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: <201001192137.35232.rjw@sisk.pl>
Date:	Tue, 19 Jan 2010 21:37:35 +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 Tuesday 19 January 2010, Oliver Neukum wrote:
> Am Montag, 18. Januar 2010 21:41:49 schrieb Rafael J. Wysocki:
> > On Monday 18 January 2010, Oliver Neukum wrote:
> > > Am Sonntag, 17. Januar 2010 14:55:55 schrieb Rafael J. Wysocki:
> > > > +void mm_force_noio_allocations(void)
> > > > +{
> > > > +       /* Wait for all slowpath allocations using the old mask to complete */
> > > > +       down_write(&gfp_allowed_mask_sem);
> > > > +       saved_gfp_allowed_mask = gfp_allowed_mask;
> > > > +       gfp_allowed_mask &= ~(__GFP_IO | __GFP_FS);
> > > > +       up_write(&gfp_allowed_mask_sem);
> > > > +}
> > > 
> > > In addition to this you probably want to exhaust all memory reserves
> > > before you fail a memory allocation
> > 
> > I'm not really sure what you mean.
> 
> Forget it, it was foolish. Instead there's a different problem.
> Suppose we are tight on memory. The problem is that we must not
> exhaust all memory. If we are really out of memory we may be unable
> to satisfy memory allocations in resume()

That doesn't make things any worse than the are already.  If we block on
I/O forever during resume, the gross result is pretty much the same.

That said, Maxim reported that in his test case the mm subsystem apparently
attempted to use I/O even if there was a plenty of free memory available and
I'd like prevent _that_ from happening.

Rafael
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