[PATCH v5 04/19] selftests/mm: skip khugepaged page cache cases without a PMD folio

[Kiryl Shutsemau]

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

The page cache caps folio order at MAX_PAGECACHE_ORDER, which is below the
PMD order on arm64 with 64K pages, where a PMD is 512M.  A PMD-sized page
cache folio is impossible there, so the kernel refuses these collapses:
MADV_COLLAPSE answers -EINVAL and khugepaged passes over the range.  Four
shmem cases ask for a PMD-sized folio anyway, fail, and the run bails out
in the middle.

Skip the shmem and file mem types where the cap is below the PMD order.

The cap is not shmem-specific: it applies to every file folio.  Add
thp_file_supported_orders() to read the orders the page cache allows.

Anonymous collapse is unaffected: its orders are not capped this way.

Assisted-by: LLM
Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxx>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
---
 .../testing/selftests/mm/hugepage_settings.h  |  9 +++++++++
 tools/testing/selftests/mm/khugepaged.c       | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/tools/testing/selftests/mm/hugepage_settings.h b/tools/testing/selftests/mm/hugepage_settings.h
index 726c73c43c05..a1d12e2ffd62 100644
--- a/tools/testing/selftests/mm/hugepage_settings.h
+++ b/tools/testing/selftests/mm/hugepage_settings.h
@@ -87,6 +87,15 @@ void thp_set_read_ahead_path(char *path);
 unsigned long thp_supported_orders(void);
 unsigned long thp_shmem_supported_orders(void);
 
+/*
+ * The per-order shmem_enabled attribute is created for the orders the page
+ * cache can hold, not just for shmem, so it answers for regular files too.
+ */
+static inline unsigned long thp_file_supported_orders(void)
+{
+	return thp_shmem_supported_orders();
+}
+
 bool thp_available(void);
 bool thp_is_enabled(void);
 
diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
index 48e0040d53b4..73bf07c39145 100644
--- a/tools/testing/selftests/mm/khugepaged.c
+++ b/tools/testing/selftests/mm/khugepaged.c
@@ -1353,6 +1353,25 @@ int main(int argc, char **argv)
 
 	setbuf(stdout, NULL);
 
+	/*
+	 * Without a PMD-order page cache folio the kernel refuses these
+	 * collapses, so there is nothing to test.
+	 */
+	if (!(thp_file_supported_orders() & (1UL << hpage_pmd_order))) {
+		if (shmem_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping shmem\n");
+			shmem_ops = NULL;
+		}
+		if (read_only_file_ops) {
+			ksft_print_msg("no PMD-order page cache folio: skipping file\n");
+			read_only_file_ops = NULL;
+			read_write_file_read_ops = NULL;
+			read_write_file_write_ops = NULL;
+		}
+		if (!anon_ops && !shmem_ops && !read_only_file_ops)
+			ksft_exit_skip("No mem_type left to run\n");
+	}
+
 	default_settings.khugepaged.max_ptes_none = hpage_pmd_nr - 1;
 	default_settings.khugepaged.max_ptes_swap = hpage_pmd_nr / 8;
 	default_settings.khugepaged.max_ptes_shared = hpage_pmd_nr / 2;
-- 
2.54.0