Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v2 2/2] mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic | Date | Tue, 17 Jun 2014 18:37:59 -0400 |
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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 <Waiman.Long@hp.com> --- mm/huge_memory.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index be84c71..e2ee131 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1650,7 +1650,7 @@ 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: -- 1.7.1
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