Re: [PATCH v5 05/19] selftests/mm: make the swap cases' swapout reliable

[Baolin Wang]

On 9/8/26 8:50 PM, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
>
> collapse_swapin_single_pte() and collapse_max_ptes_swap() swap a range out
> and then require smaps to report exactly the count they asked for.  Two
> things keep that count from arriving.
>
> MADV_PAGEOUT is best effort, so the count often turns up a moment late.
>
> And wait_for_scan() leaves the range eligible for collapsing, so
> khugepaged is still working on it.  Collapsing reads the swapped-out pages
> back in, so the daemon empties the swap as fast as the case fills it.  On
> arm64 with 64K pages max_ptes_swap is 1024 pages, which is 64M a step, and
> the case loses the race:
>
>      # Swapout 1024 of 8192 pages... Fail
>      not ok 10 collapse_max_ptes_swap
>
> Retry for up to two seconds, holding the range out of khugepaged's reach
> meanwhile.  The collapse each case runs next restores MADV_HUGEPAGE, so
> only the setup is affected.
>
> If the pages still won't swap out, skip: no swap, swap too small or full,
> a memcg cap or busy writeback. None of that is a kernel bug.
>
> Assisted-by: LLM
> Reviewed-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
> Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> ---

Make sense to me. So
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>