This
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+mechanism will also defend that region from allocations which could use
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+highmem or lowmem).
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+
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+The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
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+in defending these lower zones.
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+
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+If you have a machine which uses highmem or ISA DMA and your
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+applications are using mlock(), or if you are running with no swap then
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+you probably should change the lowmem_reserve_ratio setting.
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+
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+The lowmem_reserve_ratio is an array. You can see them by reading this file.
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+-
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+% cat /proc/sys/vm/lowmem_reserve_ratio
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+256 256 32
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+-
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+Note: # of this elements is one fewer than number of zones. Because the highest
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+ zone's value is not necessary for following calculation.
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+
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+But, these values are not used directly. The kernel calculates # of protection
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+pages for each zones from them. These are shown as array of protection pages
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+in /proc/zoneinfo like followings. (This is an example of x86-64 box).
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+Each zone has an array of protection pages like this.
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+
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+-
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+Node 0, zone DMA
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+ pages free 1355
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+ min 3
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+ low 3
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+ high 4
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+ :
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+ :
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+ numa_other 0
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+ protection: (0, 2004, 2004, 2004)
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+ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+ pagesets
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+ cpu: 0 pcp: 0
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+ :
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+-
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+These protections are added to score to judge whether this zone should be used
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+for page allocation or should be reclaimed.
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+
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+In this example, if normal pages (index=2) are required to this DMA zone and
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+pages_high is used for watermark, the kernel judges this zone should not be
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+used because pages_free(1355) is smaller than watermark + protection[2]
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+(4 + 2004 = 2008). If this protection value is 0, this zone would be used for
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+normal page requirement. If requirement is DMA zone(index=0), protection[0]
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+(=0) is used.
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+
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+zone[i]'s protection[j] is calculated by following expression.
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+
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+(i < j):
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+ zone[i]->protection[j]
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+ = (total sums of present_pages from zone[i+1] to zone[j] on the node)
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+ / lowmem_reserve_ratio[i];
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+(i = j):
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+ (should not be protected. = 0;
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+(i > j):
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+ (not necessary, but looks 0)
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+
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+The default values of lowmem_reserve_ratio[i] are
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+ 256 (if zone[i] means DMA or DMA32 zone)
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+ 32 (others).
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+As above expression, they are reciprocal number of ratio.
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+256 means 1/256. # of protection pages becomes about "0.39%" of total present
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+pages of higher zones on the node.
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+
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+If you would like to protect more pages, smaller values are effective.
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+The minimum value is 1 (1/1 -> 100%).
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-It may be beneficial to switch off zone reclaim if the system is
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-used for a file server and all of memory should be used for caching files
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-from disk. In that case the caching effect is more important than
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-data locality.
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+==============================================================
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-Allowing zone reclaim to write out pages stops processes that are
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-writing large amounts of data from dirtying pages on other nodes. Zone
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-reclaim will write out dirty pages if a zone fills up and so effectively
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-throttle the process. This may decrease the performance of a single process
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-since it cannot use all of system memory to buffer the outgoing writes
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-anymore but it preserve the memory on other nodes so that the performance
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-of other processes running on other nodes will not be affected.
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+max_map_count:
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-Allowing regular swap effectively restricts allocations to the local
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-node unless explicitly overridden by memory policies or cpuset
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-configurations.
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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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-=============================================================
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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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-min_unmapped_ratio:
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+The default value is 65536.
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-This is available only on NUMA kernels.
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+==============================================================
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-A percentage of the total pages in each zone. Zone reclaim will only
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-occur if more than this percentage of pages are file backed and unmapped.
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-This is to insure that a minimal amount of local pages is still available for
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-file I/O even if the node is overallocated.
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+min_free_kbytes:
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-The default is 1 percent.
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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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+Some minimal amount of memory is needed to satisfy PF_MEMALLOC
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+allocations; if you set this to lower than 1024KB, your system will
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+become subtly broken, and prone to deadlock under high loads.
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+
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+Setting this too high will OOM your machine instantly.
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=============================================================
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@@ -211,82 +306,73 @@ and may not be fast.
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=============================================================
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-panic_on_oom
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+min_unmapped_ratio:
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|
|
-This enables or disables panic on out-of-memory feature.
|
|
|
+This is available only on NUMA kernels.
|
|
|
|
|
|
-If this is set to 0, the kernel will kill some rogue process,
|
|
|
-called oom_killer. Usually, oom_killer can kill rogue processes and
|
|
|
-system will survive.
|
|
|
+A percentage of the total pages in each zone. Zone reclaim will only
|
|
|
+occur if more than this percentage of pages are file backed and unmapped.
|
|
|
+This is to insure that a minimal amount of local pages is still available for
|
|
|
+file I/O even if the node is overallocated.
|
|
|
|
|
|
-If this is set to 1, the kernel panics when out-of-memory happens.
|
|
|
-However, if a process limits using nodes by mempolicy/cpusets,
|
|
|
-and those nodes become memory exhaustion status, one process
|
|
|
-may be killed by oom-killer. No panic occurs in this case.
|
|
|
-Because other nodes' memory may be free. This means system total status
|
|
|
-may be not fatal yet.
|
|
|
+The default is 1 percent.
|
|
|
|
|
|
-If this is set to 2, the kernel panics compulsorily even on the
|
|
|
-above-mentioned.
|
|
|
+==============================================================
|
|
|
|
|
|
-The default value is 0.
|
|
|
-1 and 2 are for failover of clustering. Please select either
|
|
|
-according to your policy of failover.
|
|
|
+mmap_min_addr
|
|
|
|
|
|
-=============================================================
|
|
|
+This file indicates the amount of address space which a user process will
|
|
|
+be restricted from mmaping. Since kernel null dereference bugs could
|
|
|
+accidentally operate based on the information in the first couple of pages
|
|
|
+of memory userspace processes should not be allowed to write to them. By
|
|
|
+default this value is set to 0 and no protections will be enforced by the
|
|
|
+security module. Setting this value to something like 64k will allow the
|
|
|
+vast majority of applications to work correctly and provide defense in depth
|
|
|
+against future potential kernel bugs.
|
|
|
|
|
|
-oom_dump_tasks
|
|
|
+==============================================================
|
|
|
|
|
|
-Enables a system-wide task dump (excluding kernel threads) to be
|
|
|
-produced when the kernel performs an OOM-killing and includes such
|
|
|
-information as pid, uid, tgid, vm size, rss, cpu, oom_adj score, and
|
|
|
-name. This is helpful to determine why the OOM killer was invoked
|
|
|
-and to identify the rogue task that caused it.
|
|
|
+nr_hugepages
|
|
|
|
|
|
-If this is set to zero, this information is suppressed. On very
|
|
|
-large systems with thousands of tasks it may not be feasible to dump
|
|
|
-the memory state information for each one. Such systems should not
|
|
|
-be forced to incur a performance penalty in OOM conditions when the
|
|
|
-information may not be desired.
|
|
|
+Change the minimum size of the hugepage pool.
|
|
|
|
|
|
-If this is set to non-zero, this information is shown whenever the
|
|
|
-OOM killer actually kills a memory-hogging task.
|
|
|
+See Documentation/vm/hugetlbpage.txt
|
|
|
|
|
|
-The default value is 0.
|
|
|
+==============================================================
|
|
|
|
|
|
-=============================================================
|
|
|
+nr_overcommit_hugepages
|
|
|
|
|
|
-oom_kill_allocating_task
|
|
|
+Change the maximum size of the hugepage pool. The maximum is
|
|
|
+nr_hugepages + nr_overcommit_hugepages.
|
|
|
|
|
|
-This enables or disables killing the OOM-triggering task in
|
|
|
-out-of-memory situations.
|
|
|
+See Documentation/vm/hugetlbpage.txt
|
|
|
|
|
|
-If this is set to zero, the OOM killer will scan through the entire
|
|
|
-tasklist and select a task based on heuristics to kill. This normally
|
|
|
-selects a rogue memory-hogging task that frees up a large amount of
|
|
|
-memory when killed.
|
|
|
+==============================================================
|
|
|
|
|
|
-If this is set to non-zero, the OOM killer simply kills the task that
|
|
|
-triggered the out-of-memory condition. This avoids the expensive
|
|
|
-tasklist scan.
|
|
|
+nr_pdflush_threads
|
|
|
|
|
|
-If panic_on_oom is selected, it takes precedence over whatever value
|
|
|
-is used in oom_kill_allocating_task.
|
|
|
+The current number of pdflush threads. This value is read-only.
|
|
|
+The value changes according to the number of dirty pages in the system.
|
|
|
|
|
|
-The default value is 0.
|
|
|
+When neccessary, additional pdflush threads are created, one per second, up to
|
|
|
+nr_pdflush_threads_max.
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
-mmap_min_addr
|
|
|
+nr_trim_pages
|
|
|
|
|
|
-This file indicates the amount of address space which a user process will
|
|
|
-be restricted from mmaping. Since kernel null dereference bugs could
|
|
|
-accidentally operate based on the information in the first couple of pages
|
|
|
-of memory userspace processes should not be allowed to write to them. By
|
|
|
-default this value is set to 0 and no protections will be enforced by the
|
|
|
-security module. Setting this value to something like 64k will allow the
|
|
|
-vast majority of applications to work correctly and provide defense in depth
|
|
|
-against future potential kernel bugs.
|
|
|
+This is available only on NOMMU kernels.
|
|
|
+
|
|
|
+This value adjusts the excess page trimming behaviour of power-of-2 aligned
|
|
|
+NOMMU mmap allocations.
|
|
|
+
|
|
|
+A value of 0 disables trimming of allocations entirely, while a value of 1
|
|
|
+trims excess pages aggressively. Any value >= 1 acts as the watermark where
|
|
|
+trimming of allocations is initiated.
|
|
|
+
|
|
|
+The default value is 1.
|
|
|
+
|
|
|
+See Documentation/nommu-mmap.txt for more information.
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
@@ -335,34 +421,199 @@ this is causing problems for your system/application.
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
-nr_hugepages
|
|
|
+oom_dump_tasks
|
|
|
|
|
|
-Change the minimum size of the hugepage pool.
|
|
|
+Enables a system-wide task dump (excluding kernel threads) to be
|
|
|
+produced when the kernel performs an OOM-killing and includes such
|
|
|
+information as pid, uid, tgid, vm size, rss, cpu, oom_adj score, and
|
|
|
+name. This is helpful to determine why the OOM killer was invoked
|
|
|
+and to identify the rogue task that caused it.
|
|
|
|
|
|
-See Documentation/vm/hugetlbpage.txt
|
|
|
+If this is set to zero, this information is suppressed. On very
|
|
|
+large systems with thousands of tasks it may not be feasible to dump
|
|
|
+the memory state information for each one. Such systems should not
|
|
|
+be forced to incur a performance penalty in OOM conditions when the
|
|
|
+information may not be desired.
|
|
|
+
|
|
|
+If this is set to non-zero, this information is shown whenever the
|
|
|
+OOM killer actually kills a memory-hogging task.
|
|
|
+
|
|
|
+The default value is 0.
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
-nr_overcommit_hugepages
|
|
|
+oom_kill_allocating_task
|
|
|
|
|
|
-Change the maximum size of the hugepage pool. The maximum is
|
|
|
-nr_hugepages + nr_overcommit_hugepages.
|
|
|
+This enables or disables killing the OOM-triggering task in
|
|
|
+out-of-memory situations.
|
|
|
|
|
|
-See Documentation/vm/hugetlbpage.txt
|
|
|
+If this is set to zero, the OOM killer will scan through the entire
|
|
|
+tasklist and select a task based on heuristics to kill. This normally
|
|
|
+selects a rogue memory-hogging task that frees up a large amount of
|
|
|
+memory when killed.
|
|
|
+
|
|
|
+If this is set to non-zero, the OOM killer simply kills the task that
|
|
|
+triggered the out-of-memory condition. This avoids the expensive
|
|
|
+tasklist scan.
|
|
|
+
|
|
|
+If panic_on_oom is selected, it takes precedence over whatever value
|
|
|
+is used in oom_kill_allocating_task.
|
|
|
+
|
|
|
+The default value is 0.
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
-nr_trim_pages
|
|
|
+overcommit_memory:
|
|
|
|
|
|
-This is available only on NOMMU kernels.
|
|
|
+This value contains a flag that enables memory overcommitment.
|
|
|
|
|
|
-This value adjusts the excess page trimming behaviour of power-of-2 aligned
|
|
|
-NOMMU mmap allocations.
|
|
|
+When this flag is 0, the kernel attempts to estimate the amount
|
|
|
+of free memory left when userspace requests more memory.
|
|
|
|
|
|
-A value of 0 disables trimming of allocations entirely, while a value of 1
|
|
|
-trims excess pages aggressively. Any value >= 1 acts as the watermark where
|
|
|
-trimming of allocations is initiated.
|
|
|
+When this flag is 1, the kernel pretends there is always enough
|
|
|
+memory until it actually runs out.
|
|
|
|
|
|
-The default value is 1.
|
|
|
+When this flag is 2, the kernel uses a "never overcommit"
|
|
|
+policy that attempts to prevent any overcommit of memory.
|
|
|
|
|
|
-See Documentation/nommu-mmap.txt for more information.
|
|
|
+This feature can be very useful because there are a lot of
|
|
|
+programs that malloc() huge amounts of memory "just-in-case"
|
|
|
+and don't use much of it.
|
|
|
+
|
|
|
+The default value is 0.
|
|
|
+
|
|
|
+See Documentation/vm/overcommit-accounting and
|
|
|
+security/commoncap.c::cap_vm_enough_memory() for more information.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+overcommit_ratio:
|
|
|
+
|
|
|
+When overcommit_memory is set to 2, the committed address
|
|
|
+space is not permitted to exceed swap plus this percentage
|
|
|
+of physical RAM. See above.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+page-cluster
|
|
|
+
|
|
|
+page-cluster controls the number of pages which are written to swap in
|
|
|
+a single attempt. The swap I/O size.
|
|
|
+
|
|
|
+It is a logarithmic value - setting it to zero means "1 page", setting
|
|
|
+it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
|
|
|
+
|
|
|
+The default value is three (eight pages at a time). There may be some
|
|
|
+small benefits in tuning this to a different value if your workload is
|
|
|
+swap-intensive.
|
|
|
+
|
|
|
+=============================================================
|
|
|
+
|
|
|
+panic_on_oom
|
|
|
+
|
|
|
+This enables or disables panic on out-of-memory feature.
|
|
|
+
|
|
|
+If this is set to 0, the kernel will kill some rogue process,
|
|
|
+called oom_killer. Usually, oom_killer can kill rogue processes and
|
|
|
+system will survive.
|
|
|
+
|
|
|
+If this is set to 1, the kernel panics when out-of-memory happens.
|
|
|
+However, if a process limits using nodes by mempolicy/cpusets,
|
|
|
+and those nodes become memory exhaustion status, one process
|
|
|
+may be killed by oom-killer. No panic occurs in this case.
|
|
|
+Because other nodes' memory may be free. This means system total status
|
|
|
+may be not fatal yet.
|
|
|
+
|
|
|
+If this is set to 2, the kernel panics compulsorily even on the
|
|
|
+above-mentioned.
|
|
|
+
|
|
|
+The default value is 0.
|
|
|
+1 and 2 are for failover of clustering. Please select either
|
|
|
+according to your policy of failover.
|
|
|
+
|
|
|
+=============================================================
|
|
|
+
|
|
|
+percpu_pagelist_fraction
|
|
|
+
|
|
|
+This is the fraction of pages at most (high mark pcp->high) in each zone that
|
|
|
+are allocated for each per cpu page list. The min value for this is 8. It
|
|
|
+means that we don't allow more than 1/8th of pages in each zone to be
|
|
|
+allocated in any single per_cpu_pagelist. This entry only changes the value
|
|
|
+of hot per cpu pagelists. User can specify a number like 100 to allocate
|
|
|
+1/100th of each zone to each per cpu page list.
|
|
|
+
|
|
|
+The batch value of each per cpu pagelist is also updated as a result. It is
|
|
|
+set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8)
|
|
|
+
|
|
|
+The initial value is zero. Kernel does not use this value at boot time to set
|
|
|
+the high water marks for each per cpu page list.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+stat_interval
|
|
|
+
|
|
|
+The time interval between which vm statistics are updated. The default
|
|
|
+is 1 second.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+swappiness
|
|
|
+
|
|
|
+This control is used to define how aggressive the kernel will swap
|
|
|
+memory pages. Higher values will increase agressiveness, lower values
|
|
|
+descrease the amount of swap.
|
|
|
+
|
|
|
+The default value is 60.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+vfs_cache_pressure
|
|
|
+------------------
|
|
|
+
|
|
|
+Controls the tendency of the kernel to reclaim the memory which is used for
|
|
|
+caching of directory and inode objects.
|
|
|
+
|
|
|
+At the default value of vfs_cache_pressure=100 the kernel will attempt to
|
|
|
+reclaim dentries and inodes at a "fair" rate with respect to pagecache and
|
|
|
+swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
|
|
|
+to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
|
|
|
+causes the kernel to prefer to reclaim dentries and inodes.
|
|
|
+
|
|
|
+==============================================================
|
|
|
+
|
|
|
+zone_reclaim_mode:
|
|
|
+
|
|
|
+Zone_reclaim_mode allows someone to set more or less aggressive approaches to
|
|
|
+reclaim memory when a zone runs out of memory. If it is set to zero then no
|
|
|
+zone reclaim occurs. Allocations will be satisfied from other zones / nodes
|
|
|
+in the system.
|
|
|
+
|
|
|
+This is value ORed together of
|
|
|
+
|
|
|
+1 = Zone reclaim on
|
|
|
+2 = Zone reclaim writes dirty pages out
|
|
|
+4 = Zone reclaim swaps pages
|
|
|
+
|
|
|
+zone_reclaim_mode is set during bootup to 1 if it is determined that pages
|
|
|
+from remote zones will cause a measurable performance reduction. The
|
|
|
+page allocator will then reclaim easily reusable pages (those page
|
|
|
+cache pages that are currently not used) before allocating off node pages.
|
|
|
+
|
|
|
+It may be beneficial to switch off zone reclaim if the system is
|
|
|
+used for a file server and all of memory should be used for caching files
|
|
|
+from disk. In that case the caching effect is more important than
|
|
|
+data locality.
|
|
|
+
|
|
|
+Allowing zone reclaim to write out pages stops processes that are
|
|
|
+writing large amounts of data from dirtying pages on other nodes. Zone
|
|
|
+reclaim will write out dirty pages if a zone fills up and so effectively
|
|
|
+throttle the process. This may decrease the performance of a single process
|
|
|
+since it cannot use all of system memory to buffer the outgoing writes
|
|
|
+anymore but it preserve the memory on other nodes so that the performance
|
|
|
+of other processes running on other nodes will not be affected.
|
|
|
+
|
|
|
+Allowing regular swap effectively restricts allocations to the local
|
|
|
+node unless explicitly overridden by memory policies or cpuset
|
|
|
+configurations.
|
|
|
+
|
|
|
+============ End of Document =================================
|
Ingo Molnar