[PATCH v3 00/13] s390/dasd: ESE thin-provisioning performance improvements

[Stefan Haberland <sth@linux.ibm.com>]

Extent Space Efficient (ESE) volumes allocate a track on its first write.
Today the first write to an unallocated track fails with No Record Found
(or similar), the driver formats the track and retries the write.
That NRF loop dominates the write path of a freshly provisioned volume.

This series lets the driver write and allocate a track in a single
operation using WRITE_FULL_TRACK, so the common "write to a
not-yet-allocated track" case avoids the NRF penalty.
Because full-track writes are only a win while a volume is still sparse, an
adaptive heuristic (exposed through a single sysfs knob) probes
the workload and falls back to normal writes once the device is mostly
allocated. On top of that the series adds an on-disk format label so an
ESE volume can be recognised without querying the hardware, and re-enables
discard for ESE volumes so freed space can be returned to the pool.

The sysfs knob is 0..100. 0 pins normal writes, 100 pins full-track,
and the default of 50 enables the heuristic; the adaptive range
interpolates the heuristic parameters between the two ends.

Patch 12 releases whole extents only: a discard range is rounded inward to
extent boundaries and partially covered boundary tracks are dropped, so an
extent shared with a live allocation is never released. Sub-extent discards
that cover no whole extent are rejected rather than over-released and
corrupting data.

Patch 13 fixes a use-after-free: the CCW build path read the base address
and LSS directly from conf.ned, which the reload worker can free
concurrently with I/O. The values are now read from the copies kept in the
device uid / private structure, refreshed under the ccwdev lock when the
configuration is (re)read.

Stefan Haberland (13):
  s390/dasd: Optimize max blocks per request for track alignment
  s390/dasd: Add infrastructure for ESE full-track write
  s390/dasd: Add range-based format-track collision detection
  s390/dasd: Extend prepare_itcw() to support WRITE_FULL_TRACK
  s390/dasd: Add dasd_eckd_build_cp_tpm_writefulltrack()
  s390/dasd: Use WRITE_FULL_TRACK in ESE format handler
  s390/dasd: Add full_track_bias sysfs attribute to control fulltrack
    write mode
  s390/dasd: Derive adaptive ESE fulltrack heuristic from ft_bias
  s390/dasd: Stamp a format label into newly formatted volumes
  s390/dasd: Detect ESE volumes from the on-disk format label
  s390/dasd: Report ESE capability and format mode at device online
  s390/dasd: Re-enable discard support for ESE volumes
  s390/dasd: Read cached unit address and LSS in the CCW build path

 drivers/s390/block/dasd.c        |  205 ++++--
 drivers/s390/block/dasd_devmap.c |   81 ++-
 drivers/s390/block/dasd_eckd.c   | 1168 ++++++++++++++++++++++++++----
 drivers/s390/block/dasd_eckd.h   |   55 +-
 drivers/s390/block/dasd_erp.c    |    8 +-
 drivers/s390/block/dasd_int.h    |  145 +++-
 6 files changed, 1471 insertions(+), 191 deletions(-)

-- 
2.53.0