MFV r247578: 3581 spa_zio_taskq[ZIO_TYPE_FREE][ZIO_TASKQ_ISSUE]->tq_lock is piping hot

illumos/illumos-gate@ec94d32216ed5705f5176582355cc311cf848e73

MFC after:	9 days
Sponsored by:	HybridCluster [merge]
MFV r255255: 4045 zfs write throttle & i/o scheduler performance work

illumos/illumos-gate@69962b5647e4a8b9b14998733b765925381b727e

Please note the following changes:
- zio_ioctl has lost its priority parameter and now TRIM is executed
  with 'now' priority
- some knobs are gone and some new knobs are added; not all of them are
  exposed as tunables / sysctls yet

MFC after:	10 days
Sponsored by:	HybridCluster [merge]
MFV r255256: 3954 metaslabs continue to load even after hitting zfs_mg_alloc_failure limit

4080 zpool clear fails to clear pool
4081 need zfs_mg_noalloc_threshold

illumos/illumos-gate@22e30981d82a0b6dc89253596ededafae8655e00

MFC after:	10 days
Sponsored by:	HybridCluster [merge]
MFV r258376: 3964 L2ARC should always compress metadata buffers

illumos/illumos-gate@e4be62a2b74a8f09bb669217a1a39eee069b13a1

MFC after:	10 days
Sponsored by:	HybridCluster [merge]