Re: [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 00:57 +0200, Rafael J. Wysocki wrote:
> > > > Well, I'm not sure.  First, we don't really know what the value of it should be
> > > > and this alone is a good enough reason for making it tunable, IMHO.  Second, I
> > > > think different systems may need different PAGES_FOR_IO and taking just the
> > > > maximum (even if we learn how much that actually is) seems to be wasteful in
> > > 
> > > Well,  it is wasteful as in "we save slightly smaller image than we
> > > could". That's okay with me.
> > 
> > No. If the driver can't allocate the memory, your call to device_suspend
> > will fail. This isn't about image size but about success or failure to
> > hibernate.
> 
> If we take PAGES_FOR_IO to be the maximum over all possible configurations
> that can hibernate, the majority of systems will just create smaller images than
> they could have created for smaller PAGES_FOR_IO, but all of them will be
> able to hibernate. :-)

You also use PAGES_FOR_IO in enough_free_mem. Say you set it to the 9000
pages I mentioned before (35M). On a machine with 64 megabytes of
memory, you'll never be able to suspend because you'll never satisfy

free > nr_pages + PAGES_FOR_IO + meta

I'll freely admit that 64 megabytes is tiny nowadays, but it's not
completely unknown. The point is really that you're effectively making
swsusp unusable for machines with RAM < (PAGES_FOR_IO * (say) 3). But
what do you set PAGES_FOR_IO to? There'll always be someone with
$WHIZ_BANG_CONFIG who is pushing to have the value increased, and every
increase knocks out more of your lowend users.

Regards,

Nigel