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btrfs: qgroup: allow quick inherit if snapshot is created and added to the same parent

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Currently "btrfs subvolume snapshot -i <qgroupid>" would always mark the
qgroup inconsistent.

This can be annoying if the fs has a lot of snapshots, and needs qgroup
to get the accounting for the amount of bytes it can free for each
snapshot.

Although we have the new simple quote as a solution, there is also a
case where we can skip the full scan, if all the following conditions
are met:

- The source subvolume belongs to a higher level parent qgroup
- The parent qgroup already owns all its bytes exclusively
- The new snapshot is also added to the same parent qgroup

In that case, we only need to add nodesize to the parent qgroup and
avoid a full rescan.

This patch would add the extra quick accounting update for such inherit.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
2024-02-26 14:21:13 +10:30
committed by David Sterba
parent 86211eea8a
commit b20fe56cd2
1 changed files with 72 additions and 7 deletions
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79
fs/btrfs/qgroup.c
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@@ -3138,6 +3138,62 @@ static int qgroup_auto_inherit(struct btrfs_fs_info *fs_info,
return 0;
}
/*
* Check if we can skip rescan when inheriting qgroups. If @src has a single
* @parent, and that @parent is owning all its bytes exclusively, we can skip
* the full rescan, by just adding nodesize to the @parent's excl/rfer.
*
* Return <0 for fatal errors (like srcid/parentid has no qgroup).
* Return 0 if a quick inherit is done.
* Return >0 if a quick inherit is not possible, and a full rescan is needed.
*/
static int qgroup_snapshot_quick_inherit(struct btrfs_fs_info *fs_info,
u64 srcid, u64 parentid)
{
struct btrfs_qgroup *src;
struct btrfs_qgroup *parent;
struct btrfs_qgroup_list *list;
int nr_parents = 0;
src = find_qgroup_rb(fs_info, srcid);
if (!src)
return -ENOENT;
parent = find_qgroup_rb(fs_info, parentid);
if (!parent)
return -ENOENT;
/*
* Source has no parent qgroup, but our new qgroup would have one.
* Qgroup numbers would become inconsistent.
*/
if (list_empty(&src->groups))
return 1;
list_for_each_entry(list, &src->groups, next_group) {
/* The parent is not the same, quick update is not possible. */
if (list->group->qgroupid != parentid)
return 1;
nr_parents++;
/*
* More than one parent qgroup, we can't be sure about accounting
* consistency.
*/
if (nr_parents > 1)
return 1;
}
/*
* The parent is not exclusively owning all its bytes. We're not sure
* if the source has any bytes not fully owned by the parent.
*/
if (parent->excl != parent->rfer)
return 1;
parent->excl += fs_info->nodesize;
parent->rfer += fs_info->nodesize;
return 0;
}
/*
* Copy the accounting information between qgroups. This is necessary
* when a snapshot or a subvolume is created. Throwing an error will
@@ -3306,6 +3362,13 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
qgroup_dirty(fs_info, dstgroup);
qgroup_dirty(fs_info, srcgroup);
/*
* If the source qgroup has parent but the new one doesn't,
* we need a full rescan.
*/
if (!inherit && !list_empty(&srcgroup->groups))
need_rescan = true;
}
if (!inherit)
@@ -3320,14 +3383,16 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
if (ret)
goto unlock;
}
if (srcid) {
/* Check if we can do a quick inherit. */
ret = qgroup_snapshot_quick_inherit(fs_info, srcid, *i_qgroups);
if (ret < 0)
goto unlock;
if (ret > 0)
need_rescan = true;
ret = 0;
}
++i_qgroups;
/*
* If we're doing a snapshot, and adding the snapshot to a new
* qgroup, the numbers are guaranteed to be incorrect.
*/
if (srcid)
need_rescan = true;
}
for (i = 0; i < inherit->num_ref_copies; ++i, i_qgroups += 2) {