Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755435AbcKKKG0 (ORCPT ); Fri, 11 Nov 2016 05:06:26 -0500 Received: from mail-it0-f65.google.com ([209.85.214.65]:34217 "EHLO mail-it0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755282AbcKKKGU (ORCPT ); Fri, 11 Nov 2016 05:06:20 -0500 MIME-Version: 1.0 X-Originating-IP: [217.173.44.24] In-Reply-To: References: <1477380887-21333-1-git-send-email-mszeredi@redhat.com> <1477380887-21333-4-git-send-email-mszeredi@redhat.com> <20161025115748.ydhkkp5cfcdnjzwn@home.ouaza.com> From: Miklos Szeredi Date: Fri, 11 Nov 2016 11:06:18 +0100 Message-ID: Subject: Re: [PATCH 3/3] ovl: redirect on rename-dir To: Konstantin Khlebnikov Cc: Amir Goldstein , Raphael Hertzog , Miklos Szeredi , "linux-unionfs@vger.kernel.org" , Guillem Jover , linux-fsdevel , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2144 Lines: 50 On Fri, Nov 11, 2016 at 10:46 AM, Konstantin Khlebnikov wrote: > On Fri, Nov 11, 2016 at 1:56 AM, Amir Goldstein wrote: >> On Mon, Nov 7, 2016 at 3:38 PM, Amir Goldstein wrote: >>> On Mon, Nov 7, 2016 at 12:08 PM, Konstantin Khlebnikov wrote: >>>> On Mon, Nov 7, 2016 at 1:04 PM, Miklos Szeredi wrote: >>>>> On Mon, Nov 7, 2016 at 10:58 AM, Konstantin Khlebnikov wrote: >>>>> >>>>>> I've stumbled on somehow related problem - concurrent copy-ups are >>>>>> strictly serialized by rename locks. >>>>>> Obviously, file copying could be done in parallel: locks are required >>>>>> only for final rename. >>>>>> Because of that overlay slower that aufs for some workloads. >>>>> >>>>> Easy to fix: for each copy up create a separate subdir of "work". >>>>> Then the contention is only for the time of creating the subdir, which >>>>> is very short. >>>> >>>> Yeah, but lock_rename() also takes per-sb s_vfs_rename_mutex (kludge by Al Viro) >>>> I think proper synchronization for concurrent copy-up (for example >>>> round flag on ovl_entry) and locking rename only for rename could be >>>> better. >>> >>> Removing s_vfs_rename_mutex from copy-up path is something I have been >>> pondering about. >>> Assuming that I understand Al's comment above vfs_rename() correctly, >>> the sole purpose of per-sb serialization is to prevent loop creations. >>> However, how can one create a loop by moving a non-directory? >>> So it looks like at least for the non-dir copy up case, a much finer grained >>> lock is in order. >>> >> >> >> I posted patches to relax the s_vfs_rename_mutex for copy-up and >> whiteout in some use cases. >> >> Konstantin, >> >> It would be useful to know if those patches help with your use case. >> > > Well.. I think relaxing only s_vfs_rename_mutex wouldn't help much here. > Copying is still serialized by i_mutex on workdir? > Data copying should be done without rename locks at all. We do need something to prevent multiple copy-ups starting up in parallel on the same file, though. Thanks, Miklos