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

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Message-Id: <201001202212.49925.rjw@sisk.pl>
Date:	Wed, 20 Jan 2010 22:12:49 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bastien ROUCARIES <roucaries.bastien@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-pm@...ts.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable)

On Wednesday 20 January 2010, Oliver Neukum wrote:
> Am Mittwoch, 20. Januar 2010 00:17:51 schrieb Benjamin Herrenschmidt:
> > On Tue, 2010-01-19 at 10:04 +0100, Bastien ROUCARIES wrote:
> > > Instead of masking bit could we only check if incompatible flags are
> > > used during suspend, and warm deeply. Call stack will be therefore
> > > identified, and we could have some metrics about such problem.
> > > 
> > > It will be a debug option like lockdep but pretty low cost.
> > 
> > I still believe it would just be a giant can of worms to require every
> > call site of memory allocators to "know" whether suspend has been
> > started or not.... Along the same reasons why we added that stuff for
> > boot time allocs.
> 
> But we have the freezer. So generally we don't require that knowledge.
> We can expect no normal IO to happen.
> The question is in the suspend paths. We never may use anything
> but GFP_NOIO (and GFP_ATOMIC) in the suspend() path. We can
> take care of that requirement in the allocator only if the whole system
> is suspended. As soon as a driver does runtime power management,
> it is on its own.

If you start new kernel threads using the async framework, for example,
GFP_KERNEL allocations are going to be used.

As I said before, IMnshO , duplicating every piece of code that allocates
memory and can be run during suspend/resume as well as in other circumstances
doesn't make sense.

Rafael
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