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=-5.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 35C0BC47082 for ; Sat, 5 Jun 2021 22:55:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A3FA613F7 for ; Sat, 5 Jun 2021 22:55:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230050AbhFEW47 (ORCPT ); Sat, 5 Jun 2021 18:56:59 -0400 Received: from smtp.hosts.co.uk ([85.233.160.19]:28362 "EHLO smtp.hosts.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229998AbhFEW46 (ORCPT ); Sat, 5 Jun 2021 18:56:58 -0400 X-Greylist: delayed 1000 seconds by postgrey-1.27 at vger.kernel.org; Sat, 05 Jun 2021 18:56:58 EDT Received: from host86-157-72-169.range86-157.btcentralplus.com ([86.157.72.169] helo=[192.168.1.65]) by smtp.hosts.co.uk with esmtpa (Exim) (envelope-from ) id 1lpew0-000CKG-Ap; Sat, 05 Jun 2021 23:38:28 +0100 Subject: Re: [Bug Report] Discard bios cannot be correctly merged in blk-mq To: Wang Shanker , linux-block@vger.kernel.org Cc: linux-raid@vger.kernel.org References: <85F98DA6-FB28-4C1F-A47D-C410A7C22A3D@gmail.com> From: antlists Message-ID: <6c407281-ee90-f577-d6db-d36211b1fdc0@youngman.org.uk> Date: Sat, 5 Jun 2021 23:38:28 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <85F98DA6-FB28-4C1F-A47D-C410A7C22A3D@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 05/06/2021 21:54, Wang Shanker wrote: > You may wonder the importance of merging discard operations. In the > implementation of RAID456, bios are committed in 4k trunks (they call > them as stripes in the code and the size is determined by DEFAULT_STRIPE_SIZE). > The proper merging of the bios is of vital importance for a reasonable > operating performance of RAID456 devices. Note that I have seen reports (I'm not sure where or how true they are), that even when requests are sent as 512k or whatever, certain upper layers break them into 4k's, presumably expecting lower layers to merge them again. You might have better luck looking for and suppressing the breaking up of large chunks. Cheers, Wol