bio_split_rw is designed to split read and write bios with a payload.
Currently it is called by __bio_split_to_limits for all operations not
explicitly list, which works because bio_may_need_split explicitly checks
for bi_vcnt == 1 and thus skips the bypass if there is no payload and
bio_for_each_bvec loop will never execute it's body if bi_size is 0.
But all this is hard to understand, fragile and wasted pointless cycles.
Switch __bio_split_to_limits to only call bio_split_rw for READ and
WRITE command and don't attempt any kind split for operation that do not
require splitting.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
block/blk.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/block/blk.h b/block/blk.h
index 61c2afa67daabb..32f4e9f630a3ac 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -372,7 +372,8 @@ static inline struct bio *__bio_split_to_limits(struct bio *bio,
const struct queue_limits *lim, unsigned int *nr_segs)
{
switch (bio_op(bio)) {
- default:
+ case REQ_OP_READ:
+ case REQ_OP_WRITE:
if (bio_may_need_split(bio, lim))
return bio_split_rw(bio, lim, nr_segs);
*nr_segs = 1;
@@ -384,6 +385,10 @@ static inline struct bio *__bio_split_to_limits(struct bio *bio,
return bio_split_discard(bio, lim, nr_segs);
case REQ_OP_WRITE_ZEROES:
return bio_split_write_zeroes(bio, lim, nr_segs);
+ default:
+ /* other operations can't be split */
+ *nr_segs = 0;
+ return bio;
}
}
--
2.43.0
