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Diffstat (limited to 'Documentation/sysctl/vm.txt')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 56 |
1 files changed, 48 insertions, 8 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 391dd64363e..a46c10fcddf 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -28,6 +28,7 @@ Currently, these files are in /proc/sys/vm: - block_dump - drop-caches - zone_reclaim_mode +- zone_reclaim_interval ============================================================== @@ -126,15 +127,54 @@ the high water marks for each per cpu page list. zone_reclaim_mode: -This is set during bootup to 1 if it is determined that pages from -remote zones will cause a significant performance reduction. The +Zone_reclaim_mode allows to set more or less agressive 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 +8 = Also do a global slab reclaim pass + +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 going off node. +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. + +It may be advisable to allow slab reclaim if the system makes heavy +use of files and builds up large slab caches. However, the slab +shrink operation is global, may take a long time and free slabs +in all nodes of the system. + +================================================================ + +zone_reclaim_interval: + +The time allowed for off node allocations after zone reclaim +has failed to reclaim enough pages to allow a local allocation. -The user can override this setting. 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. +Time is set in seconds and set by default to 30 seconds. -It may be beneficial to switch this on if one wants to do zone -reclaim regardless of the numa distances in the system. +Reduce the interval if undesired off node allocations occur. However, too +frequent scans will have a negative impact onoff node allocation performance. |