On 06/18/2014 08:24 AM, Kirill A. Shutemov wrote:
On Tue, Jun 17, 2014 at 06:37:58PM -0400, Waiman Long wrote:
In the __split_huge_page_map() function, the check for
page_mapcount(page) is invariant within the for loop. Because of the
fact that the macro is implemented using atomic_read(), the redundant
check cannot be optimized away by the compiler leading to unnecessary
read to the page structure.
This patch moves the invariant bug check out of the loop so that it
will be done only once. On a 3.16-rc1 based kernel, the execution
time of a microbenchmark that broke up 1000 transparent huge pages
using munmap() had an execution time of 38,245us and 38,548us with
and without the patch respectively. The performance gain is about 1%.
For this low difference it would be nice to average over few runs +
stddev. It can easily can be a noise.
The timing data was the average of 5 runs with a SD of 100-200us.
Signed-off-by: Waiman Long<Waiman.Long@xxxxxx>
But okay:
Acked-by: Kirill A. Shutemov<kirill.shutemov@xxxxxxxxxxxxxxx>
Thank for the review.
-Longman
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