From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35BD0C433E0 for ; Tue, 26 May 2020 07:23:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CD822070A for ; Tue, 26 May 2020 07:23:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="ZrYNnWfc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731567AbgEZHXV (ORCPT ); Tue, 26 May 2020 03:23:21 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:35054 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731519AbgEZHXU (ORCPT ); Tue, 26 May 2020 03:23:20 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04Q7Lhg9107945; Tue, 26 May 2020 07:23:14 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : subject : to : references : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=a65xRIo3urv/NzNhdPk03L/O/OFbH9wIqgkpFufbZd0=; b=ZrYNnWfcym2B9nNQbPp61f8Noidr3YYC47mVdNhKpSxUW+nkTeHY96p3HylEqVFRlq0x qa8ga4pW6ZHr8ktSaeu8QYQwPKhxgx50UPfAueO2BmYGHyNVa0xGhU8pnP0rWztyOG6R BUVlnoj9lq2uo7qf8DQfUOVkG0Hv4H+d0022OtQ2EPWOQOAR1KMazUgBzPi+eX7adm8m /2DLff7uAFbA9jq2yVZMoffB4Kv++0JykrIbSSW4kUfk37q2vEikpd8uILUTvfwqYHmd c81mjAeqplmcd6hT70z55iHempVd581EgaTejd84O54m4+tAm2SKFswqB+JvZDmZ5hZg FA== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2120.oracle.com with ESMTP id 318xbjr2vp-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 26 May 2020 07:23:14 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04Q7Mvvj084045; Tue, 26 May 2020 07:23:13 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3030.oracle.com with ESMTP id 317ddndkmj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 26 May 2020 07:23:13 +0000 Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 04Q7NC6r017488; Tue, 26 May 2020 07:23:12 GMT Received: from [192.168.1.102] (/39.109.177.87) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 26 May 2020 00:23:11 -0700 From: Anand Jain Subject: Re: [PATCH v7 rebased 0/5] readmirror feature (sysfs and in-memory only approach; with new read_policy device) To: dsterba@suse.cz, dsterba@suse.com, linux-btrfs@vger.kernel.org References: <1586173871-5559-1-git-send-email-anand.jain@oracle.com> <20200515195858.GS18421@twin.jikos.cz> <20200522134656.GL18421@twin.jikos.cz> Message-ID: Date: Tue, 26 May 2020 15:23:08 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200522134656.GL18421@twin.jikos.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9632 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 bulkscore=0 mlxscore=0 phishscore=0 adultscore=0 suspectscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005260057 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9632 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 spamscore=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 cotscore=-2147483648 suspectscore=0 bulkscore=0 clxscore=1015 impostorscore=0 malwarescore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005260057 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 22/5/20 9:46 pm, David Sterba wrote: > On Tue, May 19, 2020 at 06:02:32PM +0800, Anand Jain wrote: >> On 16/5/20 3:58 am, David Sterba wrote: >>> On Thu, Apr 30, 2020 at 05:02:27PM +0800, Anand Jain wrote: >>>> I am not sure if this will be integrated in 5.8 and worth the time to >>>> rebase. Kindly suggest. >>> >>> The preparatory work is ok, but the actual mirror selection policy >>> addresses a usecase that I think is not the one most users are >>> interested in. Devices of vastly different performance capabilities like >>> rotational disks vs nvme vs ssd vs network block devices in one >>> filesystem are not something commonly found. >>> >>> What we really need is a saner balancing mechanism than pid-based, that >>> is also going to be used any time there are more devices from the same >>> speed class for the fast devices too. >> >> There are two things here, the read_policy framework in the preparatory >> patches and a new balancing or read_policy, device. >> >>> So, no the patchset is not on track for a merge without the improved >>> default balancing. >> >> It can be worked on top of the preparatory read_policy framework? > > Yes. > >> This patchset does not change any default read_policy (or balancing) >> which is pid as of now. Working on a default read_policy/balancing >> was out of the scope of this patchset. >> >>> The preferred device for reads can be one of the >>> policies, I understand the usecase and have not problem with that >>> although wouldn't probably have use for it. >> >> For us, read_policy:device helps to reproduce raid1 data corruption >> https://patchwork.kernel.org/patch/11475417/ >> And xfstests btrfs/14[0-3] can be improved so that the reads directly >> go the device of the choice, instead of waiting for the odd/even pid. >> >> Common configuration won't need this, advance configurations assembled >> with heterogeneous devices where read performance is more critical than >> write will find read_policy:device useful. > > Yes that's the usecase and the possibility to make more targeted tests > is also good, but that still means the feature is half-baked and missing > the main part. If it was out of scope, ok fair, but I don't want to > merge it at that state. It would be embarassing to announce mirror > selection followed by "ah no it's useless for anything than this special > usecase". I didn't realize the need for default policy is prioritized before this patch set. Potential default read policy is interesting, looking into it. Thanks, Anand