From: Waiman Long Date: Thu, 26 Jun 2014 00:42:35 +0000 (+1000) Subject: mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=a2e03c300c9351249cacf2a531dfd03b74a3df6c;p=karo-tx-linux.git mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic In some architectures like x86, atomic_add() is a full memory barrier. In that case, an additional smp_mb() is just a waste of time. This patch replaces that smp_mb() by smp_mb__after_atomic() which will avoid the redundant memory barrier in some architectures. With a 3.16-rc1 based kernel, this patch reduced the execution time of breaking 1000 transparent huge pages from 38,245us to 30,964us. A reduction of 19% which is quite sizeable. It also reduces the %cpu time of the __split_huge_page_refcount function in the perf profile from 2.18% to 1.15%. Signed-off-by: Waiman Long Acked-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Mel Gorman Cc: Rik van Riel Cc: Scott J Norton Signed-off-by: Andrew Morton --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 7a834d13413b..dbe3b19b97a3 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1681,7 +1681,7 @@ static void __split_huge_page_refcount(struct page *page, &page_tail->_count); /* after clearing PageTail the gup refcount can be released */ - smp_mb(); + smp_mb__after_atomic(); /* * retain hwpoison flag of the poisoned tail page: