io_uring: move submit side state closer in the ring

We recently added the submit side req cache, but it was placed at the
end of the struct. Move it near the other submission state for better
memory placement, and reshuffle a few other members at the same time.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -346,6 +346,13 @@ struct io_ring_ctx {
 		struct io_uring_sqe	*sq_sqes;
 	} ____cacheline_aligned_in_smp;
 
+	struct {
+		struct mutex		uring_lock;
+		wait_queue_head_t	wait;
+	} ____cacheline_aligned_in_smp;
+
+	struct io_submit_state		submit_state;
+
 	struct io_rings	*rings;
 
 	/* IO offload */
@@ -413,11 +420,6 @@ struct io_ring_ctx {
 		struct eventfd_ctx	*cq_ev_fd;
 	} ____cacheline_aligned_in_smp;
 
-	struct {
-		struct mutex		uring_lock;
-		wait_queue_head_t	wait;
-	} ____cacheline_aligned_in_smp;
-
 	struct {
 		spinlock_t		completion_lock;
 
@@ -441,9 +443,10 @@ struct io_ring_ctx {
 	struct list_head		rsrc_ref_list;
 	spinlock_t			rsrc_ref_lock;
 
-	struct work_struct		exit_work;
 	struct io_restriction		restrictions;
-	struct io_submit_state		submit_state;
+
+	/* Keep this last, we don't need it for the fast path */
+	struct work_struct		exit_work;
 };
 
 /*