Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754404AbZD3AEF (ORCPT ); Wed, 29 Apr 2009 20:04:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753140AbZD3ADy (ORCPT ); Wed, 29 Apr 2009 20:03:54 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:52899 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752010AbZD3ADx (ORCPT ); Wed, 29 Apr 2009 20:03:53 -0400 Date: Wed, 29 Apr 2009 16:59:40 -0700 From: Andrew Morton To: Mathieu Desnoyers Cc: torvalds@linux-foundation.org, nickpiggin@yahoo.com.au, mingo@elte.hu, kosaki.motohiro@jp.fujitsu.com, a.p.zijlstra@chello.nl, thomas.pi@arcor.dea, ylalym@gmail.com, linux-kernel@vger.kernel.org, ltt-dev@lists.casi.polymtl.ca Subject: Re: [PATCH] Fix dirty page accounting in redirty_page_for_writepage() Message-Id: <20090429165940.094efd0a.akpm@linux-foundation.org> In-Reply-To: <20090429232546.GB15782@Krystal> References: <20090429232546.GB15782@Krystal> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2157 Lines: 58 On Wed, 29 Apr 2009 19:25:46 -0400 Mathieu Desnoyers wrote: > Basically, the following execution : > > dd if=/dev/zero of=/tmp/testfile > > will slowly fill _all_ ram available without taking into account memory > pressure. > > This is because the dirty page accounting is incorrect in > redirty_page_for_writepage. > > This patch adds missing dirty page accounting in redirty_page_for_writepage(). The patch changes __set_page_dirty_nobuffers(), not redirty_page_for_writepage(). __set_page_dirty_nobuffers() has a huge number of callers. > --- linux-2.6-lttng.orig/mm/page-writeback.c 2009-04-29 18:14:48.000000000 -0400 > +++ linux-2.6-lttng/mm/page-writeback.c 2009-04-29 18:23:59.000000000 -0400 > @@ -1237,6 +1237,12 @@ int __set_page_dirty_nobuffers(struct pa > if (!mapping) > return 1; > > + /* > + * Take care of setting back page accounting correctly. > + */ > + inc_zone_page_state(page, NR_FILE_DIRTY); > + inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > + > spin_lock_irq(&mapping->tree_lock); > mapping2 = page_mapping(page); > if (mapping2) { /* Race with truncate? */ > But __set_page_dirty_nobuffers() calls account_page_dirtied(), which already does the above two operations. afacit we're now double-accounting. Now, it's possible that the accounting goes wrong very occasionally in the "/* Race with truncate? */" case. If the truncate path clears the page's dirty bit then it will decrement the dirty-page accounting, but this code path will fail to perform the increment of the dirty-page accounting. IOW, once this function has set PG_Dirty, it is committed to altering some or all of the page-dirty accounting. But afacit your test case will not trigger the race-with-truncate anyway? Can you determine at approximately what frequency (pages-per-second) this accounting leak is occurring in your test? -- 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/