• Tejun Heo's avatar
    block, cfq: move icq creation and rq->elv.icq association to block core · f1f8cc94
    Tejun Heo authored
    Now block layer knows everything necessary to create and associate
    icq's with requests.  Move ioc_create_icq() to blk-ioc.c and update
    get_request() such that, if elevator_type->icq_size is set, requests
    are automatically associated with their matching icq's before
    elv_set_request().  io_context reference is also managed by block core
    on request alloc/free.
    
    * Only ioprio/cgroup changed handling remains from cfq_get_cic().
      Collapsed into cfq_set_request().
    
    * This removes queue kicking on icq allocation failure (for now).  As
      icq allocation failure is rare and the only effect of queue kicking
      achieved was possibily accelerating queue processing, this change
      shouldn't be noticeable.
    
      There is a larger underlying problem.  Unlike request allocation,
      icq allocation is not guaranteed to succeed eventually after
      retries.  The number of icq is unbound and thus mempool can't be the
      solution either.  This effectively adds allocation dependency on
      memory free path and thus possibility of deadlock.
    
      This usually wouldn't happen because icq allocation is not a hot
      path and, even when the condition triggers, it's highly unlikely
      that none of the writeback workers already has icq.
    
      However, this is still possible especially if elevator is being
      switched under high memory pressure, so we better get it fixed.
      Probably the only solution is just bypassing elevator and appending
      to dispatch queue on any elevator allocation failure.
    
    * Comment added to explain how icq's are managed and synchronized.
    
    This completes cleanup of io_context interface.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    f1f8cc94
blk.h 7.5 KB