selftests: vm: add KSM unmerge test

Add check_ksm_unmerge() function to verify that KSM is properly unmerging
shared pages.  For this, two duplicate pages are merged first and then
their contents are modified.  Since they are not identical anymore, the
pages must be unmerged and the number of merged pages has to be 0.  The
test is run as follows: ./ksm_tests -U

Link: https://lkml.kernel.org/r/c0f55420440d704d5b094275b4365aa1b2ad46b5.1626252248.git.zhansayabagdaulet@gmail.comSigned-off-by: Zhansaya Bagdauletkyzy <zhansayabagdaulet@gmail.com>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/ksm_tests.c

@@ -23,6 +23,11 @@ struct ksm_sysfs {
 	unsigned long use_zero_pages;
 };
 
+enum ksm_test_name {
+	CHECK_KSM_MERGE,
+	CHECK_KSM_UNMERGE
+};
+
 static int ksm_write_sysfs(const char *file_path, unsigned long val)
 {
 	FILE *f = fopen(file_path, "w");
@@ -75,7 +80,12 @@ static int str_to_prot(char *prot_str)
 
 static void print_help(void)
 {
-	printf("usage: ksm_tests [-h] [-a prot] [-p page_count] [-l timeout]\n");
+	printf("usage: ksm_tests [-h] <test type> [-a prot] [-p page_count] [-l timeout]\n");
+
+	printf("Supported <test type>:\n"
+	       " -M (page merging)\n"
+	       " -U (page unmerging)\n\n");
+
 	printf(" -a: specify the access protections of pages.\n"
 	       "     <prot> must be of the form [rwx].\n"
 	       "     Default: %s\n", KSM_PROT_STR_DEFAULT);
@@ -239,6 +249,46 @@ static int check_ksm_merge(int mapping, int prot, long page_count, int timeout,
 	return KSFT_FAIL;
 }
 
+static int check_ksm_unmerge(int mapping, int prot, int timeout, size_t page_size)
+{
+	void *map_ptr;
+	struct timespec start_time;
+	int page_count = 2;
+
+	if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
+		perror("clock_gettime");
+		return KSFT_FAIL;
+	}
+
+	/* fill pages with the same data and merge them */
+	map_ptr = allocate_memory(NULL, prot, mapping, '*', page_size * page_count);
+	if (!map_ptr)
+		return KSFT_FAIL;
+
+	if (ksm_merge_pages(map_ptr, page_size * page_count, start_time, timeout))
+		goto err_out;
+
+	/* change 1 byte in each of the 2 pages -- KSM must automatically unmerge them */
+	memset(map_ptr, '-', 1);
+	memset(map_ptr + page_size, '+', 1);
+
+	/* get at least 1 scan, so KSM can detect that the pages were modified */
+	if (ksm_do_scan(1, start_time, timeout))
+		goto err_out;
+
+	/* check that unmerging was successful and 0 pages are currently merged */
+	if (assert_ksm_pages_count(0)) {
+		printf("OK\n");
+		munmap(map_ptr, page_size * page_count);
+		return KSFT_PASS;
+	}
+
+err_out:
+	printf("Not OK\n");
+	munmap(map_ptr, page_size * page_count);
+	return KSFT_FAIL;
+}
+
 int main(int argc, char *argv[])
 {
 	int ret, opt;
@@ -247,8 +297,9 @@ int main(int argc, char *argv[])
 	long page_count = KSM_PAGE_COUNT_DEFAULT;
 	size_t page_size = sysconf(_SC_PAGESIZE);
 	struct ksm_sysfs ksm_sysfs_old;
+	int test_name = CHECK_KSM_MERGE;
 
-	while ((opt = getopt(argc, argv, "ha:p:l:")) != -1) {
+	while ((opt = getopt(argc, argv, "ha:p:l:MU")) != -1) {
 		switch (opt) {
 		case 'a':
 			prot = str_to_prot(optarg);
@@ -270,6 +321,11 @@ int main(int argc, char *argv[])
 		case 'h':
 			print_help();
 			break;
+		case 'M':
+			break;
+		case 'U':
+			test_name = CHECK_KSM_UNMERGE;
+			break;
 		default:
 			return KSFT_FAIL;
 		}
@@ -294,8 +350,16 @@ int main(int argc, char *argv[])
 	    ksm_write_sysfs(KSM_FP("pages_to_scan"), page_count))
 		return KSFT_FAIL;
 
-	ret = check_ksm_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count, ksm_scan_limit_sec,
-			      page_size);
+	switch (test_name) {
+	case CHECK_KSM_MERGE:
+		ret = check_ksm_merge(MAP_PRIVATE | MAP_ANONYMOUS, prot, page_count,
+				      ksm_scan_limit_sec, page_size);
+		break;
+	case CHECK_KSM_UNMERGE:
+		ret = check_ksm_unmerge(MAP_PRIVATE | MAP_ANONYMOUS, prot, ksm_scan_limit_sec,
+					page_size);
+		break;
+	}
 
 	if (ksm_restore(&ksm_sysfs_old)) {
 		printf("Cannot restore default tunables\n");

tools/testing/selftests/vm/run_vmtests.sh

@@ -380,7 +380,23 @@ fi
 echo "-------------------------------------------------------"
 echo "running KSM MADV_MERGEABLE test with 10 identical pages"
 echo "-------------------------------------------------------"
-./ksm_tests -p 10
+./ksm_tests -M -p 10
+ret_val=$?
+
+if [ $ret_val -eq 0 ]; then
+	echo "[PASS]"
+elif [ $ret_val -eq $ksft_skip ]; then
+	 echo "[SKIP]"
+	 exitcode=$ksft_skip
+else
+	echo "[FAIL]"
+	exitcode=1
+fi
+
+echo "------------------------"
+echo "running KSM unmerge test"
+echo "------------------------"
+./ksm_tests -U
 ret_val=$?
 
 if [ $ret_val -eq 0 ]; then