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bio: add support for inlining a number of bio_vecs inside the bio 

When we go and allocate a bio for IO, we actually do two allocations.
One for the bio itself, and one for the bi_io_vec that holds the
actual pages we are interested in.

This feature inlines a definable amount of io vecs inside the bio
itself, so we eliminate the bio_vec array allocation for IO's up
to a certain size. It defaults to 4 vecs, which is typically 16k
of IO.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-12-23 12:42:54 +01:00
parent bb799ca020
commit 392ddc3298
2 changed files with 34 additions and 5 deletions
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27
fs/bio.c
View File

@ -31,6 +31,12 @@
DEFINE_TRACE(block_split);
/*
* Test patch to inline a certain number of bi_io_vec's inside the bio
* itself, to shrink a bio data allocation from two mempool calls to one
*/
#define BIO_INLINE_VECS 4
static mempool_t *bio_split_pool __read_mostly;
/*
@ -241,7 +247,7 @@ void bio_free(struct bio *bio, struct bio_set *bs)
{
void *p;
if (bio->bi_io_vec)
if (bio_has_allocated_vec(bio))
bvec_free_bs(bs, bio->bi_io_vec, BIO_POOL_IDX(bio));
if (bio_integrity(bio))
@ -267,7 +273,8 @@ static void bio_fs_destructor(struct bio *bio)
static void bio_kmalloc_destructor(struct bio *bio)
{
kfree(bio->bi_io_vec);
if (bio_has_allocated_vec(bio))
kfree(bio->bi_io_vec);
kfree(bio);
}
@ -314,7 +321,16 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
if (likely(nr_iovecs)) {
unsigned long uninitialized_var(idx);
bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
if (nr_iovecs <= BIO_INLINE_VECS) {
idx = 0;
bvl = bio->bi_inline_vecs;
nr_iovecs = BIO_INLINE_VECS;
memset(bvl, 0, BIO_INLINE_VECS * sizeof(*bvl));
} else {
bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx,
bs);
nr_iovecs = bvec_nr_vecs(idx);
}
if (unlikely(!bvl)) {
if (bs)
mempool_free(bio, bs->bio_pool);
@ -324,7 +340,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
goto out;
}
bio->bi_flags |= idx << BIO_POOL_OFFSET;
bio->bi_max_vecs = bvec_nr_vecs(idx);
bio->bi_max_vecs = nr_iovecs;
}
bio->bi_io_vec = bvl;
}
@ -1525,6 +1541,7 @@ void bioset_free(struct bio_set *bs)
*/
struct bio_set *bioset_create(unsigned int pool_size, unsigned int front_pad)
{
unsigned int back_pad = BIO_INLINE_VECS * sizeof(struct bio_vec);
struct bio_set *bs;
bs = kzalloc(sizeof(*bs), GFP_KERNEL);
@ -1533,7 +1550,7 @@ struct bio_set *bioset_create(unsigned int pool_size, unsigned int front_pad)
bs->front_pad = front_pad;
bs->bio_slab = bio_find_or_create_slab(front_pad);
bs->bio_slab = bio_find_or_create_slab(front_pad + back_pad);
if (!bs->bio_slab) {
kfree(bs);
return NULL;

12
include/linux/bio.h
View File

@ -102,6 +102,13 @@ struct bio {
#endif
bio_destructor_t *bi_destructor; /* destructor */
/*
* We can inline a number of vecs at the end of the bio, to avoid
* double allocations for a small number of bio_vecs. This member
* MUST obviously be kept at the very end of the bio.
*/
struct bio_vec bi_inline_vecs[0];
};
/*
@ -213,6 +220,11 @@ static inline void *bio_data(struct bio *bio)
return NULL;
}
static inline int bio_has_allocated_vec(struct bio *bio)
{
return bio->bi_io_vec && bio->bi_io_vec != bio->bi_inline_vecs;
}
/*
* will die
*/