LXR linux/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 */
  36struct 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 */
  59void 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
  76static 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
 101static 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
 120int 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 */
 158struct 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;
 164again:
 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 */
 187int 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 */
 215int 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}
 233