On 2018年04月25日 13:19, Su Yue wrote: > For an extent item which contains many tree block backrefs, like > ================================================================= > In 020-extent-ref-cases/keyed_block_ref.img > > item 10 key (29470720 METADATA_ITEM 0) itemoff 3450 itemsize 222 > refs 23 gen 10 flags TREE_BLOCK > tree block skinny level 0 > tree block backref root 278 > tree block backref root 277 > tree block backref root 276 > tree block backref root 275 > tree block backref root 274 > tree block backref root 273 > tree block backref root 272 > tree block backref root 271 > tree block backref root 270 > tree block backref root 269 > tree block backref root 268 > tree block backref root 267 > tree block backref root 266 > tree block backref root 265 > tree block backref root 264 > tree block backref root 263 > tree block backref root 262 > tree block backref root 261 > tree block backref root 260 > tree block backref root 259 > tree block backref root 258 > tree block backref root 257 > ================================================================= > In find_parent_nodes(), these refs's parents are 0, then __merge_refs > will merge refs to one ref. It causes only one root to be returned. > > So, if both parents are 0, do not merge refs. > > Lowmem check calls find_parent_nodes frequently to decide whether > check an extent buffer or not. The bug influences bytes accounting. > > Signed-off-by: Su Yue <suy.f...@cn.fujitsu.com>
Reviewed-by: Qu Wenruo <w...@suse.com>
Waiting for the kernel port of backref.c to solve the problem permanently.
Thanks,
Qu
> ---
> Changelog:
> v2:
> Put judgment of ref->parent above comparison.
> Add the comment.
> Fix typos.
> v2.1:
> Remove the change of adding a new line.
> ---
> backref.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/backref.c b/backref.c
> index 51553c702187..23a394edfd02 100644
> --- a/backref.c
> +++ b/backref.c
> @@ -505,6 +505,12 @@ static void __merge_refs(struct pref_state *prefstate,
> int mode)
> if (!ref_for_same_block(ref1, ref2))
> continue;
> } else {
> + /*
> + * Parent == 0 means that the ref is tree block
> + * backref or its parent is unresolved.
> + */
> + if (!ref1->parent || !ref2->parent)
> + continue;
> if (ref1->parent != ref2->parent)
> continue;
> }
>
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