Re: [PATCH] uswsusp: automatically free the in-memory image onces2disk has finished with it

[Alan Jenkins]

Pavel Machek wrote:
> On Wed 2009-12-02 22:25:16, Mel Gorman wrote:
>   
> > 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?
> >     
>
> Nothing. But 4MB was enough to power down before, it is not enough
> now, and I'd like to understand why.
> 									Pavel
>   

Here's a new datum:

Applying this patch has left a less frequent hang.  So far it has 
happened twice.  (Once playing last night, and once today testing 
hibernation with KMS enabled).

This hang happens at a different point.  It happens _before_ writing out 
the hibernation image.  That is, I don't see the textual progress bar, 
and if I force a power-cycle then it doesn't resume (and complains about 
uncleanly unmounted filesystems).

Here is the backtrace:

[top of screen]
s2disk D c1c05580 0 5988 5809 0x00000000
...
Call Trace:
...
? wait_for_common
? default_wake_function
? kthread_create
? worker_thread
? create_workqueue_thread
? worker_thread
? __create_workqueue_thread
? stop_machine_create
? disable_nonboot_cpus
? hibernation_snapshot
? snapshot_ioctl
...
? sys_ioctl


It looks like hibernation_snapshot() calls disable_nonboot_cpus() 
_before_ we allocate the hibernation image.  (I.e. before 
swsusp_arch_suspend(), which calls swsusp_save()).

So I think Pavel's right, we still need to work out what's happening here.

Regards
Alan
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/