linux-kernel - Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures

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Message-ID: <20111121175242.GE15314@google.com>
Date:	Mon, 21 Nov 2011 09:52:42 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, pavel@....cz, lenb@...nel.org,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures

Hello,

On Mon, Nov 21, 2011 at 10:34:40PM +0530, Srivatsa S. Bhat wrote:
> >> I haven't tested this solution yet. Let me know if this solution looks
> >> good and I'll send it out as a patch after testing and analyzing some
> >> corner cases, if any.
> 
> I tested this, and it works great! I'll send the patch in some time.

Awesome.

> > * I think it would be better to remove direct access to pm_mutex and
> >   use [un]lock_system_sleep() universally.  I don't think hinging it
> >   on CONFIG_HIBERNATE_CALLBACKS buys us anything.
> > 
> 
> Which direct access to pm_mutex are you referring to?
> Other than suspend/hibernation call paths, I think mem-hotplug is the only
> subsystem trying to access pm_mutex. I haven't checked thoroughly though. 
> 
> But yes, using lock_system_sleep() for mutually excluding some code path
> from suspend/hibernation is good, and that is one reason why I wanted
> to fix this API ASAP. But as long as memory hotplug is the only direct user
> of pm_mutex, is it justified to remove the CONFIG_HIBERNATE_CALLBACKS
> restriction and make it generic? I don't know...
> 
> Or, are you saying that we should use these APIs even in suspend/hibernate
> call paths? That's not such a bad idea either...

Yeap, all.  It's just confusing to have two different types of access
to a single lock and I don't believe CONFIG_HIBERNATE_CALLBACKS is a
meaningful optimization in this case.

Thank you.

-- 
tejun
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