linux-kernel - Re: [PATCH] uswsusp: automatically free the in-memory image once s2disk has finished with it

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Date:	Wed, 2 Dec 2009 23:15:24 +0100
From:	Pavel Machek <pavel@....cz>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Alan Jenkins <alan-jenkins@...fmail.co.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [PATCH] uswsusp: automatically free the in-memory image once
 s2disk has finished with it

On Wed 2009-12-02 22:07:18, Mel Gorman wrote:
> On Wed, Dec 02, 2009 at 10:11:07PM +0100, Pavel Machek wrote:
> > On Wed 2009-12-02 14:28:12, Alan Jenkins wrote:
> > > The original in-kernel suspend (swsusp) frees the in-memory hibernation
> > > image before powering off the machine.  s2disk doesn't, so there is
> > > _much_ less free memory when it tries to power off.
> > > 
> > > This is a gratuitous difference.  The userspace suspend interface
> > > /dev/snapshot only allows the hibernation image to be read once.
> > > Once the s2disk program has read the last page, we can free the entire
> > > image.
> > > 
> > > This avoids a hang after writing the hibernation image which was
> > > triggered by commit 5f8dcc21211a3d4e3a7a5ca366b469fb88117f61
> > > "page-allocator: split per-cpu list into one-list-per-migrate-type":
> > 
> > Yes, you work around page-allocator hang. But is it right thing to do?
> > 
> 
> What's wrong with it? The hang is likely because the allocator has no
> memory to work with. The patch in question makes small changes to the
> amount of available memory but it shouldn't matter on uni-core. Some
> structures are slightly larger but it's extremely borderline. I'm at a
> loss to explain actually why it makes a difference untill things were
> extremely borderline to begin with.

We reserve 4MB, for such purposes, and we already wrote image to disk
with such constrains, so memory should not be _too_ tight.

Can you try increasing PAGES_FOR_IO to 8MB or something like that?

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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