On a recent kernel with readdir caching and FUSE_NO_OPENDIR_SUPPORT (and this follow-on patch: https://patchwork.kernel.org/patch/10785105/ ), I benchmarked our source control FUSE filesystem. With hot caches and zero requests being made to userspace, I could do a full directory crawl of a major subset of our repository in under 3 seconds. When I ran the same test against ext4 and btrfs, it took between 3 and 6 seconds. Awesome! However, though we were correctly sending FUSE_NOTIFY_INVAL_ENTRY whenever changing a directory inode's entry, this did not flush the readdir pagecache. It looks to me like FUSE_NOTIFY_INVAL_ENTRY only invalidates the readdir cache if the dcache has an entry with the given name. Whether that's true is entirely out of userspace's hands. We worked around it by also explicitly sending FUSE_NOTIFY_INVAL_INODE once per inode if we ever sent FUSE_NOTIFY_INVAL_ENTRY. But this increases our invalidation traffic and seems unnecessary. What do you think about having FUSE_NOTIFY_INVAL_ENTRY also unconditionally invalidate the readdir cache?
