8272318: Improve performance of HeapDumpAllTest

Backport-of: 73da66ffb707abf6dc38368a12e337d52597de25

Author: shipilev

test/hotspot/jtreg/serviceability/dcmd/gc/HeapDumpAllTest.java

@@ -21,6 +21,10 @@
  * questions.
  */
 
+import java.io.IOException;
+
+import jdk.test.lib.dcmd.CommandExecutor;
+
 /*
  * @test
  * @summary Test of diagnostic command GC.heap_dump -all=true
@@ -37,6 +41,14 @@ public HeapDumpAllTest() {
         heapDumpArgs = "-all=true";
     }
 
+    @Override
+    public void run(CommandExecutor executor, boolean overwrite) throws IOException {
+        // Trigger gc by hand, so the created heap dump isnt't too large and
+        // takes too long to parse.
+        System.gc();
+        super.run(executor, overwrite);
+    }
+
     /* See HeapDumpTest for test cases */
 }