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vmscan: count the number of times zone_reclaim() scans and fails 

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>
This commit is contained in:
Mel Gorman 2009-06-16 15:33:23 -07:00 committed by Linus Torvalds
parent fa5e084e43
commit 24cf72518c
3 changed files with 9 additions and 0 deletions
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3
include/linux/vmstat.h
View File

@ -36,6 +36,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
FOR_ALL_ZONES(PGSTEAL),
FOR_ALL_ZONES(PGSCAN_KSWAPD),
FOR_ALL_ZONES(PGSCAN_DIRECT),
#ifdef CONFIG_NUMA
PGSCAN_ZONE_RECLAIM_FAILED,
#endif
PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL,
PAGEOUTRUN, ALLOCSTALL, PGROTATED,
#ifdef CONFIG_HUGETLB_PAGE

3
mm/vmscan.c
View 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;
}
#endif

3
mm/vmstat.c
View File

@ -673,6 +673,9 @@ static const char * const vmstat_text[] = {
TEXTS_FOR_ZONES("pgscan_kswapd")
TEXTS_FOR_ZONES("pgscan_direct")
#ifdef CONFIG_NUMA
"zone_reclaim_failed",
#endif
"pginodesteal",
"slabs_scanned",
"kswapd_steal",