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authorVlastimil Babka <vbabka@suse.cz>2014-10-10 02:27:18 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-10 06:25:54 +0400
commit69b7189f12e0064237630e8c6bb64cad710bb268 (patch)
tree5d486d214c347cba828477f8597db05617515c12
parent8b44d2791f912566a7ef58c71a7f9cbd16c3eeae (diff)
downloadlinux-69b7189f12e0064237630e8c6bb64cad710bb268.tar.xz
mm, compaction: skip rechecks when lock was already held
Compaction scanners try to lock zone locks as late as possible by checking many page or pageblock properties opportunistically without lock and skipping them if not unsuitable. For pages that pass the initial checks, some properties have to be checked again safely under lock. However, if the lock was already held from a previous iteration in the initial checks, the rechecks are unnecessary. This patch therefore skips the rechecks when the lock was already held. This is now possible to do, since we don't (potentially) drop and reacquire the lock between the initial checks and the safe rechecks anymore. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Acked-by: Minchan Kim <minchan@kernel.org> Acked-by: Mel Gorman <mgorman@suse.de> Cc: Michal Nazarewicz <mina86@mina86.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Christoph Lameter <cl@linux.com> Cc: Rik van Riel <riel@redhat.com> Acked-by: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/compaction.c53
1 files changed, 31 insertions, 22 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 74770e40cfe5..5039c964f5c8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -367,22 +367,30 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
goto isolate_fail;
/*
- * The zone lock must be held to isolate freepages.
- * Unfortunately this is a very coarse lock and can be
- * heavily contended if there are parallel allocations
- * or parallel compactions. For async compaction do not
- * spin on the lock and we acquire the lock as late as
- * possible.
+ * If we already hold the lock, we can skip some rechecking.
+ * Note that if we hold the lock now, checked_pageblock was
+ * already set in some previous iteration (or strict is true),
+ * so it is correct to skip the suitable migration target
+ * recheck as well.
*/
- if (!locked)
+ if (!locked) {
+ /*
+ * The zone lock must be held to isolate freepages.
+ * Unfortunately this is a very coarse lock and can be
+ * heavily contended if there are parallel allocations
+ * or parallel compactions. For async compaction do not
+ * spin on the lock and we acquire the lock as late as
+ * possible.
+ */
locked = compact_trylock_irqsave(&cc->zone->lock,
&flags, cc);
- if (!locked)
- break;
+ if (!locked)
+ break;
- /* Recheck this is a buddy page under lock */
- if (!PageBuddy(page))
- goto isolate_fail;
+ /* Recheck this is a buddy page under lock */
+ if (!PageBuddy(page))
+ goto isolate_fail;
+ }
/* Found a free page, break it into order-0 pages */
isolated = split_free_page(page);
@@ -644,19 +652,20 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
page_count(page) > page_mapcount(page))
continue;
- /* If the lock is not held, try to take it */
- if (!locked)
+ /* If we already hold the lock, we can skip some rechecking */
+ if (!locked) {
locked = compact_trylock_irqsave(&zone->lru_lock,
&flags, cc);
- if (!locked)
- break;
+ if (!locked)
+ break;
- /* Recheck PageLRU and PageTransHuge under lock */
- if (!PageLRU(page))
- continue;
- if (PageTransHuge(page)) {
- low_pfn += (1 << compound_order(page)) - 1;
- continue;
+ /* Recheck PageLRU and PageTransHuge under lock */
+ if (!PageLRU(page))
+ continue;
+ if (PageTransHuge(page)) {
+ low_pfn += (1 << compound_order(page)) - 1;
+ continue;
+ }
}
lruvec = mem_cgroup_page_lruvec(page, zone);