From: Andrea Arcangeli <aarcange@redhat.com>
To: Christoph Lameter <cl@linux.com>
Cc: Minchan Kim <minchan.kim@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>, Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 1/3] When migrate_pages returns 0, all pages must have been released
Date: Thu, 20 Jan 2011 22:28:41 +0100 [thread overview]
Message-ID: <20110120212841.GB9506@random.random> (raw)
In-Reply-To: <alpine.DEB.2.00.1101201233001.20633@router.home>
On Thu, Jan 20, 2011 at 12:49:15PM -0600, Christoph Lameter wrote:
> On Thu, 20 Jan 2011, Andrea Arcangeli wrote:
>
> > Hello,
> >
> > On Thu, Jan 20, 2011 at 11:30:35AM -0600, Christoph Lameter wrote:
> > > On Fri, 21 Jan 2011, Minchan Kim wrote:
> > >
> > > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > > index 46fe8cc..7d34237 100644
> > > > --- a/mm/migrate.c
> > > > +++ b/mm/migrate.c
> > > > @@ -772,6 +772,7 @@ uncharge:
> > > > unlock:
> > > > unlock_page(page);
> > > >
> > > > +move_newpage:
> > > > if (rc != -EAGAIN) {
> > > > /*
> > > > * A page that has been migrated has all references
> > > > @@ -785,8 +786,6 @@ unlock:
> > > > putback_lru_page(page);
> > > > }
> > > >
> > > > -move_newpage:
> > > > -
> > > > /*
> > > > * Move the new page to the LRU. If migration was not successful
> > > > * then this will free the page.
> > > >
> > >
> > > What does this do? Not covered by the description.
> >
> > It makes a difference for the two goto move_newpage, when rc =
> > 0. Otherwise the function will return 0, despite
> > putback_lru_page(page) wasn't called (and the caller of migrate_pages
> > won't call putback_lru_pages if migrate_pages returned 0).
>
> Think about the difference:
>
> Moving the move_newpage will now cause another removal and freeing of the
> page if rc != -EAGAIN.
The only ones doing "goto move_newpage" after the first two memleaks
that are fixed by this patch are always run with rc = -EAGAIN. So this
makes a difference only for the first two which were leaking memory before.
> The first goto move_newpage (because page count is 1) will now mean that
> the page is freed twice. One because of the rc != EAGAIN branch and then
> another time by the following putback_lru_page().
Which following putback_lru_page()? You mean
putback_lru_page(newpage)? That is for the newly allocated page
(allocated at the very top, so always needed), it's not relevant to
the page_count(page) = 1. The page_count 1 is hold by the caller, so
it's leaking memory right now (for everything but compaction).
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next prev parent reply other threads:[~2011-01-20 21:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-20 16:17 [PATCH 1/3] When migrate_pages returns 0, all pages must have been released Minchan Kim
2011-01-20 16:17 ` [PATCH 2/3] migration: Fix page corruption during hugepage migration Minchan Kim
2011-01-20 16:17 ` [PATCH 3/3] compaction: Check migrate_pages's return value instead of list_empty Minchan Kim
2011-01-26 8:18 ` Mel Gorman
2011-01-20 17:30 ` [PATCH 1/3] When migrate_pages returns 0, all pages must have been released Christoph Lameter
2011-01-20 18:24 ` Andrea Arcangeli
2011-01-20 18:49 ` Christoph Lameter
2011-01-20 21:28 ` Andrea Arcangeli [this message]
2011-01-21 16:11 ` Christoph Lameter
2011-01-21 17:36 ` Andrea Arcangeli
2011-01-21 23:54 ` Minchan Kim
2011-01-26 8:14 ` Mel Gorman
2011-01-26 23:06 ` Andrew Morton
2011-01-26 23:21 ` Minchan Kim
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