Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754081Ab2JMTdd (ORCPT ); Sat, 13 Oct 2012 15:33:33 -0400 Received: from mail.avalus.com ([89.16.176.221]:56709 "EHLO mail.avalus.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754014Ab2JMTdc (ORCPT ); Sat, 13 Oct 2012 15:33:32 -0400 Date: Sat, 13 Oct 2012 20:33:27 +0100 From: Alex Bligh Reply-To: Alex Bligh To: Hillf Danton cc: LKML , Alex Bligh Subject: Re: Local DoS through write heavy I/O on CFQ & Deadline Message-ID: <97166AE58C26A44D45569412@nimrod.local> In-Reply-To: References: <0B138F62-16BF-4295-9AD9-64C0BB39FCE2@alex.org.uk> <20121012133044.GA10115@dhcp22.suse.cz> <20121012145838.GD22083@dhcp22.suse.cz> <3D1C85A52BB960B79E37AC30@nimrod.local> X-Mailer: Mulberry/4.0.8 (Mac OS X) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1092 Lines: 28 --On 13 October 2012 21:53:09 +0800 Hillf Danton wrote: > Take a look at the "wait for writeback" problem please. > > Linux 3.0+ Disk performance problem - wrong pdflush behaviour > https://lkml.org/lkml/2012/10/10/412 I'm guessing that's related but may not be the whole story. My test case is rather simpler, and Viktor says that with the patch causing his regression reverted, "After I've set the dirty_bytes over the file size the writes are never blocked.". That suggests to me that in order to avoid write blocking he needs dirty_bytes larger than the file size. As the bytes written in my test case exceed RAM, that's going to be be an issue as dirty_bytes is always going to be hit; I think it Viktor's case he is trying to avoid it being hit at all. Or perhaps I have the wrong end of the stick. -- Alex Bligh -- 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/