block: don't bother iter advancing a fully done bio

If we're completing nbytes and nbytes is the size of the bio, don't bother
with calling into the iterator increment helpers. Just clear the bio
size and we're done.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1278,18 +1278,7 @@ int submit_bio_wait(struct bio *bio)
 }
 EXPORT_SYMBOL(submit_bio_wait);
 
-/**
- * bio_advance - increment/complete a bio by some number of bytes
- * @bio:	bio to advance
- * @bytes:	number of bytes to complete
- *
- * This updates bi_sector, bi_size and bi_idx; if the number of bytes to
- * complete doesn't align with a bvec boundary, then bv_len and bv_offset will
- * be updated on the last bvec as well.
- *
- * @bio will then represent the remaining, uncompleted portion of the io.
- */
-void bio_advance(struct bio *bio, unsigned bytes)
+void __bio_advance(struct bio *bio, unsigned bytes)
 {
 	if (bio_integrity(bio))
 		bio_integrity_advance(bio, bytes);
@@ -1297,7 +1286,7 @@ void bio_advance(struct bio *bio, unsigned bytes)
 	bio_crypt_advance(bio, bytes);
 	bio_advance_iter(bio, &bio->bi_iter, bytes);
 }
-EXPORT_SYMBOL(bio_advance);
+EXPORT_SYMBOL(__bio_advance);
 
 void bio_copy_data_iter(struct bio *dst, struct bvec_iter *dst_iter,
 			struct bio *src, struct bvec_iter *src_iter)

include/linux/bio.h

@@ -119,6 +119,28 @@ static inline void bio_advance_iter_single(const struct bio *bio,
 		bvec_iter_advance_single(bio->bi_io_vec, iter, bytes);
 }
 
+void __bio_advance(struct bio *, unsigned bytes);
+
+/**
+ * bio_advance - increment/complete a bio by some number of bytes
+ * @bio:	bio to advance
+ * @bytes:	number of bytes to complete
+ *
+ * This updates bi_sector, bi_size and bi_idx; if the number of bytes to
+ * complete doesn't align with a bvec boundary, then bv_len and bv_offset will
+ * be updated on the last bvec as well.
+ *
+ * @bio will then represent the remaining, uncompleted portion of the io.
+ */
+static inline void bio_advance(struct bio *bio, unsigned int nbytes)
+{
+	if (nbytes == bio->bi_iter.bi_size) {
+		bio->bi_iter.bi_size = 0;
+		return;
+	}
+	__bio_advance(bio, nbytes);
+}
+
 #define __bio_for_each_segment(bvl, bio, iter, start)			\
 	for (iter = (start);						\
 	     (iter).bi_size &&						\
@@ -381,8 +403,6 @@ static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
 struct request_queue;
 
 extern int submit_bio_wait(struct bio *bio);
-extern void bio_advance(struct bio *, unsigned);
-
 extern void bio_init(struct bio *bio, struct bio_vec *table,
 		     unsigned short max_vecs);
 extern void bio_uninit(struct bio *);