Re: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to folio_check_splittable()

[Zi Yan]

On 26 Nov 2025, at 4:54, David Hildenbrand (Red Hat) wrote:

>> -	/*
>> -	 * Folios that just got truncated cannot get split. Signal to the
>> -	 * caller that there was a race.
>> -	 *
>> -	 * TODO: this will also currently refuse shmem folios that are in the
>> -	 * swapcache.
>> -	 */
>> -	if (!is_anon && !folio->mapping)
>> -		return -EBUSY;
>> -
>>   	if (new_order >= old_order)
>>   		return -EINVAL;
>>  -	if (!folio_split_supported(folio, new_order, split_type, /* warn = */ true))
>> -		return -EINVAL;
>> -
>> -	is_hzp = is_huge_zero_folio(folio);
>> -	if (is_hzp) {
>> -		pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
>> -		return -EBUSY;
>
> As we are changing that case to a VM_WARN_ONCE(), is there some path where we might trigger that?

Based on the git history, this check is added for injecting errors
to huge zero folio and triggering memory failure handling.

>
> I'm wondering about the split_huge_pages_all() function in particular. I guess the "!folio_test_lru(folio)" would protect us?

I think so.
>
> Apart from that LGTM
>
> Acked-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>
>

Thanks.


Best Regards,
Yan, Zi