Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754087Ab0LTIJO (ORCPT ); Mon, 20 Dec 2010 03:09:14 -0500 Received: from mail-iw0-f174.google.com ([209.85.214.174]:34536 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753750Ab0LTIJM convert rfc822-to-8bit (ORCPT ); Mon, 20 Dec 2010 03:09:12 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=m1H6ftyfWvc6/sYIwvaYu1H5ehhqe+pFcXcKzp7Z884bMpHUwK1H8kvCOrLJlcrXNY jnu80QNy6XGVVaD52zcIrEalKZ9U+kTbfi3U8EJCc96U6elntkm4usue1IlKioPQ3+Or VSRdXltCxBf2sKL5ZieUsua5NKPshSWJ/pmP8= MIME-Version: 1.0 In-Reply-To: <20101220133526.e075feb8.kamezawa.hiroyu@jp.fujitsu.com> References: <02ab98b3a1450f7a1c31edc48ccc57e887cee900.1292604746.git.minchan.kim@gmail.com> <20101220112227.E566.A69D9226@jp.fujitsu.com> <20101220112733.064f2fe3.kamezawa.hiroyu@jp.fujitsu.com> <20101220133526.e075feb8.kamezawa.hiroyu@jp.fujitsu.com> Date: Mon, 20 Dec 2010 17:09:11 +0900 Message-ID: Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release From: Minchan Kim To: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro , Andrew Morton , linux-mm , LKML , Nick Piggin , Al Viro Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3458 Lines: 97 On Mon, Dec 20, 2010 at 1:35 PM, KAMEZAWA Hiroyuki wrote: > 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. Because the page is locked and is detached from page cache, I guess it's no problem. Anyway, I think It's off-topic. > > Thanks, > -Kame > > > > -- Kind regards, Minchan Kim -- 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/