On Fri, Nov 11, 2016 at 10:46 AM, Konstantin Khlebnikov <koc...@gmail.com> wrote: > On Fri, Nov 11, 2016 at 1:56 AM, Amir Goldstein <amir7...@gmail.com> wrote: >> On Mon, Nov 7, 2016 at 3:38 PM, Amir Goldstein <amir7...@gmail.com> wrote: >>> On Mon, Nov 7, 2016 at 12:08 PM, Konstantin Khlebnikov <koc...@gmail.com> >>> wrote: >>>> On Mon, Nov 7, 2016 at 1:04 PM, Miklos Szeredi <mik...@szeredi.hu> wrote: >>>>> On Mon, Nov 7, 2016 at 10:58 AM, Konstantin Khlebnikov <koc...@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. >>> >> >> >> 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
