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Date: Thu, 15 Mar 2007 14:29:55 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: pavel@ucw.cz, a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] swsusp: Do not use page flags
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On Thu, 15 Mar 2007 22:05:53 +0100
"Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> On Thursday, 15 March 2007 20:08, Andrew Morton wrote:
> > > On Mon, 12 Mar 2007 22:19:20 +0100 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> > > +int create_basic_memory_bitmaps(void)
> > > +{
> > > +	struct memory_bitmap *bm1, *bm2;
> > > +	int error = 0;
> > > +
> > > +	BUG_ON(forbidden_pages_map || free_pages_map);
> > > +
> > > +	bm1 = kzalloc(sizeof(struct memory_bitmap), GFP_ATOMIC);
> > > +	if (!bm1)
> > > +		return -ENOMEM;
> > > +
> > > +	error = memory_bm_create(bm1, GFP_ATOMIC | __GFP_COLD, PG_ANY);
> > > +	if (error)
> > > +		goto Free_first_object;
> > > +
> > > +	bm2 = kzalloc(sizeof(struct memory_bitmap), GFP_ATOMIC);
> > > +	if (!bm2)
> > > +		goto Free_first_bitmap;
> > > +
> > > +	error = memory_bm_create(bm2, GFP_ATOMIC | __GFP_COLD, PG_ANY);
> > > +	if (error)
> > 
> > What is the risk that we'll go OOM here?  GFP_ATOMIC is rather unreliable.
> 
> Well, this can be called after processes (including kswapd) has been frozen.
> We can't go to sleep at this point.

So it _is_ unreliable?

> > And why _does_ suspend use GFP_ATOMIC all over the place?
> 
> Generally, because it cannot sleep.

Why not?