--- a/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.cpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.cpp	Tue Jun 30 19:00:14 2020 +0200
@@ -35,6 +35,7 @@
 #include "jfr/recorder/jfrRecorder.hpp"
 #include "jfr/recorder/repository/jfrChunkWriter.hpp"
 #include "jfr/recorder/service/jfrOptionSet.hpp"
+#include "jfr/recorder/storage/jfrEpochStorage.inline.hpp"
 #include "jfr/recorder/storage/jfrMemorySpace.inline.hpp"
 #include "jfr/recorder/storage/jfrStorageUtils.inline.hpp"
 #include "jfr/support/jfrKlassUnloading.hpp"
@@ -91,52 +92,46 @@
 }
 
 JfrCheckpointManager::JfrCheckpointManager(JfrChunkWriter& cw) :
-  _mspace(NULL),
+  _global_mspace(NULL),
+  _thread_local_mspace(NULL),
   _chunkwriter(cw) {}
 
 JfrCheckpointManager::~JfrCheckpointManager() {
   JfrTraceIdLoadBarrier::destroy();
   JfrTypeManager::destroy();
-  delete _mspace;
+  delete _global_mspace;
+  delete _thread_local_mspace;
 }
 
-static const size_t buffer_count = 2;
-static const size_t buffer_size = 512 * K;
+static const size_t global_buffer_prealloc_count = 2;
+static const size_t global_buffer_size = 512 * K;
 
-static JfrCheckpointMspace* allocate_mspace(size_t min_elem_size,
-                                            size_t free_list_cache_count_limit,
-                                            size_t cache_prealloc_count,
-                                            bool prealloc_to_free_list,
-                                            JfrCheckpointManager* mgr) {
-  return create_mspace<JfrCheckpointMspace, JfrCheckpointManager>(min_elem_size,
-                                                                  free_list_cache_count_limit,
-                                                                  cache_prealloc_count,
-                                                                  prealloc_to_free_list,
-                                                                  mgr);
-}
+static const size_t thread_local_buffer_prealloc_count = 16;
+static const size_t thread_local_buffer_size = 128;
 
 bool JfrCheckpointManager::initialize() {
-  assert(_mspace == NULL, "invariant");
-  _mspace = allocate_mspace(buffer_size, 0, 0, false, this); // post-pone preallocation
-  if (_mspace == NULL) {
+  assert(_global_mspace == NULL, "invariant");
+  _global_mspace =  create_mspace<JfrCheckpointMspace, JfrCheckpointManager>(global_buffer_size, 0, 0, false, this); // post-pone preallocation
+  if (_global_mspace == NULL) {
     return false;
   }
   // preallocate buffer count to each of the epoch live lists
-  for (size_t i = 0; i < buffer_count * 2; ++i) {
-    Buffer* const buffer = mspace_allocate(buffer_size, _mspace);
-    _mspace->add_to_live_list(buffer, i % 2 == 0);
+  for (size_t i = 0; i < global_buffer_prealloc_count * 2; ++i) {
+    Buffer* const buffer = mspace_allocate(global_buffer_size, _global_mspace);
+    _global_mspace->add_to_live_list(buffer, i % 2 == 0);
   }
-  assert(_mspace->free_list_is_empty(), "invariant");
+  assert(_global_mspace->free_list_is_empty(), "invariant");
+
+  assert(_thread_local_mspace == NULL, "invariant");
+  _thread_local_mspace = new JfrThreadLocalCheckpointMspace();
+  if (_thread_local_mspace == NULL || !_thread_local_mspace->initialize(thread_local_buffer_size,
+                                                                        JFR_MSPACE_UNLIMITED_CACHE_SIZE,
+                                                                        thread_local_buffer_prealloc_count)) {
+    return false;
+  }
   return JfrTypeManager::initialize() && JfrTraceIdLoadBarrier::initialize();
 }
 
-void JfrCheckpointManager::register_full(BufferPtr buffer, Thread* thread) {
-  // nothing here at the moment
-  assert(buffer != NULL, "invariant");
-  assert(buffer->acquired_by(thread), "invariant");
-  assert(buffer->retired(), "invariant");
-}
-
 #ifdef ASSERT
 static void assert_lease(const BufferPtr buffer) {
   assert(buffer != NULL, "invariant");
@@ -149,15 +144,28 @@
   assert(buffer->lease(), "invariant");
   assert(buffer->acquired_by_self(), "invariant");
 }
+
+static void assert_retired(const BufferPtr buffer, Thread* thread) {
+  assert(buffer != NULL, "invariant");
+  assert(buffer->acquired_by(thread), "invariant");
+  assert(buffer->retired(), "invariant");
+}
 #endif // ASSERT
 
-static BufferPtr lease(size_t size, JfrCheckpointMspace* mspace, size_t retry_count, Thread* thread, bool previous_epoch) {
+void JfrCheckpointManager::register_full(BufferPtr buffer, Thread* thread) {
+  DEBUG_ONLY(assert_retired(buffer, thread);)
+  // nothing here at the moment
+}
+
+BufferPtr JfrCheckpointManager::lease(Thread* thread, bool previous_epoch /* false */, size_t size /* 0 */) {
+  JfrCheckpointMspace* const mspace = instance()._global_mspace;
   assert(mspace != NULL, "invariant");
   static const size_t max_elem_size = mspace->min_element_size(); // min is max
   BufferPtr buffer;
   if (size <= max_elem_size) {
-    buffer = mspace_acquire_lease_with_retry(size, mspace, retry_count, thread, previous_epoch);
+    buffer = mspace_acquire_live(size, mspace, thread, previous_epoch);
     if (buffer != NULL) {
+      buffer->set_lease();
       DEBUG_ONLY(assert_lease(buffer);)
       return buffer;
     }
@@ -167,54 +175,70 @@
   return buffer;
 }
 
-static const size_t lease_retry = 100;
+const u1 thread_local_context = 1;
 
-BufferPtr JfrCheckpointManager::lease(Thread* thread, bool previous_epoch /* false */, size_t size /* 0 */) {
-  return ::lease(size, instance()._mspace, lease_retry, thread, previous_epoch);
+static bool is_thread_local(JfrBuffer* buffer) {
+  assert(buffer != NULL, "invariant");
+  return buffer->context() == thread_local_context;
 }
 
-bool JfrCheckpointManager::lookup(BufferPtr old) const {
-  assert(old != NULL, "invariant");
-  return !_mspace->in_current_epoch_list(old);
-}
-
-BufferPtr JfrCheckpointManager::lease(BufferPtr old, Thread* thread, size_t size /* 0 */) {
-  assert(old != NULL, "invariant");
-  return ::lease(size, instance()._mspace, lease_retry, thread, instance().lookup(old));
+static void retire(JfrBuffer* buffer) {
+  DEBUG_ONLY(assert_release(buffer);)
+  buffer->clear_lease();
+  buffer->set_retired();
 }
 
 /*
- * If the buffer was a lease, release back.
- *
  * The buffer is effectively invalidated for the thread post-return,
  * and the caller should take means to ensure that it is not referenced.
  */
-static void release(BufferPtr buffer, Thread* thread) {
+static void release(JfrBuffer* buffer) {
   DEBUG_ONLY(assert_release(buffer);)
-  buffer->clear_lease();
-  if (buffer->transient()) {
-    buffer->set_retired();
+  if (is_thread_local(buffer)) {
+    retire(buffer);
   } else {
+    buffer->clear_lease();
     buffer->release();
   }
 }
+BufferPtr JfrCheckpointManager::acquire_thread_local(size_t size, Thread* thread) {
+  assert(thread != NULL, "invariant");
+  JfrBuffer* const buffer = instance()._thread_local_mspace->acquire(size, thread);
+  assert(buffer != NULL, "invariant");
+  assert(buffer->free_size() >= size, "invariant");
+  buffer->set_context(thread_local_context);
+  assert(is_thread_local(buffer), "invariant");
+  buffer->set_lease();
+  return buffer;
+}
+
+BufferPtr JfrCheckpointManager::lease_thread_local(Thread* thread, size_t size /* 0 */) {
+  JfrBuffer* const buffer = acquire_thread_local(size, thread);
+  DEBUG_ONLY(assert_lease(buffer);)
+  return buffer;
+}
+
+BufferPtr JfrCheckpointManager::lease(BufferPtr old, Thread* thread, size_t size) {
+  assert(old != NULL, "invariant");
+  return is_thread_local(old) ? acquire_thread_local(size, thread) :
+                                lease(thread, instance()._global_mspace->in_previous_epoch_list(old), size);
+}
 
 BufferPtr JfrCheckpointManager::flush(BufferPtr old, size_t used, size_t requested, Thread* thread) {
   assert(old != NULL, "invariant");
   assert(old->lease(), "invariant");
   if (0 == requested) {
     // indicates a lease is being returned
-    release(old, thread);
+    release(old);
+    // signal completion of a new checkpoint
     set_constant_pending();
     return NULL;
   }
-  // migration of in-flight information
-  BufferPtr const new_buffer = lease(old, thread, used + requested);
-  if (new_buffer != NULL) {
-    migrate_outstanding_writes(old, new_buffer, used, requested);
-  }
-  release(old, thread);
-  return new_buffer; // might be NULL
+  BufferPtr new_buffer = lease(old, thread, used + requested);
+  assert(new_buffer != NULL, "invariant");
+  migrate_outstanding_writes(old, new_buffer, used, requested);
+  retire(old);
+  return new_buffer;
 }
 
 // offsets into the JfrCheckpointEntry
@@ -311,7 +335,7 @@
 
 typedef CheckpointWriteOp<JfrCheckpointManager::Buffer> WriteOperation;
 typedef MutexedWriteOp<WriteOperation> MutexedWriteOperation;
-typedef ReleaseOpWithExcision<JfrCheckpointMspace, JfrCheckpointMspace::LiveList> ReleaseOperation;
+typedef ReleaseWithExcisionOp<JfrCheckpointMspace, JfrCheckpointMspace::LiveList> ReleaseOperation;
 typedef CompositeOperation<MutexedWriteOperation, ReleaseOperation> WriteReleaseOperation;
 
 void JfrCheckpointManager::begin_epoch_shift() {
@@ -328,12 +352,13 @@
 
 size_t JfrCheckpointManager::write() {
   DEBUG_ONLY(JfrJavaSupport::check_java_thread_in_native(Thread::current()));
-  assert(_mspace->free_list_is_empty(), "invariant");
   WriteOperation wo(_chunkwriter);
   MutexedWriteOperation mwo(wo);
-  ReleaseOperation ro(_mspace, _mspace->live_list(true));
+  _thread_local_mspace->iterate(mwo, true); // previous epoch list
+  assert(_global_mspace->free_list_is_empty(), "invariant");
+  ReleaseOperation ro(_global_mspace, _global_mspace->live_list(true));
   WriteReleaseOperation wro(&mwo, &ro);
-  process_live_list(wro, _mspace, true);
+  process_live_list(wro, _global_mspace, true); // previous epoch list
   return wo.processed();
 }
 
@@ -344,10 +369,11 @@
   JfrTraceIdLoadBarrier::clear();
   clear_type_set();
   DiscardOperation discard_operation(mutexed); // mutexed discard mode
-  ReleaseOperation ro(_mspace, _mspace->live_list(true));
+  _thread_local_mspace->iterate(discard_operation, true); // previous epoch list
+  ReleaseOperation ro(_global_mspace, _global_mspace->live_list(true));
   DiscardReleaseOperation discard_op(&discard_operation, &ro);
-  assert(_mspace->free_list_is_empty(), "invariant");
-  process_live_list(discard_op, _mspace, true); // previous epoch list
+  assert(_global_mspace->free_list_is_empty(), "invariant");
+  process_live_list(discard_op, _global_mspace, true); // previous epoch list
   return discard_operation.elements();
 }
 
@@ -451,8 +477,9 @@
   if (is_constant_pending()) {
     WriteOperation wo(_chunkwriter);
     MutexedWriteOperation mwo(wo);
-    assert(_mspace->live_list_is_nonempty(), "invariant");
-    process_live_list(mwo, _mspace);
+    _thread_local_mspace->iterate(mwo); // current epoch list
+    assert(_global_mspace->live_list_is_nonempty(), "invariant");
+    process_live_list(mwo, _global_mspace); // current epoch list
   }
   return elements;
 }

--- a/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -26,14 +26,13 @@
 #define SHARE_JFR_RECORDER_CHECKPOINT_JFRCHECKPOINTMANAGER_HPP
 
 #include "jfr/recorder/storage/jfrBuffer.hpp"
+#include "jfr/recorder/storage/jfrEpochStorage.hpp"
 #include "jfr/recorder/storage/jfrMemorySpace.hpp"
 #include "jfr/recorder/storage/jfrMemorySpaceRetrieval.hpp"
 #include "jfr/utilities/jfrLinkedList.hpp"
 
 class JfrCheckpointManager;
 class JfrChunkWriter;
-class JfrSerializer;
-class JfrTypeManager;
 class Thread;
 
 struct JfrCheckpointEntry {
@@ -45,6 +44,7 @@
 };
 
 typedef JfrMemorySpace<JfrCheckpointManager, JfrMspaceRetrieval, JfrLinkedList<JfrBuffer>, JfrLinkedList<JfrBuffer>, true > JfrCheckpointMspace;
+typedef JfrEpochStorageHost<JfrBuffer, JfrMspaceRemoveRetrieval, true /* reclaim buffers eagerly*/ > JfrThreadLocalCheckpointMspace;
 
 //
 // Responsible for maintaining checkpoints and by implication types.
@@ -56,7 +56,8 @@
   typedef JfrCheckpointMspace::Node Buffer;
   typedef JfrCheckpointMspace::NodePtr BufferPtr;
  private:
-  JfrCheckpointMspace* _mspace;
+  JfrCheckpointMspace* _global_mspace;
+  JfrThreadLocalCheckpointMspace* _thread_local_mspace;
   JfrChunkWriter& _chunkwriter;
 
   JfrCheckpointManager(JfrChunkWriter& cw);
@@ -66,14 +67,16 @@
   bool initialize();
   static void destroy();
 
-  bool lookup(Buffer* old) const;
   static BufferPtr lease(Thread* thread, bool previous_epoch = false, size_t size = 0);
-  static BufferPtr lease(BufferPtr old, Thread* thread, size_t size = 0);
+  static BufferPtr lease(BufferPtr old, Thread* thread, size_t size);
+
+  static BufferPtr acquire_thread_local(size_t size, Thread* thread);
+  static BufferPtr lease_thread_local(Thread* thread, size_t size = 0);
+
   static BufferPtr flush(BufferPtr old, size_t used, size_t requested, Thread* thread);
 
   size_t clear();
   size_t write();
-  size_t flush();
   void notify_threads();
 
   size_t write_static_type_set(Thread* thread);
@@ -102,7 +105,6 @@
   friend class JfrCheckpointFlush;
   friend class JfrCheckpointWriter;
   friend class JfrSerializer;
-  friend class JfrStackTraceRepository;
   template <typename, template <typename> class, typename, typename, bool>
   friend class JfrMemorySpace;
 };

--- a/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointWriter.cpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointWriter.cpp	Tue Jun 30 19:00:14 2020 +0200
@@ -45,8 +45,8 @@
   }
 }
 
-JfrCheckpointWriter::JfrCheckpointWriter(Thread* thread, bool header /* true */, JfrCheckpointType type /* GENERIC */) :
-  JfrCheckpointWriterBase(JfrCheckpointManager::lease(thread), thread),
+JfrCheckpointWriter::JfrCheckpointWriter(Thread* thread, bool header /* true */, JfrCheckpointType type /* GENERIC */, bool global_lease /* true */) :
+  JfrCheckpointWriterBase(global_lease ? JfrCheckpointManager::lease(thread) : JfrCheckpointManager::lease_thread_local(thread), thread),
   _time(JfrTicks::now()),
   _offset(0),
   _count(0),

--- a/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointWriter.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointWriter.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -72,7 +72,7 @@
   JfrCheckpointWriter(bool previous_epoch, Thread* thread, JfrCheckpointType type = GENERIC);
  public:
   JfrCheckpointWriter(JfrCheckpointType type = GENERIC);
-  JfrCheckpointWriter(Thread* thread, bool header = true, JfrCheckpointType mode = GENERIC);
+  JfrCheckpointWriter(Thread* thread, bool header = true, JfrCheckpointType mode = GENERIC, bool global_lease = true);
   ~JfrCheckpointWriter();
   void write_type(JfrTypeId type_id);
   void write_count(u4 nof_entries);

--- a/src/hotspot/share/jfr/recorder/checkpoint/types/jfrTypeManager.cpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/checkpoint/types/jfrTypeManager.cpp	Tue Jun 30 19:00:14 2020 +0200
@@ -28,6 +28,7 @@
 #include "jfr/recorder/checkpoint/types/jfrType.hpp"
 #include "jfr/recorder/checkpoint/types/jfrTypeManager.hpp"
 #include "jfr/recorder/jfrRecorder.hpp"
+#include "jfr/support/jfrThreadLocal.hpp"
 #include "jfr/utilities/jfrIterator.hpp"
 #include "jfr/utilities/jfrLinkedList.inline.hpp"
 #include "memory/resourceArea.hpp"
@@ -105,7 +106,7 @@
   ResourceMark rm(t);
   HandleMark hm(t);
   JfrThreadConstant type_thread(t);
-  JfrCheckpointWriter writer(t, true, THREADS);
+  JfrCheckpointWriter writer(t, true, THREADS, false);
   writer.write_type(TYPE_THREAD);
   type_thread.serialize(writer);
   // create and install a checkpoint blob
@@ -115,12 +116,11 @@
 
 void JfrTypeManager::write_thread_checkpoint(Thread* t) {
   assert(t != NULL, "invariant");
-  ResourceMark rm(t);
-  HandleMark hm(t);
-  JfrThreadConstant type_thread(t);
-  JfrCheckpointWriter writer(t, true, THREADS);
-  writer.write_type(TYPE_THREAD);
-  type_thread.serialize(writer);
+  if (!t->jfr_thread_local()->has_thread_blob()) {
+    create_thread_blob(t);
+  }
+  JfrCheckpointWriter writer(t, false, THREADS, false);
+  t->jfr_thread_local()->thread_blob()->write(writer);
 }
 
 class SerializerRegistrationGuard : public StackObj {

--- a/src/hotspot/share/jfr/recorder/storage/jfrBuffer.cpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/storage/jfrBuffer.cpp	Tue Jun 30 19:00:14 2020 +0200
@@ -32,9 +32,10 @@
                          _identity(NULL),
                          _pos(NULL),
                          _top(NULL),
-                         _flags(0),
+                         _size(0),
                          _header_size(0),
-                         _size(0) {}
+                         _flags(0),
+                         _context(0) {}
 
 bool JfrBuffer::initialize(size_t header_size, size_t size) {
   assert(_next == NULL, "invariant");
@@ -52,7 +53,6 @@
 
 void JfrBuffer::reinitialize(bool exclusion /* false */) {
   acquire_critical_section_top();
-  assert(!lease(), "invariant");
   if (exclusion != excluded()) {
     // update
     if (exclusion) {
@@ -185,25 +185,25 @@
   EXCLUDED = 8
 };
 
-inline u2 load(const volatile u2* flags) {
-  assert(flags != NULL, "invariant");
-  return Atomic::load_acquire(flags);
+inline u1 load(const volatile u1* dest) {
+  assert(dest != NULL, "invariant");
+  return Atomic::load_acquire(dest);
 }
 
-inline void set(u2* flags, FLAG flag) {
-  assert(flags != NULL, "invariant");
+inline void set(u1* dest, u1 data) {
+  assert(dest != NULL, "invariant");
   OrderAccess::storestore();
-  *flags |= (u1)flag;
+  *dest |= data;
 }
 
-inline void clear(u2* flags, FLAG flag) {
-  assert(flags != NULL, "invariant");
+inline void clear(u1* dest, u1 data) {
+  assert(dest != NULL, "invariant");
   OrderAccess::storestore();
-  *flags ^= (u1)flag;
+  *dest ^= data;
 }
 
-inline bool test(const u2* flags, FLAG flag) {
-  return (u1)flag == (load(flags) & (u1)flag);
+inline bool test(const u1* dest, u1 data) {
+  return data == (load(dest) & data);
 }
 
 bool JfrBuffer::transient() const {
@@ -273,3 +273,15 @@
     clear(&_flags, RETIRED);
   }
 }
+
+u1 JfrBuffer::context() const {
+  return load(&_context);
+}
+
+void JfrBuffer::set_context(u1 context) {
+  set(&_context, context);
+}
+
+void JfrBuffer::clear_context() {
+  set(&_context, 0);
+}

--- a/src/hotspot/share/jfr/recorder/storage/jfrBuffer.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/storage/jfrBuffer.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -44,6 +44,10 @@
 // e.g. the delta must always be fully parsable.
 // _top can move concurrently by other threads but is always <= _pos.
 //
+// The _flags field holds generic tags applicable to all subsystems.
+//
+// The _context field can be used to set subsystem specific tags onto a buffer.
+//
 // Memory ordering:
 //
 //  Method                 Owner thread             Other threads
@@ -66,9 +70,10 @@
   const void* _identity;
   u1* _pos;
   mutable const u1* _top;
-  u2 _flags;
+  u4 _size;
   u2 _header_size;
-  u4 _size;
+  u1 _flags;
+  u1 _context;
 
   const u1* stable_top() const;
 
@@ -168,6 +173,10 @@
   bool excluded() const;
   void set_excluded();
   void clear_excluded();
+
+  u1 context() const;
+  void set_context(u1 context);
+  void clear_context();
 };
 
 #endif // SHARE_JFR_RECORDER_STORAGE_JFRBUFFER_HPP

--- a/src/hotspot/share/jfr/recorder/storage/jfrEpochStorage.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/storage/jfrEpochStorage.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2020, 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
@@ -33,9 +33,19 @@
 
 /*
  * Provides storage as a function of an epoch, with iteration capabilities for the current and previous epoch.
- * Iteration over the current epoch is incremental while iteration over the previous epoch is complete,
- * including storage reclamation. The design caters to use cases having multiple incremental iterations
- * over the current epoch, and a single, complete, iteration over the previous epoch.
+ *
+ * When iterating the previous epoch, where exclusive access to buffers is assumed,
+ * all buffers will be reinitialized post-callback, with retired buffers reclaimed
+ * and moved onto the free list and non-retired buffers left in-place.
+ *
+ * When iterating the current epoch, where concurrent access to buffers is assumed,
+ * there exist two modes, controlled by the EagerReclaim parameter.
+ * By default, EagerReclaim is false, meaning no retired buffers are reclaimed during the current epoch.
+ * Setting EagerReclaim to true, retired buffers will be reclaimed post-callback, by reinitialization
+ * and by moving them onto the free list, just like is done when iterating the previous epoch.
+ *
+ * The design caters to use cases having multiple incremental iterations over the current epoch,
+ * and a single iteration over the previous epoch.
  *
  * The JfrEpochStorage can be specialized by the following policies:
  *
@@ -43,10 +53,12 @@
  *
  * RetrievalPolicy   see jfrMemorySpace.hpp for a description.
  *
+ * EagerReclaim      should retired buffers be reclaimed also during the current epoch (i.e. eagerly)
+ *
  */
-template <typename NodeType, template <typename> class RetrievalPolicy>
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim = false>
 class JfrEpochStorageHost : public JfrCHeapObj {
-  typedef JfrMemorySpace<JfrEpochStorageHost<NodeType, RetrievalPolicy>,
+  typedef JfrMemorySpace<JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>,
                          RetrievalPolicy,
                          JfrConcurrentQueue<NodeType>,
                          JfrLinkedList<NodeType>,

--- a/src/hotspot/share/jfr/recorder/storage/jfrEpochStorage.inline.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/storage/jfrEpochStorage.inline.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -32,23 +32,23 @@
 #include "jfr/utilities/jfrLinkedList.inline.hpp"
 #include "logging/log.hpp"
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-JfrEpochStorageHost<NodeType, RetrievalPolicy>::JfrEpochStorageHost() : _mspace(NULL) {}
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::JfrEpochStorageHost() : _mspace(NULL) {}
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-JfrEpochStorageHost<NodeType, RetrievalPolicy>::~JfrEpochStorageHost() {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::~JfrEpochStorageHost() {
   delete _mspace;
 }
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-bool JfrEpochStorageHost<NodeType, RetrievalPolicy>::initialize(size_t min_elem_size, size_t free_list_cache_count_limit, size_t cache_prealloc_count) {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+bool JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::initialize(size_t min_elem_size, size_t free_list_cache_count_limit, size_t cache_prealloc_count) {
   assert(_mspace == NULL, "invariant");
   _mspace = new EpochMspace(min_elem_size, free_list_cache_count_limit, this);
   return _mspace != NULL && _mspace->initialize(cache_prealloc_count);
 }
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-inline NodeType* JfrEpochStorageHost<NodeType, RetrievalPolicy>::acquire(size_t size, Thread* thread) {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+inline NodeType* JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::acquire(size_t size, Thread* thread) {
   BufferPtr buffer = mspace_acquire_to_live_list(size, _mspace, thread);
   if (buffer == NULL) {
     log_warning(jfr)("Unable to allocate " SIZE_FORMAT " bytes of %s.", _mspace->min_element_size(), "epoch storage");
@@ -58,29 +58,37 @@
   return buffer;
 }
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-void JfrEpochStorageHost<NodeType, RetrievalPolicy>::release(NodeType* buffer) {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+void JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::release(NodeType* buffer) {
   assert(buffer != NULL, "invariant");
   buffer->set_retired();
 }
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-void JfrEpochStorageHost<NodeType, RetrievalPolicy>::register_full(NodeType* buffer, Thread* thread) {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+void JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::register_full(NodeType* buffer, Thread* thread) {
   // nothing here at the moment
 }
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
 template <typename Functor>
-void JfrEpochStorageHost<NodeType, RetrievalPolicy>::iterate(Functor& functor, bool previous_epoch) {
-  typedef ReleaseRetiredToFreeListOp<EpochMspace, typename EpochMspace::LiveList> ReleaseStorage;
-  typedef CompositeOperation<Functor, ReleaseStorage> PreviousEpochOperation;
+void JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::iterate(Functor& functor, bool previous_epoch) {
+  typedef ReinitializeAllReleaseRetiredOp<EpochMspace, typename EpochMspace::LiveList> PreviousEpochReleaseOperation;
+  typedef CompositeOperation<Functor, PreviousEpochReleaseOperation> PreviousEpochOperation;
+  typedef ReleaseRetiredOp<EpochMspace, typename EpochMspace::LiveList> CurrentEpochReleaseOperation;
+  typedef CompositeOperation<Functor, CurrentEpochReleaseOperation> CurrentEpochOperation;
   if (previous_epoch) {
-    ReleaseStorage rs(_mspace, _mspace->live_list(true));
-    PreviousEpochOperation peo(&functor, &rs);
-    process_live_list(peo, _mspace, true);
+    PreviousEpochReleaseOperation pero(_mspace, _mspace->live_list(true));
+    PreviousEpochOperation peo(&functor, &pero);
+    process_live_list(peo, _mspace, true); // previous epoch list
     return;
   }
-  process_live_list(functor, _mspace, false);
+  if (EagerReclaim) {
+    CurrentEpochReleaseOperation cero(_mspace, _mspace->live_list());
+    CurrentEpochOperation ceo(&functor, &cero);
+    process_live_list(ceo, _mspace, false); // current epoch list
+    return;
+  }
+  process_live_list(functor, _mspace, false); // current epoch list
 }
 
 #ifdef ASSERT
@@ -100,8 +108,8 @@
   }
 };
 
-template <typename NodeType, template <typename> class RetrievalPolicy>
-void JfrEpochStorageHost<NodeType, RetrievalPolicy>::verify_previous_empty() const {
+template <typename NodeType, template <typename> class RetrievalPolicy, bool EagerReclaim>
+void JfrEpochStorageHost<NodeType, RetrievalPolicy, EagerReclaim>::verify_previous_empty() const {
   typedef EmptyVerifier<JfrEpochStorage::Mspace> VerifyEmptyMspace;
   VerifyEmptyMspace vem(_mspace);
   process_live_list(vem, _mspace, true);

--- a/src/hotspot/share/jfr/recorder/storage/jfrMemorySpace.inline.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/storage/jfrMemorySpace.inline.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -493,14 +493,14 @@
 }
 
 template <typename Mspace, typename List>
-class ReleaseOpWithExcision : public ReleaseOp<Mspace> {
+class ReleaseWithExcisionOp : public ReleaseOp<Mspace> {
  private:
   List& _list;
   typename List::NodePtr _prev;
   size_t _count;
   size_t _amount;
  public:
-  ReleaseOpWithExcision(Mspace* mspace, List& list) :
+  ReleaseWithExcisionOp(Mspace* mspace, List& list) :
     ReleaseOp<Mspace>(mspace), _list(list), _prev(NULL), _count(0), _amount(0) {}
   bool process(typename List::NodePtr node);
   size_t processed() const { return _count; }
@@ -508,7 +508,7 @@
 };
 
 template <typename Mspace, typename List>
-inline bool ReleaseOpWithExcision<Mspace, List>::process(typename List::NodePtr node) {
+inline bool ReleaseWithExcisionOp<Mspace, List>::process(typename List::NodePtr node) {
   assert(node != NULL, "invariant");
   if (node->transient()) {
     _prev = _list.excise(_prev, node);
@@ -569,20 +569,49 @@
 }
 
 template <typename Mspace, typename FromList>
-class ReleaseRetiredToFreeListOp : public StackObj {
+class ReleaseRetiredOp : public StackObj {
+private:
+  Mspace* _mspace;
+  FromList& _list;
+  typename Mspace::NodePtr _prev;
+public:
+  typedef typename Mspace::Node Node;
+  ReleaseRetiredOp(Mspace* mspace, FromList& list) :
+    _mspace(mspace), _list(list), _prev(NULL) {}
+  bool process(Node* node);
+};
+
+template <typename Mspace, typename FromList>
+inline bool ReleaseRetiredOp<Mspace, FromList>::process(typename Mspace::Node* node) {
+  assert(node != NULL, "invariant");
+  if (node->retired()) {
+    _prev = _list.excise(_prev, node);
+    node->reinitialize();
+    assert(node->empty(), "invariant");
+    assert(!node->retired(), "invariant");
+    node->release();
+    mspace_release(node, _mspace);
+  } else {
+    _prev = node;
+  }
+  return true;
+}
+
+template <typename Mspace, typename FromList>
+class ReinitializeAllReleaseRetiredOp : public StackObj {
 private:
   Mspace* _mspace;
   FromList& _list;
   typename Mspace::NodePtr _prev;
  public:
   typedef typename Mspace::Node Node;
-  ReleaseRetiredToFreeListOp(Mspace* mspace, FromList& list) :
+  ReinitializeAllReleaseRetiredOp(Mspace* mspace, FromList& list) :
     _mspace(mspace), _list(list), _prev(NULL) {}
   bool process(Node* node);
 };
 
 template <typename Mspace, typename FromList>
-inline bool ReleaseRetiredToFreeListOp<Mspace, FromList>::process(typename Mspace::Node* node) {
+inline bool ReinitializeAllReleaseRetiredOp<Mspace, FromList>::process(typename Mspace::Node* node) {
   assert(node != NULL, "invariant");
   // assumes some means of exclusive access to node
   const bool retired = node->retired();

--- a/src/hotspot/share/jfr/recorder/stringpool/jfrStringPool.cpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/recorder/stringpool/jfrStringPool.cpp	Tue Jun 30 19:00:14 2020 +0200
@@ -208,7 +208,7 @@
 typedef StringPoolOp<StringPoolDiscarderStub> DiscardOperation;
 typedef ExclusiveOp<WriteOperation> ExclusiveWriteOperation;
 typedef ExclusiveOp<DiscardOperation> ExclusiveDiscardOperation;
-typedef ReleaseOpWithExcision<JfrStringPoolMspace, JfrStringPoolMspace::LiveList> ReleaseOperation;
+typedef ReleaseWithExcisionOp<JfrStringPoolMspace, JfrStringPoolMspace::LiveList> ReleaseOperation;
 typedef CompositeOperation<ExclusiveWriteOperation, ReleaseOperation> WriteReleaseOperation;
 typedef CompositeOperation<ExclusiveDiscardOperation, ReleaseOperation> DiscardReleaseOperation;
 

--- a/src/hotspot/share/jfr/utilities/jfrConcurrentLinkedListHost.inline.hpp	Tue Jun 30 18:10:44 2020 +0200
+++ b/src/hotspot/share/jfr/utilities/jfrConcurrentLinkedListHost.inline.hpp	Tue Jun 30 19:00:14 2020 +0200
@@ -34,7 +34,7 @@
 
 /*
  * The removal marker (i.e. the excision bit) is represented by '( )' as part of state description comments:
- * node --> next becomes (node) --> next, when node is logically deleted.
+ * "node --> next" becomes "(node) --> next", when node is logically deleted.
  */
 template <typename Node>
 inline Node* mark_for_removal(Node* node) {
@@ -47,7 +47,7 @@
 
 /*
  * The insertion marker (i.e. the insertion bit) is represented by '[ ]' as part of state description comments:
- * "node --> next" becomes "[node} --> next", in an attempt to convey node as being exlusively reserved.
+ * "node --> next" becomes "[node] --> next", in an attempt to convey node as being exlusively reserved.
  */
 template <typename Node>
 inline bool mark_for_insertion(Node* node, const Node* tail) {