On Mon, Aug 30 2010 at 5:58am -0400,
Tejun Heo <tj@xxxxxxxxxx> wrote:
> Unlike REQ_HARDBARRIER, REQ_FLUSH/FUA doesn't mandate any ordering
> against other bio's. This patch relaxes ordering around flushes.
>
> * A flush bio is no longer deferred to workqueue directly. It's
> processed like other bio's but __split_and_process_bio() uses
> md->flush_bio as the clone source. md->flush_bio is initialized to
> empty flush during md initialization and shared for all flushes.
>
> * When dec_pending() detects that a flush has completed, it checks
> whether the original bio has data. If so, the bio is queued to the
> deferred list w/ REQ_FLUSH cleared; otherwise, it's completed.
>
> * As flush sequencing is handled in the usual issue/completion path,
> dm_wq_work() no longer needs to handle flushes differently. Now its
> only responsibility is re-issuing deferred bio's the same way as
> _dm_request() would. REQ_FLUSH handling logic including
> process_flush() is dropped.
>
> * There's no reason for queue_io() and dm_wq_work() write lock
> dm->io_lock. queue_io() now only uses md->deferred_lock and
> dm_wq_work() read locks dm->io_lock.
>
> * bio's no longer need to be queued on the deferred list while a flush
> is in progress making DMF_QUEUE_IO_TO_THREAD unncessary. Drop it.
>
> This avoids stalling the device during flushes and simplifies the
> implementation.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Looks good overall.
> @@ -144,11 +143,6 @@ struct mapped_device {
> spinlock_t deferred_lock;
>
> /*
> - * An error from the flush request currently being processed.
> - */
> - int flush_error;
> -
> - /*
> * Protect barrier_error from concurrent endio processing
> * in request-based dm.
> */
Could you please document why it is OK to remove 'flush_error' in the
patch header? The -EOPNOTSUPP handling removal (done in patch 2)
obviously helps enable this but it is not clear how the
'num_flush_requests' flushes that __clone_and_map_flush() generates do
not need explicit DM error handling.
Other than that.
Acked-by: Mike Snitzer <snitzer@xxxxxxxxxx>
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