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block: don't use bio_split_rw on misc operations

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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@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Link: https://lore.kernel.org/r/20240826173820.1690925-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2024-08-26 19:37:57 +02:00 committed by Jens Axboe
parent 1e8a7f6af9
commit 1251580983
1 changed files with 6 additions and 1 deletions
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7
block/blk.h
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@ -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;
}
}