Re: [PATCH v5 12/19] selftests/mm: parameterize the mixed-source collapse case by source order

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

On 9/8/26 8:50 PM, Kiryl Shutsemau wrote:
> From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
> 
> collapse_order_mixed_sources() faults its region as order-2 folios and
> collapses them to the -c target.  Order 2 is below the contpte size on
> every arm64 page size, so nothing in this suite collapses a contpte-mapped
> 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.

Make sense. But we should validate invalid parameter combinations for 
'-s' and '-c'. For example, when I set the following unreasonable 
parameters, some test cases fail, so such invalid configurations should 
be rejected.

[root@]# ./khugepaged -s 7 -c 6 mthp_khugepaged:anon
TAP version 13
# Save THP and khugepaged settings... OK
1..8
# Allocate huge page on fault... OK
# Split huge PMD on MADV_DONTNEED... OK
ok 1 allocate on fault and split
#
# Run test: collapse_full (mthp_khugepaged:anon)
# Collapse multiple fully populated PTE table.... Fail
not ok 2 collapse_full
#
# Run test: collapse_empty (mthp_khugepaged:anon)
# Do not collapse empty PTE table.... OK
ok 3 collapse_empty
#
# Run test: collapse_single_mthp (mthp_khugepaged:anon)
# Collapse PTE table with half PTE entries present.... Fail
not ok 4 collapse_single_mthp
#
# Run test: collapse_order_single_window (mthp_khugepaged:anon)
# Collapse one fully populated window... OK
ok 5 collapse_order_single_window
#
# Run test: collapse_order_partial_window (mthp_khugepaged:anon)
# Collapse window with single PTE entry present... OK
ok 6 collapse_order_partial_window
#
# Run test: collapse_order_max_ptes_none (mthp_khugepaged:anon)
# Collapse full window, not the one missing a page... OK
ok 7 collapse_order_max_ptes_none
#
# Run test: collapse_order_mixed_sources (mthp_khugepaged:anon)
ok 8 # SKIP collapse_order_mixed_sources: no supported source order 
below target
# 1 skipped test(s) detected. Consider enabling relevant config options 
to improve coverage.
# Totals: pass:5 fail:2 xfail:0 xpass:0 skip:1 error:0

> Assisted-by: LLM
> Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
> Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> ---
>   tools/testing/selftests/mm/khugepaged.c | 17 ++++++++++-------
>   1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index fb4efaf67c40..b15cd07fc0b3 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -1352,11 +1352,13 @@ 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) {
> -		ksft_test_result_skip("%s: no source order below target\n",
> +	if (source_order >= collapse_order ||
> +	    !(thp_supported_orders() & (1UL << source_order))) {
> +		ksft_test_result_skip("%s: no supported source order below target\n",
>   				      __func__);
>   		return;
>   	}
> @@ -1364,7 +1366,7 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
>   	mthp_push_target_order();
>   
>   	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);
> @@ -1374,10 +1376,9 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
>   	 * The allocator can fall back to smaller folios under fragmentation;
>   	 * having nothing to collapse from is not a failure.
>   	 */
> -	if (!is_range_backed_by_order(p, hpage_pmd_size, MIN_MTHP_ORDER,
> +	if (!is_range_backed_by_order(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();
> @@ -1387,7 +1388,8 @@ static void collapse_order_mixed_sources(struct collapse_context *c,
>   
>   	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
>   		ksft_exit_fail_perror("madvise(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_full_pass(MTHP_PASS_TIMEOUT_S))
>   		fail("Timeout");
>   	else if (all_windows_at_order(p, hpage_pmd_size))
> @@ -1418,6 +1420,7 @@ 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    -s, if set, is the source order for the mixed-source case.\n");
>   	exit(1);
>   }
>