[-mm PATCH 0/2] 74% decrease in dispatched writes, stripe-queue take3

Neil, Andrew,

The following patches replace the stripe-queue patches currently in -mm.
Following your suggestion, Neil, I gathered blktrace data on the number
of reads generated by sequential write stimulus.  It turns out that
reduced pre-reading is not the cause of the performance increase, but
rather increased write merging.  The data, in patch #1, shows a 74%
decrease in the number of dispatched writes.  I can only assume that
this is the explanation for the 65% throughput improvement, because the
occurrence of reads actually increased with these patches applied.

This take also fixes observed data corruption while running i/o to a
synching array (it was wrong to move the flags parameter from r5dev to
r5_queue_dev as things could get out of sync... reverted).  Next step is
to test reshape under this new queuing model.

Regards,
Dan
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