Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged

["David Hildenbrand (Arm)" <david@kernel.org>]

On 8/21/26 01:55, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 07:37:29PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 5:23 PM EDT, Yeoreum Yun wrote:
>>>
>>> Well, this also works with hugepage_save_settings() and write the
>>> khugepaged/scan_sleep_millisecs with the maximum integer.
>>>
>>> I don't have a strong opinion but since it seems more hackish way to
>>> change scan_sllep_millisecs, I use madvise() with MADV_NOHUGEPATE.
>>>
>>> Would it be better to change using APIs in hugepage_setting,h?
>>
>> No. I did not realize there is no way of stopping khugepaged completely.
>>
>> BTW, I am curious about your khugepaged config causing this issue.
>> IIRC, khugepaged scan interval is about minutes and
>> the time between madvise(MADV_HUGEPAGE) and the second
>> is_backed_by_folio() should not be that long.
> 
> Yes. it's relly timing sensitive and I've failed to reproduce in the
> real hardware. but in the emulation environment it often failed with 
> the scan_sllep_millisecs as 10 seconds while the test running.
> 
>>
>> For your patch, maybe you want to check the return value of madvise() to
>> make sure it succeeds.
> 
> Yeap. but it seems enough just worning message for the madvise() with
> MADV_NOHUGEPAGE.

Yeah, I assume we can assume that we are running on a recent enough kernel that
supports MADV_NOHUGEPAGE.

-- 
Cheers,

David