linux-kernel - Re: [RFC 5/5] truncate: Remove unnecessary page release

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Message-ID: <AANLkTikOu6xUs3e_gEubidwSc_kQVuTKask+1WcCjzFs@mail.gmail.com>
Date:	Mon, 20 Dec 2010 11:49:12 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release

On Mon, Dec 20, 2010 at 11:32 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> On Mon, Dec 20, 2010 at 11:21 AM, KOSAKI Motohiro
>> <kosaki.motohiro@...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@...e.de>
>> >> Cc: Al Viro <viro@...iv.linux.org.uk>
>> >> Cc: linux-mm@...ck.org
>> >> Signed-off-by: Minchan Kim <minchan.kim@...il.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.

The page passed truncate_complete_page is only head page?
Is it possible to pass the page which isn't head of compound in
truncate_complete_page?

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



-- 
Kind regards,
Minchan Kim
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