linux-kernel - Re: [RFC PATCH] asynchronous page fault.

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Message-ID: <1262620974.6408.169.camel@laptop>
Date:	Mon, 04 Jan 2010 17:02:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	cl@...ux-foundation.org,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH] asynchronous page fault.

On Mon, 2010-01-04 at 07:55 -0800, Paul E. McKenney wrote:
> > Well, I was thinking srcu to have this force quiescent state in
> > call_srcu() much like you did for the preemptible rcu.
> 
> Ah, so the idea would be that you register a function with the srcu_struct
> that is invoked when some readers are stuck for too long in their SRCU
> read-side critical sections?  Presumably you also supply a time value for
> "too long" as well.  Hmmm...  What do you do, cancel the corresponding
> I/O or something? 

Hmm, I was more thinking along the lines of:

say IDX is the current counter idx.

if (pending > thresh) {
  flush(!IDX)
  force_flip_counter();
}

Since we explicitly hold a reference on IDX, we can actually wait for !
IDX to reach 0 and flush those callbacks.

We then force-flip the counter, so that even if all callbacks (or the
majority) were not for !IDX but part of IDX, we'd be able to flush them
on the next call_srcu() because that will then hold a ref on the new
counter index.


Or am I missing something obvious?

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