block: skip elevator data initialization for flush requests

Skip elevator initialization for flush requests by passing priv=0 to
blk_alloc_request() in get_request().  As such elv_set_request() is
never called for flush requests.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 25 insertions, 4 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 05746093b45e..ab4a7696956d 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -738,6 +738,25 @@ static void freed_request(struct request_queue *q, int sync, int priv)
 }
 
 /*
+ * Determine if elevator data should be initialized when allocating the
+ * request associated with @bio.
+ */
+static bool blk_rq_should_init_elevator(struct bio *bio)
+{
+        if (!bio)
+                return true;
+
+        /*
+         * Flush requests do not use the elevator so skip initialization.
+         * This allows a request to share the flush and elevator data.
+         */
+        if (bio->bi_rw & (REQ_FLUSH | REQ_FUA))
+                return false;
+
+        return true;
+}
+
+/*
  * Get a free request, queue_lock must be held.
  * Returns NULL on failure, with queue_lock held.
  * Returns !NULL on success, with queue_lock *not held*.
@@ -749,7 +768,7 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
         struct request_list *rl = &q->rq;
         struct io_context *ioc = NULL;
         const bool is_sync = rw_is_sync(rw_flags) != 0;
-        int may_queue, priv;
+        int may_queue, priv = 0;
 
         may_queue = elv_may_queue(q, rw_flags);
         if (may_queue == ELV_MQUEUE_NO)
@@ -793,9 +812,11 @@ static struct request *get_request(struct request_queue *q, int rw_flags,
         rl->count[is_sync]++;
         rl->starved[is_sync] = 0;
 
-        priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
-        if (priv)
-                rl->elvpriv++;
+        if (blk_rq_should_init_elevator(bio)) {
+                priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+                if (priv)
+                        rl->elvpriv++;
+        }
 
         if (blk_queue_io_stat(q))
                 rw_flags |= REQ_IO_STAT;