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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>
This commit is contained in:
Shaohua Li 2011-10-31 17:07:03 -07:00 committed by Linus Torvalds
parent 3fa36acbce
commit 3da367c3e5
1 changed files with 3 additions and 0 deletions
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3
mm/vmscan.c
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@ -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;
/*