[Linux-cachefs] How capacious and well-indexed are ext4, xfs and btrfs directories?

[David Howells]

Andreas Dilger <adilger at dilger.ca> wrote:

> As described elsewhere in the thread, allowing concurrent create and unlink
> in a directory (rename probably not needed) would be invaluable for scaling
> multi-threaded workloads.  Neil Brown posted a prototype patch to add this
> to the VFS for NFS:

Actually, one thing I'm looking at is using vfs_tmpfile() to create a new file
(or a replacement file when invalidation is required) and then using
vfs_link() to attach directory entries in the background (possibly using
vfs_link() with AT_LINK_REPLACE[1] instead of unlink+link).

Any thoughts on how that might scale?  vfs_tmpfile() doesn't appear to require
the directory inode lock.  I presume the directory is required for security
purposes in addition to being a way to specify the target filesystem.

David

[1] https://lore.kernel.org/linux-fsdevel/cover.1580251857.git.osandov@fb.com/