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

[Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>]

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