Root/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

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