[PATCH v2 10/17] selftests/mm: parameterize the mixed-source collapse case by source order

[Kiryl Shutsemau]

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, which was rejected before.  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.  Other
cases are unaffected: they enable their source order locally.

"-s 5 -c 7" on arm64/64K then collapses contpte-mapped sources into a
larger mTHP.

Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
---
 tools/testing/selftests/mm/khugepaged.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index bcaef17e430d..d3ff1b196e09 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1430,10 +1430,13 @@ 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;
@@ -1441,21 +1444,22 @@ 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();
 
-	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_exit_fail_msg("Region not backed by order-%d folios after fault\n",
-				   MIN_MTHP_ORDER);
+				   source_order);
 
 	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))
@@ -1486,6 +1490,8 @@ 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