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

Rafael J. Wysocki
2009-12-03T19:49:50Z

On Thursday 03 December 2009, Alan Jenkins wrote:
> 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.

OK, patch dropped.

Thanks,
Rafael