Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752975Ab0LTElT (ORCPT ); Sun, 19 Dec 2010 23:41:19 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:44668 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752795Ab0LTElS (ORCPT ); Sun, 19 Dec 2010 23:41:18 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Mon, 20 Dec 2010 13:35:26 +0900 From: KAMEZAWA Hiroyuki To: Minchan Kim Cc: KOSAKI Motohiro , Andrew Morton , linux-mm , LKML , Nick Piggin , Al Viro Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release Message-Id: <20101220133526.e075feb8.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <02ab98b3a1450f7a1c31edc48ccc57e887cee900.1292604746.git.minchan.kim@gmail.com> <20101220112227.E566.A69D9226@jp.fujitsu.com> <20101220112733.064f2fe3.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.0.3 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3165 Lines: 83 On Mon, 20 Dec 2010 11:58:50 +0900 Minchan Kim wrote: > On Mon, Dec 20, 2010 at 11:27 AM, KAMEZAWA Hiroyuki > wrote: > > On Mon, 20 Dec 2010 11:21:52 +0900 (JST) > > KOSAKI Motohiro 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 > >> > Cc: Al Viro > >> > Cc: linux-mm@kvack.org > >> > Signed-off-by: Minchan Kim > >> > --- > >> >  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. > > I don't think current code isn't safe. > > 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 } }; > > if (pool_id >= 0) { > VM_BUG_ON(!PageLocked(page)); > > it does check PageLocked. So caller should hold a page reference to > prevent freeing ramined PG_locked > If the caller doesn't hold a ref of page, I think it's BUG of caller. > > In our case, caller calls truncate_complete_page have to make sure it, I think. > Ah, my point is that this function trust page->index even if page->mapping is reset to NULL. And I'm not sure that there are any race that an other thread add a replacement page for (mapping, index) while a thread call this function. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/