linux-kernel - Re: [PATCH 3/3] ovl: redirect on rename-dir

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Date:   Mon, 7 Nov 2016 13:08:27 +0300
From:   Konstantin Khlebnikov <koct9i@...il.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Raphael Hertzog <hertzog@...ian.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        Guillem Jover <guillem@...ian.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] ovl: redirect on rename-dir

On Mon, Nov 7, 2016 at 1:04 PM, Miklos Szeredi <miklos@...redi.hu> wrote:
> On Mon, Nov 7, 2016 at 10:58 AM, Konstantin Khlebnikov <koct9i@...il.com> 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.