swapping01: make use of remaining runtime in test looping

Here go with default to 10 minutes for max_runtime. At the same time limit
the loop that waits for the swap usage to settle to run for a reminder
of max_runtime/2 instead of the hardcoded 30 seconds.

This fix can significantly improve timeouts on slower systems:

  # free -h
                total        used        free      shared  buff/cache   available
  Mem:          2.9Gi       1.1Gi       1.1Gi        20Mi       732Mi       1.5Gi
  Swap:         2.0Gi          0B       2.0Gi

  # time ./swapping01
  tst_kconfig.c:82: TINFO: Parsing kernel config '/boot/config-4.18.0-309.el8.x86_64+debug'
  tst_test.c:1528: TINFO: Timeout per run is 0h 02m 00s
  swapping01.c:110: TINFO: available physical memory: 1545 MB
  swapping01.c:113: TINFO: try to allocate: 2008 MB
  swapping01.c:152: TPASS: no heavy swapping detected, 218 MB swapped.
  ...

  real    0m34.241s
  user    0m0.386s
  sys     0m16.040s

Co-developed-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Li Wang <liwang@redhat.com>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>

testcases/kernel/mem/swapping/swapping01.c

@@ -58,6 +58,7 @@ static long swap_free_init;
 static long mem_over;
 static long mem_over_max;
 static pid_t pid;
+static unsigned int start_runtime;
 
 static void test_swapping(void)
 {
@@ -67,6 +68,8 @@ static void test_swapping(void)
 	FILE *file;
 	char line[PATH_MAX];
 
+	start_runtime = tst_remaining_runtime();
+
 	file = SAFE_FOPEN("/proc/swaps", "r");
 	while (fgets(line, sizeof(line), file)) {
 		if (strstr(line, "/dev/zram")) {
@@ -122,7 +125,7 @@ static void do_alloc(int allow_raise)
 
 static void check_swapping(void)
 {
-	int status, i;
+	int status;
 	long swap_free_now, swapped;
 
 	/* wait child stop */
@@ -131,14 +134,14 @@ static void check_swapping(void)
 		tst_brk(TBROK, "child was not stopped.");
 
 	/* Still occupying memory, loop for a while */
-	i = 0;
-	while (i < 30) {
+	while (tst_remaining_runtime() > start_runtime/2) {
 		swap_free_now = SAFE_READ_MEMINFO("SwapFree:");
 		sleep(1);
-		if (labs(swap_free_now - SAFE_READ_MEMINFO("SwapFree:")) < 10)
+		long diff = labs(swap_free_now - SAFE_READ_MEMINFO("SwapFree:"));
+		if (diff < 10)
 			break;
 
-		i++;
+		tst_res(TINFO, "SwapFree difference %li", diff);
 	}
 
 	swapped = SAFE_READ_PROC_STATUS(pid, "VmSwap:");
@@ -159,6 +162,7 @@ static struct tst_test test = {
 	.needs_root = 1,
 	.forks_child = 1,
 	.min_mem_avail = 10,
+	.max_runtime = 600,
 	.test_all = test_swapping,
 	.needs_kconfigs = (const char *[]) {
 		"CONFIG_SWAP=y",