On Wed, 2 Jul 2025 at 14:27, Ashmeen Kaur <ashmeen@xxxxxxxxxx> wrote: > > Hello Team, > > I have been experimenting with the FUSE > passthrough(https://docs.kernel.org/filesystems/fuse-passthrough.html) > feature. I have a question regarding its interaction with the kernel > page cache. > > During my evaluation, I observed a performance degradation when using > passthrough. My understanding is that the I/O on the passthrough > backing file descriptor bypasses the kernel page cache and goes > directly to disk. Passthrough opens the backing file with the same flags as the fuse file was opened. If it had O_DIRECT, then the backing file will be opened with O_DIRECT. If your fuse server implementation removed O_DIRECT from the open flags before opening the backing file, then this can indeed be a regression. Otherwise there is probably some other issue. Thanks, Miklos
