dm-verity, dm-crypt: align "struct bvec_iter" correctly

"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 <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 6044614bab761f78f92e234d7abe7ce065371d00..f54cd6714af3b555cdc26aedab5c3a5a5e335414 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -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;

diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 4620a98c99561803431dc7674639adc3a2d422db..db93a91169d5e6de31d344a6f37589bbc0bdb654 100644 (file)
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -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;