Commit 3da367c3 authored Oct 31, 2011 by Shaohua Li Committed by Linus Torvalds Oct 31, 2011

vmscan: add block plug for page reclaim



per-task block plug can reduce block queue lock contention and increase
request merge.  Currently page reclaim doesn't support it.  I originally
thought page reclaim doesn't need it, because kswapd thread count is
limited and file cache write is done at flusher mostly.

When I test a workload with heavy swap in a 4-node machine, each CPU is
doing direct page reclaim and swap.  This causes block queue lock
contention.  In my test, without below patch, the CPU utilization is about
2% ~ 7%.  With the patch, the CPU utilization is about 1% ~ 3%.  Disk
throughput isn't changed.  This should improve normal kswapd write and
file cache write too (increase request merge for example), but might not
be so obvious as I explain above.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3fa36acb

mm/vmscan.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -2005,12 +2005,14 @@ static void shrink_zone(int priority, struct zone *zone,
		enum lru_list l;
		unsigned long nr_reclaimed, nr_scanned;
		unsigned long nr_to_reclaim = sc->nr_to_reclaim;
		struct blk_plug plug;

		restart:
		nr_reclaimed = 0;
		nr_scanned = sc->nr_scanned;
		get_scan_count(zone, sc, nr, priority);

		blk_start_plug(&plug);
		while (nr[LRU_INACTIVE_ANON] \|\| nr[LRU_ACTIVE_FILE] \|\|
		nr[LRU_INACTIVE_FILE]) {
		for_each_evictable_lru(l) {
		@@ -2034,6 +2036,7 @@ restart:
		if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
		break;
		}
		blk_finish_plug(&plug);
		sc->nr_reclaimed += nr_reclaimed;

		/*

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