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=-2.2 required=3.0 tests=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 43DA8C2D0C0 for ; Fri, 6 Dec 2019 05:09:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A75F21823 for ; Fri, 6 Dec 2019 05:09:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726116AbfLFFJc (ORCPT ); Fri, 6 Dec 2019 00:09:32 -0500 Received: from mail.phunq.net ([66.183.183.73]:50290 "EHLO phunq.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726076AbfLFFJc (ORCPT ); Fri, 6 Dec 2019 00:09:32 -0500 Received: from [172.16.1.14] by phunq.net with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim 4.92.3) (envelope-from ) id 1id5rt-000825-1z; Thu, 05 Dec 2019 21:09:29 -0800 Subject: Re: [RFC] Thing 1: Shardmap for Ext4 To: Dave Chinner , "Theodore Y. Ts'o" Cc: Andreas Dilger , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, OGAWA Hirofumi References: <176a1773-f5ea-e686-ec7b-5f0a46c6f731@phunq.net> <20191127142508.GB5143@mit.edu> <20191128022817.GE22921@mit.edu> <3b5f28e5-2b88-47bb-1b32-5c2fed989f0b@phunq.net> <20191130175046.GA6655@mit.edu> <76ddbdba-55ba-3426-2e29-0fa17db9b6d8@phunq.net> <23F33101-065E-445A-AE5C-D05E35E2B78B@dilger.ca> <20191204234106.GC5641@mit.edu> <20191206011640.GQ2695@dread.disaster.area> From: Daniel Phillips Message-ID: <1dd1f9f6-89a4-e73a-d7b9-94a12412876c@phunq.net> Date: Thu, 5 Dec 2019 21:09:28 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191206011640.GQ2695@dread.disaster.area> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2019-12-05 5:16 p.m., Dave Chinner wrote: > On Wed, Dec 04, 2019 at 06:41:06PM -0500, Theodore Y. Ts'o wrote: >> On Wed, Dec 04, 2019 at 11:31:50AM -0700, Andreas Dilger wrote: >>> One important use case that we have for Lustre that is not yet in the >>> upstream ext4[*] is the ability to do parallel directory operations. >>> This means we can create, lookup, and/or unlink entries in the same >>> directory concurrently, to increase parallelism for large directories. >>> >>> [*] we've tried to submit the pdirops patch a couple of times, but the >>> main blocker is that the VFS has a single directory mutex and couldn't >>> use the added functionality without significant VFS changes. >>> Patch at https://git.whamcloud.com/?p=fs/lustre-release.git;f=ldiskfs/kernel_patches/patches/rhel8/ext4-pdirop.patch;hb=HEAD >>> >> >> The XFS folks recently added support for parallel directory operations >> into the VFS, for the benefit of XFS has this feature. > > The use of shared i_rwsem locking on the directory inode during > lookup/pathwalk allows for concurrent lookup/readdir operations on > a single directory. However, the parent dir i_rwsem is still held > exclusive for directory modifications like create, unlink, etc. > > IOWs, the VFS doesn't allow for concurrent directory modification > right now, and that's going to be the limiting factor no matter what > you do with internal filesystem locking. On a scale of 0 to 10, how hard do you think that would be to relax in VFS, given the restriction of no concurrent inter-directory moves?