linux-kernel - Re: [PATCH] mm: hugetlb: defer freeing pages when gathering surplus pages

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Date:	Wed, 14 Mar 2012 21:08:13 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: hugetlb: defer freeing pages when gathering surplus pages

On Wed, Mar 14, 2012 at 7:13 PM, Michal Hocko <mhocko@...e.cz> wrote:
> [Sorry for the late reply but I was away from email for quite sometime]
>

Nice to see you back:)

> On Tue 14-02-12 20:53:51, Hillf Danton wrote:
>> When gathering surplus pages, the number of needed pages is recomputed after
>> reacquiring hugetlb lock to catch changes in resv_huge_pages and
>> free_huge_pages. Plus it is recomputed with the number of newly allocated
>> pages involved.
>>
>> Thus freeing pages could be deferred a bit to see if the final page request is
>> satisfied, though pages could be allocated less than needed.
>
> The patch looks OK but I am missing a word why we need it. I guess

False negative is removed as it should be.

> your primary motivation is that we want to reduce false positives when
> we fail to allocate surplus pages while somebody freed some in the
> background.
> What is the workload that you observed such a behavior? Or is this just
> from the code review?
>
The second.

-hd
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