Btrfs: Add a leaf reference cache

Much of the IO done while dropping snapshots is done looking up
leaves in the filesystem trees to see if they point to any extents and
to drop the references on any extents found.

This creates a cache so that IO isn't required.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 226 insertions, 0 deletions

diff --git a/fs/btrfs/ref-cache.c b/fs/btrfs/ref-cache.c
new file mode 100644
index 0000000..95a9fae
--- /dev/null
+++ b/fs/btrfs/ref-cache.c
@@ -0,0 +1,226 @@
+/*
+ * Copyright (C) 2008 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/sched.h>
+#include "ctree.h"
+#include "ref-cache.h"
+#include "transaction.h"
+
+struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(int nr_extents)
+{
+	struct btrfs_leaf_ref *ref;
+
+	ref = kmalloc(btrfs_leaf_ref_size(nr_extents), GFP_NOFS);
+	if (ref) {
+		memset(ref, 0, sizeof(*ref));
+		atomic_set(&ref->usage, 1);
+	}
+	return ref;
+}
+
+void btrfs_free_leaf_ref(struct btrfs_leaf_ref *ref)
+{
+	if (!ref)
+		return;
+	WARN_ON(atomic_read(&ref->usage) == 0);
+	if (atomic_dec_and_test(&ref->usage)) {
+		BUG_ON(ref->in_tree);
+		kfree(ref);
+	}
+}
+
+static int comp_keys(struct btrfs_key *k1, struct btrfs_key *k2)
+{
+	if (k1->objectid > k2->objectid)
+		return 1;
+	if (k1->objectid < k2->objectid)
+		return -1;
+	if (k1->type > k2->type)
+		return 1;
+	if (k1->type < k2->type)
+		return -1;
+	if (k1->offset > k2->offset)
+		return 1;
+	if (k1->offset < k2->offset)
+		return -1;
+	return 0;
+}
+
+static struct rb_node *tree_insert(struct rb_root *root, struct btrfs_key *key,
+				   struct rb_node *node)
+{
+	struct rb_node ** p = &root->rb_node;
+	struct rb_node * parent = NULL;
+	struct btrfs_leaf_ref *entry;
+	int ret;
+
+	while(*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct btrfs_leaf_ref, rb_node);
+		WARN_ON(!entry->in_tree);
+
+		ret = comp_keys(key, &entry->key);
+		if (ret < 0)
+			p = &(*p)->rb_left;
+		else if (ret > 0)
+			p = &(*p)->rb_right;
+		else
+			return parent;
+	}
+	
+	entry = rb_entry(node, struct btrfs_leaf_ref, rb_node);
+	entry->in_tree = 1;
+	rb_link_node(node, parent, p);
+	rb_insert_color(node, root);
+	return NULL;
+}
+
+static struct rb_node *tree_search(struct rb_root *root, struct btrfs_key *key)
+{
+	struct rb_node * n = root->rb_node;
+	struct btrfs_leaf_ref *entry;
+	int ret;
+
+	while(n) {
+		entry = rb_entry(n, struct btrfs_leaf_ref, rb_node);
+		WARN_ON(!entry->in_tree);
+
+		ret = comp_keys(key, &entry->key);
+		if (ret < 0)
+			n = n->rb_left;
+		else if (ret > 0)
+			n = n->rb_right;
+		else
+			return n;
+	}
+	return NULL;
+}
+
+int btrfs_remove_leaf_refs(struct btrfs_root *root)
+{
+	struct rb_node *rb;
+	struct btrfs_leaf_ref *ref = NULL;
+	struct btrfs_leaf_ref_tree *tree = root->ref_tree;
+
+	if (!tree)
+		return 0;
+
+	spin_lock(&tree->lock);
+	while(!btrfs_leaf_ref_tree_empty(tree)) {
+		tree->last = NULL;
+		rb = rb_first(&tree->root);
+		ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
+		rb_erase(&ref->rb_node, &tree->root);
+		ref->in_tree = 0;
+
+		spin_unlock(&tree->lock);
+
+		btrfs_free_leaf_ref(ref);
+
+		cond_resched();
+		spin_lock(&tree->lock);
+	}
+	spin_unlock(&tree->lock);
+	return 0;
+}
+
+struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
+					     struct btrfs_key *key)
+{
+	struct rb_node *rb;
+	struct btrfs_leaf_ref *ref = NULL;
+	struct btrfs_leaf_ref_tree *tree = root->ref_tree;
+
+	if (!tree)
+		return NULL;
+
+	spin_lock(&tree->lock);
+	if (tree->last && comp_keys(key, &tree->last->key) == 0) {
+		ref = tree->last;
+	} else {
+		rb = tree_search(&tree->root, key);
+		if (rb) {
+			ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
+			tree->last = ref;
+		}
+	}
+	if (ref)
+		atomic_inc(&ref->usage);
+	spin_unlock(&tree->lock);
+	return ref;
+}
+
+int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
+{
+	int ret = 0;
+	struct rb_node *rb;
+	size_t size = btrfs_leaf_ref_size(ref->nritems);
+	struct btrfs_leaf_ref_tree *tree = root->ref_tree;
+	struct btrfs_transaction *trans = root->fs_info->running_transaction;
+
+	spin_lock(&tree->lock);
+	rb = tree_insert(&tree->root, &ref->key, &ref->rb_node);
+	if (rb) {
+		ret = -EEXIST;
+	} else {
+		spin_lock(&root->fs_info->ref_cache_lock);
+		root->fs_info->total_ref_cache_size += size;
+		if (trans && tree->generation == trans->transid)
+			root->fs_info->running_ref_cache_size += size;
+		spin_unlock(&root->fs_info->ref_cache_lock);
+
+		tree->last = ref;
+		atomic_inc(&ref->usage);
+	}
+	spin_unlock(&tree->lock);
+	return ret;
+}
+
+int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
+{
+	size_t size = btrfs_leaf_ref_size(ref->nritems);
+	struct btrfs_leaf_ref_tree *tree = root->ref_tree;
+	struct btrfs_transaction *trans = root->fs_info->running_transaction;
+
+	BUG_ON(!ref->in_tree);
+	spin_lock(&tree->lock);
+	
+	spin_lock(&root->fs_info->ref_cache_lock);
+	root->fs_info->total_ref_cache_size -= size;
+	if (trans && tree->generation == trans->transid)
+		root->fs_info->running_ref_cache_size -= size;
+	spin_unlock(&root->fs_info->ref_cache_lock);
+
+	if (tree->last == ref) {
+		struct rb_node *next = rb_next(&ref->rb_node);
+		if (next) {
+			tree->last = rb_entry(next, struct btrfs_leaf_ref,
+					      rb_node);
+		} else
+			tree->last = NULL;
+	}
+
+	rb_erase(&ref->rb_node, &tree->root);
+	ref->in_tree = 0;
+
+	spin_unlock(&tree->lock);
+
+	btrfs_free_leaf_ref(ref);
+	return 0;
+}
+