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 E7128C43603 for ; Sun, 8 Dec 2019 22:43:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C289720637 for ; Sun, 8 Dec 2019 22:43:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726818AbfLHWnD (ORCPT ); Sun, 8 Dec 2019 17:43:03 -0500 Received: from mail104.syd.optusnet.com.au ([211.29.132.246]:40652 "EHLO mail104.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726806AbfLHWnD (ORCPT ); Sun, 8 Dec 2019 17:43:03 -0500 Received: from dread.disaster.area (pa49-195-156-222.pa.nsw.optusnet.com.au [49.195.156.222]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 0E8A17E84D7; Mon, 9 Dec 2019 09:42:56 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1ie5GR-00083f-JJ; Mon, 09 Dec 2019 09:42:55 +1100 Date: Mon, 9 Dec 2019 09:42:55 +1100 From: Dave Chinner To: Daniel Phillips Cc: "Theodore Y. Ts'o" , Andreas Dilger , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, OGAWA Hirofumi Subject: Re: [RFC] Thing 1: Shardmap for Ext4 Message-ID: <20191208224255.GA29550@dread.disaster.area> References: <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> <1dd1f9f6-89a4-e73a-d7b9-94a12412876c@phunq.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1dd1f9f6-89a4-e73a-d7b9-94a12412876c@phunq.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=umqzQS5wKVu6clrBNKse/g==:117 a=umqzQS5wKVu6clrBNKse/g==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=pxVhFHJ0LMsA:10 a=ySfo2T4IAAAA:8 a=7-415B0cAAAA:8 a=ffP6t5IPy7SrnJvA8FoA:9 a=CjuIK1q_8ugA:10 a=ZUkhVnNHqyo2at-WnAgH:22 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Dec 05, 2019 at 09:09:28PM -0800, Daniel Phillips wrote: > 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? My initial reaction is to run away screaming in horror. Beyond that, I have no idea what terrible dangers lurk in the dark shadows where mortals fear to tread... -Dave. -- Dave Chinner david@fromorbit.com