From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 8A1F86B00B8 for ; Sun, 19 Dec 2010 23:41:25 -0500 (EST) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail6.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id oBK4fHBk031518 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Mon, 20 Dec 2010 13:41:17 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 49F9345DE55 for ; Mon, 20 Dec 2010 13:41:17 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 239C145DE68 for ; Mon, 20 Dec 2010 13:41:17 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 0A70FE08002 for ; Mon, 20 Dec 2010 13:41:17 +0900 (JST) Received: from m108.s.css.fujitsu.com (m108.s.css.fujitsu.com [10.249.87.108]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id B6358E18005 for ; Mon, 20 Dec 2010 13:41:16 +0900 (JST) Date: Mon, 20 Dec 2010 13:35:26 +0900 From: KAMEZAWA Hiroyuki 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: KOSAKI Motohiro , Andrew Morton , linux-mm , LKML , Nick Piggin , Al Viro List-ID: 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 > >> > --- > >> > A mm/truncate.c | A A 1 - > >> > A 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) > >> > A A A * calls cleancache_put_page (and note page->mapping is now NULL) > >> > A A A */ > >> > A A cleancache_flush_page(mapping, page); > >> > - A page_cache_release(page); A A A /* pagecache ref */ > >> > A A 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, A I can't understand > > == > > void __cleancache_flush_page(struct address_space *mapping, struct page *page) > > { > > A A A A /* careful... page->mapping is NULL sometimes when this is called */ > > A A A A int pool_id = mapping->host->i_sb->cleancache_poolid; > > A A A A 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org