Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances

[Linus Torvalds]

On Wed, Feb 12, 2020 at 7:01 AM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>
> Fundamentally proc_flush_task is an optimization.  Just getting rid of
> dentries earlier.  At least at one point it was an important
> optimization because the old process dentries would just sit around
> doing nothing for anyone.

I'm pretty sure it's still important. It's very easy to generate a
_ton_ of dentries with /proc.

> I wonder if instead of invalidating specific dentries we could instead
> fire wake up a shrinker and point it at one or more instances of proc.

It shouldn't be the dentries themselves that are a freeing problem.
They're being RCU-free'd anyway because of lookup. It's the
proc_mounts list that is the problem, isn't it?

So it's just fs_info that needs to be rcu-delayed because it contains
that list. Or is there something else?

               Linus