修复mem计算逻辑

sys/src/main/java/com/alibaba/nacos/sys/env/EnvUtil.java

@@ -328,7 +328,7 @@ public static float getCpu() {
 
     public static float getMem() {
         return (float) (1
-                - OperatingSystemBeanManager.getFreePhysicalMem() / OperatingSystemBeanManager.getTotalPhysicalMem());
+                - (double) OperatingSystemBeanManager.getFreePhysicalMem() / (double) OperatingSystemBeanManager.getTotalPhysicalMem());
     }
 
     public static String getConfPath() {

sys/src/test/java/com/alibaba/nacos/sys/env/EnvUtilTest.java

@@ -0,0 +1,36 @@
+package com.alibaba.nacos.sys.env;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.MockedStatic;
+import org.mockito.Mockito;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class EnvUtilTest {
+
+    MockedStatic<OperatingSystemBeanManager> systemBeanManagerMocked;
+
+    @BeforeEach
+    void before() {
+        systemBeanManagerMocked = Mockito.mockStatic(OperatingSystemBeanManager.class);
+    }
+
+    @AfterEach
+    void after() {
+        if (!systemBeanManagerMocked.isClosed()) {
+            systemBeanManagerMocked.close();
+        }
+    }
+
+    @Test
+    public void test() {
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getFreePhysicalMem()).thenReturn(123l);
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getTotalPhysicalMem()).thenReturn(2048l);
+        assertEquals(EnvUtil.getMem(), 1 - ((double) 123 / (double) 2048));
+
+        systemBeanManagerMocked.when(() -> OperatingSystemBeanManager.getFreePhysicalMem()).thenReturn(0l);
+        assertEquals(EnvUtil.getMem(), 1 - ((double) 0 / (double) 2048));
+    }
+}