Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755950Ab3JHK51 (ORCPT ); Tue, 8 Oct 2013 06:57:27 -0400 Received: from mail-pd0-f170.google.com ([209.85.192.170]:61917 "EHLO mail-pd0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755282Ab3JHK5Y (ORCPT ); Tue, 8 Oct 2013 06:57:24 -0400 Message-ID: <5253E50C.1060608@gmail.com> Date: Tue, 08 Oct 2013 19:57:16 +0900 From: Akira Hayakawa User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: david@fromorbit.com CC: mpatocka@redhat.com, thornber@redhat.com, devel@driverdev.osuosl.org, snitzer@redhat.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, agk@redhat.com, joe@perches.com, akpm@linux-foundation.org, dan.carpenter@oracle.com, ejt@redhat.com, cesarb@cesarb.net, m.chehab@samsung.com, ruby.wktk@gmail.com Subject: Re: [dm-devel] Reworking dm-writeboost [was: Re: staging: Add dm-writeboost] References: <20130916215357.GA5015@redhat.com> <52384E66.6050101@gmail.com> <20130917205936.GB12001@redhat.com> <523E3522.2060607@gmail.com> <524183A2.9050301@gmail.com> <20130926034325.GO26872@dastard> <20131001082654.GA10326@debian> <20131004020417.GF4446@dastard> <524FC4F4.6050401@gmail.com> <20131007234307.GP4446@dastard> In-Reply-To: <20131007234307.GP4446@dastard> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1290 Lines: 30 Dave, > i.e. there's no point justifying a behaviour with "we could do this > in future so lets ignore the impact on current users"... Sure, I am happy if we find a solution that is good for both of us or filesystem and block in other word. > e.g. what happens if a user has a mixed workload - one where > performance benefits are only seen by delaying FUA, and another that > is seriously slowed down by delaying FUA requests? This is where > knobs are problematic.... You are right. But there is no perfect solution to satisfy all. Dealing with each requirement will only complicate the code. Stepping away from the user and focusing on filesystem-block boundary >> Maybe, writeboost should disable deferring barriers >> if barrier_deadline_ms parameter is especially 0. adding the switch for the mounted filesystem to decides on/off is a simple but effective solution I believe. Deciding per bio basis instead of per device could be an another solution. I am happy if I can check the bio if it "may or may not defer the barrier". Akira -- 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/