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

commit 24cf72518c79cdcda486ed26074ff8151291cf65 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 524cd1b28ecb0ff62a9d3620f9d21d48f8c1e32e..cfdd3cae88892f7accb24354bd103ff926a34ab2 100644 (file)
--- 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_ZONE_RECLAIM_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 d51e9937ff20a49f2edf5cd19b44d33c335a307b..2500b01e7a781d6ebd93317fe9c002d4cd85fe7a 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2452,6 +2452,9 @@ 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

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 74d66dba0cbe45429f7b663c783a6f839e2ceb3f..ddb360a09efd03321ff62e30b137f8d50236c370 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -675,6 +675,9 @@ 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",