From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757261AbaFZMKh (ORCPT ); Thu, 26 Jun 2014 08:10:37 -0400 Received: from mailgw1.uni-kl.de ([131.246.120.220]:45679 "EHLO mailgw1.uni-kl.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753929AbaFZMKf (ORCPT ); Thu, 26 Jun 2014 08:10:35 -0400 Message-ID: <53AC0DB4.7070701@itwm.fraunhofer.de> Date: Thu, 26 Jun 2014 14:10:28 +0200 From: Bernd Schubert User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: =?UTF-8?B?THVrw6HFoSBDemVybmVy?= , Artem Bityutskiy CC: Dave Chinner , Thomas Knauth , David Rientjes , Maksym Planeta , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] sysctl: Add a feature to drop caches selectively References: <1403626213-7691-1-git-send-email-mcsim.planeta@gmail.com> <1403677528.7903.103.camel@sauron.fi.intel.com> <20140626010606.GT4453@dastard> <1403763199.20275.39.camel@sauron.fi.intel.com> <53ABF7C4.1000906@itwm.fraunhofer.de> <1403782263.20275.59.camel@sauron.fi.intel.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ITWM-CharSet: UTF-8 X-ITWM-Scanned-By: mail2.itwm.fhg.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/26/2014 01:57 PM, Lukáš Czerner wrote: > On Thu, 26 Jun 2014, Artem Bityutskiy wrote: >> On Thu, 2014-06-26 at 12:36 +0200, Bernd Schubert wrote: >>> On 06/26/2014 08:13 AM, Artem Bityutskiy wrote: >>>> On Thu, 2014-06-26 at 11:06 +1000, Dave Chinner wrote: >>>>> Your particular use case can be handled by directing your benchmark >>>>> at a filesystem mount point and unmounting the filesystem in between >>>>> benchmark runs. There is no ned to adding kernel functionality for >>>>> somethign that can be so easily acheived by other means, especially >>>>> in benchmark environments where *everything* is tightly controlled. >>>> >>>> If I was a benchmark writer, I would not be willing running it as root >>>> to be able to mount/unmount, I would not be willing to require the >>>> customer creating special dedicated partitions for the benchmark, >>>> because this is too user-unfriendly. Or do I make incorrect assumptions? >>> >>> But why a sysctl then? And also don't see a point for that at all, why >>> can't the benchmark use posix_fadvise(POSIX_FADV_DONTNEED)? >> >> The latter question was answered - people want a way to drop caches for >> a file. They need a method which guarantees that the caches are dropped. >> They do not need an advisory method which does not give any guarantees. I'm not sure if a benchmark really needs that so much that FADV_DONTNEED isn't sufficient. Personally I would also like to know if FADV_DONTNEED succeeded. I.e. 'ql-fstest' is to check if the written pattern went to the block device and currently it does not know if data really had been dropped from the page cache. As it reads files several times this is not critical, but only would be a nice to have - nothing worth to add a new syscall. Cheers, Bernd