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

["Zi Yan" <ziy@nvidia.com>]

On Thu Aug 20, 2026 at 5:23 PM EDT, Yeoreum Yun wrote:
> On Thu, Aug 20, 2026 at 03:51:34PM -0400, Zi Yan wrote:
>> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote:
>> > There're some random failure for split_huge_page_test when khugepaged
>> > collapses pages into pmd again which had split by the test.
>> >
>> > Prevent the khugepaged's collapses for split page by setting the
>> > mapped pmd-huge-page with MADV_NOHUGEPAGE before split.
>> 
>> Why not disable khugepaged using APIs from hugepage_setting.h?
>
> 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.

For your patch, maybe you want to check the return value of madvise() to
make sure it succeeds.

Otherwise,

feel free to add

Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks.


-- 
Best Regards,
Yan, Zi