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Commit 4e420c45 authored by Joe Thornber's avatar Joe Thornber Committed by Mike Snitzer
Browse files

dm bufio: switch from a huge hash table to an rbtree 



Converting over to using an rbtree eliminates a fixed 8MB allocation
from vmalloc space for the hash table.

Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 9b460d36

drivers/md/dm-bufio.c

+54 −43
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/vmalloc.h>

#include <linux/shrinker.h>

#include <linux/module.h>

#include <linux/rbtree.h>



#define DM_MSG_PREFIX "bufio"
@@ -47,14 +48,6 @@ 
 */

#define DM_BUFIO_INLINE_VECS		16



/*

 * Buffer hash

 */

#define DM_BUFIO_HASH_BITS	20

#define DM_BUFIO_HASH(block) \

	((((block) >> DM_BUFIO_HASH_BITS) ^ (block)) & \

	 ((1 << DM_BUFIO_HASH_BITS) - 1))



/*

 * Don't try to use kmem_cache_alloc for blocks larger than this.

 * For explanation, see alloc_buffer_data below.
@@ -106,7 +99,7 @@ struct dm_bufio_client { 


	unsigned minimum_buffers;



	struct hlist_head *cache_hash;

	struct rb_root buffer_tree;

	wait_queue_head_t free_buffer_wait;



	int async_write_error;
@@ -135,7 +128,7 @@ enum data_mode { 
};



struct dm_buffer {

	struct hlist_node hash_list;

	struct rb_node node;

	struct list_head lru_list;

	sector_t block;

	void *data;
@@ -253,6 +246,53 @@ static LIST_HEAD(dm_bufio_all_clients); 
 */

static DEFINE_MUTEX(dm_bufio_clients_lock);



/*----------------------------------------------------------------

 * A red/black tree acts as an index for all the buffers.

 *--------------------------------------------------------------*/

static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)

{

	struct rb_node *n = c->buffer_tree.rb_node;

	struct dm_buffer *b;



	while (n) {

		b = container_of(n, struct dm_buffer, node);



		if (b->block == block)

			return b;



		n = (b->block < block) ? n->rb_left : n->rb_right;

	}



	return NULL;

}



static void __insert(struct dm_bufio_client *c, struct dm_buffer *b)

{

	struct rb_node **new = &c->buffer_tree.rb_node, *parent = NULL;

	struct dm_buffer *found;



	while (*new) {

		found = container_of(*new, struct dm_buffer, node);



		if (found->block == b->block) {

			BUG_ON(found != b);

			return;

		}



		parent = *new;

		new = (found->block < b->block) ?

			&((*new)->rb_left) : &((*new)->rb_right);

	}



	rb_link_node(&b->node, parent, new);

	rb_insert_color(&b->node, &c->buffer_tree);

}



static void __remove(struct dm_bufio_client *c, struct dm_buffer *b)

{

	rb_erase(&b->node, &c->buffer_tree);

}



/*----------------------------------------------------------------*/



static void adjust_total_allocated(enum data_mode data_mode, long diff)
@@ -434,7 +474,7 @@ static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty) 
	b->block = block;

	b->list_mode = dirty;

	list_add(&b->lru_list, &c->lru[dirty]);

	hlist_add_head(&b->hash_list, &c->cache_hash[DM_BUFIO_HASH(block)]);

	__insert(b->c, b);

	b->last_accessed = jiffies;

}
@@ -448,7 +488,7 @@ static void __unlink_buffer(struct dm_buffer *b) 
	BUG_ON(!c->n_buffers[b->list_mode]);



	c->n_buffers[b->list_mode]--;

	hlist_del(&b->hash_list);

	__remove(b->c, b);

	list_del(&b->lru_list);

}
@@ -888,23 +928,6 @@ static void __check_watermark(struct dm_bufio_client *c, 
		__write_dirty_buffers_async(c, 1, write_list);

}



/*

 * Find a buffer in the hash.

 */

static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)

{

	struct dm_buffer *b;



	hlist_for_each_entry(b, &c->cache_hash[DM_BUFIO_HASH(block)],

			     hash_list) {

		dm_bufio_cond_resched();

		if (b->block == block)

			return b;

	}



	return NULL;

}



/*----------------------------------------------------------------

 * Getting a buffer

 *--------------------------------------------------------------*/
@@ -1534,11 +1557,7 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign 
		r = -ENOMEM;

		goto bad_client;

	}

	c->cache_hash = vmalloc(sizeof(struct hlist_head) << DM_BUFIO_HASH_BITS);

	if (!c->cache_hash) {

		r = -ENOMEM;

		goto bad_hash;

	}

	c->buffer_tree = RB_ROOT;



	c->bdev = bdev;

	c->block_size = block_size;
@@ -1557,9 +1576,6 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign 
		c->n_buffers[i] = 0;

	}



	for (i = 0; i < 1 << DM_BUFIO_HASH_BITS; i++)

		INIT_HLIST_HEAD(&c->cache_hash[i]);



	mutex_init(&c->lock);

	INIT_LIST_HEAD(&c->reserved_buffers);

	c->need_reserved_buffers = reserved_buffers;
@@ -1633,8 +1649,6 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign 
	}

	dm_io_client_destroy(c->dm_io);

bad_dm_io:

	vfree(c->cache_hash);

bad_hash:

	kfree(c);

bad_client:

	return ERR_PTR(r);
@@ -1661,9 +1675,7 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c) 


	mutex_unlock(&dm_bufio_clients_lock);



	for (i = 0; i < 1 << DM_BUFIO_HASH_BITS; i++)

		BUG_ON(!hlist_empty(&c->cache_hash[i]));



	BUG_ON(!RB_EMPTY_ROOT(&c->buffer_tree));

	BUG_ON(c->need_reserved_buffers);



	while (!list_empty(&c->reserved_buffers)) {
@@ -1681,7 +1693,6 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c) 
		BUG_ON(c->n_buffers[i]);



	dm_io_client_destroy(c->dm_io);

	vfree(c->cache_hash);

	kfree(c);

}

EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);