From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: [PATCH 6/6] writeback: limit write_cache_pages integrity scanning to current EOF Date: Tue, 8 Jun 2010 15:38:31 +1000 Message-ID: <20100608053831.GR26335@laptop> References: <1275957487-23633-1-git-send-email-david@fromorbit.com> <1275957487-23633-7-git-send-email-david@fromorbit.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com, akpm@linux-foundation.org To: Dave Chinner Return-path: Received: from cantor2.suse.de ([195.135.220.15]:35157 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751948Ab0FHFie (ORCPT ); Tue, 8 Jun 2010 01:38:34 -0400 Content-Disposition: inline In-Reply-To: <1275957487-23633-7-git-send-email-david@fromorbit.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Jun 08, 2010 at 10:38:07AM +1000, Dave Chinner wrote: > From: Dave Chinner > > sync can currently take a really long time if a concurrent writer is > extending a file. The problem is that the dirty pages on the address > space grow in the same direction as write_cache_pages scans, so if > the writer keeps ahead of writeback, the writeback will not > terminate until the writer stops adding dirty pages. > > For a data integrity sync, we only need to write the pages dirty at > the time we start the writeback, so we can stop scanning once we get > to the page that was at the end of the file at the time the scan > started. > > This will prevent operations like copying a large file preventing > sync from completing as it will not write back pages that were > dirtied after the sync was started. This does not impact the > existing integrity guarantees, as any dirty page (old or new) > within the EOF range at the start of the scan will still be > captured. > > This patch will not prevent sync from blocking on large writes into > holes. The writes don't have to be into holes to cause this starvation problem, do they? > That requires more complex intervention while this patch only > addresses the common append-case of this sync holdoff. Jan's tagging patch looks pretty good to me and isn't so complex. I think we should just take that.