linux-kernel - Re: [RFC][PATCH] PM / Hibernate: Add sysfs knob to control size of memory for drivers

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Message-Id: <201105182223.55312.rjw@sisk.pl>
Date:	Wed, 18 May 2011 22:23:55 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Martin Steigerwald <Martin@...htvoll.de>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM / Hibernate: Add sysfs knob to control size of memory for drivers

On Wednesday, May 18, 2011, Pavel Machek wrote:
> Hi!
> 
> > > > OK, there are no comments, so my understanding is that everyone is
> > > > fine with this patch and I can add it to my linux-next branch.
> > > 
> > > Actually no, I don't like it. Yes, knob might be useful for debugging,
> > > but having it as part of official kernel interface...
> > 
> > Well I and people with similar setups it is actually quite useful. It 
> > makes the difference between does hibernate *every time* versus does not 
> > hibernate sometimes. And I don't see why it can't go again, when the issue 
> > is taken care of elsewise in the future. I think that autotuning / drivers 
> > allocating their memory via whatnot is better, but until such a mechanism 
> > is agreed, developed and included in official kernel I do think that this 
> > knob does help.
> 
> Yes, autotuning would be better, and yes, knob is useful for you now.
> 
> I'd say the knob is for debugging and should go to debugfs somewhere.
> 
> > I think missing is some documentation so that the advanced user can figure 
> > out this knob.
> 
> ...so we can easily delete the knob when it is no longer neccessary.

_If_ drivers start to allocate memory in .prepare(), the knob won't be
necessary any more and _then_ we may consider removing it.  I guess a lot
of time will pass before that happens, though. :-)

That said, I'm not sure we should recommend using it beyond the cases in which
nothing else works.

Thanks,
Rafael
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