block: cleanup the VM accounting in submit_bio

submit_bio uses some extremely convoluted checks and confusing comments
to only account REQ_OP_READ/REQ_OP_WRITE comments.  Just switch to the
plain obvious checks instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220516063654.2782792-1-hch@lst.de
[axboe: fixup WRITE -> REQ_OP_WRITE]
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -892,19 +892,11 @@ void submit_bio(struct bio *bio)
 	if (blkcg_punt_bio_submit(bio))
 		return;
 
-	/*
-	 * If it's a regular read/write or a barrier with data attached,
-	 * go through the normal accounting stuff before submission.
-	 */
-	if (bio_has_data(bio)) {
-		unsigned int count = bio_sectors(bio);
-
-		if (op_is_write(bio_op(bio))) {
-			count_vm_events(PGPGOUT, count);
-		} else {
-			task_io_account_read(bio->bi_iter.bi_size);
-			count_vm_events(PGPGIN, count);
-		}
+	if (bio_op(bio) == REQ_OP_READ) {
+		task_io_account_read(bio->bi_iter.bi_size);
+		count_vm_events(PGPGIN, bio_sectors(bio));
+	} else if (bio_op(bio) == REQ_OP_WRITE) {
+		count_vm_events(PGPGOUT, bio_sectors(bio));
 	}
 
 	/*