Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753481AbZIGOPw (ORCPT ); Mon, 7 Sep 2009 10:15:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753351AbZIGOPw (ORCPT ); Mon, 7 Sep 2009 10:15:52 -0400 Received: from cantor.suse.de ([195.135.220.2]:59951 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752273AbZIGOPv (ORCPT ); Mon, 7 Sep 2009 10:15:51 -0400 Date: Mon, 7 Sep 2009 16:15:48 +0200 From: Nick Piggin To: Adrian Hunter Cc: chris.mason@oracle.com, david@fromorbit.com, Andrew Morton , "Bityutskiy Artem (Nokia-M/Helsinki)" , LKML Subject: Re: [RFC][PATCH] mm: write_cache_pages be more sequential Message-ID: <20090907141548.GA28054@wotan.suse.de> References: <4AA513AA.3010206@nokia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AA513AA.3010206@nokia.com> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2240 Lines: 57 On Mon, Sep 07, 2009 at 05:07:38PM +0300, Adrian Hunter wrote: > >From 6f3bb7c26936c45d810048f59c369e8d5a5623fc Mon Sep 17 00:00:00 2001 > From: Adrian Hunter > Date: Mon, 7 Sep 2009 10:49:11 +0300 > Subject: [PATCH] mm: write_cache_pages be more sequential > > If a file is written to sequentially, then writeback > should write the pages sequentially also. However, > that does not always happen. For example: > > 1) user writes pages 0, 1 and 2 but 2 is incomplete > 2) write_cache_pages writes pages 0, 1 and 2 and sets > writeback_index to 3 > 3) user finishes writing page 2 and writes pages 3 and 4 > 4) write_cache_pages writes pages 3 and 4, and then cycles > back and writes page 2 again. > > So the pages are written out in the order 0, 1, 2, 3 ,4 ,2 > instead of 0, 1, 2, 2, 3, 4. Why does page 2 get set dirty if the write was incomplete? > This situation was noticed on UBIFS because it writes > directly from writepage. Hence if there is an unexpected > power-loss, a file will end up with a hole even though > the file was written sequentially by the user. > > Signed-off-by: Adrian Hunter > --- > mm/page-writeback.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index 81627eb..7410b7a 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -960,6 +960,8 @@ int write_cache_pages(struct address_space *mapping, > pagevec_init(&pvec, 0); > if (wbc->range_cyclic) { > writeback_index = mapping->writeback_index; /* prev offset */ > + if (writeback_index) > + writeback_index -= 1; > index = writeback_index; > if (index == 0) > cycled = 1; Doesn't this just break range_cyclic? range_cyclic is supposed to work across calls to write_cache_pages, and it's there I guess so background writeout will be able to eventually get around to writing all pages relatively fairly in the presence of redirtying operations. -- 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/