server: Set free memory to zero if greater than total memory (#4571)

Fixes #4566

Sets `memoryintfreekbs` to zero if it is greater than `memorykbs`. Caused by KVM returning the RSS memory of the process running the VM rather than the free memory inside the VM.

Co-authored-by: dahn <daan.hoogland@gmail.com>

Author: davidjumani

api/src/main/java/org/apache/cloudstack/api/response/UserVmResponse.java

@@ -209,7 +209,7 @@ public class UserVmResponse extends BaseResponseWithTagInformation implements Co
     private Long memoryKBs;
 
     @SerializedName("memoryintfreekbs")
-    @Param(description = "the internal memory thats free in vm")
+    @Param(description = "the internal memory that's free in vm or zero if it can not be calculated")
     private Long memoryIntFreeKBs;
 
     @SerializedName("memorytargetkbs")

server/src/main/java/com/cloud/api/query/dao/UserVmJoinDaoImpl.java

@@ -222,8 +222,11 @@ public UserVmResponse newUserVmResponse(ResponseView view, String objectName, Us
                 userVmResponse.setDiskKbsWrite((long)vmStats.getDiskWriteKBs());
                 userVmResponse.setDiskIORead((long)vmStats.getDiskReadIOs());
                 userVmResponse.setDiskIOWrite((long)vmStats.getDiskWriteIOs());
-                userVmResponse.setMemoryKBs((long)vmStats.getMemoryKBs());
-                userVmResponse.setMemoryIntFreeKBs((long)vmStats.getIntFreeMemoryKBs());
+                long totalMemory = (long)vmStats.getMemoryKBs();
+                long freeMemory = (long)vmStats.getIntFreeMemoryKBs();
+                long correctedFreeMemory = freeMemory >= totalMemory ? 0 : freeMemory;
+                userVmResponse.setMemoryKBs(totalMemory);
+                userVmResponse.setMemoryIntFreeKBs(correctedFreeMemory);
                 userVmResponse.setMemoryTargetKBs((long)vmStats.getTargetMemoryKBs());
 
             }