Date: Wed, 2 Dec 2009 22:25:16 +0000
From: Mel Gorman <mel@csn.ul.ie>
To: Pavel Machek <pavel@ucw.cz>
Cc: Alan Jenkins <alan-jenkins@tuffmail.co.uk>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       pm list <linux-pm@lists.linux-foundation.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Kernel Testers List <kernel-testers@vger.kernel.org>
Subject: Re: [PATCH] uswsusp: automatically free the in-memory image once
	s2disk has finished with it
Message-ID: <20091202222516.GD26702@csn.ul.ie>
References: <4B1575AC.6080904@tuffmail.co.uk> <20091201214529.GA1457@csn.ul.ie> <200912012253.08522.rjw@sisk.pl> <4B16545B.3090703@tuffmail.co.uk> <20091202122019.GD1457@csn.ul.ie> <4B16797C.3010304@tuffmail.co.uk> <20091202211107.GA20830@elf.ucw.cz> <20091202220718.GI1457@csn.ul.ie> <20091202221524.GB20830@elf.ucw.cz>
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On Wed, Dec 02, 2009 at 11:15:24PM +0100, Pavel Machek wrote:
> 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?
> 

What's wrong with just freeing the memory that is no longer required?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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