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/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);