The Swift ms cluster is running Stretch and should be upgraded to Buster (or even Bullseye at this point!). Running a new kernel will be a great occasion to revising the mkfs.xfs options we're using now.
Most notably we're disabling finobt (i.e. the free inode btree) because of free space reporting problems in the past (T199198: Some swift filesystems reporting negative disk usage). While disabling finobt fixes the problem, I believe it does slow down allocations/deletions especially on old-age filesystems and in general given our pattern of creation/deletion of objects (i.e. thumbnails, the most frequent case)