diff options
Diffstat (limited to 'Documentation/sysctl/vm.txt')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 38 |
1 files changed, 30 insertions, 8 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 44518c02394..4bca2a3d917 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -127,17 +127,39 @@ 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 + +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. -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. +Allowing regular swap effectively restricts allocations to the local +node unless explicitly overridden by memory policies or cpuset +configurations. -It may be beneficial to switch this on if one wants to do zone -reclaim regardless of the numa distances in the system. ================================================================ zone_reclaim_interval: |