Btrfs: Do snapshot deletion in smaller chunks.
Before, snapshot deletion was a single atomic unit. This caused considerable
lock contention and required an unbounded amount of space. Now,
the drop_progress field in the root item is used to indicate how far along
snapshot deletion is, and to resume where it left off.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 19a30b7..aa824e2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -659,9 +659,16 @@
struct buffer_head *b;
struct buffer_head *cow_buf;
struct btrfs_node *c;
+ struct btrfs_root_item *root_item = &root->root_item;
int slot;
int ret;
int level;
+ u8 lowest_level = 0;
+
+ if (btrfs_root_refs(root_item) == 0 && root->ref_cows) {
+ lowest_level = root_item->drop_level;
+ WARN_ON(ins_len || cow);
+ }
WARN_ON(p->nodes[0] != NULL);
WARN_ON(!mutex_is_locked(&root->fs_info->fs_mutex));
@@ -718,6 +725,9 @@
slot = p->slots[level];
BUG_ON(btrfs_header_nritems(&c->header) == 1);
}
+ /* this is only true while dropping a snapshot */
+ if (level == lowest_level)
+ break;
b = read_tree_block(root, btrfs_node_blockptr(c, slot));
} else {
struct btrfs_leaf *l = (struct btrfs_leaf *)c;
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 0287bd5..73c2e75 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -333,10 +333,10 @@
u64 objectid;
u64 last_trans;
u32 blocksize;
- int ref_cows;
u32 type;
u64 highest_inode;
u64 last_inode_alloc;
+ int ref_cows;
};
/* the lower bits in the key flags defines the item type */
@@ -1073,7 +1073,7 @@
int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path);
int btrfs_leaf_free_space(struct btrfs_root *root, struct btrfs_leaf *leaf);
int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
- *root, struct buffer_head *snap);
+ *root);
/* root-item.c */
int btrfs_del_root(struct btrfs_trans_handle *trans, struct btrfs_root *root,
struct btrfs_key *key);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 5ace2c3..9455974 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1561,12 +1561,21 @@
int i;
int slot;
int ret;
+ struct btrfs_root_item *root_item = &root->root_item;
+
for(i = *level; i < BTRFS_MAX_LEVEL - 1 && path->nodes[i]; i++) {
slot = path->slots[i];
if (slot < btrfs_header_nritems(
btrfs_buffer_header(path->nodes[i])) - 1) {
+ struct btrfs_node *node;
+ node = btrfs_buffer_node(path->nodes[i]);
path->slots[i]++;
*level = i;
+ WARN_ON(*level == 0);
+ memcpy(&root_item->drop_progress,
+ &node->ptrs[path->slots[i]].key,
+ sizeof(root_item->drop_progress));
+ root_item->drop_level = i;
return 0;
} else {
ret = btrfs_free_extent(trans, root,
@@ -1587,7 +1596,7 @@
* decremented.
*/
int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
- *root, struct buffer_head *snap)
+ *root)
{
int ret = 0;
int wret;
@@ -1595,14 +1604,33 @@
struct btrfs_path *path;
int i;
int orig_level;
+ int num_walks = 0;
+ struct btrfs_root_item *root_item = &root->root_item;
path = btrfs_alloc_path();
BUG_ON(!path);
- level = btrfs_header_level(btrfs_buffer_header(snap));
+ level = btrfs_header_level(btrfs_buffer_header(root->node));
orig_level = level;
- path->nodes[level] = snap;
- path->slots[level] = 0;
+ if (btrfs_disk_key_objectid(&root_item->drop_progress) == 0) {
+ path->nodes[level] = root->node;
+ path->slots[level] = 0;
+ } else {
+ struct btrfs_key key;
+ struct btrfs_disk_key *found_key;
+ struct btrfs_node *node;
+ btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
+ wret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+ if (ret < 0) {
+ ret = wret;
+ goto out;
+ }
+ level = root_item->drop_level;
+ node = btrfs_buffer_node(path->nodes[level]);
+ found_key = &node->ptrs[path->slots[level]].key;
+ WARN_ON(memcmp(found_key, &root_item->drop_progress,
+ sizeof(*found_key)));
+ }
while(1) {
wret = walk_down_tree(trans, root, path, &level);
if (wret > 0)
@@ -1615,12 +1643,21 @@
break;
if (wret < 0)
ret = wret;
+ num_walks++;
+ if (num_walks > 10) {
+ struct btrfs_key key;
+ btrfs_disk_key_to_cpu(&key, &root_item->drop_progress);
+ ret = -EAGAIN;
+ get_bh(root->node);
+ break;
+ }
}
for (i = 0; i <= orig_level; i++) {
if (path->nodes[i]) {
btrfs_block_release(root, path->nodes[i]);
}
}
+out:
btrfs_free_path(path);
return ret;
}
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 0f494fe..4986264 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -213,10 +213,7 @@
struct dirty_root {
struct list_head list;
- struct btrfs_key snap_key;
- struct buffer_head *commit_root;
struct btrfs_root *root;
- int free_on_drop;
};
int btrfs_add_dead_root(struct btrfs_root *root, struct list_head *dead_list)
@@ -226,10 +223,7 @@
dirty = kmalloc(sizeof(*dirty), GFP_NOFS);
if (!dirty)
return -ENOMEM;
- memcpy(&dirty->snap_key, &root->root_key, sizeof(root->root_key));
- dirty->commit_root = root->node;
dirty->root = root;
- dirty->free_on_drop = 1;
list_add(&dirty->list, dead_list);
return 0;
}
@@ -241,7 +235,6 @@
struct dirty_root *dirty;
struct btrfs_root *gang[8];
struct btrfs_root *root;
- struct btrfs_root_item tmp_item;
int i;
int ret;
int err = 0;
@@ -267,13 +260,16 @@
}
dirty = kmalloc(sizeof(*dirty), GFP_NOFS);
BUG_ON(!dirty);
- memcpy(&dirty->snap_key, &root->root_key,
- sizeof(root->root_key));
- dirty->commit_root = root->commit_root;
+ dirty->root = kmalloc(sizeof(*dirty->root), GFP_NOFS);
+ BUG_ON(!dirty->root);
+
+ memset(&root->root_item.drop_progress, 0,
+ sizeof(struct btrfs_disk_key));
+ root->root_item.drop_level = 0;
+
+ memcpy(dirty->root, root, sizeof(*root));
+ dirty->root->node = root->commit_root;
root->commit_root = NULL;
- dirty->root = root;
- dirty->free_on_drop = 0;
- memcpy(&tmp_item, &root->root_item, sizeof(tmp_item));
root->root_key.offset = root->fs_info->generation;
btrfs_set_root_blocknr(&root->root_item,
@@ -283,17 +279,21 @@
&root->root_item);
if (err)
break;
- refs = btrfs_root_refs(&tmp_item);
- btrfs_set_root_refs(&tmp_item, refs - 1);
+
+ refs = btrfs_root_refs(&dirty->root->root_item);
+ btrfs_set_root_refs(&dirty->root->root_item, refs - 1);
err = btrfs_update_root(trans, root->fs_info->tree_root,
- &dirty->snap_key,
- &tmp_item);
+ &dirty->root->root_key,
+ &dirty->root->root_item);
BUG_ON(err);
- if (refs == 1)
+ if (refs == 1) {
list_add(&dirty->list, list);
- else
+ } else {
+ WARN_ON(1);
+ kfree(dirty->root);
kfree(dirty);
+ }
}
}
return err;
@@ -305,23 +305,36 @@
struct dirty_root *dirty;
struct btrfs_trans_handle *trans;
int ret = 0;
+ int err;
+
while(!list_empty(list)) {
mutex_lock(&tree_root->fs_info->fs_mutex);
dirty = list_entry(list->next, struct dirty_root, list);
list_del_init(&dirty->list);
- trans = btrfs_start_transaction(tree_root, 1);
- ret = btrfs_drop_snapshot(trans, dirty->root,
- dirty->commit_root);
+ while(1) {
+ trans = btrfs_start_transaction(tree_root, 1);
+ ret = btrfs_drop_snapshot(trans, dirty->root);
+ if (ret != -EAGAIN) {
+ break;
+ }
+ err = btrfs_update_root(trans,
+ tree_root,
+ &dirty->root->root_key,
+ &dirty->root->root_item);
+ if (err)
+ ret = err;
+ ret = btrfs_end_transaction(trans, tree_root);
+ BUG_ON(ret);
+ }
BUG_ON(ret);
- ret = btrfs_del_root(trans, tree_root, &dirty->snap_key);
+ ret = btrfs_del_root(trans, tree_root, &dirty->root->root_key);
if (ret)
break;
ret = btrfs_end_transaction(trans, tree_root);
BUG_ON(ret);
- if (dirty->free_on_drop)
- kfree(dirty->root);
+ kfree(dirty->root);
kfree(dirty);
mutex_unlock(&tree_root->fs_info->fs_mutex);
btrfs_btree_balance_dirty(tree_root);