linux-kernel - Re: [PATCH 2/3] rcu: Create rcu

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Message-ID: <20131004151323.GA16440@redhat.com>
Date:	Fri, 4 Oct 2013 17:13:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] rcu: Create rcu_sync infrastructure

On 10/04, Peter Zijlstra wrote:
>
> On Fri, Oct 04, 2013 at 03:31:35PM +0200, Oleg Nesterov wrote:
> > > I'm really starting to think we shouldn't do this in rcu_sync at all.
> >
> > I do not really understand why you insist that rcu_sync() should not
> > try to help to the users which need the exclusive mode.
>
> But what other users; you yourself said that percpu-rwsem isn't one for
> long if ever.

Not sure I understand...

percpu-rwsem will use exclusive mode, with or without the possible
improvements we can copy from cpuhp. sb_writers can probably use it
too (along with other helpers from percpu-rwsem we do not have yet).

If you mean that the "raw" rcu_sync infrastructure will never have
more users, will I am not sure, it looks "natural". But I can not
know for sure.

OK, I am not going to argue too much, let me send other patches
you seem to agree with. I am also going to send this one for the
record/review (without __complete_locked), please ack-or-nack it
explicitly.

I am not trying saying this feature is "must have", of course it
is not. The only problem, I am a bit puzzled why you dislike it
that much.

Oleg.

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