diff options
Diffstat (limited to 'Documentation/sysctl/vm.txt')
| -rw-r--r-- | Documentation/sysctl/vm.txt | 45 |
1 files changed, 29 insertions, 16 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 36ecc26c7433..1fbd4eb7b64a 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -119,8 +119,11 @@ other appears as 0 when read. dirty_background_ratio -Contains, as a percentage of total system memory, the number of pages at which -the background kernel flusher threads will start writing out dirty data. +Contains, as a percentage of total available memory that contains free pages +and reclaimable pages, the number of pages at which the background kernel +flusher threads will start writing out dirty data. + +The total avaiable memory is not equal to total system memory. ============================================================== @@ -151,9 +154,11 @@ interval will be written out next time a flusher thread wakes up. dirty_ratio -Contains, as a percentage of total system memory, the number of pages at which -a process which is generating disk writes will itself start writing out dirty -data. +Contains, as a percentage of total available memory that contains free pages +and reclaimable pages, the number of pages at which a process which is +generating disk writes will itself start writing out dirty data. + +The total avaiable memory is not equal to total system memory. ============================================================== @@ -200,17 +205,25 @@ fragmentation index is <= extfrag_threshold. The default value is 500. hugepages_treat_as_movable -This parameter is only useful when kernelcore= is specified at boot time to -create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages -are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero -value written to hugepages_treat_as_movable allows huge pages to be allocated -from ZONE_MOVABLE. - -Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge -pages pool can easily grow or shrink within. Assuming that applications are -not running that mlock() a lot of memory, it is likely the huge pages pool -can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value -into nr_hugepages and triggering page reclaim. +This parameter controls whether we can allocate hugepages from ZONE_MOVABLE +or not. If set to non-zero, hugepages can be allocated from ZONE_MOVABLE. +ZONE_MOVABLE is created when kernel boot parameter kernelcore= is specified, +so this parameter has no effect if used without kernelcore=. + +Hugepage migration is now available in some situations which depend on the +architecture and/or the hugepage size. If a hugepage supports migration, +allocation from ZONE_MOVABLE is always enabled for the hugepage regardless +of the value of this parameter. +IOW, this parameter affects only non-migratable hugepages. + +Assuming that hugepages are not migratable in your system, one usecase of +this parameter is that users can make hugepage pool more extensible by +enabling the allocation from ZONE_MOVABLE. This is because on ZONE_MOVABLE +page reclaim/migration/compaction work more and you can get contiguous +memory more likely. Note that using ZONE_MOVABLE for non-migratable +hugepages can do harm to other features like memory hotremove (because +memory hotremove expects that memory blocks on ZONE_MOVABLE are always +removable,) so it's a trade-off responsible for the users. ============================================================== |