commit 5e84ea3a9c662dc2d7a48703a4468fad954a3b7f
author Jens Axboe <jaxboe@fusionio.com> Mon Mar 21 10:14:27 2011 +0100
committer Jens Axboe <jaxboe@fusionio.com> Mon Mar 21 10:14:27 2011 +0100
tree 3fa0fb26a7c8a970213584104cc2498ef46d60a3
parent 4345caba340f051e10847924fc078ae18ed6695c

block: attempt to merge with existing requests on plug flush

One of the disadvantages of on-stack plugging is that we potentially
lose out on merging since all pending IO isn't always visible to
everybody. When we flush the on-stack plugs, right now we don't do
any checks to see if potential merge candidates could be utilized.

Correct this by adding a new insert variant, ELEVATOR_INSERT_SORT_MERGE.
It works just ELEVATOR_INSERT_SORT, but first checks whether we can
merge with an existing request before doing the insertion (if we fail
merging).

This fixes a regression with multiple processes issuing IO that
can be merged.

Thanks to Shaohua Li <shaohua.li@intel.com> for testing and fixing
an accounting bug.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>