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=-4.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 04BC1C47095 for ; Tue, 6 Oct 2020 08:50:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8CD132100A for ; Tue, 6 Oct 2020 08:49:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=veeam.com header.i=@veeam.com header.b="ZxPWIA3P" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726000AbgJFItm (ORCPT ); Tue, 6 Oct 2020 04:49:42 -0400 Received: from mx4.veeam.com ([104.41.138.86]:48200 "EHLO mx4.veeam.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbgJFItl (ORCPT ); Tue, 6 Oct 2020 04:49:41 -0400 X-Greylist: delayed 430 seconds by postgrey-1.27 at vger.kernel.org; Tue, 06 Oct 2020 04:49:41 EDT Received: from mail.veeam.com (prgmbx01.amust.local [172.24.0.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx4.veeam.com (Postfix) with ESMTPS id A280D1C0EA; Tue, 6 Oct 2020 11:42:43 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=veeam.com; s=mx4; t=1601973763; bh=e9f9XYoSs4yUz+6D/V0mbo/RjIBkU4bh11PRahPKKpM=; h=Date:From:To:CC:Subject:References:In-Reply-To:From; b=ZxPWIA3PCdH7kv811Feros9C+xubBZ2Z524Ik/NnkcTGj7Ize7riljrfCh4Uir2wK JimOg2zgRP5KbNKvez+Wkoh3JrT1YYstOeAenrBlX7SP9KSoAQ5eZUACCnQLVNOuwT FfjobPKg0OHc5Zl5qwRqLoEXFz/WId4R82X0vBqc= Received: from veeam.com (172.24.14.5) by prgmbx01.amust.local (172.24.0.171) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.595.3; Tue, 6 Oct 2020 10:42:41 +0200 Date: Tue, 6 Oct 2020 11:43:32 +0300 From: Sergei Shtepa To: Konstantin Khlebnikov CC: Jens Axboe , "mchehab+huawei@kernel.org" , David Miller , "robh@kernel.org" , "damien.lemoal@wdc.com" , Jan Kara , "ming.lei@redhat.com" , "steve@sk2.org" , "Linux Kernel Mailing List" , linux-kbuild , "linux-block@vger.kernel.org" Subject: Re: [PATCH 1/1] blk-snap - Block snapshot module This module implements snapshot and changed block tracking functionality. It is intended to create backup copies of any block devices without usage of device-mapper. Message-ID: <20201006084332.GA9979@veeam.com> References: <1601643362-7370-1-git-send-email-sergei.shtepa@veeam.com> <1601643362-7370-2-git-send-email-sergei.shtepa@veeam.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: X-Originating-IP: [172.24.14.5] X-ClientProxiedBy: prgmbx01.amust.local (172.24.0.171) To prgmbx01.amust.local (172.24.0.171) X-EsetResult: clean, is OK X-EsetId: 37303A29C604D26A657660 X-Veeam-MMEX: True X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx4.veeam.com [172.31.224.40]); Tue, 06 Oct 2020 11:42:43 +0300 (MSK) X-Veeam-MailScanner-Information: Please contact email@veeam.com if you have any problems Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks for the answer. Unfortunately, blk-rq-qos cannot be used efficiently for this purpose. blk-rq-qos is good for collecting request queue processing metrics. The level at which the interception is performed is too low - it happens after the device driver has already received the request for processing. For the filter to work efficiently, we need to ensure that the interception is performed on a higher level. It is required to put processing of multiple BIOs on hold while COW algorithm is being executed for them. We must not be blocking the request processing queue, and also we would like to avoid impacting the IO scheduler operations. -- Sergei Shtepa Veeam Software developer.