"struct bvec_iter" is defined with the __packed attribute, so it is aligned on a single byte. On X86 (and on other architectures that support unaligned addresses in hardware), "struct bvec_iter" is accessed using the 8-byte and 4-byte memory instructions, however these instructions are less efficient if they operate on unaligned addresses.
(on RISC machines that don't have unaligned access in hardware, GCC generates byte-by-byte accesses that are very inefficient - see [1]) This commit reorders the entries in "struct dm_verity_io" and "struct convert_context", so that "struct bvec_iter" is aligned on 8 bytes. [1] https://lore.kernel.org/all/ZcLuWUNRZadJr0tQ@fedora/T/ Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-crypt.c | 4 ++-- drivers/md/dm-verity.h | 4 ++-- 2 files changed, 4 insertions(+), 4 deletions(-) Index: linux-2.6/drivers/md/dm-verity.h =================================================================== --- linux-2.6.orig/drivers/md/dm-verity.h 2024-02-20 18:05:29.000000000 +0100 +++ linux-2.6/drivers/md/dm-verity.h 2024-02-20 18:40:45.000000000 +0100 @@ -80,12 +80,12 @@ struct dm_verity_io { /* original value of bio->bi_end_io */ bio_end_io_t *orig_bi_end_io; + struct bvec_iter iter; + sector_t block; unsigned int n_blocks; bool in_tasklet; - struct bvec_iter iter; - struct work_struct work; char *recheck_buffer; Index: linux-2.6/drivers/md/dm-crypt.c =================================================================== --- linux-2.6.orig/drivers/md/dm-crypt.c 2024-02-20 18:39:06.000000000 +0100 +++ linux-2.6/drivers/md/dm-crypt.c 2024-02-20 18:44:02.000000000 +0100 @@ -53,11 +53,11 @@ struct convert_context { struct completion restart; struct bio *bio_in; - struct bio *bio_out; struct bvec_iter iter_in; + struct bio *bio_out; struct bvec_iter iter_out; - u64 cc_sector; atomic_t cc_pending; + u64 cc_sector; union { struct skcipher_request *req; struct aead_request *req_aead;
