linux-kernel - Re: [PATCH] proc: change proc_subdir

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Message-ID: <CACVxJT8PRamwFeND2WpERW1K6fWv1RLvYBpjYooOVuWjqunT=g@mail.gmail.com>
Date:	Thu, 30 Jul 2015 13:04:58 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Waiman Long <Waiman.Long@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH] proc: change proc_subdir_lock to a rwlock

On Thu, Jul 30, 2015 at 1:21 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Two quick questions.
>
> - What motivates this work?  Are you seeing lots of
>   parallel reads on proc?

Well, yes, benchmark looks like very synthetic.
But even gcc opens /proc/meminfo, so might as well
apply the change.

Patch looks like obviously correct to me.

> - Why not rcu?  Additions and removal of proc generic
>   files is very rare.  Conversion to rcu for reads should
>   perform better and not take much more work.

If you want proc locking to be understood by ~10 people
on the planet then yes, there is RCU. :-)
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