Re: [PATCH v6 11/19] selftests/mm: add order-parameterized khugepaged collapse cases

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 9/19/26 8:24 AM, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
> 
> The mthp_khugepaged context runs the generic cases at a sub-PMD order,
> which answers how many folios of that order a range ends up with.  It
> cannot say which order-sized window they landed in, so "the populated
> window collapsed" and "the empty window next to it collapsed instead" look
> alike.
> 
> Add four cases that check each window on its own, with the folio-order
> helpers in vm_util:
> 
> - collapse_order_single_window(): only the populated window collapses;
> - collapse_order_partial_window(): the default max_ptes_none lets a window
>    with one present PTE collapse;
> - collapse_order_max_ptes_none(): with max_ptes_none=0 a full window
>    collapses and one missing a page does not;
> - collapse_order_mixed_sources(): sources that are already large folios of
>    a smaller order collapse to the target.
> 
> Each case faults its region before MADV_HUGEPAGE with only the target
> order enabled, so the sources are order 0 and the result can only come
> from khugepaged.  They wait for a full pass rather than for the result to
> appear: without a completed pass, "not collapsed" and "not scanned yet"
> are the same thing.
> 
> Assisted-by: LLM
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> ---

Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>