tjh.dev / kernel
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block: define bvec_iter as __packed __aligned(4)

In commit 19416123ab3e ("block: define 'struct bvec_iter' as packed"),
what we need is to save the 4byte padding, and avoid `bio` to spread on
one extra cache line.

It is enough to define it as '__packed __aligned(4)', as '__packed'
alone means byte aligned, and can cause compiler to generate horrible
code on architectures that don't support unaligned access in case that
bvec_iter is embedded in other structures.

Cc: Mikulas Patocka <mpatocka@redhat.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: 19416123ab3e ("block: define 'struct bvec_iter' as packed")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

authored by

Ming Lei and committed by
Linus Torvalds 7838b465 7fd66446

+1 -1
+1 -1
include/linux/bvec.h
··· 83 83 84 84 unsigned int bi_bvec_done; /* number of bytes completed in 85 85 current bvec */ 86 - } __packed; 86 + } __packed __aligned(4); 87 87 88 88 struct bvec_iter_all { 89 89 struct bio_vec bv;