--- a/hotspot/src/share/vm/prims/whitebox.cpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/prims/whitebox.cpp	Fri Oct 10 19:36:12 2014 +0000
@@ -335,7 +335,36 @@
   }
 WB_END
 
+WB_ENTRY(jboolean, WB_NMTChangeTrackingLevel(JNIEnv* env))
+  // Test that we can downgrade NMT levels but not upgrade them.
+  if (MemTracker::tracking_level() == NMT_off) {
+    MemTracker::transition_to(NMT_off);
+    return MemTracker::tracking_level() == NMT_off;
+  } else {
+    assert(MemTracker::tracking_level() == NMT_detail, "Should start out as detail tracking");
+    MemTracker::transition_to(NMT_summary);
+    assert(MemTracker::tracking_level() == NMT_summary, "Should be summary now");
 
+    // Can't go to detail once NMT is set to summary.
+    MemTracker::transition_to(NMT_detail);
+    assert(MemTracker::tracking_level() == NMT_summary, "Should still be summary now");
+
+    // Shutdown sets tracking level to minimal.
+    MemTracker::shutdown();
+    assert(MemTracker::tracking_level() == NMT_minimal, "Should be minimal now");
+
+    // Once the tracking level is minimal, we cannot increase to summary.
+    // The code ignores this request instead of asserting because if the malloc site
+    // table overflows in another thread, it tries to change the code to summary.
+    MemTracker::transition_to(NMT_summary);
+    assert(MemTracker::tracking_level() == NMT_minimal, "Should still be minimal now");
+
+    // Really can never go up to detail, verify that the code would never do this.
+    MemTracker::transition_to(NMT_detail);
+    assert(MemTracker::tracking_level() == NMT_minimal, "Should still be minimal now");
+    return MemTracker::tracking_level() == NMT_minimal;
+  }
+WB_END
 #endif // INCLUDE_NMT
 
 static jmethodID reflected_method_to_jmid(JavaThread* thread, JNIEnv* env, jobject method) {
@@ -962,6 +991,7 @@
   {CC"NMTReleaseMemory",    CC"(JJ)V",                (void*)&WB_NMTReleaseMemory   },
   {CC"NMTOverflowHashBucket", CC"(J)V",               (void*)&WB_NMTOverflowHashBucket},
   {CC"NMTIsDetailSupported",CC"()Z",                  (void*)&WB_NMTIsDetailSupported},
+  {CC"NMTChangeTrackingLevel", CC"()Z",               (void*)&WB_NMTChangeTrackingLevel},
 #endif // INCLUDE_NMT
   {CC"deoptimizeAll",      CC"()V",                   (void*)&WB_DeoptimizeAll     },
   {CC"deoptimizeMethod",   CC"(Ljava/lang/reflect/Executable;Z)I",

--- a/hotspot/src/share/vm/services/mallocTracker.cpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/mallocTracker.cpp	Fri Oct 10 19:36:12 2014 +0000
@@ -51,14 +51,6 @@
   return amount;
 }
 
-
-void MallocMemorySnapshot::reset() {
-  _tracking_header.reset();
-  for (int index = 0; index < mt_number_of_types; index ++) {
-    _malloc[index].reset();
-  }
-}
-
 // Make adjustment by subtracting chunks used by arenas
 // from total chunks to get total free chunck size
 void MallocMemorySnapshot::make_adjustment() {
@@ -116,14 +108,9 @@
 bool MallocTracker::transition(NMT_TrackingLevel from, NMT_TrackingLevel to) {
   assert(from != NMT_off, "Can not transition from off state");
   assert(to != NMT_off, "Can not transition to off state");
-  if (from == NMT_minimal) {
-    MallocMemorySummary::reset();
-  }
+  assert (from != NMT_minimal, "cannot transition from minimal state");
 
-  if (to == NMT_detail) {
-    assert(from == NMT_minimal || from == NMT_summary, "Just check");
-    return MallocSiteTable::initialize();
-  } else if (from == NMT_detail) {
+  if (from == NMT_detail) {
     assert(to == NMT_minimal || to == NMT_summary, "Just check");
     MallocSiteTable::shutdown();
   }

--- a/hotspot/src/share/vm/services/mallocTracker.hpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/mallocTracker.hpp	Fri Oct 10 19:36:12 2014 +0000
@@ -51,14 +51,6 @@
     DEBUG_ONLY(_peak_size  = 0;)
   }
 
-  // Reset counters
-  void reset() {
-    _size  = 0;
-    _count = 0;
-    DEBUG_ONLY(_peak_size = 0;)
-    DEBUG_ONLY(_peak_count = 0;)
-  }
-
   inline void allocate(size_t sz) {
     Atomic::add(1, (volatile MemoryCounterType*)&_count);
     if (sz > 0) {
@@ -124,11 +116,6 @@
     _arena.resize(sz);
   }
 
-  void reset() {
-    _malloc.reset();
-    _arena.reset();
-  }
-
   inline size_t malloc_size()  const { return _malloc.size(); }
   inline size_t malloc_count() const { return _malloc.count();}
   inline size_t arena_size()   const { return _arena.size();  }
@@ -176,8 +163,6 @@
     return s->by_type(mtThreadStack)->malloc_count();
   }
 
-  void reset();
-
   void copy_to(MallocMemorySnapshot* s) {
     s->_tracking_header = _tracking_header;
     for (int index = 0; index < mt_number_of_types; index ++) {
@@ -240,11 +225,6 @@
      return as_snapshot()->malloc_overhead()->size();
    }
 
-   // Reset all counters to zero
-   static void reset() {
-     as_snapshot()->reset();
-   }
-
   static MallocMemorySnapshot* as_snapshot() {
     return (MallocMemorySnapshot*)_snapshot;
   }

--- a/hotspot/src/share/vm/services/memBaseline.hpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/memBaseline.hpp	Fri Oct 10 19:36:12 2014 +0000
@@ -90,10 +90,6 @@
     _class_count(0) {
   }
 
-  ~MemBaseline() {
-    reset();
-  }
-
   bool baseline(bool summaryOnly = true);
 
   BaselineType baseline_type() const { return _baseline_type; }
@@ -169,8 +165,7 @@
   // reset the baseline for reuse
   void reset() {
     _baseline_type = Not_baselined;
-    _malloc_memory_snapshot.reset();
-    _virtual_memory_snapshot.reset();
+    // _malloc_memory_snapshot and _virtual_memory_snapshot are copied over.
     _class_count  = 0;
 
     _malloc_sites.clear();

--- a/hotspot/src/share/vm/services/memReporter.hpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/memReporter.hpp	Fri Oct 10 19:36:12 2014 +0000
@@ -96,20 +96,6 @@
   size_t                  _class_count;
 
  public:
-  // Report summary tracking data from global snapshots directly.
-  // This constructor is used for final reporting and hs_err reporting.
-  MemSummaryReporter(MallocMemorySnapshot* malloc_snapshot,
-    VirtualMemorySnapshot* vm_snapshot, outputStream* output,
-    size_t class_count = 0, size_t scale = K) :
-    MemReporterBase(output, scale),
-    _malloc_snapshot(malloc_snapshot),
-    _vm_snapshot(vm_snapshot) {
-    if (class_count == 0) {
-      _class_count = InstanceKlass::number_of_instance_classes();
-    } else {
-      _class_count = class_count;
-    }
-  }
   // This constructor is for normal reporting from a recent baseline.
   MemSummaryReporter(MemBaseline& baseline, outputStream* output,
     size_t scale = K) : MemReporterBase(output, scale),

--- a/hotspot/src/share/vm/services/memTracker.cpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/memTracker.cpp	Fri Oct 10 19:36:12 2014 +0000
@@ -144,11 +144,9 @@
 }
 
 
-// Shutdown can only be issued via JCmd, and NMT JCmd is serialized
-// by lock
+// Shutdown can only be issued via JCmd, and NMT JCmd is serialized by lock
 void MemTracker::shutdown() {
-  // We can only shutdown NMT to minimal tracking level if it is
-  // ever on.
+  // We can only shutdown NMT to minimal tracking level if it is ever on.
   if (tracking_level () > NMT_minimal) {
     transition_to(NMT_minimal);
   }
@@ -157,45 +155,36 @@
 bool MemTracker::transition_to(NMT_TrackingLevel level) {
   NMT_TrackingLevel current_level = tracking_level();
 
+  assert(level != NMT_off || current_level == NMT_off, "Cannot transition NMT to off");
+
   if (current_level == level) {
     return true;
   } else if (current_level > level) {
-    // Downgrade tracking level, we want to lower the tracking
-    // level first
+    // Downgrade tracking level, we want to lower the tracking level first
     _tracking_level = level;
     // Make _tracking_level visible immediately.
     OrderAccess::fence();
     VirtualMemoryTracker::transition(current_level, level);
     MallocTracker::transition(current_level, level);
-
-    if (level == NMT_minimal) _baseline.reset();
   } else {
-    VirtualMemoryTracker::transition(current_level, level);
-    MallocTracker::transition(current_level, level);
-
-    _tracking_level = level;
-    // Make _tracking_level visible immediately.
-    OrderAccess::fence();
+    // Upgrading tracking level is not supported and has never been supported.
+    // Allocating and deallocating malloc tracking structures is not thread safe and
+    // leads to inconsistencies unless a lot coarser locks are added.
   }
-
   return true;
 }
 
-void MemTracker::final_report(outputStream* output) {
-  assert(output != NULL, "No output stream");
-  if (tracking_level() >= NMT_summary) {
-    MallocMemorySnapshot* malloc_memory_snapshot =
-      MallocMemorySummary::as_snapshot();
-    malloc_memory_snapshot->make_adjustment();
-
-    VirtualMemorySnapshot* virtual_memory_snapshot =
-      VirtualMemorySummary::as_snapshot();
-
-    MemSummaryReporter rptr(malloc_memory_snapshot,
-      virtual_memory_snapshot, output);
-    rptr.report();
-    // shutdown NMT, the data no longer accurate
-    shutdown();
+void MemTracker::report(bool summary_only, outputStream* output) {
+ assert(output != NULL, "No output stream");
+  MemBaseline baseline;
+  if (baseline.baseline(summary_only)) {
+    if (summary_only) {
+      MemSummaryReporter rpt(baseline, output);
+      rpt.report();
+    } else {
+      MemDetailReporter rpt(baseline, output);
+      rpt.report();
+    }
   }
 }
 

--- a/hotspot/src/share/vm/services/memTracker.hpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/memTracker.hpp	Fri Oct 10 19:36:12 2014 +0000
@@ -70,6 +70,7 @@
   static inline void release_thread_stack(void* addr, size_t size) { }
 
   static void final_report(outputStream*) { }
+  static void error_report(outputStream*) { }
 };
 
 #else
@@ -270,13 +271,20 @@
   // other tools.
   static inline Mutex* query_lock() { return _query_lock; }
 
-  // Make a final report and shutdown.
-  // This function generates summary report without creating snapshots,
-  // to avoid additional memory allocation. It uses native memory summary
-  // counters, and makes adjustment to them, once the adjustment is made,
-  // the counters are no longer accurate. As the result, this function
-  // should only be used for final reporting before shutting down.
-  static void final_report(outputStream*);
+  // Make a final report or report for hs_err file.
+  static void error_report(outputStream* output) {
+    if (tracking_level() >= NMT_summary) {
+      report(true, output);  // just print summary for error case.
+    }
+   }
+
+  static void final_report(outputStream* output) {
+    NMT_TrackingLevel level = tracking_level();
+    if (level >= NMT_summary) {
+      report(level == NMT_summary, output);
+    }
+  }
+
 
   // Stored baseline
   static inline MemBaseline& get_baseline() {
@@ -291,6 +299,7 @@
 
  private:
   static NMT_TrackingLevel init_tracking_level();
+  static void report(bool summary_only, outputStream* output);
 
  private:
   // Tracking level

--- a/hotspot/src/share/vm/services/virtualMemoryTracker.cpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/virtualMemoryTracker.cpp	Fri Oct 10 19:36:12 2014 +0000
@@ -443,26 +443,28 @@
 bool VirtualMemoryTracker::walk_virtual_memory(VirtualMemoryWalker* walker) {
   assert(_reserved_regions != NULL, "Sanity check");
   ThreadCritical tc;
-  LinkedListNode<ReservedMemoryRegion>* head = _reserved_regions->head();
-  while (head != NULL) {
-    const ReservedMemoryRegion* rgn = head->peek();
-    if (!walker->do_allocation_site(rgn)) {
-      return false;
+  // Check that the _reserved_regions haven't been deleted.
+  if (_reserved_regions != NULL) {
+    LinkedListNode<ReservedMemoryRegion>* head = _reserved_regions->head();
+    while (head != NULL) {
+      const ReservedMemoryRegion* rgn = head->peek();
+      if (!walker->do_allocation_site(rgn)) {
+        return false;
+      }
+      head = head->next();
     }
-    head = head->next();
-  }
+   }
   return true;
 }
 
 // Transition virtual memory tracking level.
 bool VirtualMemoryTracker::transition(NMT_TrackingLevel from, NMT_TrackingLevel to) {
-  if (from == NMT_minimal) {
-    assert(to == NMT_summary || to == NMT_detail, "Just check");
-    VirtualMemorySummary::reset();
-  } else if (to == NMT_minimal) {
+  assert (from != NMT_minimal, "cannot convert from the lowest tracking level to anything");
+  if (to == NMT_minimal) {
     assert(from == NMT_summary || from == NMT_detail, "Just check");
     // Clean up virtual memory tracking data structures.
     ThreadCritical tc;
+    // Check for potential race with other thread calling transition
     if (_reserved_regions != NULL) {
       delete _reserved_regions;
       _reserved_regions = NULL;

--- a/hotspot/src/share/vm/services/virtualMemoryTracker.hpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/services/virtualMemoryTracker.hpp	Fri Oct 10 19:36:12 2014 +0000
@@ -62,11 +62,6 @@
     _committed -= sz;
   }
 
-  void reset() {
-    _reserved  = 0;
-    _committed = 0;
-  }
-
   inline size_t reserved()  const { return _reserved;  }
   inline size_t committed() const { return _committed; }
 };
@@ -123,12 +118,6 @@
     return amount;
   }
 
-  inline void reset() {
-    for (int index = 0; index < mt_number_of_types; index ++) {
-      _virtual_memory[index].reset();
-    }
-  }
-
   void copy_to(VirtualMemorySnapshot* s) {
     for (int index = 0; index < mt_number_of_types; index ++) {
       s->_virtual_memory[index] = _virtual_memory[index];
@@ -174,10 +163,6 @@
     as_snapshot()->copy_to(s);
   }
 
-  static inline void reset() {
-    as_snapshot()->reset();
-  }
-
   static VirtualMemorySnapshot* as_snapshot() {
     return (VirtualMemorySnapshot*)_snapshot;
   }

--- a/hotspot/src/share/vm/utilities/vmError.cpp	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/src/share/vm/utilities/vmError.cpp	Fri Oct 10 19:36:12 2014 +0000
@@ -740,7 +740,7 @@
 
   STEP(228, "(Native Memory Tracking)" )
      if (_verbose) {
-       MemTracker::final_report(st);
+       MemTracker::error_report(st);
      }
 
   STEP(230, "" )

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/test/runtime/NMT/ChangeTrackingLevel.java	Fri Oct 10 19:36:12 2014 +0000
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8059100
+ * @summary Test that you can decrease NMT tracking level but not increase it.
+ * @key nmt
+ * @library /testlibrary /testlibrary/whitebox
+ * @build ChangeTrackingLevel
+ * @run main ClassFileInstaller sun.hotspot.WhiteBox
+ *                              sun.hotspot.WhiteBox$WhiteBoxPermission
+ * @run main/othervm -Xbootclasspath/a:. -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:NativeMemoryTracking=detail ChangeTrackingLevel
+ */
+
+import com.oracle.java.testlibrary.*;
+import sun.hotspot.WhiteBox;
+
+public class ChangeTrackingLevel {
+
+    public static WhiteBox wb = WhiteBox.getWhiteBox();
+    public static void main(String args[]) throws Exception {
+        boolean testChangeLevel = wb.NMTChangeTrackingLevel();
+        if (testChangeLevel) {
+            System.out.println("NMT level change test passed.");
+        } else {
+            // it also fails if the VM asserts.
+            throw new RuntimeException("NMT level change test failed");
+        }
+    }
+};

--- a/hotspot/test/testlibrary/whitebox/sun/hotspot/WhiteBox.java	Thu Oct 09 16:41:28 2014 +0400
+++ b/hotspot/test/testlibrary/whitebox/sun/hotspot/WhiteBox.java	Fri Oct 10 19:36:12 2014 +0000
@@ -101,6 +101,7 @@
   public native void NMTOverflowHashBucket(long num);
   public native long NMTMallocWithPseudoStack(long size, int index);
   public native boolean NMTIsDetailSupported();
+  public native boolean NMTChangeTrackingLevel();
 
   // Compiler
   public native void    deoptimizeAll();