Messages in this thread | | | Date | Tue, 1 Jul 2008 08:21:28 +1000 | From | Dave Chinner <> | Subject | Re: [xfs-masters] Re: freeze vs freezer |
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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@fromorbit.com
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