Re: [syzbot] [mm?] WARNING in memory_failure

David Hildenbrand
2025-09-29T16:13:55Z

On 29.09.25 17:20, Zi Yan wrote:
> On 29 Sep 2025, at 7:08, Pankaj Raghav (Samsung) wrote:
>
>>>
>>> I want to change all the split functions in huge_mm.h and provide
>>> mapping_min_folio_order() to try_folio_split() in truncate_inode_partial_folio().
>>>
>>> Something like below:
>>>
>>> 1. no split function will change the given order;
>>> 2. __folio_split() will no longer give VM_WARN_ONCE when provided new_order
>>> is smaller than mapping_min_folio_order().
>>>
>>> In this way, for an LBS folio that cannot be split to order 0, split
>>> functions will return -EINVAL to tell caller that the folio cannot
>>> be split. The caller is supposed to handle the split failure.
>>
>> IIUC, we will remove warn on once but just return -EINVAL in __folio_split()
>> function if new_order < min_order like this:
>> ...
>> min_order = mapping_min_folio_order(folio->mapping);
>> if (new_order < min_order) {
>> - VM_WARN_ONCE(1, "Cannot split mapped folio below min-order: %u",
>> - min_order);
>> ret = -EINVAL;
>> goto out;
>> }
>> ...
>>>
>>> WDYT?
>>>
>> I think it should be fine as along as we return an error if someone is
>> trying to split < min_order for file-backed folios.
>>
>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>> index f327d62fc985..e15c3ca07e33 100644
>>> --- a/include/linux/huge_mm.h
>>> +++ b/include/linux/huge_mm.h
>>> @@ -387,34 +387,16 @@ int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
>>> * Return: 0: split is successful, otherwise split failed.
>>> */
>>> static inline int try_folio_split(struct folio *folio, struct page *page,
>>> - struct list_head *list)
>>> + struct list_head *list, unsigned int order)
>>> {
>
> OK, I will send a proper patch to fix this. Thanks.

Thanks!

--
Cheers

David / dhildenb