1 files changed, 33 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 533a2938ffd6..9fc5eafa6c0e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -568,6 +568,38 @@ cfq_merged_requests(request_queue_t *q, struct request *rq,
         cfq_remove_request(next);
 }
 
+static int cfq_allow_merge(request_queue_t *q, struct request *rq,
+                           struct bio *bio)
+{
+        struct cfq_data *cfqd = q->elevator->elevator_data;
+        const int rw = bio_data_dir(bio);
+        struct cfq_queue *cfqq;
+        pid_t key;
+
+        /*
+         * If bio is async or a write, always allow merge
+         */
+        if (!bio_sync(bio) || rw == WRITE)
+                return 1;
+
+        /*
+         * bio is sync. if request is not, disallow.
+         */
+        if (!rq_is_sync(rq))
+                return 0;
+
+        /*
+         * Ok, both bio and request are sync. Allow merge if they are
+         * from the same queue.
+         */
+        key = cfq_queue_pid(current, rw, 1);
+        cfqq = cfq_find_cfq_hash(cfqd, key, current->ioprio);
+        if (cfqq != RQ_CFQQ(rq))
+                return 0;
+
+        return 1;
+}
+
 static inline void
 __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 {
@@ -2125,6 +2157,7 @@ static struct elevator_type iosched_cfq = {
                 .elevator_merge_fn =            cfq_merge,
                 .elevator_merged_fn =           cfq_merged_request,
                 .elevator_merge_req_fn =        cfq_merged_requests,
+                .elevator_allow_merge_fn =      cfq_allow_merge,
                 .elevator_dispatch_fn =         cfq_dispatch_requests,
                 .elevator_add_req_fn =          cfq_insert_request,
                 .elevator_activate_req_fn =     cfq_activate_request,