mm: compaction: check lock contention first before taking lock

isolate_migratepages_range will take zone->lru_lock first and check if the
lock is contented, if yes, it will release the lock.  This isn't
efficient.  If the lock is truly contented, a lock/unlock pair will
increase the lock contention.  We'd better check if the lock is contended
first.  compact_trylock_irqsave perfectly meets the requirement.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index 36ff6079ba1e06cd4556b11222eda5e0b700c703..82095800db0518e47b4e7a8ad6b72c0377f6acd3 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -349,8 +349,9 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 
        /* Time to isolate some pages for migration */
        cond_resched();
-       spin_lock_irqsave(&zone->lru_lock, flags);
-       locked = true;
+       locked = compact_trylock_irqsave(&zone->lru_lock, &flags, cc);
+       if (!locked)
+               return 0;
        for (; low_pfn < end_pfn; low_pfn++) {
                struct page *page;