perf_event_open: improve the memory leak detection

The goal is to add more robust memory leak detection by periodically
sampling memory availability during the test run and checking for
significant decreases in available memory.

To avoid false postive:
  perf_event_open03.c:95: TFAIL: Likely kernel memory leak detected

Signed-off-by: Li Wang <[email protected]>
Reviewed-by: Martin Doucha <[email protected]>

testcases/kernel/syscalls/perf_event_open/perf_event_open03.c

@@ -77,22 +77,41 @@ static void check_progress(int i)
 
 static void run(void)
 {
-	long diff;
-	int i;
+	long diff, diff_total, mem_avail, mem_avail_prev;
+	int i, sample;
 
-	diff = SAFE_READ_MEMINFO("MemAvailable:");
+	sample = 0;
+	diff_total = 0;
+
+	mem_avail_prev = SAFE_READ_MEMINFO("MemAvailable:");
 	tst_timer_start(CLOCK_MONOTONIC);
 
 	/* leak about 100MB of RAM */
 	for (i = 0; i < iterations; i++) {
 		ioctl(fd, PERF_EVENT_IOC_SET_FILTER, "filter,0/0@abcd");
 		check_progress(i);
-	}
 
-	diff -= SAFE_READ_MEMINFO("MemAvailable:");
+		/*
+		 * Every 1200000 iterations, calculate the difference in memory
+		 * availability. If the difference is greater than 20 * 1024 (20MB),
+		 * increment the sample counter and log the event.
+		 */
+		if ((i % 1200000) == 0) {
+			mem_avail = SAFE_READ_MEMINFO("MemAvailable:");
+			diff = mem_avail_prev - mem_avail;
+			diff_total += diff;
+
+			if (diff > 20 * 1024) {
+				sample++;
+				tst_res(TINFO, "MemAvailable decreased by %ld kB at iteration %d", diff, i);
+			}
+
+			mem_avail_prev = mem_avail;
+		}
+	}
 
-	if (diff > 50 * 1024)
-		tst_res(TFAIL, "Likely kernel memory leak detected");
+	if ((sample > 5) || (diff_total > 100 * 1024))
+		tst_res(TFAIL, "Likely kernel memory leak detected, total decrease: %ld kB", diff_total);
 	else
 		tst_res(TPASS, "No memory leak found");
 }