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

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On Mon, Nov 7, 2016 at 12:08 PM, Konstantin Khlebnikov <koct9i@gmail.com> wrote:
> On Mon, Nov 7, 2016 at 1:04 PM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> On Mon, Nov 7, 2016 at 10:58 AM, Konstantin Khlebnikov <koct9i@gmail.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.

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.

Anyway, it's on my todo list, as concurrent operation performance on overlayfs
is important to out use case.

Amir.

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Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-06 20:20 +0100
  Re: [PATCH 3/3] ovl: redirect on rename-dir Miklos Szeredi <miklos@szeredi.hu> - 2016-11-07 09:10 +0100
    Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-07 11:00 +0100
      Re: [PATCH 3/3] ovl: redirect on rename-dir Miklos Szeredi <miklos@szeredi.hu> - 2016-11-07 11:10 +0100
        Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-07 11:10 +0100
          Re: [PATCH 3/3] ovl: redirect on rename-dir Amir Goldstein <amir73il@gmail.com> - 2016-11-07 18:50 +0100
            Re: [PATCH 3/3] ovl: redirect on rename-dir Amir Goldstein <amir73il@gmail.com> - 2016-11-11 00:00 +0100
              Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-11 10:50 +0100
                Re: [PATCH 3/3] ovl: redirect on rename-dir Miklos Szeredi <miklos@szeredi.hu> - 2016-11-11 11:10 +0100
                Re: [PATCH 3/3] ovl: redirect on rename-dir Amir Goldstein <amir73il@gmail.com> - 2016-11-11 13:50 +0100
  Re: [PATCH 3/3] ovl: redirect on rename-dir Raphael Hertzog <hertzog@debian.org> - 2016-11-07 12:10 +0100
    Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-07 12:40 +0100
      Re: [PATCH 3/3] ovl: redirect on rename-dir Raphael Hertzog <hertzog@debian.org> - 2016-11-07 14:50 +0100
        Re: [PATCH 3/3] ovl: redirect on rename-dir Miklos Szeredi <miklos@szeredi.hu> - 2016-11-10 23:40 +0100
          Re: [PATCH 3/3] ovl: redirect on rename-dir Konstantin Khlebnikov <koct9i@gmail.com> - 2016-11-11 10:50 +0100

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