Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [xfs-masters] Re: freeze vs freezer | Date | Tue, 1 Jul 2008 16:35:43 +0200 |
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On Tuesday, 1 of July 2008, Dave Chinner wrote: > On Tue, Jul 01, 2008 at 12:38:41AM +0200, Rafael J. Wysocki wrote: > > On Tuesday, 1 of July 2008, Dave Chinner wrote: > > > 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? > > > > I'm not going to let the data get to the disk. > > Yes, but you still haven't answered the original question - What are > you going to do with sync I/O that leaves a process in D state > because you've prevented the I/O from being completed?
I don't want to intercept those processes, just allow them to block on that I/O.
> > > > > 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. > > > > Well, can you please tell me how exactly that works, then? > > Try looking at the code. When we freeze a filesystem sb->s_frozen > changes state depending on the level of freeze currently obtained > by the filesystem. And: > > #define vfs_check_frozen(sb, level) \ > wait_event((sb)->s_wait_unfrozen, ((sb)->s_frozen < (level))) > > Pretty bloody simple, really.
OK
Do all of the filesystems implement the freezing?
Rafael
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