Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757578Ab0HJNaP (ORCPT ); Tue, 10 Aug 2010 09:30:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:47022 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754923Ab0HJNaI (ORCPT ); Tue, 10 Aug 2010 09:30:08 -0400 Date: Tue, 10 Aug 2010 15:29:18 +0200 From: Jan Kara To: Neil Brown Cc: KOSAKI Motohiro , Wu Fengguang , Andrew Morton , LKML , Peter Zijlstra , Dave Chinner , Christoph Hellwig , Mel Gorman , Chris Mason , Jens Axboe , Jan Kara , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" Subject: Re: [PATCH 07/13] writeback: explicit low bound for vm.dirty_ratio Message-ID: <20100810132918.GA3351@quack.suse.cz> References: <20100805163401.e9754032.akpm@linux-foundation.org> <20100806124452.GC4717@localhost> <20100809235652.7113.A69D9226@jp.fujitsu.com> <20100810135712.0eb34759@notabene> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100810135712.0eb34759@notabene> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1853 Lines: 43 On Tue 10-08-10 13:57:12, Neil Brown wrote: > On Tue, 10 Aug 2010 12:12:06 +0900 (JST) > KOSAKI Motohiro wrote: > > > > Subject: writeback: explicit low bound for vm.dirty_ratio > > > From: Wu Fengguang > > > Date: Thu Jul 15 10:28:57 CST 2010 > > > > > > Force a user visible low bound of 5% for the vm.dirty_ratio interface. > > > > > > This is an interface change. When doing > > > > > > echo N > /proc/sys/vm/dirty_ratio > > > > > > where N < 5, the old behavior is pretend to accept the value, while > > > the new behavior is to reject it explicitly with -EINVAL. This will > > > possibly break user space if they checks the return value. > > > > Umm.. I dislike this change. Is there any good reason to refuse explicit > > admin's will? Why 1-4% is so bad? Internal clipping can be changed later > > but explicit error behavior is hard to change later. > > As a data-point, I had a situation a while back where I needed a value below > 1 to get desired behaviour. The system had lots of RAM and fairly slow > write-back (over NFS) so a 'sync' could take minutes. > > So I would much prefer allowing not only 1-4, but also fraction values!!! > > I can see no justification at all for setting a lower bound of 5. Even zero > can be useful - for testing purposes mostly. If you run on a recent kernel, /proc/sys/vm/dirty_background_bytes and dirty_bytes is what was introduced exactly for these purposes. Not that I would think that magic clipping at 5% is a good thing... Honza -- Jan Kara SUSE Labs, CR -- 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/