Re: [PATCH v4 12/19] selftests/mm: parameterize the mixed-source collapse case by source order

[Lorenzo Stoakes (ARM)]

On Sat, Aug 15, 2026 at 02:58:54AM +0100, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
>
> collapse_order_mixed_sources() faults its region as order-2 folios and
> collapses them to the -c target.  Order 2 sits below the contpte threshold
> on both arm64 page-size configurations, so nothing in this suite unfolds a
> contpte source on purpose.
>
> Let -s name the source order alongside -c.  The case then faults at that
> order, keeping order 2 when -s is absent, and the source order has to be a
> supported mTHP order below the target.  The other mTHP cases are
> unaffected: mthp_push_target_order() enables only the target order.
>
> "-s 5 -c 7" on arm64/64K then collapses contpte-mapped sources into a
> larger mTHP.
>
> Assisted-by: Claude-Code:claude-opus-5
> Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>

Looks reasonable to me so:

Acked-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  tools/testing/selftests/mm/khugepaged.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index 0489967d6ee0..1844ddd77b59 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -1389,10 +1389,13 @@ static void collapse_order_max_ptes_none(struct collapse_context *c,
>  static void collapse_order_mixed_sources(struct collapse_context *c,
>  					 struct mem_ops *ops)
>  {
> +	int source_order = anon_order ? anon_order : MIN_MTHP_ORDER;
>  	struct thp_settings settings;
>  	void *p;
>
> -	if (collapse_order <= MIN_MTHP_ORDER) {
> +	/* Sources must be a supported mTHP order strictly below the target. */
> +	if (source_order >= collapse_order ||
> +	    !(thp_supported_orders() & (1UL << source_order))) {
>  		ksft_test_result_skip("%s: no source order below target\n",
>  				      __func__);
>  		return;
> @@ -1400,23 +1403,22 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
>
>  	mthp_push_target_order();
>
> -	/* Fault the whole region as order-MIN_MTHP_ORDER folios. */
> +	/* Fault the whole region as order-@source_order folios. */
>  	settings = *thp_current_settings();
> -	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
> +	settings.hugepages[source_order].enabled = THP_ALWAYS;
>  	thp_push_settings(&settings);
>  	p = ops->setup_area(1);
>  	ops->fault(p, 0, hpage_pmd_size);
>  	thp_pop_settings();
>
>  	/*
> -	 * The order is enabled, but the allocator can still fall back under
> -	 * fragmentation.  That leaves nothing to collapse from, which is the
> -	 * machine's answer rather than a reason to end the run.
> +	 * The order is enabled and supported, but the allocator can still fall
> +	 * back under fragmentation.  That leaves nothing to collapse from,
> +	 * which is the machine's answer rather than a reason to end the run.
>  	 */
> -	if (!is_range_backed_by_folio_orders(p, hpage_pmd_size, MIN_MTHP_ORDER,
> +	if (!is_range_backed_by_folio_orders(p, hpage_pmd_size, source_order,
>  					     pagemap_fd, kpageflags_fd)) {
> -		ksft_print_msg("No order-%d sources to collapse...",
> -			       MIN_MTHP_ORDER);
> +		ksft_print_msg("No order-%d sources to collapse...", source_order);
>  		skip("Skip");
>  		ops->cleanup_area(p, hpage_pmd_size);
>  		thp_pop_settings();
> @@ -1425,7 +1427,8 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
>  	}
>
>  	madvise(p, hpage_pmd_size, MADV_HUGEPAGE);
> -	ksft_print_msg("Collapse region backed by smaller large folios...");
> +	ksft_print_msg("Collapse region backed by order-%d sources...",
> +		       source_order);
>  	if (!khugepaged_wait_full_pass())
>  		fail("Timeout");
>  	else if (window_collapsed(p, hpage_pmd_size))
> @@ -1456,6 +1459,8 @@ static void usage(void)
>  	fprintf(stderr,	"\t\t-s: mTHP size, expressed as page order.\n");
>  	fprintf(stderr,	"\t\t    Defaults to 0. Use this size for anon or shmem allocations.\n");
>  	fprintf(stderr,	"\t\t-c: collapse order for mTHP collapse, expressed as page order.\n");
> +	fprintf(stderr,	"\t\t    With -s, -s names the mTHP source order for the\n");
> +	fprintf(stderr,	"\t\t    mixed-source case (source order below the target).\n");
>  	exit(1);
>  }
>
> --
> 2.54.0
>

--
Cheers, Lorenzo