vmscan: count the number of times zone_reclaim() scans and fails
authorMel Gorman <mel@csn.ul.ie>
Tue, 16 Jun 2009 22:33:23 +0000 (15:33 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 17 Jun 2009 02:47:46 +0000 (19:47 -0700)
On NUMA machines, the administrator can configure zone_reclaim_mode that
is a more targetted form of direct reclaim.  On machines with large NUMA
distances for example, a zone_reclaim_mode defaults to 1 meaning that
clean unmapped pages will be reclaimed if the zone watermarks are not
being met.

There is a heuristic that determines if the scan is worthwhile but it is
possible that the heuristic will fail and the CPU gets tied up scanning
uselessly.  Detecting the situation requires some guesswork and
experimentation so this patch adds a counter "zreclaim_failed" to
/proc/vmstat.  If during high CPU utilisation this counter is increasing
rapidly, then the resolution to the problem may be to set
/proc/sys/vm/zone_reclaim_mode to 0.

[akpm@linux-foundation.org: name things consistently]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

index ff4696c6dce3f84eebcf109cd6a6d721e02097d6..81a97cf8f0a0845a102a1200dc316aa32a47920f 100644 (file)
@@ -36,6 +36,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
index 16c82a868e2b293c2533335f5881412ffee404d8..3018ad75613375c409f6a99d2e2a105604833c81 100644 (file)
@@ -2519,6 +2519,9 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
        ret = __zone_reclaim(zone, gfp_mask, order);
        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
+       if (!ret)
+               count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
        return ret;
index 1e3aa8139f22a27f72e688c8953cba04b7a9cded..138bed53706ed325e2d4aac3ae0065cffccdda47 100644 (file)
@@ -673,6 +673,9 @@ static const char * const vmstat_text[] = {
+       "zone_reclaim_failed",