On 2/23/21 7:42 AM, Gao Xiang wrote: > Hi folks, > > On Wed, Mar 28, 2018 at 08:17:28AM +1100, Dave Chinner wrote: >> On Mon, Mar 26, 2018 at 08:46:49AM -0400, Brian Foster wrote: >>> On Sat, Mar 24, 2018 at 09:20:49AM -0700, Darrick J. Wong wrote: >>>> On Wed, Mar 07, 2018 at 05:33:48PM -0600, Eric Sandeen wrote: >>>>> Now that unlinked inode recovery is done outside of >>>>> log recovery, there is no need to dirty the log on >>>>> snapshots just to handle unlinked inodes. This means >>>>> that readonly snapshots can be mounted without requiring >>>>> -o ro,norecovery to avoid the log replay that can't happen >>>>> on a readonly block device. >>>>> >>>>> (unlinked inodes will just hang out in the agi buckets until >>>>> the next writable mount) >>>> >>>> FWIW I put these two in a test kernel to see what would happen and >>>> generic/311 failures popped up. It looked like the _check_scratch_fs >>>> found incorrect block counts on the snapshot(?) >>>> >>> >>> Interesting. Just a wild guess, but perhaps it has something to do with >>> lazy sb accounting..? I see we call xfs_initialize_perag_data() when >>> mounting an unclean fs. >> >> The freeze is calls xfs_log_sbcount() which should update the >> superblock counters from the in-memory counters and write them to >> disk. >> >> If they are out, I'm guessing it's because the in-memory per-ag >> reservations are not being returned to the global pool before the >> in-memory counters are summed during a freeze.... >> >> Cheers, >> >> Dave. >> -- >> Dave Chinner >> david@xxxxxxxxxxxxx > > I spend some time on tracking this problem. I've made a quick > modification with per-AG reservation and tested with generic/311 > it seems fine. My current question is that how such fsfreezed > images (with clean mount) work with old kernels without [PATCH 1/1]? > I'm afraid orphan inodes won't be freed with such old kernels.... > Am I missing something? It's true, a snapshot created with these patches will not have their unlinked inodes processed if mounted on an older kernel. I'm not sure how much of a problem that is; the filesystem is not inconsistent, but some space is lost, I guess. I'm not sure it's common to take a snapshot of a frozen filesystem on one kernel and then move it back to an older kernel. Maybe others have thoughts on this. -Eric
