On Tue, Apr 01, 2008 at 07:54:42PM +0900, Takashi Sato wrote: > Hi, > > David Chinner wrote: > >The timeout is not for the freeze operation - the timeout is > >only set up once the freeze is complete. i.e: > > > >$ time sudo ~/test_src/xfs_io -f -x -c 'gfreeze 10' /mnt/scratch/test > >freezing with level = 10 > > > >real 0m23.204s > >user 0m0.008s > >sys 0m0.012s > > > >The freeze takes 23s, and then the 10s timeout is started. So > >this timeout does not protect against freeze_bdev() hangs at all. > >All it does is introduce silent unfreezing of the block device that > >can not be synchronised with the application that is operating > >on the frozen device. > > Exactly my timeout feature is only for an application, not for > freeze_bdev(). > I think it is needed for the situation we can't unfreeze from userspace. > (e.g. Freezing the root filesystem) Ummm - why can't you unfreeze the root fs from userspace? freezing only prevents modification to the filesystem. A frozen filesystem is effectively a read-only filesystem... On XFS: # xfs_freeze -f / # echo $? 0 # xfs_freeze -u / # echo $? 0 The underlying filesystem is broken w.r.t. freezing if you can't read from it successfully once it's been frozen.... > >FWIW, resetting this timeout from userspace is unreliable - there's > >no guarantee that under load your userspace process will get to run > >again inside the timeout to reset it, hence leaving you with a > >unfrozen filesystem when you really want it frozen... > > The timeout period specified to the reset ioctl should be much larger than > the interval for calling the reset ioctl repeatedly. > (e.g timeout period = 2 minutes, calling interval = 5 seconds) What application developer will ever use this? > The reset ioctl will work under such setting. > If a timeout still occurs before a reset, it would imply that an unexpected > problem (e.g. deadlock) occur in an application. Right - the application is broken and needs fixing. We don't need to supply a crutch in a "new" API to support hypothetically broken applications that don't actually exist yet. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
