The patch titled
elevator.c: prevent flushing small requests to device
has been removed from the -mm tree. Its filename was
elevatorc-prevent-flushing-small-requests-to-device.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: elevator.c: prevent flushing small requests to device
From: Miquel van Smoorenburg <mikevs@xxxxxxxxxx>
While tracing I/O patterns with blktrace (a great tool) a few weeks ago I
identified a minor issue in elevator.c
When elv_insert() is called to insert a new request, and the device is
plugged, bit of code at the end of the function will unplug the device if
the number of pending requests >= q->unplug_thresh.
This means the current request is also sent to the device immidiately
while it is potentially mergeable with the next request. This has been
observed when a lot of small sequential requests are made.
By unplugging the device before we add the new request to the
queue this can be prevented.
Signed-off-by: Miquel van Smoorenburg <mikevs@xxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
block/elevator.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff -puN block/elevator.c~elevatorc-prevent-flushing-small-requests-to-device block/elevator.c
--- a/block/elevator.c~elevatorc-prevent-flushing-small-requests-to-device
+++ a/block/elevator.c
@@ -617,6 +617,20 @@ void elv_insert(struct request_queue *q,
case ELEVATOR_INSERT_SORT:
BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
+ /*
+ * If we're going to unplug the device, do it now before
+ * we put a potentially small and mergeable new
+ * request on the queue, instead of just after it.
+ */
+ if (blk_queue_plugged(q)) {
+ int nrq = q->rq.count[READ] + q->rq.count[WRITE]
+ - q->in_flight;
+ if (nrq >= q->unplug_thresh)
+ __generic_unplug_device(q);
+ if (elv_queue_empty(q))
+ blk_plug_device(q);
+ unplug_it = 0;
+ }
rq->cmd_flags |= REQ_SORTED;
q->nr_sorted++;
if (rq_mergeable(rq)) {
_
Patches currently in -mm which might be from mikevs@xxxxxxxxxx are
linux-next.patch
do_mpage_readpage-dont-submit-lots-of-small-bios-on-boundary.patch
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