[PATCH v6 04/10] mm/mlock: optimize munlock_pagevec by relocking

[Alex Shi <alex.shi@linux.alibaba.com>]

During the pagevec locking, a new page's lruvec is may same as
previous one. Thus we could save a re-locking, and only
change lock iff lruvec is newer.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-kernel@vger.kernel.org
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/mlock.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 10d15f58b061..050f999eadb1 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -289,6 +289,7 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 {
 	int i;
 	int nr = pagevec_count(pvec);
+	int delta_munlocked = -nr;
 	struct pagevec pvec_putback;
 	struct lruvec *lruvec = NULL;
 	int pgrescued = 0;
@@ -299,20 +300,19 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 	for (i = 0; i < nr; i++) {
 		struct page *page = pvec->pages[i];
 
-		lruvec = lock_page_lruvec_irq(page);
+		lruvec = relock_page_lruvec_irq(page, lruvec);
 
 		if (TestClearPageMlocked(page)) {
 			/*
 			 * We already have pin from follow_page_mask()
 			 * so we can spare the get_page() here.
 			 */
-			if (__munlock_isolate_lru_page(page, lruvec, false)) {
-				__mod_zone_page_state(zone, NR_MLOCK,  -1);
-				unlock_page_lruvec_irq(lruvec);
+			if (__munlock_isolate_lru_page(page, lruvec, false))
 				continue;
-			} else
+			else
 				__munlock_isolation_failed(page);
-		}
+		} else
+			delta_munlocked++;
 
 		/*
 		 * We won't be munlocking this page in the next phase
@@ -322,8 +322,10 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 		 */
 		pagevec_add(&pvec_putback, pvec->pages[i]);
 		pvec->pages[i] = NULL;
-		unlock_page_lruvec_irq(lruvec);
 	}
+	__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
+	if (lruvec)
+		unlock_page_lruvec_irq(lruvec);
 
 	/* Now we can release pins of pages that we are not munlocking */
 	pagevec_release(&pvec_putback);
-- 
1.8.3.1