From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH v2 1/2] mm, thp: move invariant bug check out of loop in __split_huge_page_map
Date: Wed, 18 Jun 2014 15:24:42 +0300 [thread overview]
Message-ID: <20140618122442.GB5957@node.dhcp.inet.fi> (raw)
In-Reply-To: <1403044679-9993-2-git-send-email-Waiman.Long@hp.com>
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.
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
But okay:
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2014-06-18 12:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-17 22:37 [PATCH v2 0/2] mm, thp: two THP splitting performance fixes Waiman Long
2014-06-17 22:37 ` [PATCH v2 1/2] mm, thp: move invariant bug check out of loop in __split_huge_page_map Waiman Long
2014-06-18 12:24 ` Kirill A. Shutemov [this message]
2014-06-18 15:31 ` Waiman Long
2014-06-17 22:37 ` [PATCH v2 2/2] mm, thp: replace smp_mb after atomic_add by smp_mb__after_atomic Waiman Long
2014-06-18 12:17 ` Kirill A. Shutemov
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