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=-5.3 required=3.0 tests=BAYES_00, 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 25C72C43465 for ; Mon, 21 Sep 2020 14:00:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5E89320756 for ; Mon, 21 Sep 2020 14:00:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E89320756 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 73CC190006A; Mon, 21 Sep 2020 10:00:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6EB2D900069; Mon, 21 Sep 2020 10:00:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6022190006A; Mon, 21 Sep 2020 10:00:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0241.hostedemail.com [216.40.44.241]) by kanga.kvack.org (Postfix) with ESMTP id 49526900069 for ; Mon, 21 Sep 2020 10:00:24 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id E5E97180AD81D for ; Mon, 21 Sep 2020 14:00:23 +0000 (UTC) X-FDA: 77287228326.21.price52_460a12727145 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 50D62180445EB for ; Mon, 21 Sep 2020 14:00:16 +0000 (UTC) X-HE-Tag: price52_460a12727145 X-Filterd-Recvd-Size: 2239 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Mon, 21 Sep 2020 14:00:15 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A75DA68AFE; Mon, 21 Sep 2020 16:00:11 +0200 (CEST) Date: Mon, 21 Sep 2020 16:00:10 +0200 From: Christoph Hellwig To: Coly Li Cc: Christoph Hellwig , Jens Axboe , Song Liu , Hans de Goede , Richard Weinberger , Minchan Kim , Johannes Thumshirn , Justin Sanders , linux-mtd@lists.infradead.org, dm-devel@redhat.com, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, drbd-dev@lists.linbit.com, linux-raid@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org Subject: Re: [PATCH 03/13] bcache: inherit the optimal I/O size Message-ID: <20200921140010.GA14672@lst.de> References: <20200921080734.452759-1-hch@lst.de> <20200921080734.452759-4-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000131, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 21, 2020 at 05:54:59PM +0800, Coly Li wrote: > I am not sure whether virtual bcache device's optimal request size can > be simply set like this. > > Most of time inherit backing device's optimal request size is fine, but > there are two exceptions, > - Read request hits on cache device > - User sets sequential_cuttoff as 0, all writing may go into cache > device firstly. > For the above two conditions, all I/Os goes into cache device, using > optimal request size of backing device might be improper. > > Just a guess, is it OK to set the optimal request size of the virtual > bcache device as the least common multiple of cache device's and backing > device's optimal request sizes ? Well, if the optimal I/O size is wrong, the read ahead size also is wrong. Can we just drop the setting?