From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S270805AbTGPM5D (ORCPT ); Wed, 16 Jul 2003 08:57:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S270776AbTGPM5B (ORCPT ); Wed, 16 Jul 2003 08:57:01 -0400 Received: from ppp-217-133-42-200.cust-adsl.tiscali.it ([217.133.42.200]:42385 "EHLO dualathlon.random") by vger.kernel.org with ESMTP id S270763AbTGPM47 (ORCPT ); Wed, 16 Jul 2003 08:56:59 -0400 Date: Wed, 16 Jul 2003 15:11:28 +0200 From: Andrea Arcangeli To: Jens Axboe Cc: Alan Cox , Marcelo Tosatti , Chris Mason , lkml , "Stephen C. Tweedie" , Jeff Garzik , Andrew Morton , Alexander Viro Subject: Re: RFC on io-stalls patch Message-ID: <20030716131128.GG4978@dualathlon.random> References: <20030714131206.GJ833@suse.de> <20030714195138.GX833@suse.de> <20030714201637.GQ16313@dualathlon.random> <20030715052640.GY833@suse.de> <1058268126.3857.25.camel@dhcp22.swansea.linux.org.uk> <20030715112737.GQ833@suse.de> <20030716124355.GE4978@dualathlon.random> <20030716124656.GY833@suse.de> <20030716125933.GF4978@dualathlon.random> <20030716130442.GZ833@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030716130442.GZ833@suse.de> User-Agent: Mutt/1.4i X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 16, 2003 at 03:04:42PM +0200, Jens Axboe wrote: > On Wed, Jul 16 2003, Andrea Arcangeli wrote: > > On Wed, Jul 16, 2003 at 02:46:56PM +0200, Jens Axboe wrote: > > > Well it's a combined problem. Threshold too high on dirty memory, > > > someone doing a read well get stuck flushing out as well. > > > > a pure read not. the write throttling should be per-process, then there > > will be little risk. > > A read from user space, dirtying data along the way. it doesn't necessairly block on dirty memory. We even _free_ ram clean if needed, exactly because of that. You can raise the amount of _free_ ram up to 99% of the whole ram in your box to be almost guaranteed to never wait on dirty memory freeing. Of course the default tries to optimize for writeback cache and there's a reasonable margin to avoid writing dirty stuff. the sysctl is there for special usages where you want to never block in a read from userspace regardless whatever the state of the system. Andrea