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

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Message-Id: <20101220112227.E566.A69D9226@jp.fujitsu.com>
Date:	Mon, 20 Dec 2010 11:21:52 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	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

> 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 
cleancache_flush_page() doesn't cause NULL deref?



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