[JVM] Fix maximum/total memory calculation (#3125)

Fixes #2609

Author: the-thing

metrics-jvm/src/main/java/com/codahale/metrics/jvm/MemoryUsageGaugeSet.java

@@ -47,8 +47,8 @@ public Map<String, Metric> getMetrics() {
                 mxBean.getNonHeapMemoryUsage().getInit());
         gauges.put("total.used", (Gauge<Long>) () -> mxBean.getHeapMemoryUsage().getUsed() +
                 mxBean.getNonHeapMemoryUsage().getUsed());
-        gauges.put("total.max", (Gauge<Long>) () -> mxBean.getHeapMemoryUsage().getMax() +
-                mxBean.getNonHeapMemoryUsage().getMax());
+        gauges.put("total.max", (Gauge<Long>) () -> mxBean.getNonHeapMemoryUsage().getMax() == -1 ?
+                -1 : mxBean.getHeapMemoryUsage().getMax() + mxBean.getNonHeapMemoryUsage().getMax());
         gauges.put("total.committed", (Gauge<Long>) () -> mxBean.getHeapMemoryUsage().getCommitted() +
                 mxBean.getNonHeapMemoryUsage().getCommitted());
 
@@ -72,7 +72,7 @@ protected Ratio getRatio() {
             @Override
             protected Ratio getRatio() {
                 final MemoryUsage usage = mxBean.getNonHeapMemoryUsage();
-                return Ratio.of(usage.getUsed(), usage.getMax());
+                return Ratio.of(usage.getUsed(), usage.getMax() == -1 ? usage.getCommitted() : usage.getMax());
             }
         });
 

metrics-jvm/src/test/java/com/codahale/metrics/jvm/MemoryUsageGaugeSetTest.java

@@ -130,6 +130,16 @@ public void hasAGaugeForTotalMax() {
                 .isEqualTo(44L);
     }
 
+    @Test
+    public void hasAGaugeForTotalMaxWhenNonHeapMaxUndefined() {
+        when(nonHeap.getMax()).thenReturn(-1L);
+
+        final Gauge gauge = (Gauge) gauges.getMetrics().get("total.max");
+
+        assertThat(gauge.getValue())
+                .isEqualTo(-1L);
+    }
+
     @Test
     public void hasAGaugeForHeapCommitted() {
         final Gauge gauge = (Gauge) gauges.getMetrics().get("heap.committed");
@@ -210,6 +220,15 @@ public void hasAGaugeForNonHeapUsage() {
                 .isEqualTo(0.75);
     }
 
+    @Test
+    public void hasAGaugeForNonHeapUsageWhenNonHeapMaxUndefined() {
+        when(nonHeap.getMax()).thenReturn(-1L);
+        final Gauge gauge = (Gauge) gauges.getMetrics().get("non-heap.usage");
+
+        assertThat(gauge.getValue())
+                .isEqualTo(3.0);
+    }
+
     @Test
     public void hasAGaugeForMemoryPoolUsage() {
         final Gauge gauge = (Gauge) gauges.getMetrics().get("pools.Big-Pool.usage");