Re: [PATCH v2] huge_memory: return -EINVAL in folio split functions when THP is disabled

[Pankaj Raghav <kernel@pankajraghav.com>]

On 9/4/25 17:26, Kiryl Shutsemau wrote:
> On Thu, Sep 04, 2025 at 11:51:29AM +0200, Pankaj Raghav (Samsung) wrote:
>> From: Pankaj Raghav <p.raghav@samsung.com>
>>
>> split_huge_page_to_list_[to_order](), split_huge_page() and
>> try_folio_split() return 0 on success and error codes on failure.
>>
>> When THP is disabled, these functions return 0 indicating success even
>> though an error code should be returned as it is not possible to split a
>> folio when THP is disabled.
>>
>> Make all these functions return -EINVAL to indicate failure instead of
>> 0. As large folios depend on CONFIG_THP, issue warning as this function
>> should not be called without a large folio.
>>
>> Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
> 
> Acked-by: Kiryl Shutsemau <kas@kernel.org>
> 
> Just curious, did you give BUILD_BUG() a try?
> 

Yes, I tried BUILD_BUG() but it actually fails the build because truncate_inode_partial_folio()
calls try_folio_split().

It won't be called in runtime because there is a check for large folios before we call this
function. So a runtime warning is better in this case.

--
Pankaj