Re: [PATCH v3 1/4] mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order

[Zi Yan <ziy@nvidia.com>]

On 24 Oct 2025, at 11:58, Lorenzo Stoakes wrote:

> On Tue, Oct 21, 2025 at 11:35:27PM -0400, Zi Yan wrote:
>> folio split clears PG_has_hwpoisoned, but the flag should be preserved in
>> after-split folios containing pages with PG_hwpoisoned flag if the folio is
>> split to >0 order folios. Scan all pages in a to-be-split folio to
>> determine which after-split folios need the flag.
>>
>> An alternatives is to change PG_has_hwpoisoned to PG_maybe_hwpoisoned to
>> avoid the scan and set it on all after-split folios, but resulting false
>> positive has undesirable negative impact. To remove false positive, caller
>> of folio_test_has_hwpoisoned() and folio_contain_hwpoisoned_page() needs to
>> do the scan. That might be causing a hassle for current and future callers
>> and more costly than doing the scan in the split code. More details are
>> discussed in [1].
>>
>> It is OK that current implementation does not do this, because memory
>> failure code always tries to split to order-0 folios and if a folio cannot
>> be split to order-0, memory failure code either gives warnings or the split
>> is not performed.
>>
>> Link: https://lore.kernel.org/all/CAHbLzkoOZm0PXxE9qwtF4gKR=cpRXrSrJ9V9Pm2DJexs985q4g@mail.gmail.com/ [1]
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>
> I guess this was split out to [0]? :)
>
> [0]: https://lore.kernel.org/linux-mm/44310717-347c-4ede-ad31-c6d375a449b9@linux.dev/

Yes. The decision is based on the discussion with David[1] and announced at[2].

[1] https://lore.kernel.org/all/d3d05898-5530-4990-9d61-8268bd483765@redhat.com/
[2] https://lore.kernel.org/all/1AE28DE5-1E0A-432B-B21B-61E0E3F54909@nvidia.com/

--
Best Regards,
Yan, Zi