Re: [RFC] [PATCH] bio-set patch on latest bk source tree

[Jens Axboe]

On Mon, Jan 31 2005, Dave Olien wrote:
> 
> Hi, Jens,
> 
> I sent you a patch for review about a week ago.  Here is that same
> patch, applied to the latest bk kernel.  Thanks in advance for the review

Thanks Dave, I think we should queue this up with Andrew soonish. A few
minor things need fixing, though:

> ===== drivers/md/dm.c 1.61 vs edited =====
> --- 1.61/drivers/md/dm.c	2005-01-25 13:50:21 -08:00
> +++ edited/drivers/md/dm.c	2005-01-31 11:37:27 -08:00
> @@ -96,10 +96,16 @@ struct mapped_device {
>  static kmem_cache_t *_io_cache;
>  static kmem_cache_t *_tio_cache;
>  
> +static struct bio_set *dm_set;
> +
>  static int __init local_init(void)
>  {
>  	int r;
>  
> +	dm_set = bioset_create(512, 512, 1);
> +	if (!dm_set)
> +		return -ENOMEM;
> +

You consistently use 512, that's a _lot_ of reserved bio's/vecs! For the
full range of bio_vec pools, that will eat quite a large piece of memory
per bio_set allocated. The idea with a mempool isn't to have a huge free
number of elements, but rather just a few to maintain progress with
memory pressure. I think this 512 should be heavily reduced.

>  static int zero_map(struct dm_target *ti, struct bio *bio,
> ===== fs/bio.c 1.73 vs edited =====
> --- 1.73/fs/bio.c	2005-01-20 21:02:13 -08:00
> +++ edited/fs/bio.c	2005-01-31 14:50:37 -08:00
> @@ -28,7 +28,6 @@
>  
>  #define BIO_POOL_SIZE 256
>  
> -static mempool_t *bio_pool;
>  static kmem_cache_t *bio_slab;
>  
>  #define BIOVEC_NR_POOLS 6
> @@ -40,11 +39,10 @@ static kmem_cache_t *bio_slab;
>  #define BIO_SPLIT_ENTRIES 8	
>  mempool_t *bio_split_pool;
>  
> -struct biovec_pool {
> +struct biovec_slab {
>  	int nr_vecs;
>  	char *name; 
>  	kmem_cache_t *slab;
> -	mempool_t *pool;
>  };
>  
>  /*
> @@ -54,15 +52,32 @@ struct biovec_pool {
>   */
>  
>  #define BV(x) { .nr_vecs = x, .name = "biovec-"__stringify(x) }
> -static struct biovec_pool bvec_array[BIOVEC_NR_POOLS] = {
> +static struct biovec_slab bvec_slabs[BIOVEC_NR_POOLS] = {
>  	BV(1), BV(4), BV(16), BV(64), BV(128), BV(BIO_MAX_PAGES),
>  };
>  #undef BV
>  
> -static inline struct bio_vec *bvec_alloc(int gfp_mask, int nr, unsigned long *idx)
> +/*
> + * bio_set is used to allow other portions of the IO system to
> + * allocate their own private memory pools for bio and iovec structures.
> + * These memory pools in turn all allocate from the bio_slab
> + * and the bvec_slabs[].
> + */
> +struct bio_set {
> +	mempool_t *bio_pool;
> +	mempool_t *bvec_pools[BIOVEC_NR_POOLS];
> +};
> +
> +/*
> + * fs_bio_set is the bio_set containing bio and iovec memory pools used by
> + * IO code that does not need private memory pools.
> + */
> +static struct bio_set *fs_bio_set;
> +
> +static inline struct bio_vec *bvec_alloc_bs(int gfp_mask, int nr, unsigned long *idx, struct bio_set *bs)
>  {
> -	struct biovec_pool *bp;
>  	struct bio_vec *bvl;
> +	struct biovec_slab *bp;
>  
>  	/*
>  	 * see comment near bvec_array define!
> @@ -80,26 +95,27 @@ static inline struct bio_vec *bvec_alloc
>  	/*
>  	 * idx now points to the pool we want to allocate from
>  	 */
> -	bp = bvec_array + *idx;
>  
> -	bvl = mempool_alloc(bp->pool, gfp_mask);
> +	bp = bvec_slabs + *idx;
> +	bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
>  	if (bvl)
>  		memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));
> +
>  	return bvl;
>  }
>  
>  /*
> - * default destructor for a bio allocated with bio_alloc()
> + * default destructor for a bio allocated with bio_alloc_bs()
>   */
>  static void bio_destructor(struct bio *bio)
>  {
>  	const int pool_idx = BIO_POOL_IDX(bio);
> -	struct biovec_pool *bp = bvec_array + pool_idx;
> +	struct bio_set *bs = bio->bi_set;
>  
>  	BIO_BUG_ON(pool_idx >= BIOVEC_NR_POOLS);
>  
> -	mempool_free(bio->bi_io_vec, bp->pool);
> -	mempool_free(bio, bio_pool);
> +	mempool_free(bio->bi_io_vec, bs->bvec_pools[pool_idx]);
> +	mempool_free(bio, bs->bio_pool);
>  }
>  
>  inline void bio_init(struct bio *bio)
> @@ -121,18 +137,21 @@ inline void bio_init(struct bio *bio)
>  }
>  
>  /**
> - * bio_alloc - allocate a bio for I/O
> + * bio_alloc_bs - allocate a bio for I/O
>   * @gfp_mask:   the GFP_ mask given to the slab allocator
>   * @nr_iovecs:	number of iovecs to pre-allocate

bs is awefully close to 'block size' when it comes to acronyms in this
area, I would prefer if you just called it bio_alloc_bioset() instead.

> +void bioset_free(struct bio_set *bs)
> +{
> +	if (!bs->bio_pool)
> +		mempool_destroy(bs->bio_pool);

That check looks suspect, surely you mean to check for non-NULL.

> +
> +	biovec_free_pools(bs);
> +
> +	kfree(bs);
> +}
> +
> +struct bio_set *bioset_create(int bio_pool_size, int bvec_pool_size, int scale)
> +{
> +	struct bio_set *bs = kmalloc(sizeof(*bs), GFP_KERNEL);
> +
> +	if (!bs)
> +		return NULL;
> +
> +	memset(bs, 0, sizeof(*bs));
> +	bs->bio_pool = mempool_create(bio_pool_size, mempool_alloc_slab,
> +			mempool_free_slab, bio_slab);
> +
> +	if (!bs->bio_pool) 
> +		goto bad;
> +	
> +	if (biovec_create_pools(bs, bvec_pool_size, scale))
> +		goto bad;
> +
> +	return bs;
> +
> +bad:
> +	bioset_free(bs);
> +	return NULL;
> +}

Please drop the last goto

        if (!biovec_create_pools(bs, bvec_pool_size, scale))
                return bs;

is nicer.

-- 
Jens Axboe

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