From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Oliver Neukum <oliver@neukum.org>
Subject: Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable)
Date: Wed, 20 Jan 2010 22:12:49 +0100
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Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Bastien ROUCARIES <roucaries.bastien@gmail.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Maxim Levitsky <maximlevitsky@gmail.com>,
       linux-pm@lists.linux-foundation.org,
       LKML <linux-kernel@vger.kernel.org>, "linux-mm" <linux-mm@kvack.org>,
       Andrew Morton <akpm@linux-foundation.org>
References: <20100118110324.AE30.A69D9226@jp.fujitsu.com> <1263943071.724.540.camel@pasglop> <201001201231.17540.oliver@neukum.org>
In-Reply-To: <201001201231.17540.oliver@neukum.org>
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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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