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block: Consolidate bio_alloc_bioset(), bio_kmalloc()
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Previously, bio_kmalloc() and bio_alloc_bioset() behaved slightly
different because there was some almost-duplicated code - this fixes
some of that.

The important change is that previously bio_kmalloc() always set
bi_io_vec = bi_inline_vecs, even if nr_iovecs == 0 - unlike
bio_alloc_bioset(). This would cause bio_has_data() to return true; I
don't know if this resulted in any actual bugs but it was certainly
wrong.

bio_kmalloc() and bio_alloc_bioset() also have different arbitrary
limits on nr_iovecs - 1024 (UIO_MAXIOV) for bio_kmalloc(), 256
(BIO_MAX_PAGES) for bio_alloc_bioset(). This patch doesn't fix that, but
at least they're enforced closer together and hopefully they will be
fixed in a later patch.

This'll also help with some future cleanups - there are a fair number of
functions that allocate bios (e.g. bio_clone()), and now they don't have
to be duplicated for bio_alloc(), bio_alloc_bioset(), and bio_kmalloc().

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Jens Axboe <axboe@kernel.dk>
v7: Re-add dropped comments, improv patch description
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Kent Overstreet authored and Jens Axboe committed Sep 9, 2012
1 parent 4254bba commit 3f86a82
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Showing 2 changed files with 49 additions and 77 deletions.
110 changes: 37 additions & 73 deletions fs/bio.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ static struct biovec_slab bvec_slabs[BIOVEC_NR_POOLS] __read_mostly = {
* IO code that does not need private memory pools.
*/
struct bio_set *fs_bio_set;
EXPORT_SYMBOL(fs_bio_set);

/*
* Our slab pool management
Expand Down Expand Up @@ -301,39 +302,58 @@ EXPORT_SYMBOL(bio_reset);
* @bs: the bio_set to allocate from.
*
* Description:
* bio_alloc_bioset will try its own mempool to satisfy the allocation.
* If %__GFP_WAIT is set then we will block on the internal pool waiting
* for a &struct bio to become free.
**/
* If @bs is NULL, uses kmalloc() to allocate the bio; else the allocation is
* backed by the @bs's mempool.
*
* When @bs is not NULL, if %__GFP_WAIT is set then bio_alloc will always be
* able to allocate a bio. This is due to the mempool guarantees. To make this
* work, callers must never allocate more than 1 bio at a time from this pool.
* Callers that need to allocate more than 1 bio must always submit the
* previously allocated bio for IO before attempting to allocate a new one.
* Failure to do so can cause deadlocks under memory pressure.
*
* RETURNS:
* Pointer to new bio on success, NULL on failure.
*/
struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
{
unsigned front_pad;
unsigned inline_vecs;
unsigned long idx = BIO_POOL_NONE;
struct bio_vec *bvl = NULL;
struct bio *bio;
void *p;

p = mempool_alloc(bs->bio_pool, gfp_mask);
if (!bs) {
if (nr_iovecs > UIO_MAXIOV)
return NULL;

p = kmalloc(sizeof(struct bio) +
nr_iovecs * sizeof(struct bio_vec),
gfp_mask);
front_pad = 0;
inline_vecs = nr_iovecs;
} else {
p = mempool_alloc(bs->bio_pool, gfp_mask);
front_pad = bs->front_pad;
inline_vecs = BIO_INLINE_VECS;
}

if (unlikely(!p))
return NULL;
bio = p + bs->front_pad;

bio = p + front_pad;
bio_init(bio);
bio->bi_pool = bs;

if (unlikely(!nr_iovecs))
goto out_set;

if (nr_iovecs <= BIO_INLINE_VECS) {
bvl = bio->bi_inline_vecs;
nr_iovecs = BIO_INLINE_VECS;
} else {
if (nr_iovecs > inline_vecs) {
bvl = bvec_alloc_bs(gfp_mask, nr_iovecs, &idx, bs);
if (unlikely(!bvl))
goto err_free;

nr_iovecs = bvec_nr_vecs(idx);
} else if (nr_iovecs) {
bvl = bio->bi_inline_vecs;
}
out_set:

bio->bi_pool = bs;
bio->bi_flags |= idx << BIO_POOL_OFFSET;
bio->bi_max_vecs = nr_iovecs;
bio->bi_io_vec = bvl;
Expand All @@ -345,62 +365,6 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, int nr_iovecs, struct bio_set *bs)
}
EXPORT_SYMBOL(bio_alloc_bioset);

/**
* bio_alloc - allocate a new bio, memory pool backed
* @gfp_mask: allocation mask to use
* @nr_iovecs: number of iovecs
*
* bio_alloc will allocate a bio and associated bio_vec array that can hold
* at least @nr_iovecs entries. Allocations will be done from the
* fs_bio_set. Also see @bio_alloc_bioset and @bio_kmalloc.
*
* If %__GFP_WAIT is set, then bio_alloc will always be able to allocate
* a bio. This is due to the mempool guarantees. To make this work, callers
* must never allocate more than 1 bio at a time from this pool. Callers
* that need to allocate more than 1 bio must always submit the previously
* allocated bio for IO before attempting to allocate a new one. Failure to
* do so can cause livelocks under memory pressure.
*
* RETURNS:
* Pointer to new bio on success, NULL on failure.
*/
struct bio *bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
{
return bio_alloc_bioset(gfp_mask, nr_iovecs, fs_bio_set);
}
EXPORT_SYMBOL(bio_alloc);

/**
* bio_kmalloc - allocate a bio for I/O using kmalloc()
* @gfp_mask: the GFP_ mask given to the slab allocator
* @nr_iovecs: number of iovecs to pre-allocate
*
* Description:
* Allocate a new bio with @nr_iovecs bvecs. If @gfp_mask contains
* %__GFP_WAIT, the allocation is guaranteed to succeed.
*
**/
struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
{
struct bio *bio;

if (nr_iovecs > UIO_MAXIOV)
return NULL;

bio = kmalloc(sizeof(struct bio) + nr_iovecs * sizeof(struct bio_vec),
gfp_mask);
if (unlikely(!bio))
return NULL;

bio_init(bio);
bio->bi_flags |= BIO_POOL_NONE << BIO_POOL_OFFSET;
bio->bi_max_vecs = nr_iovecs;
bio->bi_io_vec = bio->bi_inline_vecs;

return bio;
}
EXPORT_SYMBOL(bio_kmalloc);

void zero_fill_bio(struct bio *bio)
{
unsigned long flags;
Expand Down
16 changes: 12 additions & 4 deletions include/linux/bio.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -212,11 +212,21 @@ extern void bio_pair_release(struct bio_pair *dbio);
extern struct bio_set *bioset_create(unsigned int, unsigned int);
extern void bioset_free(struct bio_set *);

extern struct bio *bio_alloc(gfp_t, unsigned int);
extern struct bio *bio_kmalloc(gfp_t, unsigned int);
extern struct bio *bio_alloc_bioset(gfp_t, int, struct bio_set *);
extern void bio_put(struct bio *);

extern struct bio_set *fs_bio_set;

static inline struct bio *bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
{
return bio_alloc_bioset(gfp_mask, nr_iovecs, fs_bio_set);
}

static inline struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
{
return bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
}

extern void bio_endio(struct bio *, int);
struct request_queue;
extern int bio_phys_segments(struct request_queue *, struct bio *);
Expand Down Expand Up @@ -304,8 +314,6 @@ struct biovec_slab {
struct kmem_cache *slab;
};

extern struct bio_set *fs_bio_set;

/*
* a small number of entries is fine, not going to be performance critical.
* basically we just need to survive
Expand Down

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