[Devel] [PATCH vz9 v2 00/65] ploop optimistations and scalling

[Konstantin Khorenko]

Ploop processes requsts in a different threads in parallel
where possible which results in significant improvement in
performance and makes further optimistations possible.

v1:
  - addressed feedback, i've left a few requests to merge changes
    into bigger patches out, as to keep changes in smaller chunks
  - patches merged and separated changes - generic cleanup
  - fix endio for md page writeback
  - background async allocation of space
  - move enospc pios dispatch from timer to thread
  - fixed allocations in atomic context
  - fixed locking wrt userspace/interrupt context
  - reworked discard cleanup
  - removed workqueue, only use kthread code
  - make metadata writeback works in parallel
  - end fsync pios in parallel
  - fixed current flags manipulation

v2:
  - commit "dm-ploop: introduce pio.llist" appeared
    It introduces the the pio.llist along with pio.list, gathered in an
    union, so during the processes of switching between list users and
    llist users, we could use appropriate fields without strict pointers
    casts.

TODO:
  - there are multiple INIT_LIST_HEAD() left in the code, most of them
    are just not needed, but let's looks precisely at each case.
    Same for "pio->llist.next = NULL;"

  - md_page.wb_link switched to llist and later - back to list along
    with introducing ploop.wb_batch_list and ploop.wb_batch_list_prio.
    Need to understand if we want the latter to be lists or llists and
    don't push wb_link back and forth.

RFC series:
v6 changes:
 - locking fixes
 - use READ_ONCE/WRITE_ONCE
 - properly handle DIO errors (ENOTBLK)
 - added support for data pios with REQ_FUA
 - convert more lists to lockless variants
 - resize/grow is good

v5 with changes in v4:
 - BAT writeback delay
 - Lists/Locking moving to lockless lists to reduce locking
 - Requests are prepared in the caller to reduce load of worker thread
 - REQ_FUA and REQ_PREFLUSH support
 - Convert bit fields to use atomic bitops - reduce locking
 - remove fsync worker to guarantee order of execution
 - Map all md pages at creation time - they are only freed on device
    destroy

Known bugs:
  - delayed metadata writeback is not working and is missing error handling
     - patch to disable it until fixed
  - fast path is not working - causes rcu lockups - patch to disable it

Further improvements:
  - optimize md pages lookups

Alexander Atanasov (42):
  dm-ploop: md_pages map all pages at creation time
  dm-ploop: Use READ_ONCE/WRITE_ONCE to access md page data
  dm-ploop: fsync after all pios are sent
  dm-ploop: move md status to use proper bitops
  dm-ploop: convert wait_list and wb_batch_llist to use lockless lists
  dm-ploop: convert enospc handling to use lockless lists
  dm-ploop: convert suspended_pios list to use lockless list
  dm-ploop: move from wq to kthread
  dm-ploop: do not use a wrapper for set_bit to make a page writeback
  dm-ploop: BAT use only one list for writeback
  dm-ploop: make md writeback timeout to be per page
  dm-ploop: add interface to disable bat writeback delay
  dm-ploop: convert wb_batch_list to lockless variant
  dm-ploop: convert high_prio to status
  dm-ploop: convert md page rw lock to spin lock
  dm-ploop: convert bat_rwlock to bat_lock spinlock
  dm-ploop: prepare bat updates under bat_lock
  dm-ploop: make ploop_bat_write_complete ready for parallel pio
    completion
  dm-ploop: make ploop_submit_metadata_writeback return number of
    requests sent
  dm-ploop: introduce pio runner threads
  dm-ploop: add pio list ids to be used when passing pios to runners
  dm-ploop: disable metadata writeback delay
  dm-ploop: use lockless lists for chained cow updates list
  dm-ploop: use lockless lists for data ready pios
  dm-ploop: give runner threads better name
  dm-ploop: resize operation - add holes bitmap locking
  dm-ploop: remove unnecessary operations
  dm-ploop: use filp per thread
  dm-ploop: catch if we try to advance pio past bio end
  dm-ploop: support REQ_FUA for data pios
  dm-ploop: proplerly access nr_bat_entries
  dm-ploop: fix locking and improve error handling when submitting pios
  dm-ploop: fix how ENOTBLK is handled
  dm-ploop: sync when suspended or stopping
  dm-ploop: rework logic in pio processing
  dm-ploop: end fsync pios in parallel
  dm-ploop: make filespace preallocations async
  dm-ploop: resubmit enospc pios from dispatcher thread
  dm-ploop: dm-ploop: simplify discard completion
  dm-ploop: use GFP_ATOMIC instead of GFP_NOIO
  dm-ploop: fix locks used in mixed context
  dm-ploop: fix how current flags are managed inside threads

Andrey Zhadchenko (13):
  dm-ploop: do not flush after metadata writes
  dm-ploop: set IOCB_DSYNC on all FUA requests
  dm-ploop: remove extra ploop_cluster_is_in_top_delta()
  dm-ploop: introduce per-md page locking
  dm-ploop: reduce BAT accesses on discard completion
  dm-ploop: simplify llseek
  dm-ploop: speed up ploop_prepare_bat_update()
  dm-ploop: make new allocations immediately visible in BAT
  dm-ploop: drop ploop_cluster_is_in_top_delta()
  dm-ploop: do not wait for BAT update for non-FUA requests
  dm-ploop: add delay for metadata writeback
  dm-ploop: submit all postponed metadata on REQ_OP_FLUSH
  dm-ploop: handle REQ_PREFLUSH

Konstantin Khorenko (10):
  dm-ploop: drop md_page.wb_link initialization
  dm-ploop: introduce pio.llist
  dm-ploop: convert the rest of the lists to use llist variant
  dm-ploop: combine processing of pios thru prepare list and remove
    fsync worker
  dm-ploop: move preparations of pios into the caller from worker
  dm-ploop: fast path execution for reads
  dm-ploop: split cow processing into two functions
  dm-ploop: process pios via runners
  dm-ploop: disable fast path
  dm-ploop: rework bat completion logic

 drivers/md/dm-ploop-bat.c    |   74 +-
 drivers/md/dm-ploop-cmd.c    |  174 ++--
 drivers/md/dm-ploop-map.c    | 1599 ++++++++++++++++++++++++----------
 drivers/md/dm-ploop-target.c |  168 +++-
 drivers/md/dm-ploop.h        |  120 ++-
 5 files changed, 1484 insertions(+), 651 deletions(-)

-- 
2.43.5