mm: move pagevec stripping to save unlock-relock

In shrink_active_list() after the deactivation loop, we strip buffer heads
from the potentially remaining pages in the pagevec.

Currently, this drops the zone's lru lock for stripping, only to reacquire
it again afterwards to update statistics.

It is not necessary to strip the pages before updating the stats, so move
the whole thing out of the protected region and save the extra locking.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: MinChan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 51f2df04d7cf4749e5d3c4669dfeb5460cdd52e2..988aef9330161d60b29bffd0a0c2edbbcf7bc99c 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1298,14 +1298,11 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
        }
        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
        pgdeactivate += pgmoved;
-       if (buffer_heads_over_limit) {
-               spin_unlock_irq(&zone->lru_lock);
-               pagevec_strip(&pvec);
-               spin_lock_irq(&zone->lru_lock);
-       }
        __count_zone_vm_events(PGREFILL, zone, pgscanned);
        __count_vm_events(PGDEACTIVATE, pgdeactivate);
        spin_unlock_irq(&zone->lru_lock);
+       if (buffer_heads_over_limit)
+               pagevec_strip(&pvec);
        if (vm_swap_full())
                pagevec_swap_free(&pvec);