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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Minchan Kim <minchan.kim@gmail.com>
Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release
Cc: kosaki.motohiro@jp.fujitsu.com, Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Nick Piggin <npiggin@suse.de>, Al Viro <viro@zeniv.linux.org.uk>
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Date: Mon, 20 Dec 2010 11:32:13 +0900 (JST)
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> On Mon, Dec 20, 2010 at 11:21 AM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> >> This patch series changes remove_from_page_cache's page ref counting
> >> rule. page cache ref count is decreased in remove_from_page_cache.
> >> So we don't need call again in caller context.
> >>
> >> Cc: Nick Piggin <npiggin@suse.de>
> >> Cc: Al Viro <viro@zeniv.linux.org.uk>
> >> Cc: linux-mm@kvack.org
> >> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> >> ---
> >>  mm/truncate.c |    1 -
> >>  1 files changed, 0 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/mm/truncate.c b/mm/truncate.c
> >> index 9ee5673..8decb93 100644
> >> --- a/mm/truncate.c
> >> +++ b/mm/truncate.c
> >> @@ -114,7 +114,6 @@ truncate_complete_page(struct address_space *mapping, struct page *page)
> >>        * calls cleancache_put_page (and note page->mapping is now NULL)
> >>        */
> >>       cleancache_flush_page(mapping, page);
> >> -     page_cache_release(page);       /* pagecache ref */
> >>       return 0;
> >
> > Do we _always_ have stable page reference here? IOW, I can assume
> 
> I think so.
> Because the page is locked so caller have to hold a ref to unlock it.

Hmm...

Perhaps, I'm missing something. But I think  __memory_failure() only lock 
compaund_head page. not all. example.

> 
> > cleancache_flush_page() doesn't cause NULL deref?