The Probabilistic Skiplist is a O(lgn) data structure, and we want to apply this for later use, mainly for RCU-skiplist.
Note: a) The skiplist is probabilistic, and it is the distribution of node sizes that is maintained, but the strict order is not required[1]. b) This skiplist cannot be resized once it is created, so here is a level limit 16 and an associated (and fixed) probability 0.25 that determines the distribution of nodes[1]. c) The level limit may need to be adjusted. I know it is a magic number, but now for simplicity we just keep it at 16, and then each skiplist is able to contain (2^32-1)/3 nodes at most. [1] http://www.csee.umbc.edu/courses/undergraduate/341/fall01/Lectures/SkipLists/skip_lists/skip_lists.html Signed-off-by: Liu Bo <liubo2...@cn.fujitsu.com> --- fs/btrfs/Makefile | 2 +- fs/btrfs/skiplist.c | 98 ++++++++++++++++++++++++ fs/btrfs/skiplist.h | 210 +++++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 309 insertions(+), 1 deletions(-) create mode 100644 fs/btrfs/skiplist.c create mode 100644 fs/btrfs/skiplist.h diff --git a/fs/btrfs/Makefile b/fs/btrfs/Makefile index c0ddfd2..3284462 100644 --- a/fs/btrfs/Makefile +++ b/fs/btrfs/Makefile @@ -8,6 +8,6 @@ btrfs-y += super.o ctree.o extent-tree.o print-tree.o root-tree.o dir-item.o \ extent_io.o volumes.o async-thread.o ioctl.o locking.o orphan.o \ export.o tree-log.o free-space-cache.o zlib.o lzo.o \ compression.o delayed-ref.o relocation.o delayed-inode.o scrub.o \ - reada.o backref.o + reada.o backref.o skiplist.o btrfs-$(CONFIG_BTRFS_FS_POSIX_ACL) += acl.o diff --git a/fs/btrfs/skiplist.c b/fs/btrfs/skiplist.c new file mode 100644 index 0000000..c803478 --- /dev/null +++ b/fs/btrfs/skiplist.c @@ -0,0 +1,98 @@ +/* + The Probabilistic Skiplist + (C) 2011 Liu Bo <liubo2...@cn.fujitsu.com> + + Based on the skiplist experiments of Con Kolivas <ker...@kolivas.org> + for BFS cpu scheduler. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + 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 License + along with this program; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA +*/ + +#include <linux/random.h> +#include <linux/slab.h> +#include "skiplist.h" + +inline int sl_fill_node(struct sl_node *node, int level, gfp_t mask) +{ + struct sl_node **p; + struct sl_node **q; + int num; + + BUG_ON(level > MAXLEVEL); + + num = level + 1; + p = kmalloc(sizeof(*p) * num, mask); + BUG_ON(!p); + if (!p) + return -ENOMEM; + q = kmalloc(sizeof(*q) * num, mask); + BUG_ON(!q); + if (!q) { + kfree(p); + return -ENOMEM; + } + + node->next = p; + node->prev = q; + node->level = level; + return 0; +} + +inline void sl_link_node(struct sl_node *node, struct sl_node **backlook, + int level) +{ + struct sl_node *p, *q; + int i = 0; + + do { + p = backlook[i]; + q = p->next[i]; + + node->next[i] = q; + node->prev[i] = p; + p->next[i] = node; + q->prev[i] = node; + + i++; + } while (i <= level); +} + +void sl_erase(struct sl_node *node, struct sl_list *list) +{ + struct sl_node *prev, *next; + struct sl_node *head; + int level; + int i; + + level = node->level; + + for (i = 0; i <= level; i++) { + prev = node->prev[i]; + next = node->next[i]; + + prev->next[i] = next; + next->prev[i] = prev; + node->next[i] = node; + node->prev[i] = node; + } + + head = list->head; + if (level == list->level) { + while (head->next[level] == head && + head->prev[level] == head && level > 0) + level--; + list->level = level; + } +} diff --git a/fs/btrfs/skiplist.h b/fs/btrfs/skiplist.h new file mode 100644 index 0000000..3e414b5 --- /dev/null +++ b/fs/btrfs/skiplist.h @@ -0,0 +1,210 @@ +/* + The Probabilistic Skiplist + (C) 2011 Liu Bo <liubo2...@cn.fujitsu.com> + + Based on the skiplist experiments of Con Kolivas <ker...@kolivas.org> + for BFS cpu scheduler. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + 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 License + along with this program; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + + To use skiplist you'll have to implement your own insert and search cores to + aviod us to use callbacks and to drop drammatically perfromances. + + Here is some examples of insert and search: + +------------------------------------------------------------------------------- +static inline +struct extent_map *next_entry(struct sl_node *p, int l, struct sl_node **q) +{ + struct extent_map *ret; + struct sl_node *next; + + next = p->next[l]; + ret = sl_entry(next, struct extent_map, sl_node); + *q = next; + return ret; +} + +static inline +struct sl_node *sl_search(struct sl_list *list, u64 offset) +{ + struct sl_node *p, *q; + struct extent_map *entry; + int level; + + level = list->level; + p = list->head; + do { + while (entry = next_entry(p, level, &q), entry->off <= offset) + p = q; + + entry = sl_entry(p, struct sl_node, sl_node); + if (entry->off == offset) + return p; + + level--; + } while (level >= 0); + return NULL; +} + +static +struct sl_node *sl_insert_node(struct sl_list *list, u64 offset, + struct sl_node *node) +{ + struct extent_map *entry; + struct sl_node *backlook[MAXLEVEL], *p, *q; + u64 randseed; + int level; + int ret; + + level = list->level; + p = list->head; + do { + while (entry = next_entry(p, level, &q), entry->off <= offset) + p = q; + + entry = sl_entry(p, struct sl_node, sl_node); + if (entry->off == offset) + return p; + + level--; + } while (level >= 0); + + get_random_bytes(&randseed, sizeof(u64)); + level = generate_node_level(randseed); + if (level > list->level) { + list->level++; + level = list->level; + backlook[level] = list->head; + } + + if (ret = sl_fill_node(node, level, GFP_ATOMIC)) + return ERR_PTR(ret); + sl_link_node(node, backlook, level); + return NULL; +} +------------------------------------------------------------------------------- +*/ + +#ifndef _SKIPLIST_H +#define _SKIPLIST_H + +#include <linux/random.h> + +#define MAXLEVEL 16 +/* double p = 0.25; */ + +struct sl_node { + struct sl_node **next; + struct sl_node **prev; + unsigned int level; + unsigned int head:1; +}; + +struct sl_list { + struct sl_node *head; + struct sl_node *h_next[MAXLEVEL]; + struct sl_node *h_prev[MAXLEVEL]; + unsigned int level; +}; + +#define sl_entry(ptr, type, member) container_of(ptr, type, member) + +static inline int sl_empty(const struct sl_node *head) +{ + return head->next[0] == head; +} + +static inline struct sl_node *__sl_next_with_level(struct sl_node *node, + int level) +{ + return node->next[level]; +} + +static inline struct sl_node *__sl_prev_with_level(struct sl_node *node, + int level) +{ + return node->prev[level]; +} + +static inline struct sl_node *sl_next(struct sl_node *node) +{ + struct sl_node *ret; + + ret = __sl_next_with_level(node, 0); + if (ret->head) + return NULL; + + return ret; +} + +static inline struct sl_node *sl_prev(struct sl_node *node) +{ + struct sl_node *ret; + + ret = __sl_prev_with_level(node, 0); + if (ret->head) + return NULL; + + return ret; +} + +static inline void sl_init_list(struct sl_list *list, struct sl_node *head) +{ + int i; + + list->head = head; + list->level = 0; + for (i = 0; i < MAXLEVEL; i++) + list->h_next[i] = list->h_prev[i] = list->head; + + head->next = list->h_next; + head->prev = list->h_prev; + head->head = 1; +} + +static inline void sl_init_node(struct sl_node *node) +{ + node->head = 0; + node->level = 0; + node->next = NULL; + node->prev = NULL; +} + +static inline void sl_free_node(struct sl_node *node) +{ + kfree(node->next); + kfree(node->prev); +} + +static inline int generate_node_level(u64 randseed) +{ + int level = 0; + + while (randseed && !(randseed & 3)) { + randseed >>= 2; + level++; + } + + return (level > MAXLEVEL ? MAXLEVEL : level); +} + + +inline int sl_fill_node(struct sl_node *node, int level, gfp_t mask); +inline void sl_link_node(struct sl_node *node, struct sl_node **backlook, + int level); +void sl_erase(struct sl_node *node, struct sl_list *list); + +#endif /* _SKIPLIST_H */ -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
