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Btrfs: Do snapshot deletion in smaller chunks.

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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>
This commit is contained in:
Chris Mason
2007-08-07 15:52:19 -04:00
committed by David Woodhouse
parent 8578f0f1fd
commit 9f3a742736
4 changed files with 91 additions and 31 deletions
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45
fs/btrfs/extent-tree.c
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@@ -1561,12 +1561,21 @@ static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
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 @@ static int walk_up_tree(struct btrfs_trans_handle *trans, struct btrfs_root
* 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 @@ int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
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 @@ int btrfs_drop_snapshot(struct btrfs_trans_handle *trans, struct btrfs_root
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;
}