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 06f8e38582512eb7be8713f5579887cdd559a813..57f7b1091511b3103e9850c893a7fe7fb7a37f3a 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 021a44a7bd20e65f363e4fa06711034325dc35d9..88804017e7d65fc38bc7566c5ff2b2902cacfb31 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 1bbbbd9776ade1962a277c4e9c6d2161a2963c97..df7a6748231d67e524e2cea0c0a663d91f5d63d2 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",