On 7/20/15 5:36 PM, Dave Chinner wrote: > On Mon, Jul 20, 2015 at 11:18:49AM -0400, Mike Snitzer wrote: >> If XFS fails to write metadata it will retry the write indefinitely >> (with the hope that the write will succeed at some point in the future). >> >> Others can possibly speak to historic reason(s) why this is a sane >> default for XFS. But when XFS is deployed ontop of DM thin provisioning >> this infinite retry is very unwelcome -- especially if DM thinp was >> configured to be automatically extended with free space but the admin >> hasn't provided (or restored) adequate free space. >> >> To fix this infinite retry a new bdev_has_space () hook is added to XFS >> to break out of its metadata retry loop if the underlying block device >> reports it no longer has free space. DM thin provisioning is now >> trained to respond accordingly, which enables XFS to not cause a cascade >> of tasks blocked on IO waiting for XFS's infinite retry. >> >> All other block devices, which don't implement a .has_space method in >> block_device_operations, will always return true for bdev_has_space(). >> >> With this change XFS will fail the metadata IO, force shutdown, and the >> XFS filesystem may be unmounted. This enables an admin to recover from >> their oversight, of not having provided enough free space, without >> having to force a hard reset of the system to get XFS to unwedge. >> >> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> > > Shouldn't dm-thinp just return the bio with ENOSPC as it's error? > The scsi layers already do this for hardware thinp ENOSPC failures, > so dm-thinp should behave exactly the same (i.e. via > __scsi_error_from_host_byte()). The behaviour of the filesystem > should be the same in all cases - making it conditional on whether > the thinp implementation can be polled for available space is wrong > as most hardware thinp can't be polled by the kernel forthis info.. > > > If dm-thinp just returns ENOSPC from on the BIO like other hardware > thinp devices, then it is up to the filesystem to handle that > appropriately. i.e. whether an ENOSPC IO error is fatal to the > filesystem is determined by filesystem configuration and context of > the IO error, not whether the block device has no space (which we > should already know from the ENOSPC error delivered by IO > completion). The issue we had discussed previously is that there is no agreement across block devices about whether ENOSPC is a permanent or temporary condition. Asking the admin to tune the fs to each block device's behavior sucks, IMHO. This interface could at least be defined to reflect a permanent and unambiguous state... -Eric -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
