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

From: KOSAKI Motohiro
Date: Tue Jan 19 2010 - 19:33:22 EST

> On Tuesday 19 January 2010, Benjamin Herrenschmidt wrote:
> > On Tue, 2010-01-19 at 10:19 +0900, KOSAKI Motohiro wrote:
> > > I think the race happen itself is bad. memory and I/O subsystem can't solve such race
> > > elegantly. These doesn't know enough suspend state knowlege. I think the practical
> > > solution is that higher level design prevent the race happen.
> > >
> > >
> > > > My patch attempts to avoid these two problems as well as the problem with
> > > > drivers using GFP_KERNEL allocations during suspend which I admit might be
> > > > solved by reworking the drivers.
> > >
> > > Agreed. In this case, only drivers change can solve the issue.
> >
> > As I explained earlier, this is near to impossible since the allocations
> > are too often burried deep down the call stack or simply because the
> > driver doesn't know that we started suspending -another- driver...
> >
> > I don't think trying to solve those problems at the driver level is
> > realistic to be honest. This is one of those things where we really just
> > need to make allocators 'just work' from a driver perspective.
> >
> > It can't be perfect of course, as mentioned earlier, there will be a
> > problem if too little free memory is really available due to lots of
> > dirty pages around, but most of this can be somewhat alleviated in
> > practice, for example by pushing things out a bit at suspend time,
> > making some more memory free etc... But yeah, nothing replaces proper
> > error handling in drivers for allocation failures even with
> > GFP_KERNEL :-)
> Agreed.
> Moreover, I didn't try to do anything about that before, because memory
> allocation problems during suspend/resume just didn't happen. We kind of knew
> they were possible, but since they didn't show up, it wasn't immediately
> necessary to address them.
> Now, however, people started to see these problems in testing and I'm quite
> confident that this is a result of recent changes in the mm subsystem. Namely,
> if you read the Maxim's report carefully, you'll notice that in his test case
> the mm subsystem apparently attempted to use I/O even though there was free
> memory available in the system. This is the case I want to prevent from
> happening in the first place.

Hi Rafael,

Do you mean this is the unrelated issue of nVidia bug? 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?

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