Re: Getting rid of freezer for suspend [was Re: [fuse-devel][PATCH] fuse: make fuse daemon frozen along with kernel threads]

From: Pavel Machek
Date: Sun Feb 10 2013 - 13:55:20 EST


> > > > The whole memory shrinking we do for hibernation is now done by allocating
> > > > memory, so the freezer is not necessary for *that* and there's *zero*
> > > > difference between suspend and hibernation with respect to why the freezer is
> > > > used.
> > >
> > > Funny. Freezer was put there so that hibernation image was safe to
> > > write out. You need disk subsystems in workable state for hibernation.
> >
> > I'm not really sure what you're talking about. Why do you think the freezer is
> > necessary for that?

Well, from freezer you need:

1) user process frozen.

2) essential locks _not_ held so that block devices are still functional.

> > > mmap... what is problem with mmap? For suspend, memory is powered, so
> > > you can permit people changing it.
> >
> > Suppose mmap is used to make the registers of some device available to user
> > space. Yes, that can happen.

"Don't do it, then". Yes, can happen, but hopefully is not too common
these days. [And... freezer doing 1) but not 2) would be enough to
handle that. Freezer doing 1) but not 2) would also be simpler...]

> > Again, I'm not sure what you're talking about. Once the image has been
> > created, it can be saved while user space is running just fine.
> Of course, we don't want random changes to be made to persistent storage after
> the image has been created, because those changes might not be consistent with
> the memory contents stored in the image, and that's why user space is still
> frozen when we're saving the image.

Yes. That's the reason 1) for freezer.

(cesky, pictures)
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