Re: [RFC] ext3 freeze feature

David Chinner
2008-01-26T05:39:52Z

On Sat, Jan 26, 2008 at 04:35:26PM +1100, David Chinner wrote:
> On Fri, Jan 25, 2008 at 07:59:38PM +0900, Takashi Sato wrote:
> > The points of the implementation are followings.
> > - Add calls of the freeze function (freeze_bdev) and
> > the unfreeze function (thaw_bdev) in ext3_ioctl().
> >
> > - ext3_freeze_timeout() which calls the unfreeze function (thaw_bdev)
> > is registered to the delayed work queue to unfreeze the filesystem
> > automatically after the lapse of the specified time.
>
> Seems like pointless complexity to me - what happens if a
> timeout occurs while the filsystem is still freezing?
>
> It's not uncommon for a freeze to take minutes if memory
> is full of dirty data that needs to be flushed out, esp. if
> dm-snap is doing COWs for every write issued....

Sorry, ignore this bit - I just realised the timer is set
up after the freeze has occurred....

Still, that makes it potentially dangerous to whatever is being
done while the filesystem is frozen....

Cheers,

Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group