On 10/11/23 18:02, Damien Le Moal wrote:
Some have stated interest in CDL in NVMe-oF context, which could
imply that combining CDL and lifetime may be something useful to do
in that space...
We are having this discussion because bi_ioprio is sixteen bits wide and
because we don't want to make struct bio larger. How about expanding the
bi_ioprio field from 16 to 32 bits and to use separate bits for CDL
information and data lifetimes?
This patch does not make struct bio bigger because it changes a three
byte hole with a one byte hole:
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -268,8 +268,8 @@ struct bio {
* req_flags.
*/
unsigned short bi_flags; /* BIO_* below */
- unsigned short bi_ioprio;
blk_status_t bi_status;
+ u32 bi_ioprio;
atomic_t __bi_remaining;
struct bvec_iter bi_iter;
From the pahole output:
struct bio {
struct bio * bi_next; /* 0 8 */
struct block_device * bi_bdev; /* 8 8 */
blk_opf_t bi_opf; /* 16 4 */
short unsigned int bi_flags; /* 20 2 */
blk_status_t bi_status; /* 22 1 */
/* XXX 1 byte hole, try to pack */
u32 bi_ioprio; /* 24 4 */
atomic_t __bi_remaining; /* 28 4 */
struct bvec_iter bi_iter; /* 32 20 */
blk_qc_t bi_cookie; /* 52 4 */
bio_end_io_t * bi_end_io; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
void * bi_private; /* 64 8 */
struct bio_crypt_ctx * bi_crypt_context; /* 72 8 */
union {
struct bio_integrity_payload * bi_integrity; /* 80
8 */
}; /* 80 8 */
short unsigned int bi_vcnt; /* 88 2 */
short unsigned int bi_max_vecs; /* 90 2 */
atomic_t __bi_cnt; /* 92 4 */
struct bio_vec * bi_io_vec; /* 96 8 */
struct bio_set * bi_pool; /* 104 8 */
struct bio_vec bi_inline_vecs[]; /* 112 0 */
/* size: 112, cachelines: 2, members: 19 */
/* sum members: 111, holes: 1, sum holes: 1 */
/* last cacheline: 48 bytes */
};
Thanks,
Bart.
