Add mallocTrim command to vmTool

Author: kkHAIKE

arthas-vmtool/src/main/java/arthas/VmTool.java

@@ -116,4 +116,10 @@ public Class<?>[] getAllLoadedClasses() {
         return getAllLoadedClasses0(Class.class);
     }
 
+    @Override
+    public boolean mallocTrim() {
+        return mallocTrim0();
+    }
+
+    private static synchronized native boolean mallocTrim0();
 }

arthas-vmtool/src/main/java/arthas/VmToolMXBean.java

@@ -57,4 +57,9 @@ public interface VmToolMXBean {
      * 获取所有已加载的类
      */
     public Class<?>[] getAllLoadedClasses();
+
+    /**
+     * glibc 释放空闲内存
+     */
+    public boolean mallocTrim();
 }

arthas-vmtool/src/main/native/src/jni-library.cpp

@@ -4,6 +4,9 @@
 #include <jvmti.h>
 #include "arthas_VmTool.h" // under target/native/javah/
 
+#ifdef __GLIBC__
+#include <malloc.h>
+#endif
 
 static jvmtiEnv *jvmti;
 static jlong tagCounter = 0;
@@ -204,4 +207,16 @@ JNIEXPORT jobjectArray JNICALL Java_arthas_VmTool_getAllLoadedClasses0
     }
     jvmti->Deallocate(reinterpret_cast<unsigned char *>(classes));
     return array;
-}
+}
+
+
+extern "C"
+JNIEXPORT jboolean JNICALL Java_arthas_VmTool_mallocTrim
+        (JNIEnv *env, jclass thisClass) {
+#ifdef __GLIBC__
+    if (!::malloc_trim(0)) {
+        return JNI_FALSE;
+    }
+#endif
+    return JNI_TRUE;
+}

core/src/main/java/com/taobao/arthas/core/command/monitor200/VmToolCommand.java

@@ -157,7 +157,7 @@ public void setThreadId(int threadId) {
     }
 
     public enum VmToolAction {
-        getInstances, forceGc, interruptThread
+        getInstances, forceGc, interruptThread, mallocTrim
     }
 
     @Override
@@ -238,6 +238,11 @@ public void process(final CommandProcess process) {
                 process.write("\n");
                 process.end();
 
+                return;
+            } else if (VmToolAction.mallocTrim.equals(action)) {
+                boolean result = vmToolInstance().mallocTrim();
+                process.write("\n");
+                process.end(result ? 0 : -1, "mallocTrim result: " + result);
                 return;
             }