Re: [PATCH v4 09/16] erofs: use folio_attach/detach_private() instead of direct assignment

[David Hildenbrand (Arm)]

On 9/14/26 04:24, Zi Yan wrote:
> erofs_onlinefolio_init/split/end() use folio->private without setting
> PG_private or increasing folio refcount and it works. But after PG_private
> is replaced by checking folio->private in a future commit, it can break
> folio_expected_ref_count(), since the folio has private data without
> elevated refcount. Change them to use folio_attach/detach_private().
> Folios during this process are locked as they are in the process of
> readahead, so no parallel migration/folio split can happen.
> 
> Furthermore, because folio->private is used to store in-flight I/O counter
> and the counter reaches 0 when all I/O completes successfully without error
> or being dirty, ->private=0 causes folio_detach_private() to not drop the
> elevated folio refcount. Solve this issue by using bias=1 for the counter,
> so that ->private stays non NULL throughout every attach-to-detach process.
> Add a macro EROFS_ONLINEFOLIO_BIAS=1. While at it, fix the comment about
> ->private bit layout and add EROFS_ONLINEFOLIO_COUNT_MASK.
> 
> It prepares for a future commit that removes PG_private.
> 
> Assisted-by: LLM
> To: Gao Xiang <xiang@xxxxxxxxxx>
> To: Chao Yu <chao@xxxxxxxxxx>
> Cc: Yue Hu <zbestahu@xxxxxxxxx>
> Cc: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> Cc: Sandeep Dhavale <dhavale@xxxxxxxxxx>
> Cc: Hongbo Li <hongbohbli@xxxxxxxxxxx>
> Cc: Chunhai Guo <guochunhai@xxxxxxxx>
> Cc: linux-erofs@xxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Reviewed-by: Gao Xiang <xiang@xxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David