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SubjectRe: [PATCH 1/9] ksm: fix mlockfreed to munlocked
On Thu, 26 Nov 2009, Mel Gorman wrote:
> On Tue, Nov 24, 2009 at 04:40:55PM +0000, Hugh Dickins wrote:
> > When KSM merges an mlocked page, it has been forgetting to munlock it:
> > that's been left to free_page_mlock(), which reports it in /proc/vmstat
> > as unevictable_pgs_mlockfreed instead of unevictable_pgs_munlocked (and
> > whinges "Page flag mlocked set for process" in mmotm, whereas mainline
> > is silently forgiving). Call munlock_vma_page() to fix that.
> >
> > Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
>
> Acked-by: Mel Gorman <mel@csn.ul.ie>

Rik & Mel, thanks for the Acks.

But please clarify: that patch was for mmotm and hopefully 2.6.33,
but the vmstat issue (minus warning message) is there in 2.6.32-rc.
Should I

(a) forget it for 2.6.32
(b) rush Linus a patch for 2.6.32 final
(c) send a patch for 2.6.32.stable later on

? I just don't have a feel for how important this is.

Typically, these pages are immediately freed, and the only issue is
which stats they get added to; but if fork has copied them into other
mms, then such pages might stay unevictable indefinitely, despite no
longer being in any mlocked vma.

There's a remark in munlock_vma_page(), apropos a different issue,
/*
* We lost the race. let try_to_unmap() deal
* with it. At least we get the page state and
* mlock stats right. However, page is still on
* the noreclaim list. We'll fix that up when
* the page is eventually freed or we scan the
* noreclaim list.
*/
which implies that sometimes we scan the unevictable list and resolve
such cases. But I wonder if that's nowadays the case?
>
> > ---
> > Is this a fix that I ought to backport to 2.6.32? It does rely on part of
> > an earlier patch (moved unlock_page down), so does not apply cleanly as is.

Thanks,
Hugh


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