path: root/fs/bio.c

/*
 * Copyright (C) 2001 Jens Axboe <axboe@kernel.dk>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public Licens
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
 *
 */
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mempool.h>
#include <linux/workqueue.h>
#include <linux/blktrace_api.h>
#include <scsi/sg.h>		/* for struct sg_iovec */

#define BIO_POOL_SIZE 256

static struct kmem_cache *bio_slab __read_mostly;

#define BIOVEC_NR_POOLS 6

/*
 * a small number of entries is fine, not going to be performance critical.
 * basically we just need to survive
 */
#define BIO_SPLIT_ENTRIES 8	
mempool_t *bio_split_pool __read_mostly;

struct biovec_slab {
	int nr_vecs;
	char *name; 
	struct kmem_cache *slab;
};

/*
 * if you change this list, also change bvec_alloc or things will
 * break badly! cannot be bigger than what you can fit into an
 * unsigned short
 */

#define BV(x) { .nr_vecs = x, .name = "biovec-"__stringify(x) }
static struct biovec_slab bvec_slabs[BIOVEC_NR_POOLS] __read_mostly = {
	BV(1), BV(4), BV(16), BV(64), BV(128), BV(BIO_MAX_PAGES),
};
#undef BV

/*
 * 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(gfp_t gfp_mask, int nr, unsigned long *idx, struct bio_set *bs)
{
	struct bio_vec *bvl;

	/*
	 * see comment near bvec_array define!
	 */
	switch (nr) {
		case   1        : *idx = 0; break;
		case   2 ...   4: *idx = 1; break;
		case   5 ...  16: *idx = 2; break;
		case  17 ...  64: *idx = 3; break;
		case  65 ... 128: *idx = 4; break;
		case 129 ... BIO_MAX_PAGES: *idx = 5; break;
		default:
			return NULL;
	}
	/*
	 * idx now points to the pool we want to allocate from
	 */

	bvl = mempool_alloc(bs->bvec_pools[*idx], gfp_mask);
	if (bvl) {
		struct biovec_slab *bp = bvec_slabs + *idx;

		memset(bvl, 0, bp->nr_vecs * sizeof(struct bio_vec));