[PATCH] zone_reclaim: configurable off node allocation period.

Currently the zone_reclaim code has a fixed window of 30 seconds of off node
allocations should a local zone have no unused pagecache pages left.  Reclaim
will be attempted again after this timeout period to avoid repeated useless
scans for memory.  This is also useful to established sufficiently large off
node allocation chunks to relieve the local node.

It may be beneficial to adjust that time period for some special situations.
For example if memory use was exceeding node capacity one may want to give up
for longer periods of time.  If memory spikes intermittendly then one may want
to shorten the time period to reduce the number of off node allocations.

This patch allows just that....

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 391dd64363e7..44518c023949 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
 
 ==============================================================
 
@@ -137,4 +138,15 @@ of memory should be used for caching files from disk.
 
 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:
+
+The time allowed for off node allocations after zone reclaim
+has failed to reclaim enough pages to allow a local allocation.
+
+Time is set in seconds and set by default to 30 seconds.
+
+Reduce the interval if undesired off node allocations occur. However, too
+frequent scans will have a negative impact onoff node allocation performance.