+ selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch added to mm-new branch

+ selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: add order-parameterized khugepaged collapse cases
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: selftests/mm: add order-parameterized khugepaged collapse cases
Date: Tue, 8 Sep 2026 13:50:57 +0100

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
Link: https://lore.kernel.org/20260908125105.1510704-12-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/khugepaged.c |  212 ++++++++++++++++++++++
 1 file changed, 212 insertions(+)

--- a/tools/testing/selftests/mm/khugepaged.c~selftests-mm-add-order-parameterized-khugepaged-collapse-cases
+++ a/tools/testing/selftests/mm/khugepaged.c
@@ -30,6 +30,8 @@ static unsigned long page_size;
 static int hpage_pmd_nr;
 static int anon_order;
 static int collapse_order;
+static int pagemap_fd = -1;
+static int kpageflags_fd = -1;
 
 #define PID_SMAPS "/proc/self/smaps"
 #define TEST_FILE "collapse_test_file"
@@ -1212,6 +1214,198 @@ static void madvise_retracted_page_table
 	ksft_test_result_report(exit_status, "%s\n", __func__);
 }
 
+/* Smallest order khugepaged will consider for mTHP collapse */
+#define MIN_MTHP_ORDER 2
+
+/* Time budget for one khugepaged pass in the collapse_order_* cases */
+#define MTHP_PASS_TIMEOUT_S 30
+
+static size_t mthp_window_size(void)
+{
+	return page_size << collapse_order;
+}
+
+static void mthp_push_target_order(void)
+{
+	struct thp_settings settings = *thp_current_settings();
+	int i;
+
+	/*
+	 * Only the target order, and only for madvise: the cases fault their
+	 * region first, so the sources stay order 0 whatever -s asked for.
+	 */
+	settings.thp_enabled = THP_NEVER;
+	for (i = 0; i < NR_ORDERS; i++)
+		settings.hugepages[i].enabled = THP_NEVER;
+	settings.hugepages[collapse_order].enabled = THP_MADVISE;
+	thp_push_settings(&settings);
+}
+
+static bool all_windows_at_order(void *p, size_t len)
+{
+	return is_range_backed_by_order(p, len, collapse_order,
+					pagemap_fd, kpageflags_fd);
+}
+
+static bool any_window_at_order(void *p, size_t len)
+{
+	size_t window = mthp_window_size();
+	char *addr = p;
+
+	for (; len >= window; addr += window, len -= window) {
+		if (all_windows_at_order(addr, window))
+			return true;
+	}
+	return false;
+}
+
+static void collapse_order_single_window(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, window, 2 * window);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse one fully populated window...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p + window, window) &&
+		 !any_window_at_order(p, window) &&
+		 !any_window_at_order(p + 2 * window,
+				      hpage_pmd_size - 2 * window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, window, 2 * window);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_partial_window(struct collapse_context *c,
+					  struct mem_ops *ops)
+{
+	void *p;
+
+	mthp_push_target_order();
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, page_size);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse window with single PTE entry present...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, mthp_window_size()))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_max_ptes_none(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	size_t window = mthp_window_size();
+	void *p;
+
+	mthp_push_target_order();
+	settings = *thp_current_settings();
+	settings.khugepaged.max_ptes_none = 0;
+	thp_push_settings(&settings);
+
+	p = ops->setup_area(1);
+	ops->fault(p, 0, 2 * window - page_size);
+	if (any_window_at_order(p, hpage_pmd_size))
+		ksft_exit_fail_msg("Unexpected large folio after fault\n");
+
+	if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
+		ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
+	ksft_print_msg("Collapse full window, not the one missing a page...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, window) &&
+		 !any_window_at_order(p + window, window))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, 2 * window - page_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
+static void collapse_order_mixed_sources(struct collapse_context *c,
+					 struct mem_ops *ops)
+{
+	struct thp_settings settings;
+	void *p;
+
+	if (collapse_order <= MIN_MTHP_ORDER) {
+		ksft_test_result_skip("%s: no source order below target\n",
+				      __func__);
+		return;
+	}
+
+	mthp_push_target_order();
+
+	settings = *thp_current_settings();
+	settings.hugepages[MIN_MTHP_ORDER].enabled = THP_ALWAYS;
+	thp_push_settings(&settings);
+	p = ops->setup_area(1);
+	ops->fault(p, 0, hpage_pmd_size);
+	thp_pop_settings();
+
+	/*
+	 * 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,
+				      pagemap_fd, kpageflags_fd)) {
+		ksft_print_msg("No order-%d sources to collapse...",
+			       MIN_MTHP_ORDER);
+		skip("Skip");
+		ops->cleanup_area(p, hpage_pmd_size);
+		thp_pop_settings();
+		ksft_test_result_report(exit_status, "%s\n", __func__);
+		return;
+	}
+
+	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...");
+	if (!khugepaged_full_pass(MTHP_PASS_TIMEOUT_S))
+		fail("Timeout");
+	else if (all_windows_at_order(p, hpage_pmd_size))
+		success("OK");
+	else
+		fail("Fail");
+
+	validate_memory(p, 0, hpage_pmd_size);
+	ops->cleanup_area(p, hpage_pmd_size);
+	thp_pop_settings();
+	ksft_test_result_report(exit_status, "%s\n", __func__);
+}
+
 static void usage(void)
 {
 	fprintf(stderr, "\nUsage: ./khugepaged [OPTIONS] <test type> [dir]\n\n");
@@ -1380,6 +1574,20 @@ int main(int argc, char **argv)
 
 	parse_test_type(argc, argv);
 
+	if (mthp_khugepaged_context &&
+	    !(thp_supported_orders() & (1UL << collapse_order)))
+		ksft_exit_skip("Order %d is not a supported anon THP order\n",
+			       collapse_order);
+
+	if (mthp_khugepaged_context) {
+		pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+		if (pagemap_fd < 0)
+			ksft_exit_fail_perror("open(/proc/self/pagemap)");
+		kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
+		if (kpageflags_fd < 0)
+			ksft_exit_fail_perror("open(/proc/kpageflags)");
+	}
+
 	setbuf(stdout, NULL);
 
 	/*
@@ -1430,6 +1638,10 @@ int main(int argc, char **argv)
 	TEST(collapse_empty, madvise_context, anon_ops);
 
 	TEST(collapse_single_mthp, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_single_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_partial_window, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_max_ptes_none, mthp_khugepaged_context, anon_ops);
+	TEST(collapse_order_mixed_sources, mthp_khugepaged_context, anon_ops);
 
 	TEST(collapse_single_pte_entry, khugepaged_context, anon_ops);
 	TEST(collapse_single_pte_entry, khugepaged_context, read_only_file_ops);
_

Patches currently in -mm which might be from kas@kernel.org are

mm-huge_memory-do-not-touch-frozen-folios-in-deferred_split_isolate.patch
mm-huge_memory-dequeue-the-deferred-split-after-the-split-freeze.patch
selftests-mm-raise-the-khugepaged-test-case-cap.patch
selftests-mm-skip-collapse_compound_extreme-where-the-pmd-is-too-large.patch
selftests-mm-scale-khugepageds-collapse-wait-with-the-pmd-size.patch
selftests-mm-skip-khugepaged-page-cache-cases-without-a-pmd-folio.patch
selftests-mm-make-the-swap-cases-swapout-reliable.patch
selftests-mm-stop-khugepaged-during-the-madv_collapse-cases.patch
selftests-mm-move-is_backed_by_folio-into-vm_util.patch
selftests-mm-add-folio-order-check-for-address-ranges.patch
selftests-mm-add-folio-order-detection-self-check.patch
selftests-mm-add-khugepaged-completion-barrier-helper.patch
selftests-mm-add-order-parameterized-khugepaged-collapse-cases.patch
selftests-mm-parameterize-the-mixed-source-collapse-case-by-source-order.patch
selftests-mm-cover-a-shared-source-collapse-write-race.patch
selftests-mm-run-every-supported-collapse-order-by-default.patch
selftests-mm-check-that-one-khugepaged-pass-collapses-one-window.patch
selftests-mm-add-khugepaged-race-harness.patch
selftests-mm-race-the-collapse-of-windows-with-holes.patch
selftests-mm-add-memory-pressure-threads-to-the-khugepaged-race-harness.patch
selftests-mm-zap-whole-pte-tables-in-the-khugepaged-race-harness.patch