io_uring: inform block layer of how many requests we are submitting

The block layer can use this knowledge to make smarter decisions on
how to handle the request, if it knows that N more may be coming. Switch
to using blk_start_plug_nr_ios() to pass in that information.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -317,6 +317,7 @@ struct io_submit_state {
 
 	bool			plug_started;
 	bool			need_plug;
+	unsigned short		submit_nr;
 	struct blk_plug		plug;
 };
 
@@ -7060,7 +7061,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		if (state->need_plug && io_op_defs[opcode].plug) {
 			state->plug_started = true;
 			state->need_plug = false;
-			blk_start_plug(&state->plug);
+			blk_start_plug_nr_ios(&state->plug, state->submit_nr);
 		}
 
 		req->file = io_file_get(ctx, req, READ_ONCE(sqe->fd),
@@ -7181,6 +7182,7 @@ static void io_submit_state_start(struct io_submit_state *state,
 {
 	state->plug_started = false;
 	state->need_plug = max_ios > 2;
+	state->submit_nr = max_ios;
 	/* set only head, no need to init link_last in advance */
 	state->link.head = NULL;
 }