Btrfs: implement memory reclaim for leaf reference cache

The memory reclaiming issue happens when snapshot exists. In that
case, some cache entries may not be used during old snapshot dropping,
so they will remain in the cache until umount.

The patch adds a field to struct btrfs_leaf_ref to record create time. Besides,
the patch makes all dead roots of a given snapshot linked together in order of
create time. After a old snapshot was completely dropped, we check the dead
root list and remove all cache entries created before the oldest dead root in
the list.
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

@@ -3275,4 +3275,3 @@ int btrfs_previous_item(struct btrfs_root *root,
 	}
 	return 1;
 }
-

fs/btrfs/ctree.h

@@ -666,7 +666,8 @@ struct btrfs_root {
 	/* the dirty list is only used by non-reference counted roots */
 	struct list_head dirty_list;
 
-	spinlock_t orphan_lock;
+	spinlock_t list_lock;
+	struct list_head dead_list;
 	struct list_head orphan_list;
 };
 

fs/btrfs/dir-item.c

@@ -340,4 +340,3 @@ int btrfs_delete_one_dir_name(struct btrfs_trans_handle *trans,
 	}
 	return 0;
 }
-

fs/btrfs/disk-io.c

@@ -735,8 +735,9 @@ static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
 
 	INIT_LIST_HEAD(&root->dirty_list);
 	INIT_LIST_HEAD(&root->orphan_list);
+	INIT_LIST_HEAD(&root->dead_list);
 	spin_lock_init(&root->node_lock);
-	spin_lock_init(&root->orphan_lock);
+	spin_lock_init(&root->list_lock);
 	mutex_init(&root->objectid_mutex);
 
 	btrfs_leaf_ref_tree_init(&root->ref_tree_struct);

fs/btrfs/extent-tree.c

@@ -1048,7 +1048,7 @@ int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		struct btrfs_leaf_ref *ref;
 		struct btrfs_extent_info *info;
 
-		ref = btrfs_alloc_leaf_ref(nr_file_extents);
+		ref = btrfs_alloc_leaf_ref(root, nr_file_extents);
 		if (!ref) {
 			WARN_ON(1);
 			goto out;
@@ -1085,7 +1085,7 @@ int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 		BUG_ON(!root->ref_tree);
 		ret = btrfs_add_leaf_ref(root, ref);
 		WARN_ON(ret);
-		btrfs_free_leaf_ref(ref);
+		btrfs_free_leaf_ref(root, ref);
 	}
 out:
 	return 0;
@@ -2521,7 +2521,7 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
 				ret = drop_leaf_ref(trans, root, ref);
 				BUG_ON(ret);
 				btrfs_remove_leaf_ref(root, ref);
-				btrfs_free_leaf_ref(ref);
+				btrfs_free_leaf_ref(root, ref);
 				*level = 0;
 				break;
 			}

fs/btrfs/extent_io.c

@@ -3497,4 +3497,3 @@ int try_release_extent_buffer(struct extent_io_tree *tree, struct page *page)
 	return ret;
 }
 EXPORT_SYMBOL(try_release_extent_buffer);
-

fs/btrfs/file-item.c

@@ -422,4 +422,3 @@ int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
 	BUG_ON(ret);
 	return ret;
 }
-

fs/btrfs/file.c

@@ -1095,4 +1095,3 @@ struct file_operations btrfs_file_operations = {
 	.compat_ioctl	= btrfs_ioctl,
 #endif
 };
-

fs/btrfs/inode.c

@@ -835,17 +835,17 @@ int btrfs_orphan_add(struct btrfs_trans_handle *trans, struct inode *inode)
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	int ret = 0;
 
-	spin_lock(&root->orphan_lock);
+	spin_lock(&root->list_lock);
 
 	/* already on the orphan list, we're good */
 	if (!list_empty(&BTRFS_I(inode)->i_orphan)) {
-		spin_unlock(&root->orphan_lock);
+		spin_unlock(&root->list_lock);
 		return 0;
 	}
 
 	list_add(&BTRFS_I(inode)->i_orphan, &root->orphan_list);
 
-	spin_unlock(&root->orphan_lock);
+	spin_unlock(&root->list_lock);
 
 	/*
 	 * insert an orphan item to track this unlinked/truncated file
@@ -864,20 +864,20 @@ int btrfs_orphan_del(struct btrfs_trans_handle *trans, struct inode *inode)
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	int ret = 0;
 
-	spin_lock(&root->orphan_lock);
+	spin_lock(&root->list_lock);
 
 	if (list_empty(&BTRFS_I(inode)->i_orphan)) {
-		spin_unlock(&root->orphan_lock);
+		spin_unlock(&root->list_lock);
 		return 0;
 	}
 
 	list_del_init(&BTRFS_I(inode)->i_orphan);
 	if (!trans) {
-		spin_unlock(&root->orphan_lock);
+		spin_unlock(&root->list_lock);
 		return 0;
 	}
 
-	spin_unlock(&root->orphan_lock);
+	spin_unlock(&root->list_lock);
 
 	ret = btrfs_del_orphan_item(trans, root, inode->i_ino);
 
@@ -973,9 +973,9 @@ void btrfs_orphan_cleanup(struct btrfs_root *root)
 		 * add this inode to the orphan list so btrfs_orphan_del does
 		 * the proper thing when we hit it
 		 */
-		spin_lock(&root->orphan_lock);
+		spin_lock(&root->list_lock);
 		list_add(&BTRFS_I(inode)->i_orphan, &root->orphan_list);
-		spin_unlock(&root->orphan_lock);
+		spin_unlock(&root->list_lock);
 
 		/*
 		 * if this is a bad inode, means we actually succeeded in
@@ -3269,13 +3269,13 @@ void btrfs_destroy_inode(struct inode *inode)
 	    BTRFS_I(inode)->i_default_acl != BTRFS_ACL_NOT_CACHED)
 		posix_acl_release(BTRFS_I(inode)->i_default_acl);
 
-	spin_lock(&BTRFS_I(inode)->root->orphan_lock);
+	spin_lock(&BTRFS_I(inode)->root->list_lock);
 	if (!list_empty(&BTRFS_I(inode)->i_orphan)) {
 		printk(KERN_ERR "BTRFS: inode %lu: inode still on the orphan"
 		       " list\n", inode->i_ino);
 		dump_stack();
 	}
-	spin_unlock(&BTRFS_I(inode)->root->orphan_lock);
+	spin_unlock(&BTRFS_I(inode)->root->list_lock);
 
 	while(1) {
 		ordered = btrfs_lookup_first_ordered_extent(inode, (u64)-1);

fs/btrfs/locking.c

@@ -56,4 +56,3 @@ int btrfs_tree_locked(struct extent_buffer *eb)
 {
 	return mutex_is_locked(&eb->mutex);
 }
-

fs/btrfs/print-tree.c

@@ -198,4 +198,3 @@ void btrfs_print_tree(struct btrfs_root *root, struct extent_buffer *c)
 		free_extent_buffer(next);
 	}
 }
-

fs/btrfs/ref-cache.c

@@ -21,12 +21,18 @@
 #include "ref-cache.h"
 #include "transaction.h"
 
-struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(int nr_extents)
+struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
+					    int nr_extents)
 {
 	struct btrfs_leaf_ref *ref;
+	size_t size = btrfs_leaf_ref_size(nr_extents);
 
-	ref = kmalloc(btrfs_leaf_ref_size(nr_extents), GFP_NOFS);
+	ref = kmalloc(size, GFP_NOFS);
 	if (ref) {
+		spin_lock(&root->fs_info->ref_cache_lock);
+		root->fs_info->total_ref_cache_size += size;
+		spin_unlock(&root->fs_info->ref_cache_lock);
+
 		memset(ref, 0, sizeof(*ref));
 		atomic_set(&ref->usage, 1);
 		INIT_LIST_HEAD(&ref->list);
@@ -34,14 +40,20 @@ struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(int nr_extents)
 	return ref;
 }
 
-void btrfs_free_leaf_ref(struct btrfs_leaf_ref *ref)
+void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 {
 	if (!ref)
 		return;
 	WARN_ON(atomic_read(&ref->usage) == 0);
 	if (atomic_dec_and_test(&ref->usage)) {
+		size_t size = btrfs_leaf_ref_size(ref->nritems);
+
 		BUG_ON(ref->in_tree);
 		kfree(ref);
+
+		spin_lock(&root->fs_info->ref_cache_lock);
+		root->fs_info->total_ref_cache_size -= size;
+		spin_unlock(&root->fs_info->ref_cache_lock);
 	}
 }
 
@@ -91,9 +103,8 @@ static struct rb_node *tree_search(struct rb_root *root, u64 bytenr)
 	return NULL;
 }
 
-int btrfs_remove_leaf_refs(struct btrfs_root *root)
+int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen)
 {
-	struct rb_node *rb;
 	struct btrfs_leaf_ref *ref = NULL;
 	struct btrfs_leaf_ref_tree *tree = root->ref_tree;
 
@@ -101,17 +112,18 @@ int btrfs_remove_leaf_refs(struct btrfs_root *root)
 		return 0;
 
 	spin_lock(&tree->lock);
-	while(!btrfs_leaf_ref_tree_empty(tree)) {
-		rb = rb_first(&tree->root);
-		ref = rb_entry(rb, struct btrfs_leaf_ref, rb_node);
+	while(!list_empty(&tree->list)) {
+		ref = list_entry(tree->list.next, struct btrfs_leaf_ref, list);
+		BUG_ON(!ref->in_tree);
+		if (ref->root_gen > max_root_gen)
+			break;
+
 		rb_erase(&ref->rb_node, &tree->root);
 		ref->in_tree = 0;
 		list_del_init(&ref->list);
 
 		spin_unlock(&tree->lock);
-
-		btrfs_free_leaf_ref(ref);
-
+		btrfs_free_leaf_ref(root, ref);
 		cond_resched();
 		spin_lock(&tree->lock);
 	}
@@ -143,7 +155,6 @@ 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;
 
 	spin_lock(&tree->lock);
@@ -151,9 +162,6 @@ int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 	if (rb) {
 		ret = -EEXIST;
 	} else {
-		spin_lock(&root->fs_info->ref_cache_lock);
-		root->fs_info->total_ref_cache_size += size;
-		spin_unlock(&root->fs_info->ref_cache_lock);
 		atomic_inc(&ref->usage);
 		list_add_tail(&ref->list, &tree->list);
 	}
@@ -163,23 +171,17 @@ int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref)
 
 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;
 
 	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;
-	spin_unlock(&root->fs_info->ref_cache_lock);
-
 	rb_erase(&ref->rb_node, &tree->root);
 	ref->in_tree = 0;
 	list_del_init(&ref->list);
 
 	spin_unlock(&tree->lock);
 
-	btrfs_free_leaf_ref(ref);
+	btrfs_free_leaf_ref(root, ref);
 	return 0;
 }
-

fs/btrfs/ref-cache.h

@@ -30,6 +30,7 @@ struct btrfs_leaf_ref {
 	int in_tree;
 	atomic_t usage;
 
+	u64 root_gen;
 	u64 bytenr;
 	u64 owner;
 	u64 generation;
@@ -48,7 +49,6 @@ static inline size_t btrfs_leaf_ref_size(int nr_extents)
 static inline void btrfs_leaf_ref_tree_init(struct btrfs_leaf_ref_tree *tree)
 {
 	tree->root.rb_node = NULL;
-	tree->last = NULL;
 	INIT_LIST_HEAD(&tree->list);
 	spin_lock_init(&tree->lock);
 }
@@ -59,12 +59,13 @@ static inline int btrfs_leaf_ref_tree_empty(struct btrfs_leaf_ref_tree *tree)
 }
 
 void btrfs_leaf_ref_tree_init(struct btrfs_leaf_ref_tree *tree);
-struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(int nr_extents);
-void btrfs_free_leaf_ref(struct btrfs_leaf_ref *ref);
+struct btrfs_leaf_ref *btrfs_alloc_leaf_ref(struct btrfs_root *root,
+					    int nr_extents);
+void btrfs_free_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref);
 struct btrfs_leaf_ref *btrfs_lookup_leaf_ref(struct btrfs_root *root,
 					     u64 bytenr);
 int btrfs_add_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref);
-int btrfs_remove_leaf_refs(struct btrfs_root *root);
+int btrfs_remove_leaf_refs(struct btrfs_root *root, u64 max_root_gen);
 int btrfs_remove_leaf_ref(struct btrfs_root *root, struct btrfs_leaf_ref *ref);
 
 #endif

fs/btrfs/transaction.c

@@ -98,20 +98,24 @@ static noinline int record_root_in_trans(struct btrfs_root *root)
 			BUG_ON(!dirty);
 			dirty->root = kmalloc(sizeof(*dirty->root), GFP_NOFS);
 			BUG_ON(!dirty->root);
-
 			dirty->latest_root = root;
 			INIT_LIST_HEAD(&dirty->list);
 
 			root->commit_root = btrfs_root_node(root);
-			root->dirty_root = dirty;
 
 			memcpy(dirty->root, root, sizeof(*root));
-			dirty->root->ref_tree = &root->ref_tree_struct;
-
 			spin_lock_init(&dirty->root->node_lock);
+			spin_lock_init(&dirty->root->list_lock);
 			mutex_init(&dirty->root->objectid_mutex);
+			INIT_LIST_HEAD(&dirty->root->dead_list);
 			dirty->root->node = root->commit_root;
 			dirty->root->commit_root = NULL;
+
+			spin_lock(&root->list_lock);
+			list_add(&dirty->root->dead_list, &root->dead_list);
+			spin_unlock(&root->list_lock);
+
+			root->dirty_root = dirty;
 		} else {
 			WARN_ON(1);
 		}
@@ -356,8 +360,6 @@ int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,
 		list_del_init(next);
 		root = list_entry(next, struct btrfs_root, dirty_list);
 		update_cowonly_root(trans, root);
-		if (root->fs_info->closing)
-			btrfs_remove_leaf_refs(root);
 	}
 	return 0;
 }
@@ -411,6 +413,10 @@ static noinline int add_dirty_roots(struct btrfs_trans_handle *trans,
 				free_extent_buffer(root->commit_root);
 				root->commit_root = NULL;
 
+				spin_lock(&root->list_lock);
+				list_del_init(&dirty->root->dead_list);
+				spin_unlock(&root->list_lock);
+
 				kfree(dirty->root);
 				kfree(dirty);
 
@@ -497,6 +503,7 @@ static noinline int drop_dirty_roots(struct btrfs_root *tree_root,
 	unsigned long nr;
 	u64 num_bytes;
 	u64 bytes_used;
+	u64 max_useless;
 	int ret = 0;
 	int err;
 
@@ -554,10 +561,25 @@ static noinline int drop_dirty_roots(struct btrfs_root *tree_root,
 		}
 		mutex_unlock(&root->fs_info->drop_mutex);
 
+		spin_lock(&root->list_lock);
+		list_del_init(&dirty->root->dead_list);
+		if (!list_empty(&root->dead_list)) {
+			struct btrfs_root *oldest;
+			oldest = list_entry(root->dead_list.prev,
+					    struct btrfs_root, dead_list);
+			max_useless = oldest->root_key.offset - 1;
+		} else {
+			max_useless = root->root_key.offset - 1;
+		}
+		spin_unlock(&root->list_lock);
+
 		nr = trans->blocks_used;
 		ret = btrfs_end_transaction(trans, tree_root);
 		BUG_ON(ret);
 
+		ret = btrfs_remove_leaf_refs(root, max_useless);
+		BUG_ON(ret);
+
 		free_extent_buffer(dirty->root->node);
 		kfree(dirty->root);
 		kfree(dirty);
@@ -785,10 +807,9 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 	put_transaction(cur_trans);
 	put_transaction(cur_trans);
 
+	list_splice_init(&dirty_fs_roots, &root->fs_info->dead_roots);
 	if (root->fs_info->closing)
 		list_splice_init(&root->fs_info->dead_roots, &dirty_fs_roots);
-	else
-		list_splice_init(&dirty_fs_roots, &root->fs_info->dead_roots);
 
 	mutex_unlock(&root->fs_info->trans_mutex);
 	kmem_cache_free(btrfs_trans_handle_cachep, trans);
@@ -814,4 +835,3 @@ int btrfs_clean_old_snapshots(struct btrfs_root *root)
 	}
 	return 0;
 }
-

fs/btrfs/volumes.c

@@ -2527,4 +2527,3 @@ int btrfs_read_chunk_tree(struct btrfs_root *root)
 error:
 	return ret;
 }
-