[PATCH v10 3/3] ksm: add mremap selftests for ksm_rmap_walk

[xu.xin16]

From: xu xin <xu.xin16@xxxxxxxxxx>

The existing tools/testing/selftests/mm/rmap.c has already one testcase
for ksm_rmap_walk in TEST_F(migrate, ksm), which takes use of migration
of page from one NUMA node to another NUMA node. However, it just lacks
the scenario of mremapped VMAs.

We add the calling of mremap() and then trigger KSM to merge pages before
migrating, which is specifically to test an optimization which is
introduced by this patch ("ksm: Optimize rmap_walk_ksm by passing a
suitable address pgoff").

This test can reproduce the issue that Hugh points out at
https://lore.kernel.org/all/02e1b8df-d568-8cbb-b8f6-46d5476d9d75@xxxxxxxxxx/

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
---
 tools/testing/selftests/mm/rmap.c | 107 ++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/tools/testing/selftests/mm/rmap.c b/tools/testing/selftests/mm/rmap.c
index 53f2058b0ef2..ad731bdff4fa 100644
--- a/tools/testing/selftests/mm/rmap.c
+++ b/tools/testing/selftests/mm/rmap.c
@@ -430,4 +430,111 @@ TEST_F(migrate, ksm)
 	propagate_children(_metadata, data);
 }

+/*
+ * Check if All PFNs of the region are the same to the input pfn.
+ *
+ * @pagemap_fd: file descriptor of /proc/pid/pagemap.
+ * @region: the start address of the associated region.
+ * @nr_pages: the number of pages that the region contains.
+ * @pfn: the referenced PFN.
+ */
+static bool merged_to_pfn(int pagemap_fd, void *region, int nr_pages,
+		unsigned long pfn)
+{
+	int i;
+
+	for (i = 0; i < nr_pages; i++)
+		if (pagemap_get_pfn(pagemap_fd, region + i * getpagesize()) != pfn)
+			return false;
+
+	return true;
+}
+
+static int mremap_merge_and_migrate(struct global_data *data)
+{
+	int ret, pagemap_fd;
+	void *old_region;
+	void *new_region;
+	int nr_pages = 32;
+	unsigned long old_pfn;
+
+	/* Allocate exactly pages for the test */
+	data->mapsize = nr_pages * getpagesize();
+	data->region = mmap(NULL, data->mapsize, PROT_READ | PROT_WRITE,
+			    MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (data->region == MAP_FAILED)
+		ksft_exit_fail_perror("mmap failed");
+	memset(data->region, 0x77, data->mapsize);
+
+	/*
+	 * Mremap the second half region to the first half location (FIXED).
+	 */
+	old_region = data->region;
+	new_region = mremap(old_region + data->mapsize / 2, data->mapsize / 2,
+			    data->mapsize / 2, MREMAP_MAYMOVE | MREMAP_FIXED,
+			    old_region);
+	if (new_region == MAP_FAILED) {
+		ksft_print_msg("mremap failed: %s\n", strerror(errno));
+		return FAIL_ON_CHECK;
+	}
+	data->region = new_region;
+	data->mapsize /= 2;
+
+	/* madvise MADV_MERGABLE and merge these pages */
+	madvise(data->region, data->mapsize, MADV_MERGEABLE);
+	if (ksm_start() < 0)
+		return FAIL_ON_WORK;
+
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd == -1)
+		return FAIL_ON_CHECK;
+
+	*data->expected_pfn = pagemap_get_pfn(pagemap_fd, data->region);
+	if (*data->expected_pfn == -1ul)
+		return FAIL_ON_CHECK;
+	old_pfn = *data->expected_pfn;
+
+	/* Before migrating, check if All pages's PFN are the same */
+	if (!merged_to_pfn(pagemap_fd, data->region, nr_pages / 2,
+		 *data->expected_pfn)) {
+		ksft_print_msg("After KSM merging, PFNs are not the same\n");
+		return FAIL_ON_CHECK;
+	}
+
+	/* Attempt to migrate the merged KSM page */
+	ret = try_to_move_page(data->region);
+	if (ret) {
+		ksft_print_msg("migration of KSM page after mremap failed\n");
+		return FAIL_ON_CHECK;
+	}
+
+	/* After migrating, check if all PFN aren't the old */
+	*data->expected_pfn = pagemap_get_pfn(pagemap_fd, data->region);
+	if (*data->expected_pfn == -1ul || *data->expected_pfn == old_pfn)
+		return FAIL_ON_CHECK;
+
+	if (*data->expected_pfn == old_pfn ||
+		!merged_to_pfn(pagemap_fd, data->region, nr_pages / 2,
+		*data->expected_pfn)) {
+		ksft_print_msg("Bug migration: still old PFN or PFNs are not expected\n");
+		return FAIL_ON_CHECK;
+	}
+
+	return 0;
+}
+
+
+TEST_F(migrate, ksm_and_mremap)
+{
+	struct global_data *data = &self->data;
+
+	/* Skip if KSM is not available */
+	if (ksm_stop() < 0)
+		SKIP(return, "accessing \"/sys/kernel/mm/ksm/run\" failed");
+	if (ksm_get_full_scans() < 0)
+		SKIP(return, "accessing \"/sys/kernel/mm/ksm/full_scan\" failed");
+
+	ASSERT_EQ(mremap_merge_and_migrate(data), 0);
+}
+
 TEST_HARNESS_MAIN
-- 
2.25.1