In FUSE, as of now, uncached lookups are expensive over the wire. E.g additional latencies and stressing (meta data) servers from thousands of clients. These lookup calls possibly can be avoided in some cases. Incoming three patches address this issue. Fist patch handles the case where we are creating a file with O_CREAT. Before we go for file creation, we do a lookup on the file which is most likely non-existent. After this lookup is done, we again go into libfuse to create file. Such lookups where file is most likely non-existent, can be avoided. Second patch handles the case where we open first time a file/dir but do a lookup first on it. After lookup is performed we make another call into libfuse to open the file. Now these two separate calls into libfuse can be combined and performed as a single call into libfuse. Third patch handles the case when we are opening an already existing file (positive dentry). Before this open call, we re-validate the inode and this re-validation does a lookup on the file and verify the inode. This separate lookup also can be avoided (for non-dir) and combined with open call into libfuse. After open returns we can revalidate the inode. This optimisation is performed only when we do not have default permissions enabled. Here is the link to performance numbers https://lore.kernel.org/linux-fsdevel/20220322121212.5087-1-dharamhans87@xxxxxxxxx/ Dharmendra Singh (3): FUSE: Implement atomic lookup + create Implement atomic lookup + open Avoid lookup in d_revalidate() fs/fuse/dir.c | 211 +++++++++++++++++++++++++++++++++++--- fs/fuse/file.c | 30 +++++- fs/fuse/fuse_i.h | 16 ++- fs/fuse/inode.c | 4 +- fs/fuse/ioctl.c | 2 +- include/uapi/linux/fuse.h | 5 + 6 files changed, 246 insertions(+), 22 deletions(-) --- v4: Addressed all comments and refactored the code into 3 separate patches respectively for Atomic create, Atomic open, optimizing lookup in d_revalidate(). ---
