[PATCH v5 11/19] selftests/mm: add order-parameterized khugepaged collapse cases

[Kiryl Shutsemau]

From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>

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
Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
---
 tools/testing/selftests/mm/khugepaged.c | 212 ++++++++++++++++++++++++
 1 file changed, 212 insertions(+)

diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index e9bc8fe8a1f8..fb4efaf67c40 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -31,6 +31,8 @@ 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"
@@ -1207,6 +1209,198 @@ static void madvise_retracted_page_tables(struct collapse_context *c,
 	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");
@@ -1375,6 +1569,20 @@ 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);
 
 	/*
@@ -1425,6 +1633,10 @@ 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);
-- 
2.54.0