Re: [linux-pm] [RFD] swsusp problem: Drivers allocate much memory during suspend (was: Re: 2.6.21-rc5: swsusp: Not enough free memory)

[Nigel Cunningham <nigel@nigel.suspend2.net>]

Hi.

On Sat, 2007-04-14 at 00:38 +0200, Pavel Machek wrote:
> Hi!
> 
> > > > > > Well, it looks like someone allocated about 6000 pages after we had freed
> > > > > > enough memory for suspending.
> > > > > 
> > > > > We have a tunable allowance in Suspend2 for this, because fglrx
> > > > > allocates a lot of pages in its suspend routine if DRI is enabled. I
> > > > > think some other drivers do too, but fglrx is the main one I know.
> > > > 
> > > > I wasn't aware of that, thanks for the information.
> > > > 
> > > > I think this means we'll probably need to add a tunable, similar to image_size,
> > > > that will allow the users to specify how much spare memory they want to reserve
> > > > for suspending (instead of the constant PAGES_FOR_IO).  IMO we can call it
> > > > 'spare_memory'.
> > > 
> > > Just increase PAGES_FOR_IO. This should not be tunable.
> > 
> > If we don't have a means for drivers to pre-allocate or say how much
> > memory they need, it should be tunable. Frankly, I'm startled that you
> > guys haven't heard of this issue before now. I can't believe everyone
> > who has ever wanted to hibernate with DRM enabled has been using
> > Suspend2. Maybe this is one of the sources of complaints that swsusp
> > isn't reliable?
> 
> We do not support closed-source drivers, and open-source drivers are
> well behaved.

I didn't say fglrx was the only example. Any system using DRI (not DRM,
sorry), would, I think, be expected. I just mention fglrx because I have
a Radeon 200M that can only use fglrx for Beryl etc at the mo - it's the
one I'm familiar with.

> > > > IMO to really fix the problem, we should let the drivers that need much memory
> > > > for suspending allocate it _before_ the memory shrinker is called.  For this
> > > > purpose we can use notifiers that will be called before we start the shrinking
> > > > of memory.  Namely, if a driver needs to allocate substantial amount
> > > > of memory
> > > 
> > > Yes please. Using that notifier without leaking the memory will be
> > > "interesting" but if someone needs so much memory during suspend, let
> > > them eat their own complexity.
> > 
> > It doesn't need to be that complex. Add another (optional) function to
> > the driver model to let drivers say how much they want and it becomes
> > trivial. Maybe this idea should be preferred over the notifier chain.
> 
> Actually, it is trivial to prealocate during boot ;-). As the notifier
> chain can be useful for other stuff, too, I'd go that way.

Pavel! Talk sense! You're not seriously suggesting squirreling away 35
megabytes of a user's memory at boot just because they might want to
hibernate with DRI enabled later? Yes, 35 megabytes is a realistic
amount.

Regards,

Nigel

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