v2: no code changes. The only change is my author address: v1 went out on 2026-10-10 from my previous address. Please apply this version instead of v1.
These patches fix two problems in dm-zoned's reclaim worker, found while running md RAID5 on three dm-zoned targets on 27 TB host-managed SMR drives (WD Ultrastar DC HC680), each target with a regular cache device. 1. On a target with cache zones and no free sequential zone, an idle target keeps copying random zones into other random zones, forever (patch 2; patch 1 makes the resulting -ENOSPC back off instead of spinning). After a full md rebuild every chunk is mapped, so this happens right after a rebuild: the idle member read and wrote about 72 MB/s nonstop for hours. 2. After a reclaim pass that ends while the target is busy, the idle poll is never re-armed, so zones filled under load are not reclaimed when the target goes idle (patch 3). Users notice it as "the buffer never drains"; the workaround has been a timer sending "dmsetup message <dev> 0 reclaim". Testing: the three patches were built as an out-of-tree dm-zoned module for 7.2.6 (the changed code is identical in current master) and tested - on emulated host-managed drives (tcmu-runner ZBC handler) in a VM: the idle copy loop reproduced with the stock module (340 MB/s on an idle target, zone counters unchanged), 0 MB/s with the patches; - on the three real drives since 2026-10-05: crash test, three 1.5 TiB write benchmarks, and eight conversions between single-device and cache-device layouts; emptied zones were reclaimed within minutes of the targets going idle without the reclaim timer. - with a reproducer that needs no special hardware (scsi_debug zbc=managed, 64 MiB zones, plus a 1 GiB loop cache device): stock module ~600 MB/s of read+write on the idle target with unchanged zone counters, patched module 0 MB/s: https://github.com/illofspeed/synology-host-managed-smr/tree/main/repro Not done: a test on current master itself (only 7.2.6), and a rebuild onto a cached member with the patches (the first problem was seen after a rebuild with the stock module). Related, not addressed here: the double-free in dmz_load_sb() reported on dm-devel on 2026-05-30. The problems were found and the patches written with the help of an AI coding assistant (hence Assisted-by); the analysis, the tests on real hardware and this description were reviewed by me. illofspeed (3): dm zoned: back off when reclaim finds no destination zone dm zoned: do not reclaim a random zone into another random zone dm zoned: keep polling for idle reclaim after a reclaim pass drivers/md/dm-zoned-reclaim.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) -- 2.47.3
