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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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63
fs/btrfs/transaction.c
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@@ -213,10 +213,7 @@ static int wait_for_commit(struct btrfs_root *root,
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 @@ int btrfs_add_dead_root(struct btrfs_root *root, struct list_head *dead_list)
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 @@ static int add_dirty_roots(struct btrfs_trans_handle *trans,
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 @@ static int add_dirty_roots(struct btrfs_trans_handle *trans,
}
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 @@ static int add_dirty_roots(struct btrfs_trans_handle *trans,
&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 @@ static int drop_dirty_roots(struct btrfs_root *tree_root,
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);