The patch titled
Subject: mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic
has been removed from the -mm tree. Its filename was
mm-thp-replace-smp_mb-after-atomic_add-by-smp_mb__after_atomic.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Waiman Long <Waiman.Long@xxxxxx>
Subject: 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 <Waiman.Long@xxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/huge_memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/huge_memory.c~mm-thp-replace-smp_mb-after-atomic_add-by-smp_mb__after_atomic mm/huge_memory.c
--- a/mm/huge_memory.c~mm-thp-replace-smp_mb-after-atomic_add-by-smp_mb__after_atomic
+++ a/mm/huge_memory.c
@@ -1681,7 +1681,7 @@ static void __split_huge_page_refcount(s
&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:
_
Patches currently in -mm which might be from Waiman.Long@xxxxxx are
origin.patch
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