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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Date:	Sun, 17 Jan 2010 14:27:27 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	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>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable)

On Sunday 17 January 2010, Oliver Neukum wrote:
> Am Sonntag, 17. Januar 2010 01:38:37 schrieb Rafael J. Wysocki:
> > > Now having said that, we've been considering a change that will turn all
> > > GFP_KERNEL allocations into GFP_NOIO during suspend/resume, so perhaps I'll
> > > prepare a patch to do that and let's see what people think.
> > 
> > If I didn't confuse anything (which is likely, because it's a bit late here
> > now), the patch below should do the trick.  I have only checked that it doesn't
> > break compilation, so please take it with a grain of salt.
> > 
> > Comments welcome.
> 
> I think this is a bad idea as it makes the mm subsystem behave differently
> in the runtime and in the whole system cases.

s/runtime/suspend/ ?

Yes it will, but why exactly shouldn't it?  System suspend/resume _is_ a
special situation anyway.

> What's so hard about telling people that they need to use GFP_NOIO in
> suspend() and resume()?

Memory allocations are made for other purposes during suspend/resume too.  For
example, new kernel threads may be created (for async suspend/resume among
other things).

Besides, the fact that you tell people to do something doesn't necessary imply
that they will listen. :-)

I have discussed that with Ben for a couple of times and we have generally
agreed that memory allocation problems during suspend/resume are not avoidable
in general unless we disable __GFP_FS and __GFP_IO at the high level.

Rafael
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