fs/btrfs/ref-cache.c

   1 /*
   2  * Copyright (C) 2008 Oracle.  All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public
   6  * License v2 as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public
  14  * License along with this program; if not, write to the
  15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16  * Boston, MA 021110-1307, USA.
  17  */
  18
  19 #include <linux/sched.h>
  20 #include <linux/sort.h>
  21 #include "ctree.h"
  22 #include "ref-cache.h"
  23 #include "transaction.h"
  24
  25 /*
  26  * leaf refs are used to cache the information about which extents
  27  * a given leaf has references on.  This allows us to process that leaf
  28  * in btrfs_drop_snapshot without needing to read it back from disk.
  29  */
  30
  31 /*
  32  * kmalloc a leaf reference struct and update the counters for the
  33  * total ref cache size
  34  */
  35 struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
  36                                             int nr_extents)
  37 {
  38         struct btrfs_leaf_ref *ref;
  39         size_t size = btrfs_leaf_ref_size(nr_extents);
  40
  41         ref = kmalloc(size, GFP_NOFS);
  42         if (ref) {
  43                 spin_lock(&root->fs_info->ref_cache_lock);
  44                 root->fs_info->total_ref_cache_size += size;
  45                 spin_unlock(&root->fs_info->ref_cache_lock);
  46
  47                 memset(ref, 0, sizeof(*ref));
  48                 atomic_set(&ref->usage, 1);
  49                 INIT_LIST_HEAD(&ref->list);
  50         }
  51         return ref;
  52 }
  53
  54 /*
  55  * free a leaf reference struct and update the counters for the
  56  * total ref cache size
  57  */
  58 void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
  59 {
  60         if (!ref)
  61                 return;
  62         WARN_ON(atomic_read(&ref->usage) == 0);
  63         if (atomic_dec_and_test(&ref->usage)) {
  64                 size_t size = btrfs_leaf_ref_size(ref->nritems);
  65
  66                 BUG_ON(ref->in_tree);
  67                 kfree(ref);
  68
  69                 spin_lock(&root->fs_info->ref_cache_lock);
  70                 root->fs_info->total_ref_cache_size -= size;
  71                 spin_unlock(&root->fs_info->ref_cache_lock);
  72         }
  73 }
  74
  75 static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
  76                                    struct rb_node *node)
  77 {
  78         struct rb_node **p = &root->rb_node;
  79         struct rb_node *parent = NULL;
  80         struct btrfs_leaf_ref *entry;
  81
  82         while (*p) {
  83                 parent = *p;
  84                 entry = rb_entry(parent, struct btrfs_leaf_ref, rb_node);
  85
  86                 if (bytenr < entry->bytenr)
  87                         p = &(*p)->rb_left;
  88                 else if (bytenr > entry->bytenr)
  89                         p = &(*p)->rb_right;
  90                 else
  91                         return parent;
  92         }
  93
  94         entry = rb_entry(node, struct btrfs_leaf_ref, rb_node);
  95         rb_link_node(node, parent, p);
  96         rb_insert_color(node, root);
  97         return NULL;
  98 }
  99
 100 static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
 101 {
 102         struct rb_node *n = root->rb_node;
 103         struct btrfs_leaf_ref *entry;
 104
 105         while (n) {
 106                 entry = rb_entry(n, struct btrfs_leaf_ref, rb_node);
 107                 WARN_ON(!entry->in_tree);
 108
 109                 if (bytenr < entry->bytenr)
 110                         n = n->rb_left;
 111                 else if (bytenr > entry->bytenr)
 112                         n = n->rb_right;
 113                 else
 114                         return n;
 115         }
 116         return NULL;
 117 }
 118
 119 int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen,
 120                            int shared)
 121 {
 122         struct btrfs_leaf_ref *ref = NULL;
 123         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 124
 125         if (shared)
 126                 tree = &root->fs_info->shared_ref_tree;
 127         if (!tree)
 128                 return 0;
 129
 130         spin_lock(&tree->lock);
 131         while (!list_empty(&tree->list)) {
 132                 ref = list_entry(tree->list.next, struct btrfs_leaf_ref, list);
 133                 BUG_ON(ref->tree != tree);
 134                 if (ref->root_gen > max_root_gen)
 135                         break;
 136                 if (!xchg(&ref->in_tree, 0)) {
 137                         cond_resched_lock(&tree->lock);
 138                         continue;
 139                 }
 140
 141                 rb_erase(&ref->rb_node, &tree->root);
 142                 list_del_init(&ref->list);
 143
 144                 spin_unlock(&tree->lock);
 145                 btrfs_free_leaf_ref(root, ref);
 146                 cond_resched();
 147                 spin_lock(&tree->lock);
 148         }
 149         spin_unlock(&tree->lock);
 150         return 0;
 151 }
 152
 153 /*
 154  * find the leaf ref for a given extent.  This returns the ref struct with
 155  * a usage reference incremented
 156  */
 157 struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
 158                                              u64 bytenr)
 159 {
 160         struct rb_node *rb;
 161         struct btrfs_leaf_ref *ref = NULL;
 162         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 163 again:
 164         if (tree) {
 165                 spin_lock(&tree->lock);
 166                 rb = tree_search(&tree->root, bytenr);
 167                 if (rb)
 168                         ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
 169                 if (ref)
 170                         atomic_inc(&ref->usage);
 171                 spin_unlock(&tree->lock);
 172                 if (ref)
 173                         return ref;
 174         }
 175         if (tree != &root->fs_info->shared_ref_tree) {
 176                 tree = &root->fs_info->shared_ref_tree;
 177                 goto again;
 178         }
 179         return NULL;
 180 }
 181
 182 /*
 183  * add a fully filled in leaf ref struct
 184  * remove all the refs older than a given root generation
 185  */
 186 int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref,
 187                        int shared)
 188 {
 189         int ret = 0;
 190         struct rb_node *rb;
 191         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 192
 193         if (shared)
 194                 tree = &root->fs_info->shared_ref_tree;
 195
 196         spin_lock(&tree->lock);
 197         rb = tree_insert(&tree->root, ref->bytenr, &ref->rb_node);
 198         if (rb) {
 199                 ret = -EEXIST;
 200         } else {
 201                 atomic_inc(&ref->usage);
 202                 ref->tree = tree;
 203                 ref->in_tree = 1;
 204                 list_add_tail(&ref->list, &tree->list);
 205         }
 206         spin_unlock(&tree->lock);
 207         return ret;
 208 }
 209
 210 /*
 211  * remove a single leaf ref from the tree.  This drops the ref held by the tree
 212  * only
 213  */
 214 int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 215 {
 216         struct btrfs_leaf_ref_tree *tree;
 217
 218         if (!xchg(&ref->in_tree, 0))
 219                 return 0;
 220
 221         tree = ref->tree;
 222         spin_lock(&tree->lock);
 223
 224         rb_erase(&ref->rb_node, &tree->root);
 225         list_del_init(&ref->list);
 226
 227         spin_unlock(&tree->lock);
 228
 229         btrfs_free_leaf_ref(root, ref);
 230         return 0;
 231 }