forked from luck/tmp_suning_uos_patched
0ff38490c8
Currently one can enable slab reclaim by setting an explicit option in /proc/sys/vm/zone_reclaim_mode. Slab reclaim is then used as a final option if the freeing of unmapped file backed pages is not enough to free enough pages to allow a local allocation. However, that means that the slab can grow excessively and that most memory of a node may be used by slabs. We have had a case where a machine with 46GB of memory was using 40-42GB for slab. Zone reclaim was effective in dealing with pagecache pages. However, slab reclaim was only done during global reclaim (which is a bit rare on NUMA systems). This patch implements slab reclaim during zone reclaim. Zone reclaim occurs if there is a danger of an off node allocation. At that point we 1. Shrink the per node page cache if the number of pagecache pages is more than min_unmapped_ratio percent of pages in a zone. 2. Shrink the slab cache if the number of the nodes reclaimable slab pages (patch depends on earlier one that implements that counter) are more than min_slab_ratio (a new /proc/sys/vm tunable). The shrinking of the slab cache is a bit problematic since it is not node specific. So we simply calculate what point in the slab we want to reach (current per node slab use minus the number of pages that neeed to be allocated) and then repeately run the global reclaim until that is unsuccessful or we have reached the limit. I hope we will have zone based slab reclaim at some point which will make that easier. The default for the min_slab_ratio is 5% Also remove the slab option from /proc/sys/vm/zone_reclaim_mode. [akpm@osdl.org: cleanups] Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
208 lines
7.2 KiB
Plaintext
208 lines
7.2 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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- min_unmapped_ratio
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- min_slab_ratio
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- panic_on_oom
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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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Zone_reclaim_mode allows to set more or less agressive 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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This is value ORed together of
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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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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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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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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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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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=============================================================
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min_unmapped_ratio:
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This is available only on NUMA kernels.
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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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The default is 1 percent.
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=============================================================
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min_slab_ratio:
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This is available only on NUMA kernels.
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A percentage of the total pages in each zone. On Zone reclaim
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(fallback from the local zone occurs) slabs will be reclaimed if more
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than this percentage of pages in a zone are reclaimable slab pages.
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This insures that the slab growth stays under control even in NUMA
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systems that rarely perform global reclaim.
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The default is 5 percent.
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Note that slab reclaim is triggered in a per zone / node fashion.
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The process of reclaiming slab memory is currently not node specific
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and may not be fast.
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=============================================================
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panic_on_oom
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This enables or disables panic on out-of-memory feature. If this is set to 1,
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the kernel panics when out-of-memory happens. If this is set to 0, the kernel
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will kill some rogue process, called oom_killer. Usually, oom_killer can kill
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rogue processes and system will survive. If you want to panic the system
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rather than killing rogue processes, set this to 1.
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The default value is 0.
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