linux-kernel - Re: [BUG] Commit d065bd81 severely regresses huge page allocation success rates

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Date:	Thu, 11 Nov 2010 04:25:00 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Rik van Riel <riel@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ying Han <yinghan@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [BUG] Commit d065bd81 severely regresses huge page allocation
 success rates

On Thu, Nov 11, 2010 at 4:15 AM, Mel Gorman <mel@....ul.ie> wrote:
> When testing 2.6.37-rc1, I noticed that huge page allocation success
> rates were severely impaired. Bisection showed that commit [d065bd81: mm:
> retry page fault when blocking on disk transfer] was the biggest factor.
> Reverting the patch confirmed this. Here are the results of a high-order
> allocation stress test. The vanilla kernel is 2.6.37-rc1 and the revert
> kernel has this commit removed with minor conflicts cleaned up.
[...]
> I have not digested what the patch is doing but am reporting it in case
> people familiar with the patch spot the problem quickly.

There was a bug in that commit, which was fixed in
d88c0922fa0e2c021a028b310a641126c6d4b7dc

I think this may explain the issue; compaction won't work well if
extra references are kept :/

Can you check that this indeed solves your test case ?

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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