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 "ctree.h"
  21 #include "ref-cache.h"
  22 #include "transaction.h"
  23
  24 /*
  25  * leaf refs are used to cache the information about which extents
  26  * a given leaf has references on.  This allows us to process that leaf
  27  * in btrfs_drop_snapshot without needing to read it back from disk.
  28  */
  29
  30 /*
  31  * kmalloc a leaf reference struct and update the counters for the
  32  * total ref cache size
  33  */
  34 struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
  35                                             int nr_extents)
  36 {
  37         struct btrfs_leaf_ref *ref;
  38         size_t size = btrfs_leaf_ref_size(nr_extents);
  39
  40         ref = kmalloc(size, GFP_NOFS);
  41         if (ref) {
  42                 spin_lock(&root->fs_info->ref_cache_lock);
  43                 root->fs_info->total_ref_cache_size += size;
  44                 spin_unlock(&root->fs_info->ref_cache_lock);
  45
  46                 memset(ref, 0, sizeof(*ref));
  47                 atomic_set(&ref->usage, 1);
  48                 INIT_LIST_HEAD(&ref->list);
  49         }
  50         return ref;
  51 }
  52
  53 /*
  54  * free a leaf reference struct and update the counters for the
  55  * total ref cache size
  56  */
  57 void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
  58 {
  59         if (!ref)
  60                 return;
  61         WARN_ON(atomic_read(&ref->usage) == 0);
  62         if (atomic_dec_and_test(&ref->usage)) {
  63                 size_t size = btrfs_leaf_ref_size(ref->nritems);
  64
  65                 BUG_ON(ref->in_tree);
  66                 kfree(ref);
  67
  68                 spin_lock(&root->fs_info->ref_cache_lock);
  69                 root->fs_info->total_ref_cache_size -= size;
  70                 spin_unlock(&root->fs_info->ref_cache_lock);
  71         }
  72 }
  73
  74 static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
  75                                    struct rb_node *node)
  76 {
  77         struct rb_node **p = &root->rb_node;
  78         struct rb_node *parent = NULL;
  79         struct btrfs_leaf_ref *entry;
  80
  81         while (*p) {
  82                 parent = *p;
  83                 entry = rb_entry(parent, struct btrfs_leaf_ref, rb_node);
  84
  85                 if (bytenr < entry->bytenr)
  86                         p = &(*p)->rb_left;
  87                 else if (bytenr > entry->bytenr)
  88                         p = &(*p)->rb_right;
  89                 else
  90                         return parent;
  91         }
  92
  93         entry = rb_entry(node, struct btrfs_leaf_ref, rb_node);
  94         rb_link_node(node, parent, p);
  95         rb_insert_color(node, root);
  96         return NULL;
  97 }
  98
  99 static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
 100 {
 101         struct rb_node *n = root->rb_node;
 102         struct btrfs_leaf_ref *entry;
 103
 104         while (n) {
 105                 entry = rb_entry(n, struct btrfs_leaf_ref, rb_node);
 106                 WARN_ON(!entry->in_tree);
 107
 108                 if (bytenr < entry->bytenr)
 109                         n = n->rb_left;
 110                 else if (bytenr > entry->bytenr)
 111                         n = n->rb_right;
 112                 else
 113                         return n;
 114         }
 115         return NULL;
 116 }
 117
 118 int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen,
 119                            int shared)
 120 {
 121         struct btrfs_leaf_ref *ref = NULL;
 122         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 123
 124         if (shared)
 125                 tree = &root->fs_info->shared_ref_tree;
 126         if (!tree)
 127                 return 0;
 128
 129         spin_lock(&tree->lock);
 130         while (!list_empty(&tree->list)) {
 131                 ref = list_entry(tree->list.next, struct btrfs_leaf_ref, list);
 132                 BUG_ON(ref->tree != tree);
 133                 if (ref->root_gen > max_root_gen)
 134                         break;
 135                 if (!xchg(&ref->in_tree, 0)) {
 136                         cond_resched_lock(&tree->lock);
 137                         continue;
 138                 }
 139
 140                 rb_erase(&ref->rb_node, &tree->root);
 141                 list_del_init(&ref->list);
 142
 143                 spin_unlock(&tree->lock);
 144                 btrfs_free_leaf_ref(root, ref);
 145                 cond_resched();
 146                 spin_lock(&tree->lock);
 147         }
 148         spin_unlock(&tree->lock);
 149         return 0;
 150 }
 151
 152 /*
 153  * find the leaf ref for a given extent.  This returns the ref struct with
 154  * a usage reference incremented
 155  */
 156 struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
 157                                              u64 bytenr)
 158 {
 159         struct rb_node *rb;
 160         struct btrfs_leaf_ref *ref = NULL;
 161         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 162 again:
 163         if (tree) {
 164                 spin_lock(&tree->lock);
 165                 rb = tree_search(&tree->root, bytenr);
 166                 if (rb)
 167                         ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
 168                 if (ref)
 169                         atomic_inc(&ref->usage);
 170                 spin_unlock(&tree->lock);
 171                 if (ref)
 172                         return ref;
 173         }
 174         if (tree != &root->fs_info->shared_ref_tree) {
 175                 tree = &root->fs_info->shared_ref_tree;
 176                 goto again;
 177         }
 178         return NULL;
 179 }
 180
 181 /*
 182  * add a fully filled in leaf ref struct
 183  * remove all the refs older than a given root generation
 184  */
 185 int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref,
 186                        int shared)
 187 {
 188         int ret = 0;
 189         struct rb_node *rb;
 190         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 191
 192         if (shared)
 193                 tree = &root->fs_info->shared_ref_tree;
 194
 195         spin_lock(&tree->lock);
 196         rb = tree_insert(&tree->root, ref->bytenr, &ref->rb_node);
 197         if (rb) {
 198                 ret = -EEXIST;
 199         } else {
 200                 atomic_inc(&ref->usage);
 201                 ref->tree = tree;
 202                 ref->in_tree = 1;
 203                 list_add_tail(&ref->list, &tree->list);
 204         }
 205         spin_unlock(&tree->lock);
 206         return ret;
 207 }
 208
 209 /*
 210  * remove a single leaf ref from the tree.  This drops the ref held by the tree
 211  * only
 212  */
 213 int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 214 {
 215         struct btrfs_leaf_ref_tree *tree;
 216
 217         if (!xchg(&ref->in_tree, 0))
 218                 return 0;
 219
 220         tree = ref->tree;
 221         spin_lock(&tree->lock);
 222
 223         rb_erase(&ref->rb_node, &tree->root);
 224         list_del_init(&ref->list);
 225
 226         spin_unlock(&tree->lock);
 227
 228         btrfs_free_leaf_ref(root, ref);
 229         return 0;
 230 }