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

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Date:	Mon, 18 Jan 2010 11:17:57 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	<linux-pm@...ts.linux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume
 (was: Re: Memory allocations in .suspend became very unreliable)

On Mon, 18 Jan 2010, Oliver Neukum wrote:

> Am Montag, 18. Januar 2010 00:00:23 schrieb Rafael J. Wysocki:
> > On Sunday 17 January 2010, Benjamin Herrenschmidt wrote:
> > > On Sun, 2010-01-17 at 14:27 +0100, Rafael J. Wysocki wrote:
> > ...
> > > However, it's hard to deal with the case of allocations that have
> > > already started waiting for IOs. It might be possible to have some VM
> > > hook to make them wakeup, re-evaluate the situation and get out of that
> > > code path but in any case it would be tricky.
> > 
> > In the second version of the patch I used an rwsem that made us wait for these
> > allocations to complete before we changed gfp_allowed_mask.
> 
> This will be a very, very hot semaphore. What's the impact on performance?

Can it be replaced with something having lower overhead, such as SRCU?

Alan Stern

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