linux-kernel - Re: [RFC PATCH] futex: Remove requirement for lock_page in get_futex

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Message-ID: <20150224165540.GA32264@breakpoint.cc>
Date:	Tue, 24 Feb 2015 17:55:40 +0100
From:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
To:	Mel Gorman <mgorman@...e.de>, Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Chris Mason <chris.mason@...ionio.com>,
	Chris Mason <clm@...com>, LKML <linux-kernel@...r.kernel.org>,
	Sebastian Sewior <bigeasy@...utronix.de>
Subject: Re: [RFC PATCH] futex: Remove requirement for lock_page in
 get_futex_key

On 2014-02-11 16:51:55 [+0100], Thomas Gleixner wrote:
> On Wed, 30 Oct 2013, Mel Gorman wrote:
> > On Wed, Oct 30, 2013 at 09:45:31AM +0100, Thomas Gleixner wrote:
> > > On Tue, 29 Oct 2013, Mel Gorman wrote:
> > > > Patch boots and futextest did not explode but I did no comparison
> > > > performance tests. Thomas, do you have details of the workload that
> > > > drove you to examine this problem? Alternatively, can you test it and
> > > The scenario is simple. All you need is a PSHARED futex.
> > > 
> > > Task A 
> > >      get_futex_key()
> > >      lock_page()
> > > 
> > > ---> preemption
> > > 
> > Do please. I'd rather not sink time into trying to reproduce a hypothetical
> > problem when people who are already familiar with it can provide better
> Took some time, but the folks finally came around to give it a try and
> it fixes their problem. I did not explode either, but I doubt, that
> their workload can trigger any of the corner cases.

I just stumbled uppon this patch and now I am curious about its status.
tglx said that it solves the problem in question (with doubt of
triggering all the corner cases). Chris pointed out that moving
put_page() might be worth doing.

Sebastian
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