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

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Message-ID: <20120315144400.GA19855@tiehlicka.suse.cz>
Date:	Thu, 15 Mar 2012 15:44:00 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Hillf Danton <dhillf@...il.com>
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 14-03-12 21:08:13, Hillf Danton wrote:
> 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:)

Thanks

> 
> > 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.

Right, I meant false negative. Would be nice to have it in the
changelog... Anyway, Andrew has already picked up the patch I guess.
Just in case

Reviewed-by: Michal Hocko <mhocko@...e.cz>

> > 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.

OK

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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