Date: Mon, 6 Jun 2011 14:38:51 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan.kim@gmail.com>, akpm@linux-foundation.org,
        Ury Stankevich <urykhy@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@kernel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous
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On Mon, Jun 06, 2011 at 11:39:24AM +0100, Mel Gorman wrote:
> Well spotted.
> 
> Acked-by: Mel Gorman <mgorman@suse.de>
> 
> Minor nit. swapper_space is rarely referred to outside of the swap
> code. Might it be more readable to use
> 
> 	/*
> 	 * swapcache is accounted as NR_FILE_PAGES but it is not
> 	 * accounted as NR_SHMEM
> 	 *
> 	if (PageSwapBacked(page) && !PageSwapCache(page))

I thought the comparison on swapper_space would be faster as it was
immediate vs register in CPU, instead of forcing a memory
access. Otherwise I would have used the above. Now the test_bit is
written in C and lockless so it's not likely to be very different
considering the cacheline is hot in the CPU but it's still referencing
memory instead register vs immediate comparison.
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