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Date: Wed, 12 Feb 2020 10:45:06 -0800
From: Linus Torvalds <>
To: "Eric W. Biederman" <>
Cc: LKML <>, 
	Kernel Hardening <>, Linux API <>, 
	Linux FS Devel <>, 
	Linux Security Module <>, 
	Akinobu Mita <>, Alexander Viro <>, 
	Alexey Dobriyan <>, Andrew Morton <>, 
	Andy Lutomirski <>, Daniel Micay <>, 
	Djalal Harouni <>, "Dmitry V . Levin" <>, 
	Greg Kroah-Hartman <>, Ingo Molnar <>, 
	"J . Bruce Fields" <>, Jeff Layton <>, 
	Jonathan Corbet <>, Kees Cook <>, Oleg Nesterov <>, 
	Solar Designer <>
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances

On Wed, Feb 12, 2020 at 7:01 AM Eric W. Biederman <> 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?


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