8253727: [cgroups v2] Memory and swap limits reported incorrectly

Account for interface files for swap and memory being reported independently.
The cgroup v1-like value is now reported by adding the memory.max value to
the memory.swap.max value, and memory.current and memory.swap.current
respectively.

Reviewed-by: bobv, shade

src/java.base/linux/classes/jdk/internal/platform/cgroupv2/CgroupV2Subsystem.java

@@ -274,15 +274,37 @@ public class CgroupV2Subsystem implements CgroupSubsystem {
         return CgroupV2SubsystemController.getLongEntry(unified, "memory.stat", "sock");
     }
 
+    /**
+     * Note that for cgroups v2 the actual limits set for swap and
+     * memory live in two different files, memory.swap.max and memory.max
+     * respectively. In order to properly report a cgroup v1 like
+     * compound value we need to sum the two values. Setting a swap limit
+     * without also setting a memory limit is not allowed.
+     */
     @Override
     public long getMemoryAndSwapLimit() {
         String strVal = CgroupSubsystemController.getStringValue(unified, "memory.swap.max");
-        return limitFromString(strVal);
+        long swapLimit = limitFromString(strVal);
+        if (swapLimit >= 0) {
+            long memoryLimit = getMemoryLimit();
+            assert memoryLimit >= 0;
+            return memoryLimit + swapLimit;
+        }
+        return swapLimit;
     }
 
+    /**
+     * Note that for cgroups v2 the actual values set for swap usage and
+     * memory usage live in two different files, memory.current and memory.swap.current
+     * respectively. In order to properly report a cgroup v1 like
+     * compound value we need to sum the two values. Setting a swap limit
+     * without also setting a memory limit is not allowed.
+     */
     @Override
     public long getMemoryAndSwapUsage() {
-        return getLongVal("memory.swap.current");
+        long swapUsage = getLongVal("memory.swap.current");
+        long memoryUsage = getMemoryUsage();
+        return memoryUsage + swapUsage;
     }
 
     @Override