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

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Message-Id: <201105170122.04402.rjw@sisk.pl>
Date:	Tue, 17 May 2011 01:22:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	nigel@...onice.net
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 Monday, May 16, 2011, Nigel Cunningham wrote:
> Hi.
> 
> On 15/05/11 19:36, Rafael J. Wysocki wrote:
> > In fact, if drivers allocated their memory from suspend/hibernate notifiers,
> > that would be practically equivalent to setting reserved_size to the total
> > amount of memory reserved by the drivers.  However, it may be difficult
> > for drivers to predict how much memory they will need at the time the
> > notifiers are called (they are called before freezing user space).
> > 
> > Thus I'm considering a change that will cause device drivers' ->prepare()
> > callbacks to be executed before the preallocation of memory takes place.
> > In that case the drivers may allocate memory from their ->prepare()
> > callbacks _after_ user space has been frozen and that will make more
> > sense overall.
> > 
> > For now, however, I think that exposing reserved_size is the right choice.
> 
> Sorry for not commenting earlier - too busy with Drupal development and
> only came across this thread by chance (yes, I'm still subscribed to the
> PM list, but haven't been reading it. Hibernation isn't high on my list
> of priorities at the moment because TOI is feature complete and stable.
> I know I'm supposed to be sending you patches, but other things have
> been taking the time that would be used for that).
> 
> Anyway...
> 
> This sounds to me like a great development. As far as TuxOnIce goes,
> we've had a knob for ages that has allowed the user to specify an amount
> of memory to be kept aside for driver allocations, and we calculate and
> report how much they used in the debugging info sysfs entry. Because
> TuxOnIce works differently to [u]swsusp, this is the only source of
> potential out-of-memory related failures, and the measures just
> mentioned made things much more reliable.
> 
> If things went in the direction you're suggesting here, they'd get
> better again. I'm all in favour!

Thanks Nigel!
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