Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932313AbWH1B24 (ORCPT ); Sun, 27 Aug 2006 21:28:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932317AbWH1B24 (ORCPT ); Sun, 27 Aug 2006 21:28:56 -0400 Received: from omx2-ext.sgi.com ([192.48.171.19]:43679 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S932313AbWH1B24 (ORCPT ); Sun, 27 Aug 2006 21:28:56 -0400 Date: Mon, 28 Aug 2006 11:28:30 +1000 From: David Chinner To: Jens Axboe Cc: Neil Brown , David Chinner , Andi Kleen , linux-kernel@vger.kernel.org, akpm@osdl.org Subject: Re: RFC - how to balance Dirty+Writeback in the face of slow writeback. Message-ID: <20060828012830.GH807830@melbourne.sgi.com> References: <20060818001102.GW51703024@melbourne.sgi.com> <20060817232942.c35b1371.akpm@osdl.org> <20060818070314.GE798@suse.de> <17640.65491.458305.525471@cse.unsw.edu.au> <20060821031505.GQ51703024@melbourne.sgi.com> <17641.24478.496091.79901@cse.unsw.edu.au> <20060821135132.GG4290@suse.de> <17646.32332.572865.919526@cse.unsw.edu.au> <20060825063723.GO24258@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060825063723.GO24258@kernel.dk> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1105 Lines: 29 On Fri, Aug 25, 2006 at 08:37:24AM +0200, Jens Axboe wrote: > On Fri, Aug 25 2006, Neil Brown wrote: > > > I'm beginning to think that the current scheme really works very well > > - except for a few 'bugs'(*). > > It works ok, but it makes it hard to experiment with larger queue depths > when the vm falls apart :-). It's not a big deal, though, even if the > design isn't very nice - nr_requests is not a well defined entity. It > can be anywhere from 512b to megabyte(s) in size. So throttling on X > number of requests tends to be pretty vague and depends hugely on the > workload (random vs sequential IO). So maybe we need a different control parameter - the amount of memory we allow to be backed up in a queue rather than the number of requests the queue can take... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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/