Messages in this thread Patch in this message | | | From | Mel Gorman <> | Subject | [PATCH 3/3] Count the number of times zone_reclaim() scans and fails | Date | Thu, 11 Jun 2009 11:47:53 +0100 |
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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.
Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reviewed-by: Rik van Riel <riel@redhat.com> --- include/linux/vmstat.h | 3 +++ mm/vmscan.c | 3 +++ mm/vmstat.c | 3 +++ 3 files changed, 9 insertions(+), 0 deletions(-)
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h index ff4696c..416f748 100644 --- a/include/linux/vmstat.h +++ b/include/linux/vmstat.h @@ -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_ZONERECLAIM_FAILED, +#endif PGINODESTEAL, SLABS_SCANNED, KSWAPD_STEAL, KSWAPD_INODESTEAL, PAGEOUTRUN, ALLOCSTALL, PGROTATED, #ifdef CONFIG_HUGETLB_PAGE diff --git a/mm/vmscan.c b/mm/vmscan.c index 7b8eb3f..42c1013 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2492,6 +2492,9 @@ 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_ZONERECLAIM_FAILED); + return ret; } #endif diff --git a/mm/vmstat.c b/mm/vmstat.c index 1e3aa81..02677d1 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -673,6 +673,9 @@ static const char * const vmstat_text[] = { TEXTS_FOR_ZONES("pgscan_kswapd") TEXTS_FOR_ZONES("pgscan_direct") +#ifdef CONFIG_NUMA + "zreclaim_failed", +#endif "pginodesteal", "slabs_scanned", "kswapd_steal", -- 1.5.6.5
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