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-rw-r--r--block/cfq-iosched.c33
1 files changed, 33 insertions, 0 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 533a2938ffd..9fc5eafa6c0 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,