Re: suspend.c vs driver-model.txt

[Pavel Machek <pavel-AlSwsSmVLrQ@public.gmane.org>]

Hi!

> >(Most comments were added 5 minutes ago).
> >
> >Does it look understendable now?
> 
> Yes, definitely more clear, there are probably interesting bits
> in there to re-use for suspend-to-ram as well.
> However, the mucking with kernel threads is definitely specific
> to your need of keeping the target block device up without getting
> nasty filesystem-originated requests.

Stopping processes is needed (and being used) by suspend-to-ram,
because anything else is too hard for the drivers (I believe).

> Actually, I'm considering we could probably do both :) That is
> suspend-to-disk is actually a superset of suspend-to-RAM. So
> we could suspend-to-RAM-and-disk, basically allowing us to
> wakeup fast from RAM, but still be able to wakeup from disk
> if battery is exhausted.

Good idea. Thinkpads could do that, it was called RediSafe or
something like that. Disadvantage is that suspend then takes quite
long time.

> Anyway, in your scheme, the main thing I'm currently concerned
> about is the free_some_memory/do_suspend_sync/driver_suspend
> thing which is nasty. How do you deal with memory beeing
> re-allocated after free_some_memory ? (typically driver needing
> RAM for saving state or a non-filesystem-related daemon doing
> a kmalloc (or a driver from a tasklet). 

I free as much memory as possible. So, if driver allocation fails, it
would fail on running system, too. If there was anything that could be
swapped out, I'd already swapped it out.

> Also, do you push
> as much as possible to swap ? 

Yes.

> Or may such an allocation still
> cause more swap activity ? 

No.

> This can be nasty especially since
> swap here can be an mmap'd file, or a swap file, thus possibly
> racing with the fact you stopped filesystem specific daemons.

swsusp actually suspends right into swap *partition*. So I indeed need
swap partition and not swap file.

> Then, finally, the drivers_suspend() state must be broken in
> pieces, that is needed for both suspend-to-RAM and -to-disk,
> (see my other email).

Well, if you are willing to live with ugly-but-harmless
spindown-then-spinup and blank-then-unblank, its actually possible to
keep current system.
								Pavel
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