Commit 12515809 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

block: don't use bio_split_rw on misc operations 



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: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDamien Le Moal <dlemoal@kernel.org>
Tested-by: default avatarHans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: default avatarHans Holmberg <hans.holmberg@wdc.com>
Link: https://lore.kernel.org/r/20240826173820.1690925-5-hch@lst.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 1e8a7f6a

block/blk.h

+6 −1
Original line number Diff line number Diff line
@@ -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;

	}

}