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=-5.5 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 18404C433E0 for ; Wed, 22 Jul 2020 07:18:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D0E80206F5 for ; Wed, 22 Jul 2020 07:18:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D0E80206F5 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 4FF436B0005; Wed, 22 Jul 2020 03:18:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4D3DC6B0006; Wed, 22 Jul 2020 03:18:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 410E86B0007; Wed, 22 Jul 2020 03:18:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0088.hostedemail.com [216.40.44.88]) by kanga.kvack.org (Postfix) with ESMTP id 2D8356B0005 for ; Wed, 22 Jul 2020 03:18:17 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D7E101844DB19 for ; Wed, 22 Jul 2020 07:18:16 +0000 (UTC) X-FDA: 77064858192.15.ducks77_420722526f34 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id A18E81809DA2F for ; Wed, 22 Jul 2020 07:18:16 +0000 (UTC) X-HE-Tag: ducks77_420722526f34 X-Filterd-Recvd-Size: 2212 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf04.hostedemail.com (Postfix) with ESMTP for ; Wed, 22 Jul 2020 07:18:15 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 5D2936736F; Wed, 22 Jul 2020 09:18:11 +0200 (CEST) Date: Wed, 22 Jul 2020 09:18:09 +0200 From: Christoph Hellwig To: Johannes Thumshirn Cc: Christoph Hellwig , Jens Axboe , Song Liu , Hans de Goede , Richard Weinberger , Minchan Kim , "linux-mtd@lists.infradead.org" , "dm-devel@redhat.com" , "linux-block@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 06/14] block: lift setting the readahead size into the block layer Message-ID: <20200722071809.GA25816@lst.de> References: <20200722062552.212200-1-hch@lst.de> <20200722062552.212200-7-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-Rspamd-Queue-Id: A18E81809DA2F X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 22, 2020 at 07:13:54AM +0000, Johannes Thumshirn wrote: > On 22/07/2020 08:27, Christoph Hellwig wrote: > > + q->backing_dev_info->ra_pages = > > + max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES); > > Dumb question, wouldn't a '>> PAGE_SHIFT' be better instead of a potentially > costly division? > > Or aren't we caring at all as it's a) not in the fast-path and b) compilers > can optimize it to a shift? That's my thinking. If anyone has a strong preference I can change it.