selftests/mm: put general ksm operation into vm_util

Patch series "test that rmap behaves as expected", v4.

As David suggested, currently we don't have a high level test case to
verify the behavior of rmap. This patch set introduce the verification
on rmap by migration.

Patch 1 is a preparation to move ksm related operations into vm_util.
Patch 2 is the new test case for rmap.

Currently it covers following four scenarios:

  * anonymous page
  * shmem page
  * pagecache page
  * ksm page


This patch (of 2):

There are some general ksm operations could be used by other related
test cases. Put them into vm_util for common use.

This is a preparation patch for later use.

Link: https://lkml.kernel.org/r/20250819080047.10063-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20250819080047.10063-2-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 123 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 741fc129313d..56e9bd541edd 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -578,3 +578,126 @@ bool detect_huge_zeropage(void)
 	close(fd);
 	return enabled;
 }
+
+long ksm_get_self_zero_pages(void)
+{
+	int proc_self_ksm_stat_fd;
+	char buf[200];
+	char *substr_ksm_zero;
+	size_t value_pos;
+	ssize_t read_size;
+
+	proc_self_ksm_stat_fd = open("/proc/self/ksm_stat", O_RDONLY);
+	if (proc_self_ksm_stat_fd < 0)
+		return -errno;
+
+	read_size = pread(proc_self_ksm_stat_fd, buf, sizeof(buf) - 1, 0);
+	close(proc_self_ksm_stat_fd);
+	if (read_size < 0)
+		return -errno;
+
+	buf[read_size] = 0;
+
+	substr_ksm_zero = strstr(buf, "ksm_zero_pages");
+	if (!substr_ksm_zero)
+		return 0;
+
+	value_pos = strcspn(substr_ksm_zero, "0123456789");
+	return strtol(substr_ksm_zero + value_pos, NULL, 10);
+}
+
+long ksm_get_self_merging_pages(void)
+{
+	int proc_self_ksm_merging_pages_fd;
+	char buf[10];
+	ssize_t ret;
+
+	proc_self_ksm_merging_pages_fd = open("/proc/self/ksm_merging_pages",
+						O_RDONLY);
+	if (proc_self_ksm_merging_pages_fd < 0)
+		return -errno;
+
+	ret = pread(proc_self_ksm_merging_pages_fd, buf, sizeof(buf) - 1, 0);
+	close(proc_self_ksm_merging_pages_fd);
+	if (ret <= 0)
+		return -errno;
+	buf[ret] = 0;
+
+	return strtol(buf, NULL, 10);
+}
+
+long ksm_get_full_scans(void)
+{
+	int ksm_full_scans_fd;
+	char buf[10];
+	ssize_t ret;
+
+	ksm_full_scans_fd = open("/sys/kernel/mm/ksm/full_scans", O_RDONLY);
+	if (ksm_full_scans_fd < 0)
+		return -errno;
+
+	ret = pread(ksm_full_scans_fd, buf, sizeof(buf) - 1, 0);
+	close(ksm_full_scans_fd);
+	if (ret <= 0)
+		return -errno;
+	buf[ret] = 0;
+
+	return strtol(buf, NULL, 10);
+}
+
+int ksm_use_zero_pages(void)
+{
+	int ksm_use_zero_pages_fd;
+	ssize_t ret;
+
+	ksm_use_zero_pages_fd = open("/sys/kernel/mm/ksm/use_zero_pages", O_RDWR);
+	if (ksm_use_zero_pages_fd < 0)
+		return -errno;
+
+	ret = write(ksm_use_zero_pages_fd, "1", 1);
+	close(ksm_use_zero_pages_fd);
+	return ret == 1 ? 0 : -errno;
+}
+
+int ksm_start(void)
+{
+	int ksm_fd;
+	ssize_t ret;
+	long start_scans, end_scans;
+
+	ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
+	if (ksm_fd < 0)
+		return -errno;
+
+	/* Wait for two full scans such that any possible merging happened. */
+	start_scans = ksm_get_full_scans();
+	if (start_scans < 0) {
+		close(ksm_fd);
+		return start_scans;
+	}
+	ret = write(ksm_fd, "1", 1);
+	close(ksm_fd);
+	if (ret != 1)
+		return -errno;
+	do {
+		end_scans = ksm_get_full_scans();
+		if (end_scans < 0)
+			return end_scans;
+	} while (end_scans < start_scans + 2);
+
+	return 0;
+}
+
+int ksm_stop(void)
+{
+	int ksm_fd;
+	ssize_t ret;
+
+	ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
+	if (ksm_fd < 0)
+		return -errno;
+
+	ret = write(ksm_fd, "2", 1);
+	close(ksm_fd);
+	return ret == 1 ? 0 : -errno;
+}