Re: [PATCH V4 1/2] mm/khugepaged: map dirty/writeback pages failures to EAGAIN

[David Hildenbrand (Red Hat)]

On 12/15/25 09:46, Shivank Garg wrote:
> When collapse_file encounters dirty or writeback pages in file-backed
> mappings, it currently returns SCAN_FAIL which maps to -EINVAL. This is
> misleading as EINVAL suggests invalid arguments, whereas dirty/writeback
> pages represent transient conditions that may resolve on retry.
>
> Introduce SCAN_PAGE_DIRTY_OR_WRITEBACK to cover both dirty and writeback
> states, mapping it to -EAGAIN. For MADV_COLLAPSE, this provides userspace
> with a clear signal that retry may succeed after writeback completes.
> For khugepaged, this is harmless as it will naturally revisit the range
> during periodic scans after async writeback completes.
>
> Reported-by: Branden Moore <Branden.Moore@xxxxxxx>
> Closes: https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@xxxxxxx
> Fixes: 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE")
> Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
> Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Reviewed-by: wang lian <lianux.mm@xxxxxxxxx>
> Signed-off-by: Shivank Garg <shivankg@xxxxxxx>

Acked-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>

--
Cheers

David