mm: account for the number of times direct reclaimers get throttled

Under significant pressure when writing back to network-backed storage,
direct reclaimers may get throttled.  This is expected to be a short-lived
event and the processes get woken up again but processes do get stalled.
This patch counts how many times such stalling occurs.  It's up to the
administrator whether to reduce these stalls by increasing
min_free_kbytes.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 06f8e38..57f7b10 100644 (file)
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -30,6 +30,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                FOR_ALL_ZONES(PGSTEAL_DIRECT),
                FOR_ALL_ZONES(PGSCAN_KSWAPD),
                FOR_ALL_ZONES(PGSCAN_DIRECT),
+               PGSCAN_DIRECT_THROTTLE,
 #ifdef CONFIG_NUMA
                PGSCAN_ZONE_RECLAIM_FAILED,
 #endif

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 021a44a..8880401 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2167,6 +2167,9 @@ static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
        if (pfmemalloc_watermark_ok(pgdat))
                return;
 
+       /* Account for the throttling */
+       count_vm_event(PGSCAN_DIRECT_THROTTLE);
+
        /*
         * If the caller cannot enter the filesystem, it's possible that it
         * is due to the caller holding an FS lock or performing a journal

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1bbbbd9..df7a674 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -745,6 +745,7 @@ const char * const vmstat_text[] = {
        TEXTS_FOR_ZONES("pgsteal_direct")
        TEXTS_FOR_ZONES("pgscan_kswapd")
        TEXTS_FOR_ZONES("pgscan_direct")
+       "pgscan_direct_throttle",
 
 #ifdef CONFIG_NUMA
        "zone_reclaim_failed",