linux-kernel - Re: Subject: [RFC MM] mmap_sem scaling: Use mutex and percpu counter instead

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Message-ID: <alpine.DEB.1.10.0911101519250.14300@V090114053VZO-1>
Date:	Tue, 10 Nov 2009 15:20:41 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	npiggin@...e.de, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>
Subject: Re: Subject: [RFC MM] mmap_sem scaling: Use mutex and percpu counter
  instead

On Sat, 7 Nov 2009, Minchan Kim wrote:

> On Sat, Nov 7, 2009 at 2:10 AM, Christoph Lameter
> <cl@...ux-foundation.org> wrote:
> > On Sat, 7 Nov 2009, Minchan Kim wrote:
> >
> >> How about change from 'mm_readers' to 'is_readers' to improve your
> >> goal 'scalibility'?
> >
> > Good idea. Thanks. Next rev will use your suggestion.
> >
> > Any creative thoughts on what to do about the 1 millisecond wait period?
> >
>
> Hmm,
> it would be importatn to prevent livelock for reader to hold lock
> continuously before
> hodling writer than 1 msec write ovhead.

Livelock because there are too frequent readers?

We could just keep the mutex locked to ensure that no new readers arrive.

> First of all, After we solve it, second step is that optimize write
> overhead, I think.

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