Re: [PATCH v2 2/2] mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic

[Kirill A. Shutemov]

On Tue, Jun 17, 2014 at 06:37:59PM -0400, Waiman Long wrote:
> 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>

-- 
 Kirill A. Shutemov
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