Re: [PATCH v5 08/17] erofs: mm/pagemap: add readahead_folio_last() to avoid folio->private

[Lance Yang]

On 2026/9/21 10:28, Zi Yan wrote:
> erofs needs to traverse readahead folios in reverse order to achieve
> maximum performance by
> 1. reading all folios from readahead_folio();
> 2. storing the prior folio pointer in folio->private;
> 3. traverse from the last folio to the first one.
>
> Add readahead_folio_last() to achieve the same function without using
> folio->private. __readahead_advance() helper shares readahead_control
> adjustment code among __readahead_folio(), readahead_folio_last(), and
> __readahead_batch() by checking new private member, _forward, of
> readahead_control.
>
> It prepares for a future commit that replaces PG_private checks with
> !folio->private checks. After switching the checks, erofs's use of
> folio->private without bumping folio refcount can cause unexpected
> outcomes, e.g., in filemap_release_folio(), try_to_free_buffers() becomes
> reachable.
>
> No functional change intended.
>
> Assisted-by: LLM
> To: Gao Xiang <xiang@xxxxxxxxxx>
> To: Chao Yu <chao@xxxxxxxxxx>
> To: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
> To: Jan Kara <jack@xxxxxxx>
> 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
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---

Nothing jumped out at me, feel free to add:

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>