Re: [PATCH 1/2] mm/huge_memory: do not change split_huge_page*() target order silently.

[Zi Yan <ziy@nvidia.com>]

On 12 Oct 2025, at 4:24, Pankaj Raghav (Samsung) wrote:

> On Fri, Oct 10, 2025 at 01:39:05PM -0400, Zi Yan wrote:
>> Page cache folios from a file system that support large block size (LBS)
>> can have minimal folio order greater than 0, thus a high order folio might
>> not be able to be split down to order-0. Commit e220917fa507 ("mm: split a
>> folio in minimum folio order chunks") bumps the target order of
>> split_huge_page*() to the minimum allowed order when splitting a LBS folio.
>> This causes confusion for some split_huge_page*() callers like memory
>> failure handling code, since they expect after-split folios all have
>> order-0 when split succeeds but in really get min_order_for_split() order
>> folios.
>>
>> Fix it by failing a split if the folio cannot be split to the target order.
>>
>> Fixes: e220917fa507 ("mm: split a folio in minimum folio order chunks")
>> [The test poisons LBS folios, which cannot be split to order-0 folios, and
>> also tries to poison all memory. The non split LBS folios take more memory
>> than the test anticipated, leading to OOM. The patch fixed the kernel
>> warning and the test needs some change to avoid OOM.]
>> Reported-by: syzbot+e6367ea2fdab6ed46056@syzkaller.appspotmail.com
>> Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@google.com/
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
> LGTM with the suggested changes to the !CONFIG_THP try_folio_split().
>
> Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>

Thanks.

--
Best Regards,
Yan, Zi