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=-4.0 required=3.0 tests=BAYES_00, 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 46433C433E3 for ; Thu, 23 Jul 2020 15:00:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A9B820709 for ; Thu, 23 Jul 2020 15:00:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729554AbgGWPAO (ORCPT ); Thu, 23 Jul 2020 11:00:14 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:43439 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729323AbgGWPAO (ORCPT ); Thu, 23 Jul 2020 11:00:14 -0400 Received: from callcc.thunk.org (pool-96-230-252-158.bstnma.fios.verizon.net [96.230.252.158]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 06NF07ln026768 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 23 Jul 2020 11:00:08 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 14030420304; Thu, 23 Jul 2020 11:00:07 -0400 (EDT) Date: Thu, 23 Jul 2020 11:00:06 -0400 From: tytso@mit.edu To: Andreas Dilger Cc: Ext4 Developers List , Alex Zhuravlev , Shuichi Ihara Subject: Re: [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Message-ID: <20200723150006.GF1536749@mit.edu> References: <20200717155352.1053040-1-tytso@mit.edu> <20200717155352.1053040-2-tytso@mit.edu> <1F791FDF-75A7-48D9-A0A7-764D5AEC8E4B@dilger.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1F791FDF-75A7-48D9-A0A7-764D5AEC8E4B@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Tue, Jul 21, 2020 at 01:42:54AM -0600, Andreas Dilger wrote: > > I re-reviewed the patch with the changes, and it looks OK. I see that > you reduced the prefetch limit from 32 to 4 group blocks, presumably to > keep the latency low? It would be useful to see what impact that has > on the mount time and IO performance of a large filesystem. No, I didn't change it. As before, it's 4 times the size of the flex_bg size (assuming the file system has flex bg's enabled); otherwise it's 128 (4 times 32). I'm actually worried that this is too aggressive on storage devies where LBA's which are adjacent to each other aren't necessarily adjacent to each other on the physical storage device. For example, on dm-thin, some qemu-img formats, and potentially some cloud virtual block devices.... Unfortunately, there isn't a good way to query a block device to determine whether adjacent LBA's are really adjacent in the real world. - Ted