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authorMel Gorman <mgorman@techsingularity.net>2021-06-29 05:42:24 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 20:53:55 +0300
commit74f44822097c665041010994502b5971d6cd9f04 (patch)
tree308a8f1e7f8087b1f39ea0bc87813ae7c5519186 /Documentation/admin-guide
parentc49c2c47dab6b8d45022b3fabf0642a0e62e3109 (diff)
downloadlinux-74f44822097c665041010994502b5971d6cd9f04.tar.xz
mm/page_alloc: introduce vm.percpu_pagelist_high_fraction
This introduces a new sysctl vm.percpu_pagelist_high_fraction. It is similar to the old vm.percpu_pagelist_fraction. The old sysctl increased both pcp->batch and pcp->high with the higher pcp->high potentially reducing zone->lock contention. However, the higher pcp->batch value also potentially increased allocation latency while the PCP was refilled. This sysctl only adjusts pcp->high so that zone->lock contention is potentially reduced but allocation latency during a PCP refill remains the same. # grep -E "high:|batch" /proc/zoneinfo | tail -2 high: 649 batch: 63 # sysctl vm.percpu_pagelist_high_fraction=8 # grep -E "high:|batch" /proc/zoneinfo | tail -2 high: 35071 batch: 63 # sysctl vm.percpu_pagelist_high_fraction=64 high: 4383 batch: 63 # sysctl vm.percpu_pagelist_high_fraction=0 high: 649 batch: 63 [mgorman@techsingularity.net: fix documentation] Link: https://lkml.kernel.org/r/20210528151010.GQ30378@techsingularity.net Link: https://lkml.kernel.org/r/20210525080119.5455-7-mgorman@techsingularity.net Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hillf Danton <hdanton@sina.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/sysctl/vm.rst21
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 2fcafccb53a8..2da25735a629 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -64,6 +64,7 @@ Currently, these files are in /proc/sys/vm:
- overcommit_ratio
- page-cluster
- panic_on_oom
+- percpu_pagelist_high_fraction
- stat_interval
- stat_refresh
- numa_stat
@@ -789,6 +790,26 @@ panic_on_oom=2+kdump gives you very strong tool to investigate
why oom happens. You can get snapshot.
+percpu_pagelist_high_fraction
+=============================
+
+This is the fraction of pages in each zone that are can be stored to
+per-cpu page lists. It is an upper boundary that is divided depending
+on the number of online CPUs. The min value for this is 8 which means
+that we do not allow more than 1/8th of pages in each zone to be stored
+on per-cpu page lists. This entry only changes the value of hot per-cpu
+page lists. A user can specify a number like 100 to allocate 1/100th of
+each zone between per-cpu lists.
+
+The batch value of each per-cpu page list remains the same regardless of
+the value of the high fraction so allocation latencies are unaffected.
+
+The initial value is zero. Kernel uses this value to set the high pcp->high
+mark based on the low watermark for the zone and the number of local
+online CPUs. If the user writes '0' to this sysctl, it will revert to
+this default behavior.
+
+
stat_interval
=============