Allow elevators to sort/merge discard requests

But blkdev_issue_discard() still emits requests which are interpreted as
soft barriers, because naïve callers might otherwise issue subsequent
writes to those same sectors, which might cross on the queue (if they're
reallocated quickly enough).

Callers still _can_ issue non-barrier discard requests, but they have to
take care of queue ordering for themselves.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/block/elevator.c b/block/elevator.c
index ed6f8f32d27e..4f5127054e3f 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -75,6 +75,12 @@ int elv_rq_merge_ok(struct request *rq, struct bio *bio)
                 return 0;
 
         /*
+         * Don't merge file system requests and discard requests
+         */
+        if (bio_discard(bio) != bio_discard(rq->bio))
+                return 0;
+
+        /*
          * different data direction or already started, don't merge
          */
         if (bio_data_dir(bio) != rq_data_dir(rq))
@@ -438,6 +444,8 @@ void elv_dispatch_sort(struct request_queue *q, struct request *rq)
         list_for_each_prev(entry, &q->queue_head) {
                 struct request *pos = list_entry_rq(entry);
 
+                if (blk_discard_rq(rq) != blk_discard_rq(pos))
+                        break;
                 if (rq_data_dir(rq) != rq_data_dir(pos))
                         break;
                 if (pos->cmd_flags & stop_flags)
@@ -607,7 +615,7 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
                 break;
 
         case ELEVATOR_INSERT_SORT:
-                BUG_ON(!blk_fs_request(rq));
+                BUG_ON(!blk_fs_request(rq) && !blk_discard_rq(rq));
                 rq->cmd_flags |= REQ_SORTED;
                 q->nr_sorted++;
                 if (rq_mergeable(rq)) {
@@ -692,7 +700,7 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where,
                  * this request is scheduling boundary, update
                  * end_sector
                  */
-                if (blk_fs_request(rq)) {
+                if (blk_fs_request(rq) || blk_discard_rq(rq)) {
                         q->end_sector = rq_end_sector(rq);
                         q->boundary_rq = rq;
                 }