From 69b7189f12e0064237630e8c6bb64cad710bb268 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Thu, 9 Oct 2014 15:27:18 -0700 Subject: [PATCH] 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 Reviewed-by: Zhang Yanfei Reviewed-by: Naoya Horiguchi Acked-by: Minchan Kim Acked-by: Mel Gorman Cc: Michal Nazarewicz Cc: Naoya Horiguchi Cc: Christoph Lameter Cc: Rik van Riel Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 53 +++++++++++++++++++++++++++++-------------------- 1 file 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); -- 2.30.2