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/slab.h>
  21 #include <linux/sort.h>
  22 #include "ctree.h"
  23 #include "ref-cache.h"
  24 #include "transaction.h"
  25
  26 /*
  27  * leaf refs are used to cache the information about which extents
  28  * a given leaf has references on.  This allows us to process that leaf
  29  * in btrfs_drop_snapshot without needing to read it back from disk.
  30  */
  31
  32 /*
  33  * kmalloc a leaf reference struct and update the counters for the
  34  * total ref cache size
  35  */
  36 struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
  37                                             int nr_extents)
  38 {
  39         struct btrfs_leaf_ref *ref;
  40         size_t size = btrfs_leaf_ref_size(nr_extents);
  41
  42         ref = kmalloc(size, GFP_NOFS);
  43         if (ref) {
  44                 spin_lock(&root->fs_info->ref_cache_lock);
  45                 root->fs_info->total_ref_cache_size += size;
  46                 spin_unlock(&root->fs_info->ref_cache_lock);
  47
  48                 memset(ref, 0, sizeof(*ref));
  49                 atomic_set(&ref->usage, 1);
  50                 INIT_LIST_HEAD(&ref->list);
  51         }
  52         return ref;
  53 }
  54
  55 /*
  56  * free a leaf reference struct and update the counters for the
  57  * total ref cache size
  58  */
  59 void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
  60 {
  61         if (!ref)
  62                 return;
  63         WARN_ON(atomic_read(&ref->usage) == 0);
  64         if (atomic_dec_and_test(&ref->usage)) {
  65                 size_t size = btrfs_leaf_ref_size(ref->nritems);
  66
  67                 BUG_ON(ref->in_tree);
  68                 kfree(ref);
  69
  70                 spin_lock(&root->fs_info->ref_cache_lock);
  71                 root->fs_info->total_ref_cache_size -= size;
  72                 spin_unlock(&root->fs_info->ref_cache_lock);
  73         }
  74 }
  75
  76 static struct rb_node *tree_insert(struct rb_root *root, u64 bytenr,
  77                                    struct rb_node *node)
  78 {
  79         struct rb_node **p = &root->rb_node;
  80         struct rb_node *parent = NULL;
  81         struct btrfs_leaf_ref *entry;
  82
  83         while (*p) {
  84                 parent = *p;
  85                 entry = rb_entry(parent, struct btrfs_leaf_ref, rb_node);
  86
  87                 if (bytenr < entry->bytenr)
  88                         p = &(*p)->rb_left;
  89                 else if (bytenr > entry->bytenr)
  90                         p = &(*p)->rb_right;
  91                 else
  92                         return parent;
  93         }
  94
  95         entry = rb_entry(node, struct btrfs_leaf_ref, rb_node);
  96         rb_link_node(node, parent, p);
  97         rb_insert_color(node, root);
  98         return NULL;
  99 }
 100
 101 static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
 102 {
 103         struct rb_node *n = root->rb_node;
 104         struct btrfs_leaf_ref *entry;
 105
 106         while (n) {
 107                 entry = rb_entry(n, struct btrfs_leaf_ref, rb_node);
 108                 WARN_ON(!entry->in_tree);
 109
 110                 if (bytenr < entry->bytenr)
 111                         n = n->rb_left;
 112                 else if (bytenr > entry->bytenr)
 113                         n = n->rb_right;
 114                 else
 115                         return n;
 116         }
 117         return NULL;
 118 }
 119
 120 int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen,
 121                            int shared)
 122 {
 123         struct btrfs_leaf_ref *ref = NULL;
 124         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 125
 126         if (shared)
 127                 tree = &root->fs_info->shared_ref_tree;
 128         if (!tree)
 129                 return 0;
 130
 131         spin_lock(&tree->lock);
 132         while (!list_empty(&tree->list)) {
 133                 ref = list_entry(tree->list.next, struct btrfs_leaf_ref, list);
 134                 BUG_ON(ref->tree != tree);
 135                 if (ref->root_gen > max_root_gen)
 136                         break;
 137                 if (!xchg(&ref->in_tree, 0)) {
 138                         cond_resched_lock(&tree->lock);
 139                         continue;
 140                 }
 141
 142                 rb_erase(&ref->rb_node, &tree->root);
 143                 list_del_init(&ref->list);
 144
 145                 spin_unlock(&tree->lock);
 146                 btrfs_free_leaf_ref(root, ref);
 147                 cond_resched();
 148                 spin_lock(&tree->lock);
 149         }
 150         spin_unlock(&tree->lock);
 151         return 0;
 152 }
 153
 154 /*
 155  * find the leaf ref for a given extent.  This returns the ref struct with
 156  * a usage reference incremented
 157  */
 158 struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
 159                                              u64 bytenr)
 160 {
 161         struct rb_node *rb;
 162         struct btrfs_leaf_ref *ref = NULL;
 163         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 164 again:
 165         if (tree) {
 166                 spin_lock(&tree->lock);
 167                 rb = tree_search(&tree->root, bytenr);
 168                 if (rb)
 169                         ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
 170                 if (ref)
 171                         atomic_inc(&ref->usage);
 172                 spin_unlock(&tree->lock);
 173                 if (ref)
 174                         return ref;
 175         }
 176         if (tree != &root->fs_info->shared_ref_tree) {
 177                 tree = &root->fs_info->shared_ref_tree;
 178                 goto again;
 179         }
 180         return NULL;
 181 }
 182
 183 /*
 184  * add a fully filled in leaf ref struct
 185  * remove all the refs older than a given root generation
 186  */
 187 int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref,
 188                        int shared)
 189 {
 190         int ret = 0;
 191         struct rb_node *rb;
 192         struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 193
 194         if (shared)
 195                 tree = &root->fs_info->shared_ref_tree;
 196
 197         spin_lock(&tree->lock);
 198         rb = tree_insert(&tree->root, ref->bytenr, &ref->rb_node);
 199         if (rb) {
 200                 ret = -EEXIST;
 201         } else {
 202                 atomic_inc(&ref->usage);
 203                 ref->tree = tree;
 204                 ref->in_tree = 1;
 205                 list_add_tail(&ref->list, &tree->list);
 206         }
 207         spin_unlock(&tree->lock);
 208         return ret;
 209 }
 210
 211 /*
 212  * remove a single leaf ref from the tree.  This drops the ref held by the tree
 213  * only
 214  */
 215 int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 216 {
 217         struct btrfs_leaf_ref_tree *tree;
 218
 219         if (!xchg(&ref->in_tree, 0))
 220                 return 0;
 221
 222         tree = ref->tree;
 223         spin_lock(&tree->lock);
 224
 225         rb_erase(&ref->rb_node, &tree->root);
 226         list_del_init(&ref->list);
 227
 228         spin_unlock(&tree->lock);
 229
 230         btrfs_free_leaf_ref(root, ref);
 231         return 0;
 232 }