On 2019-12-05 5:16 p.m., Dave Chinner wrote: > On Wed, Dec 04, 2019 at 06:41:06PM -0500, Theodore Y. Ts'o wrote: >> On Wed, Dec 04, 2019 at 11:31:50AM -0700, Andreas Dilger wrote: >>> One important use case that we have for Lustre that is not yet in the >>> upstream ext4[*] is the ability to do parallel directory operations. >>> This means we can create, lookup, and/or unlink entries in the same >>> directory concurrently, to increase parallelism for large directories. >>> >>> [*] we've tried to submit the pdirops patch a couple of times, but the >>> main blocker is that the VFS has a single directory mutex and couldn't >>> use the added functionality without significant VFS changes. >>> Patch at https://git.whamcloud.com/?p=fs/lustre-release.git;f=ldiskfs/kernel_patches/patches/rhel8/ext4-pdirop.patch;hb=HEAD >>> >> >> The XFS folks recently added support for parallel directory operations >> into the VFS, for the benefit of XFS has this feature. > > The use of shared i_rwsem locking on the directory inode during > lookup/pathwalk allows for concurrent lookup/readdir operations on > a single directory. However, the parent dir i_rwsem is still held > exclusive for directory modifications like create, unlink, etc. > > IOWs, the VFS doesn't allow for concurrent directory modification > right now, and that's going to be the limiting factor no matter what > you do with internal filesystem locking. On a scale of 0 to 10, how hard do you think that would be to relax in VFS, given the restriction of no concurrent inter-directory moves?
