On Mon, Nov 7, 2016 at 12:08 PM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> wrote: > On Mon, Nov 7, 2016 at 1:04 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >> On Mon, Nov 7, 2016 at 10:58 AM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
