Done. Panic still occurs, albeit after a longer time (about 30 minutes).
This time --- marks a 2 second pause.

vfs.hammer.contention_count: 2066
vfs.hammer.zone_limit: 0
vfs.hammer.count_io_running_write: 0
vfs.hammer.count_io_locked: 1
vfs.hammer.count_io_running_read: 1
vfs.hammer.count_reservations: 384
vfs.hammer.count_refedbufs: 9
vfs.hammer.count_dirtybufs: 90
vfs.hammer.count_nodes: 10
vfs.hammer.count_buffers: 195
vfs.hammer.count_volumes: 1
vfs.hammer.count_record_datas: 29
vfs.hammer.count_records: 195614
vfs.hammer.count_reclaiming: 0
vfs.hammer.count_iqueued: 18
vfs.hammer.count_inodes: 39332
vfs.hammer.limit_iqueued: 26846
vfs.hammer.limit_recs: 320000
vfs.hammer.limit_irecs: 20000
vfs.hammer.limit_dirtybufs: 1610
---
vfs.hammer.contention_count: 2066
vfs.hammer.zone_limit: 0
vfs.hammer.count_io_running_write: 0
vfs.hammer.count_io_locked: 1
vfs.hammer.count_io_running_read: 1
vfs.hammer.count_reservations: 397
vfs.hammer.count_refedbufs: 9
vfs.hammer.count_dirtybufs: 90
vfs.hammer.count_nodes: 10
vfs.hammer.count_buffers: 195
vfs.hammer.count_volumes: 1
vfs.hammer.count_record_datas: 29
vfs.hammer.count_records: 202090
vfs.hammer.count_reclaiming: 0
vfs.hammer.count_iqueued: 18
vfs.hammer.count_inodes: 39332
vfs.hammer.limit_iqueued: 26846
vfs.hammer.limit_recs: 320000
vfs.hammer.limit_irecs: 20000
vfs.hammer.limit_dirtybufs: 1610
---
vfs.hammer.contention_count: 2066
vfs.hammer.zone_limit: 0
vfs.hammer.count_io_running_write: 0
vfs.hammer.count_io_locked: 1
vfs.hammer.count_io_running_read: 1
vfs.hammer.count_reservations: 418
vfs.hammer.count_refedbufs: 10
vfs.hammer.count_dirtybufs: 90
vfs.hammer.count_nodes: 11
vfs.hammer.count_buffers: 196
vfs.hammer.count_volumes: 1
vfs.hammer.count_record_datas: 31
vfs.hammer.count_records: 213006
vfs.hammer.count_reclaiming: 0
vfs.hammer.count_iqueued: 18
vfs.hammer.count_inodes: 39333
vfs.hammer.limit_iqueued: 26846
vfs.hammer.limit_recs: 320000
vfs.hammer.limit_irecs: 20000
vfs.hammer.limit_dirtybufs: 1610
---
panic: hammer_mount: malloc limit exceeded
...