From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Sandeen Subject: Re: [PATCH 3/3] ext4: update writeback_index based on last page scanned Date: Mon, 25 Oct 2010 16:39:10 -0500 Message-ID: <4CC5F8FE.6000100@redhat.com> References: <4CC2023A.7060607@redhat.com> <4CC205ED.4090007@redhat.com> <20101025213550.GK16981@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: ext4 development To: "Ted Ts'o" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:2931 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755409Ab0JYVjV (ORCPT ); Mon, 25 Oct 2010 17:39:21 -0400 In-Reply-To: <20101025213550.GK16981@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: Ted Ts'o wrote: > On Fri, Oct 22, 2010 at 04:45:17PM -0500, Eric Sandeen wrote: >> As pointed out in a prior patch, updating the mapping's >> writeback_index based on pages written isn't quite right; >> what the writeback index is really supposed to reflect is >> the next page which should be scanned for writeback during >> periodic flush. >> >> As in write_cache_pages(), write_cache_pages_da() does >> this scanning for us as we assemble the mpd for later >> writeout. If we keep track of the next page after the >> current scan, we can easily update writeback_index without >> worrying about pages written vs. pages skipped, etc. >> >> Without this, an fsync will reset writeback_index to >> 0 (its starting index) + however many pages it wrote, which >> can mess up the progress of periodic flush. >> >> Signed-off-by: Eric Sandeen > > Have you done any benchmarks with and without this patch series? > > Say, compilebench on a used and mildly fragmented file system? > > - Ted Not compilebench specifically, but I did do some benchmarking with out of cache buffered IO; to be honest I didn't see striking performance differences, but I did see the writeback behave better in terms of not wandering all over, even if it might recover well. I can try compilebench; do you have specific concerns? -Eric