On Mon, Jan 25, 2021 at 1:36 PM Jens Axboe [off-list ref] wrote:

    Patch 2 is the
mostly ugly part, but not sure how we can do this any better - we need
to ensure that any sort of revalidation or sync in ->getattr() honors
it too.

Yeah, that's not pretty, but I agree - it looks like this just
requires the filesystem to check whether it needs to revalidate or
not.

But I think that patch could do better than what your patch does. Some
of them are "filesystems could decide to be more finegrained") -  your
cifs patch comes to mind - but some of your "return -EAGAIN if cached"
seem to be just plain pointless.

In afs, for example, you return -EAGAIN instead of just doing the
read-seqlock thing. That's a really cheap CPU-only operation. We're
talking "cheaper than a spinlock" sequence.

           Linus