Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752007AbZIJPyk (ORCPT ); Thu, 10 Sep 2009 11:54:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751652AbZIJPyk (ORCPT ); Thu, 10 Sep 2009 11:54:40 -0400 Received: from casper.infradead.org ([85.118.1.10]:34806 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751607AbZIJPyj (ORCPT ); Thu, 10 Sep 2009 11:54:39 -0400 Subject: Re: [RFC][PATCH 7/7] writeback: balance_dirty_pages() shall write more than dirtied pages From: Peter Zijlstra To: Wu Fengguang Cc: Chris Mason , Jan Kara , Andrew Morton , Jens Axboe , Dave Chinner , Christoph Hellwig , Artem Bityutskiy , LKML , "linux-fsdevel@vger.kernel.org" In-Reply-To: <20090910154116.GA10856@localhost> References: <20090909145141.293229693@intel.com> <20090909150601.159061863@intel.com> <20090909154413.GC7949@duck.suse.cz> <20090910014201.GB10957@localhost> <20090910125742.GH5106@think> <20090910132154.GA6446@localhost> <1252594564.7205.36.camel@laptop> <20090910151458.GA10767@localhost> <1252596698.7205.59.camel@laptop> <20090910154116.GA10856@localhost> Content-Type: text/plain Date: Thu, 10 Sep 2009 17:54:29 +0200 Message-Id: <1252598069.7205.87.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1334 Lines: 37 On Thu, 2009-09-10 at 23:41 +0800, Wu Fengguang wrote: > > > So btrfs_file_write() explicitly calls > > > balance_dirty_pages_ratelimited_nr() to get throttled. > > > > Right, so what is wrong with than, and how does this patch fix that? > > > > [ the only thing you have to be careful with is that you don't > > excessively grow the error bound on the dirty limit ] > > Then we could form a loop: > > btrfs_file_write(): dirty 1024 pages > balance_dirty_pages(): write up to 12 pages (= ratelimit_pages * 1.5) > > in which the writeback rate cannot keep up with dirty rate, > and the dirty pages go all the way beyond dirty_thresh. Ah, ok so this is to keep the error bound on the dirty limit bounded, because we can break out of balance_dirty_pages() early, the /* We've done our duty */ break. Which unbalances the duty vs the dirty ratio. I figure that with the task dirty limit stuff we could maybe try to get rid of this break.. worth a try. > Sorry for writing such a vague changelog! np, as long as we get there :-) Change makes sense now, thanks! -- 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/