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

[Pavel Machek <pavel@suse.cz>]

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.

> > > 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
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