Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable)

[Rafael J. Wysocki]

On Thursday 21 January 2010, KOSAKI Motohiro wrote:
> > > Hi Rafael,
> > > 
> > > Do you mean this is the unrelated issue of nVidia bug?
> > 
> > The nvidia driver _is_ buggy, but Maxim said he couldn't reproduce the
> > problem if all the allocations made by the nvidia driver during suspend
> > were changed to GFP_ATOMIC.
> > 
> > > Probably I haven't catch your point. I don't find Maxim's original bug
> > > report. Can we share the test-case and your analysis detail?
> > 
> > The Maxim's original report is here:
> > https://lists.linux-foundation.org/pipermail/linux-pm/2010-January/023982.html
> > 
> > and the message I'm referring to is at:
> > https://lists.linux-foundation.org/pipermail/linux-pm/2010-January/023990.html
> 
> Hmmm...
> 
> Usually, Increasing I/O isn't caused MM change. either subsystem change
> memory alloc/free pattern and another subsystem receive such effect ;)
> I don't think this message indicate MM fault.
> 
> And, 2.6.33 MM change is not much. if the fault is in MM change
> (note: my guess is no), The most doubtful patch is my "killing shrink_all_zones"
> patch. If old shrink_all_zones reclaimed memory much rather than required. 
> The patch fixed it. IOW, the patch can reduce available free memory to be used
> buggy .suspend of the driver. but I don't think it is MM fault.
> 
> As I said, drivers can't use memory freely as their demand in suspend method.
> It's obvious. They should stop such unrealistic assumption. but How should we fix
> this?
>  - Gurantee suspend I/O device at last?
>  - Make much much free memory before calling .suspend method? even though
>    typical drivers don't need.

That doesn't help already.  Maxim tried to increase SPARE_PAGES (in
kernel/power/power.h) and that had no effect.

>  - Ask all drivers how much they require memory before starting suspend and
>    Make enough free memory at first?

That's equivalent to reworking all drivers to allocate memory before suspend
eg. with the help of PM notifiers.  Which IMHO is unrealistic.

>  - Or, do we have an alternative way?

The $subject patch?

> Probably we have multiple option. but I don't think GFP_NOIO is good
> option. It assume the system have lots non-dirty cache memory and it isn't
> guranteed.

Basically nothing is guaranteed in this case.  However, does it actually make
things _worse_?  What _exactly_ does happen without the $subject patch if the
system doesn't have non-dirty cache memory and someone makes a GFP_KERNEL
allocation during suspend?

Rafael
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