Re: [linux-next:master] [lockref] d042dae6ad: unixbench.throughput -33.7% regression

[Linus Torvalds]

On Tue, 2 Jul 2024 at 10:03, Mateusz Guzik <mjguzik@xxxxxxxxx> wrote:
>
> I was thinking a different approach.
>
> A lookup variant which resolves everything and returns the dentry + an
> information whether this is rcu mode.

That would work equally.

But the end result ends up being very similar: you need to hook into
that final complete_walk() -> try_to_unlazy() -> legitimize_path() and
check a flag whether you actually then do "get_lockref_or_dead()" or
not.

It really *shouldn't* be too bad, but this is just so subtle code that
it just takes a lot of care. Even if the patch itself ends up not
necessarily being very large.

As mentioned, I've looked at it, but it always ended up being _just_
scary enough that I never really started doing it.

               Linus