From: Nick Piggin <npiggin@suse.de>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: mark gross <mgross@linux.intel.com>, linux-mm@kvack.org
Subject: Re: possible bug in find_get_pages
Date: Tue, 10 Mar 2009 11:49:47 +0100 [thread overview]
Message-ID: <20090310104947.GB4594@wotan.suse.de> (raw)
In-Reply-To: <alpine.DEB.1.10.0903061426190.20182@qirst.com>
On Fri, Mar 06, 2009 at 02:28:50PM -0500, Christoph Lameter wrote:
> On Fri, 6 Mar 2009, mark gross wrote:
>
> > It seems that page->_count == 0 at some point on some overnight runs
> > with locks the system into a tight loop from the repeat: and a goto
> > repeat in find_get_pages.
>
> A page with ref count zero should not be in any mapping. If the page is in
> a mapping then the page is used. Therefore the refcount should be > 0.
>
> If there is a page with zero refcount and its in a mapping then something
> erroneously decreased the refcount.
Just for posterity, this isn't _quite_ true any more with Hugh's
variation to the speculative reference method. We now in some
places set the page's refcount to 0 in order to hold off new
speculative references from turning into real references (eg. right
before final checks before page reclaim).
But yes, such a page should not remain both in a mapping and with a
0 refcount for long periods.
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next prev parent reply other threads:[~2009-03-10 10:49 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-06 19:26 possible bug in find_get_pages mark gross
2009-03-06 19:28 ` Christoph Lameter
2009-03-06 21:13 ` mark gross
2009-03-06 21:29 ` Christoph Lameter
2009-03-10 10:49 ` Nick Piggin [this message]
2009-03-06 23:47 ` Minchan Kim
2009-03-09 16:43 ` mark gross
2009-03-10 10:45 ` Nick Piggin
2009-03-10 22:49 ` mark gross
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