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From: Peter Zijlstra <peterz@infradead.org>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux-foundation.org>,
	Nick Piggin <npiggin@suse.de>, Paul Menage <menage@google.com>,
	Derek Fults <dfults@sgi.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [patch 6/7] cpusets: per cpuset dirty ratios
Date: Thu, 30 Oct 2008 10:34:16 +0100	[thread overview]
Message-ID: <1225359256.7803.52.camel@twins> (raw)
In-Reply-To: <alpine.DEB.2.00.0810300154040.29917@chino.kir.corp.google.com>

On Thu, 2008-10-30 at 02:03 -0700, David Rientjes wrote:
> On Thu, 30 Oct 2008, Peter Zijlstra wrote:
> 
> > On Tue, 2008-10-28 at 09:08 -0700, David Rientjes wrote:
> > 
> > > +/*
> > > + * Determine the dirty ratios for the currently active cpuset
> > > + */
> > > +void cpuset_get_current_dirty_ratios(int *background, int *throttle)
> > > +{
> > > +	mutex_lock(&callback_mutex);
> > > +	task_lock(current);
> > > +	*background = task_cs(current)->dirty_background_ratio;
> > > +	*throttle = task_cs(current)->cpuset_dirty_ratio;
> > > +	task_unlock(current);
> > > +	mutex_unlock(&callback_mutex);
> > > +
> > > +	if (*background == -1)
> > > +		*background = dirty_background_ratio;
> > > +	if (*throttle == -1)
> > > +		*throttle = vm_dirty_ratio;
> > > +}
> > 
> > That's rather an awful lot of locking to read just two integers.
> > 
> 
> As far as I know, task_lock(current) is required to dereference 
> task_cs(current) and callback_mutex is required to ensure its the same 
> cpuset.

Since we read these things for every evaluation, getting it wrong isn't
too harmful.

So I would suggest just enough locking to ensure we don't reference any
NULL pointers and such.

IIRC the cpuset stuff is RCU freed, so some racy read should be
possible, no?

  reply	other threads:[~2008-10-30  9:34 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-10-28 16:08 [patch 1/7] cpusets: add dirty map to struct address_space David Rientjes
2008-10-28 16:08 ` [patch 2/7] pdflush: allow the passing of a nodemask parameter David Rientjes
2008-10-28 16:08 ` [patch 3/7] mm: make page writeback obey cpuset constraints David Rientjes
2008-10-28 17:31   ` Peter Zijlstra
2008-10-28 19:16     ` David Rientjes
2008-10-28 17:32   ` Peter Zijlstra
2008-10-28 19:18     ` David Rientjes
2008-10-30  8:42       ` Peter Zijlstra
2008-10-30  9:10         ` David Rientjes
2008-10-30  9:34           ` Peter Zijlstra
2008-10-28 16:08 ` [patch 4/7] mm: cpuset aware reclaim writeout David Rientjes
2008-10-28 16:08 ` [patch 5/7] mm: throttle writeout with cpuset awareness David Rientjes
2008-10-28 16:08 ` [patch 6/7] cpusets: per cpuset dirty ratios David Rientjes
2008-10-30  6:59   ` Paul Menage
2008-10-30  8:48     ` David Rientjes
2008-10-30 15:28     ` Christoph Lameter
2008-10-30  8:44   ` Peter Zijlstra
2008-10-30  9:03     ` David Rientjes
2008-10-30  9:34       ` Peter Zijlstra [this message]
2008-10-30 10:02         ` David Rientjes
2008-10-28 16:08 ` [patch 7/7] cpusets: update documentation for writeback throttling David Rientjes
2008-10-30 16:06   ` Christoph Lameter
2008-10-28 17:37 ` [patch 1/7] cpusets: add dirty map to struct address_space Peter Zijlstra
2008-10-28 20:48   ` David Rientjes
2008-10-29  1:13     ` David Rientjes
2008-10-29  2:24       ` David Rientjes
2008-10-30  8:38       ` Peter Zijlstra
2008-10-28 17:46 ` Peter Zijlstra
2008-10-28 19:19   ` David Rientjes
2008-10-30 19:23 [patch 0/7] cpuset writeback throttling David Rientjes
2008-10-30 19:23 ` [patch 6/7] cpusets: per cpuset dirty ratios David Rientjes

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