On Mon, Jun 30, 2008 at 11:00:43PM +0200, Rafael J. Wysocki wrote:
> On Monday, 30 of June 2008, Dave Chinner wrote:
> > On Sun, Jun 29, 2008 at 11:37:31PM -0700, Jeremy Fitzhardinge wrote:
> > > Dave Chinner wrote:
> > >> On Mon, Jun 30, 2008 at 01:22:47AM +0200, Rafael J. Wysocki wrote:
> > >>> Well, it seems we can handle this on the block layer level, by
> > >>> temporarily
> > >>> replacing the elevator with something that will selectively prevent fs
> > >>> I/O
> > >>> from reaching the layers below it.
> > >>
> > >> Why? What part of freeze_bdev() doesn't work for you?
> > >
> > > Well, my original problem - which is still an issue - is that a process
> > > writing to a frozen XFS filesystem is stuck in D state, and therefore
> > > cannot be frozen as part of suspend.
>
> I thought we were talking about the post-freezer situation.
>
> > Silly me - how could I forget the three headed monkey getting in
> > the way of our happy trip to beer island?
> >
> > Seriously, though, how is stopping I/O in the elevator is going to
> > change that?
>
> We can do that after creating the image and before we let devices run again.
> This way we won't need to worry about the freezer.
You're suggesting that you let processes trying to do I/O continue
until *after* the memory image is taken? How is that going to work?
You've got to quiesce the filesystems totally *before* taking an image
of memory - it's the only way to guarantee that they are the
in-memory state and on disk state are consistent state on resume.
Don't re-invent the wheel - use the API we already have that does
exactly what needs to be done.
> > What do you do with a sync I/O (read or write)? The
> > process is going to have to go to sleep somewhere in D state waiting
> > for that I/O to complete. If you're going to intercept such
> > processes somewhere else to do something magic, then why not put
> > that magic in vfs_check_frozen()?
>
> This might work too, but it would be nice to do something independent of the
> freezer, so that we can drop the freezer when we want and not when we are
> forced to.
vfs_check_frozen() is completely independent of the process freezer.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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