linux-kernel - Re: CONFIG_NUMA breaks hibernation on x86-32 with PAE

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Date:	Tue, 11 Nov 2008 15:20:21 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	kernel list <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: CONFIG_NUMA breaks hibernation on x86-32 with PAE

On Tuesday, 11 of November 2008, Pavel Machek wrote:
> On Mon 2008-11-10 19:28:03, Rafael J. Wysocki wrote:
> > On Monday, 10 of November 2008, Andi Kleen wrote:
> > > Ingo Molnar <mingo@...e.hu> writes:
> > > >
> > > > No good ideas - the bug description gives me the impression of memory 
> > > > maps save/restore hickup in the hibernation code - and memory maps are 
> > > > pretty much the only thing that are significantly different on NUMA. 
> > > 
> > > I assume the problem happened on a single node system.
> > > On single node the memory map should be actually quite similar
> > > to the UMA case.
> > 
> > It is.  However, the problem is 100% reproducible on any 32-bit single-node
> > system with CONFIG_NUMA set, from what I can tell.
> > 
> > It doesn't happen if the kernel is booted with highmem=0, so it looks like
> > the code that saves highmem causes the problem to happen.  However, this
> > same code works well for all of the !CONFIG_NUMA cases and practically only
> > the only non-open-coded it uses is kmap_atomic().
> > 
> > > One possibility would be to bisect if it ever worked?
> > 
> > Not sure it did, probably not. :-(
> 
> Well, interesting point would be just before this commit:
> 
> 
> commit 8357376d3df21b7d6f857931a57ac50da9c66e26 
> tree daf2c369e9b79d24c1666323b3ae75189e482a4a 
> parent bf73bae6ba0dc4bd4f1e570feb34a06b72725af6 
> author Rafael J. Wysocki <rjw@...k.pl> Wed, 06 Dec 2006 20:34:18 -0800 
> committer Linus Torvalds <torvalds@...dy.osdl.org> Thu, 07 Dec 2006
> 08:39:27 -0800 
> 
>     [PATCH] swsusp: Improve handling of highmem
>     
>     Currently swsusp saves the contents of highmem pages by copying
> them to the
>     normal zone which is quite inefficient (eg.  it requires two
> normal pages
>     to be used for saving one highmem page).  This may be improved by
> using
>     highmem for saving the contents of saveable highmem pages.
> 
> ...highmem handling was way simpler in those good old days ;-)

Please stop kidding, this is a serious issue.

The hibernation code _works_ with all kinds of highmem when CONFIG_NUMA is
unset.

Thanks,
Rafael
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