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

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Message-Id: <20101220112733.064f2fe3.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 20 Dec 2010 11:27:33 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Minchan Kim <minchan.kim@...il.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

On Mon, 20 Dec 2010 11:21:52 +0900 (JST)
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 
> cleancache_flush_page() doesn't cause NULL deref?
> 
Hmm, my review was bad.

I think cleancache_flush_page() here should eat (mapping, index) as argument
rather than "page".

BTW,  I can't understand
==
void __cleancache_flush_page(struct address_space *mapping, struct page *page)
{
        /* careful... page->mapping is NULL sometimes when this is called */
        int pool_id = mapping->host->i_sb->cleancache_poolid;
        struct cleancache_filekey key = { .u.key = { 0 } };
==

Why above is safe...
I think (mapping,index) should be passed instead of page.


-Kame

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