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    md: implment REQ_FLUSH/FUA support · e9c7469b
    Tejun Heo 提交于
    This patch converts md to support REQ_FLUSH/FUA instead of now
    deprecated REQ_HARDBARRIER.  In the core part (md.c), the following
    changes are notable.
    
    * Unlike REQ_HARDBARRIER, REQ_FLUSH/FUA don't interfere with
      processing of other requests and thus there is no reason to mark the
      queue congested while FLUSH/FUA is in progress.
    
    * REQ_FLUSH/FUA failures are final and its users don't need retry
      logic.  Retry logic is removed.
    
    * Preflush needs to be issued to all member devices but FUA writes can
      be handled the same way as other writes - their processing can be
      deferred to request_queue of member devices.  md_barrier_request()
      is renamed to md_flush_request() and simplified accordingly.
    
    For linear, raid0 and multipath, the core changes are enough.  raid1,
    5 and 10 need the following conversions.
    
    * raid1: Handling of FLUSH/FUA bio's can simply be deferred to
      request_queues of member devices.  Barrier related logic removed.
    
    * raid5: Queue draining logic dropped.  FUA bit is propagated through
      biodrain and stripe resconstruction such that all the updated parts
      of the stripe are written out with FUA writes if any of the dirtying
      writes was FUA.  preread_active_stripes handling in make_request()
      is updated as suggested by Neil Brown.
    
    * raid10: FUA bit needs to be propagated to write clones.
    
    linear, raid0, 1, 5 and 10 tested.
    Signed-off-by: NTejun Heo <tj@kernel.org>
    Reviewed-by: NNeil Brown <neilb@suse.de>
    Signed-off-by: NJens Axboe <jaxboe@fusionio.com>
    e9c7469b
md.c 188.4 KB