8020151: PSR:PERF Large performance regressions when code cache is filled

Summary: Code cache sweeping based on method hotness; removed speculatively disconnect
Reviewed-by: kvn, iveresov

15 files changed, 242 insertions, 420 deletions

diff --git a/src/share/vm/code/codeCache.cpp b/src/share/vm/code/codeCache.cpp
index 65c1e5f2e..fcdab3d5a 100644
--- a/src/share/vm/code/codeCache.cpp
+++ b/src/share/vm/code/codeCache.cpp
@@ -124,7 +124,6 @@ int CodeCache::_number_of_nmethods = 0;
 int CodeCache::_number_of_nmethods_with_dependencies = 0;
 bool CodeCache::_needs_cache_clean = false;
 nmethod* CodeCache::_scavenge_root_nmethods = NULL;
-nmethod* CodeCache::_saved_nmethods = NULL;
 
 int CodeCache::_codemem_full_count = 0;
 
@@ -464,96 +463,11 @@ void CodeCache::verify_perm_nmethods(CodeBlobClosure* f_or_null) {
 }
 #endif //PRODUCT
 
-/**
- * Remove and return nmethod from the saved code list in order to reanimate it.
- */
-nmethod* CodeCache::reanimate_saved_code(Method* m) {
-  MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
-  nmethod* saved = _saved_nmethods;
-  nmethod* prev = NULL;
-  while (saved != NULL) {
-    if (saved->is_in_use() && saved->method() == m) {
-      if (prev != NULL) {
-        prev->set_saved_nmethod_link(saved->saved_nmethod_link());
-      } else {
-        _saved_nmethods = saved->saved_nmethod_link();
-      }
-      assert(saved->is_speculatively_disconnected(), "shouldn't call for other nmethods");
-      saved->set_speculatively_disconnected(false);
-      saved->set_saved_nmethod_link(NULL);
-      if (PrintMethodFlushing) {
-        saved->print_on(tty, " ### nmethod is reconnected");
-      }
-      if (LogCompilation && (xtty != NULL)) {
-        ttyLocker ttyl;
-        xtty->begin_elem("nmethod_reconnected compile_id='%3d'", saved->compile_id());
-        xtty->method(m);
-        xtty->stamp();
-        xtty->end_elem();
-      }
-      return saved;
-    }
-    prev = saved;
-    saved = saved->saved_nmethod_link();
-  }
-  return NULL;
-}
-
-/**
- * Remove nmethod from the saved code list in order to discard it permanently
- */
-void CodeCache::remove_saved_code(nmethod* nm) {
-  // For conc swpr this will be called with CodeCache_lock taken by caller
-  assert_locked_or_safepoint(CodeCache_lock);
-  assert(nm->is_speculatively_disconnected(), "shouldn't call for other nmethods");
-  nmethod* saved = _saved_nmethods;
-  nmethod* prev = NULL;
-  while (saved != NULL) {
-    if (saved == nm) {
-      if (prev != NULL) {
-        prev->set_saved_nmethod_link(saved->saved_nmethod_link());
-      } else {
-        _saved_nmethods = saved->saved_nmethod_link();
-      }
-      if (LogCompilation && (xtty != NULL)) {
-        ttyLocker ttyl;
-        xtty->begin_elem("nmethod_removed compile_id='%3d'", nm->compile_id());
-        xtty->stamp();
-        xtty->end_elem();
-      }
-      return;
-    }
-    prev = saved;
-    saved = saved->saved_nmethod_link();
-  }
-  ShouldNotReachHere();
-}
-
-void CodeCache::speculatively_disconnect(nmethod* nm) {
-  assert_locked_or_safepoint(CodeCache_lock);
-  assert(nm->is_in_use() && !nm->is_speculatively_disconnected(), "should only disconnect live nmethods");
-  nm->set_saved_nmethod_link(_saved_nmethods);
-  _saved_nmethods = nm;
-  if (PrintMethodFlushing) {
-    nm->print_on(tty, " ### nmethod is speculatively disconnected");
-  }
-  if (LogCompilation && (xtty != NULL)) {
-    ttyLocker ttyl;
-    xtty->begin_elem("nmethod_disconnected compile_id='%3d'", nm->compile_id());
-    xtty->method(nm->method());
-    xtty->stamp();
-    xtty->end_elem();
-  }
-  nm->method()->clear_code();
-  nm->set_speculatively_disconnected(true);
-}
-
 
 void CodeCache::gc_prologue() {
   assert(!nmethod::oops_do_marking_is_active(), "oops_do_marking_epilogue must be called");
 }
 
-
 void CodeCache::gc_epilogue() {
   assert_locked_or_safepoint(CodeCache_lock);
   FOR_ALL_ALIVE_BLOBS(cb) {
diff --git a/src/share/vm/code/codeCache.hpp b/src/share/vm/code/codeCache.hpp
index 3e8eda6e2..e190b11ae 100644
--- a/src/share/vm/code/codeCache.hpp
+++ b/src/share/vm/code/codeCache.hpp
@@ -57,7 +57,6 @@ class CodeCache : AllStatic {
   static int _number_of_nmethods_with_dependencies;
   static bool _needs_cache_clean;
   static nmethod* _scavenge_root_nmethods;  // linked via nm->scavenge_root_link()
-  static nmethod* _saved_nmethods;          // Linked list of speculatively disconnected nmethods.
 
   static void verify_if_often() PRODUCT_RETURN;
 
@@ -167,17 +166,12 @@ class CodeCache : AllStatic {
   static size_t  capacity()                      { return _heap->capacity(); }
   static size_t  max_capacity()                  { return _heap->max_capacity(); }
   static size_t  unallocated_capacity()          { return _heap->unallocated_capacity(); }
-  static bool    needs_flushing()                { return unallocated_capacity() < CodeCacheFlushingMinimumFreeSpace; }
   static double  reverse_free_ratio();
 
   static bool needs_cache_clean()                { return _needs_cache_clean; }
   static void set_needs_cache_clean(bool v)      { _needs_cache_clean = v;    }
   static void clear_inline_caches();             // clear all inline caches
 
-  static nmethod* reanimate_saved_code(Method* m);
-  static void remove_saved_code(nmethod* nm);
-  static void speculatively_disconnect(nmethod* nm);
-
   // Deoptimization
   static int  mark_for_deoptimization(DepChange& changes);
 #ifdef HOTSWAP
diff --git a/src/share/vm/code/nmethod.cpp b/src/share/vm/code/nmethod.cpp
index 4f8608f08..cfc2ddeab 100644
--- a/src/share/vm/code/nmethod.cpp
+++ b/src/share/vm/code/nmethod.cpp
@@ -462,7 +462,6 @@ void nmethod::init_defaults() {
   _state                      = alive;
   _marked_for_reclamation     = 0;
   _has_flushed_dependencies   = 0;
-  _speculatively_disconnected = 0;
   _has_unsafe_access          = 0;
   _has_method_handle_invokes  = 0;
   _lazy_critical_native       = 0;
@@ -481,7 +480,6 @@ void nmethod::init_defaults() {
   _osr_link                = NULL;
   _scavenge_root_link      = NULL;
   _scavenge_root_state     = 0;
-  _saved_nmethod_link      = NULL;
   _compiler                = NULL;
 
 #ifdef HAVE_DTRACE_H
@@ -686,6 +684,7 @@ nmethod::nmethod(
     _osr_entry_point         = NULL;
     _exception_cache         = NULL;
     _pc_desc_cache.reset_to(NULL);
+    _hotness_counter         = NMethodSweeper::hotness_counter_reset_val();
 
     code_buffer->copy_values_to(this);
     if (ScavengeRootsInCode && detect_scavenge_root_oops()) {
@@ -770,6 +769,7 @@ nmethod::nmethod(
     _osr_entry_point         = NULL;
     _exception_cache         = NULL;
     _pc_desc_cache.reset_to(NULL);
+    _hotness_counter         = NMethodSweeper::hotness_counter_reset_val();
 
     code_buffer->copy_values_to(this);
     debug_only(verify_scavenge_root_oops());
@@ -842,6 +842,7 @@ nmethod::nmethod(
     _comp_level              = comp_level;
     _compiler                = compiler;
     _orig_pc_offset          = orig_pc_offset;
+    _hotness_counter         = NMethodSweeper::hotness_counter_reset_val();
 
     // Section offsets
     _consts_offset           = content_offset()      + code_buffer->total_offset_of(code_buffer->consts());
@@ -1176,7 +1177,7 @@ void nmethod::cleanup_inline_caches() {
 
 // This is a private interface with the sweeper.
 void nmethod::mark_as_seen_on_stack() {
-  assert(is_not_entrant(), "must be a non-entrant method");
+  assert(is_alive(), "Must be an alive method");
   // Set the traversal mark to ensure that the sweeper does 2
   // cleaning passes before moving to zombie.
   set_stack_traversal_mark(NMethodSweeper::traversal_count());
@@ -1261,7 +1262,7 @@ void nmethod::make_unloaded(BoolObjectClosure* is_alive, oop cause) {
 
   set_osr_link(NULL);
   //set_scavenge_root_link(NULL); // done by prune_scavenge_root_nmethods
-  NMethodSweeper::notify(this);
+  NMethodSweeper::notify();
 }
 
 void nmethod::invalidate_osr_method() {
@@ -1351,6 +1352,15 @@ bool nmethod::make_not_entrant_or_zombie(unsigned int state) {
       nmethod_needs_unregister = true;
     }
 
+    // Must happen before state change. Otherwise we have a race condition in
+    // nmethod::can_not_entrant_be_converted(). I.e., a method can immediately
+    // transition its state from 'not_entrant' to 'zombie' without having to wait
+    // for stack scanning.
+    if (state == not_entrant) {
+      mark_as_seen_on_stack();
+      OrderAccess::storestore();
+    }
+
     // Change state
     _state = state;
 
@@ -1369,11 +1379,6 @@ bool nmethod::make_not_entrant_or_zombie(unsigned int state) {
       HandleMark hm;
       method()->clear_code();
     }
-
-    if (state == not_entrant) {
-      mark_as_seen_on_stack();
-    }
-
   } // leave critical region under Patching_lock
 
   // When the nmethod becomes zombie it is no longer alive so the
@@ -1416,7 +1421,7 @@ bool nmethod::make_not_entrant_or_zombie(unsigned int state) {
   }
 
   // Make sweeper aware that there is a zombie method that needs to be removed
-  NMethodSweeper::notify(this);
+  NMethodSweeper::notify();
 
   return true;
 }
@@ -1451,10 +1456,6 @@ void nmethod::flush() {
     CodeCache::drop_scavenge_root_nmethod(this);
   }
 
-  if (is_speculatively_disconnected()) {
-    CodeCache::remove_saved_code(this);
-  }
-
 #ifdef SHARK
   ((SharkCompiler *) compiler())->free_compiled_method(insts_begin());
 #endif // SHARK
diff --git a/src/share/vm/code/nmethod.hpp b/src/share/vm/code/nmethod.hpp
index 4929ea820..538bcf778 100644
--- a/src/share/vm/code/nmethod.hpp
+++ b/src/share/vm/code/nmethod.hpp
@@ -119,7 +119,6 @@ class nmethod : public CodeBlob {
   // To support simple linked-list chaining of nmethods:
   nmethod*  _osr_link;         // from InstanceKlass::osr_nmethods_head
   nmethod*  _scavenge_root_link; // from CodeCache::scavenge_root_nmethods
-  nmethod*  _saved_nmethod_link; // from CodeCache::speculatively_disconnect
 
   static nmethod* volatile _oops_do_mark_nmethods;
   nmethod*        volatile _oops_do_mark_link;
@@ -165,7 +164,6 @@ class nmethod : public CodeBlob {
 
   // protected by CodeCache_lock
   bool _has_flushed_dependencies;            // Used for maintenance of dependencies (CodeCache_lock)
-  bool _speculatively_disconnected;          // Marked for potential unload
 
   bool _marked_for_reclamation;              // Used by NMethodSweeper (set only by sweeper)
   bool _marked_for_deoptimization;           // Used for stack deoptimization
@@ -180,7 +178,7 @@ class nmethod : public CodeBlob {
   unsigned int _has_wide_vectors:1;          // Preserve wide vectors at safepoints
 
   // Protected by Patching_lock
-  unsigned char _state;                      // {alive, not_entrant, zombie, unloaded}
+  volatile unsigned char _state;             // {alive, not_entrant, zombie, unloaded}
 
 #ifdef ASSERT
   bool _oops_are_stale;  // indicates that it's no longer safe to access oops section
@@ -202,11 +200,18 @@ class nmethod : public CodeBlob {
 
   // not_entrant method removal. Each mark_sweep pass will update
   // this mark to current sweep invocation count if it is seen on the
-  // stack.  An not_entrant method can be removed when there is no
+  // stack.  An not_entrant method can be removed when there are no
   // more activations, i.e., when the _stack_traversal_mark is less than
   // current sweep traversal index.
   long _stack_traversal_mark;
 
+  // The _hotness_counter indicates the hotness of a method. The higher
+  // the value the hotter the method. The hotness counter of a nmethod is
+  // set to [(ReservedCodeCacheSize / (1024 * 1024)) * 2] each time the method
+  // is active while stack scanning (mark_active_nmethods()). The hotness
+  // counter is decreased (by 1) while sweeping.
+  int _hotness_counter;
+
   ExceptionCache *_exception_cache;
   PcDescCache     _pc_desc_cache;
 
@@ -382,6 +387,10 @@ class nmethod : public CodeBlob {
 
   int total_size        () const;
 
+  void dec_hotness_counter()        { _hotness_counter--; }
+  void set_hotness_counter(int val) { _hotness_counter = val; }
+  int  hotness_counter() const      { return _hotness_counter; }
+
   // Containment
   bool consts_contains       (address addr) const { return consts_begin       () <= addr && addr < consts_end       (); }
   bool insts_contains        (address addr) const { return insts_begin        () <= addr && addr < insts_end        (); }
@@ -408,8 +417,8 @@ class nmethod : public CodeBlob {
   // alive.  It is used when an uncommon trap happens.  Returns true
   // if this thread changed the state of the nmethod or false if
   // another thread performed the transition.
-  bool  make_not_entrant()                        { return make_not_entrant_or_zombie(not_entrant); }
-  bool  make_zombie()                             { return make_not_entrant_or_zombie(zombie); }
+  bool  make_not_entrant() { return make_not_entrant_or_zombie(not_entrant); }
+  bool  make_zombie()      { return make_not_entrant_or_zombie(zombie); }
 
   // used by jvmti to track if the unload event has been reported
   bool  unload_reported()                         { return _unload_reported; }
@@ -437,9 +446,6 @@ class nmethod : public CodeBlob {
   bool  has_method_handle_invokes() const         { return _has_method_handle_invokes; }
   void  set_has_method_handle_invokes(bool z)     { _has_method_handle_invokes = z; }
 
-  bool  is_speculatively_disconnected() const     { return _speculatively_disconnected; }
-  void  set_speculatively_disconnected(bool z)    { _speculatively_disconnected = z; }
-
   bool  is_lazy_critical_native() const           { return _lazy_critical_native; }
   void  set_lazy_critical_native(bool z)          { _lazy_critical_native = z; }
 
@@ -499,9 +505,6 @@ public:
   nmethod* scavenge_root_link() const                  { return _scavenge_root_link; }
   void     set_scavenge_root_link(nmethod *n)          { _scavenge_root_link = n; }
 
-  nmethod* saved_nmethod_link() const                  { return _saved_nmethod_link; }
-  void     set_saved_nmethod_link(nmethod *n)          { _saved_nmethod_link = n; }
-
  public:
 
   // Sweeper support
diff --git a/src/share/vm/compiler/compileBroker.cpp b/src/share/vm/compiler/compileBroker.cpp
index e8f57b24e..594c58b5d 100644
--- a/src/share/vm/compiler/compileBroker.cpp
+++ b/src/share/vm/compiler/compileBroker.cpp
@@ -634,19 +634,36 @@ CompileTask* CompileQueue::get() {
   NMethodSweeper::possibly_sweep();
 
   MutexLocker locker(lock());
-  // Wait for an available CompileTask.
+  // If _first is NULL we have no more compile jobs. There are two reasons for
+  // having no compile jobs: First, we compiled everything we wanted. Second,
+  // we ran out of code cache so compilation has been disabled. In the latter
+  // case we perform code cache sweeps to free memory such that we can re-enable
+  // compilation.
   while (_first == NULL) {
-    // There is no work to be done right now.  Wait.
-    if (UseCodeCacheFlushing && (!CompileBroker::should_compile_new_jobs() || CodeCache::needs_flushing())) {
-      // During the emergency sweeping periods, wake up and sweep occasionally
-      bool timedout = lock()->wait(!Mutex::_no_safepoint_check_flag, NmethodSweepCheckInterval*1000);
-      if (timedout) {
+    if (UseCodeCacheFlushing && !CompileBroker::should_compile_new_jobs()) {
+      // Wait a certain amount of time to possibly do another sweep.
+      // We must wait until stack scanning has happened so that we can
+      // transition a method's state from 'not_entrant' to 'zombie'.
+      long wait_time = NmethodSweepCheckInterval * 1000;
+      if (FLAG_IS_DEFAULT(NmethodSweepCheckInterval)) {
+        // Only one thread at a time can do sweeping. Scale the
+        // wait time according to the number of compiler threads.
+        // As a result, the next sweep is likely to happen every 100ms
+        // with an arbitrary number of threads that do sweeping.
+        wait_time = 100 * CICompilerCount;
+      }
+      bool timeout = lock()->wait(!Mutex::_no_safepoint_check_flag, wait_time);
+      if (timeout) {
         MutexUnlocker ul(lock());
-        // When otherwise not busy, run nmethod sweeping
         NMethodSweeper::possibly_sweep();
       }
     } else {
-      // During normal operation no need to wake up on timer
+      // If there are no compilation tasks and we can compile new jobs
+      // (i.e., there is enough free space in the code cache) there is
+      // no need to invoke the sweeper. As a result, the hotness of methods
+      // remains unchanged. This behavior is desired, since we want to keep
+      // the stable state, i.e., we do not want to evict methods from the
+      // code cache if it is unnecessary.
       lock()->wait();
     }
   }
@@ -1227,16 +1244,9 @@ nmethod* CompileBroker::compile_method(methodHandle method, int osr_bci,
         return method_code;
       }
     }
-    if (method->is_not_compilable(comp_level)) return NULL;
-
-    if (UseCodeCacheFlushing) {
-      nmethod* saved = CodeCache::reanimate_saved_code(method());
-      if (saved != NULL) {
-        method->set_code(method, saved);
-        return saved;
-      }
+    if (method->is_not_compilable(comp_level)) {
+      return NULL;
     }
-
   } else {
     // osr compilation
 #ifndef TIERED
@@ -1585,9 +1595,6 @@ void CompileBroker::compiler_thread_loop() {
       if (CodeCache::unallocated_capacity() < CodeCacheMinimumFreeSpace) {
         // the code cache is really full
         handle_full_code_cache();
-      } else if (UseCodeCacheFlushing && CodeCache::needs_flushing()) {
-        // Attempt to start cleaning the code cache while there is still a little headroom
-        NMethodSweeper::handle_full_code_cache(false);
       }
 
       CompileTask* task = queue->get();
@@ -1943,7 +1950,11 @@ void CompileBroker::handle_full_code_cache() {
     }
 #endif
     if (UseCodeCacheFlushing) {
-      NMethodSweeper::handle_full_code_cache(true);
+      // Since code cache is full, immediately stop new compiles
+      if (CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation)) {
+        NMethodSweeper::log_sweep("disable_compiler");
+        NMethodSweeper::possibly_sweep();
+      }
     } else {
       UseCompiler               = false;
       AlwaysCompileLoopMethods  = false;
diff --git a/src/share/vm/oops/method.cpp b/src/share/vm/oops/method.cpp
index 30631fa3b..9d30c40f9 100644
--- a/src/share/vm/oops/method.cpp
+++ b/src/share/vm/oops/method.cpp
@@ -901,16 +901,6 @@ address Method::make_adapters(methodHandle mh, TRAPS) {
 // This function must not hit a safepoint!
 address Method::verified_code_entry() {
   debug_only(No_Safepoint_Verifier nsv;)
-  nmethod *code = (nmethod *)OrderAccess::load_ptr_acquire(&_code);
-  if (code == NULL && UseCodeCacheFlushing) {
-    nmethod *saved_code = CodeCache::reanimate_saved_code(this);
-    if (saved_code != NULL) {
-      methodHandle method(this);
-      assert( ! saved_code->is_osr_method(), "should not get here for osr" );
-      set_code( method, saved_code );
-    }
-  }
-
   assert(_from_compiled_entry != NULL, "must be set");
   return _from_compiled_entry;
 }
diff --git a/src/share/vm/runtime/arguments.cpp b/src/share/vm/runtime/arguments.cpp
index 53454e558..9a76b1b6a 100644
--- a/src/share/vm/runtime/arguments.cpp
+++ b/src/share/vm/runtime/arguments.cpp
@@ -1130,6 +1130,9 @@ void Arguments::set_tiered_flags() {
     Tier3InvokeNotifyFreqLog = 0;
     Tier4InvocationThreshold = 0;
   }
+  if (FLAG_IS_DEFAULT(NmethodSweepFraction)) {
+    FLAG_SET_DEFAULT(NmethodSweepFraction, 1 + ReservedCodeCacheSize / (16 * M));
+  }
 }
 
 #if INCLUDE_ALL_GCS
@@ -2333,6 +2336,10 @@ bool Arguments::check_vm_args_consistency() {
                 (2*G)/M);
     status = false;
   }
+
+  status &= verify_interval(NmethodSweepFraction, 1, ReservedCodeCacheSize/K, "NmethodSweepFraction");
+  status &= verify_interval(NmethodSweepActivity, 0, 2000, "NmethodSweepActivity");
+
   return status;
 }
 
diff --git a/src/share/vm/runtime/globals.hpp b/src/share/vm/runtime/globals.hpp
index 9d429cd76..394358d78 100644
--- a/src/share/vm/runtime/globals.hpp
+++ b/src/share/vm/runtime/globals.hpp
@@ -2868,6 +2868,10 @@ class CommandLineFlags {
   product(intx, NmethodSweepCheckInterval, 5,                               \
           "Compilers wake up every n seconds to possibly sweep nmethods")   \
                                                                             \
+  product(intx, NmethodSweepActivity, 10,                                   \
+          "Removes cold nmethods from code cache if > 0. Higher values "    \
+          "result in more aggressive sweeping")                             \
+                                                                            \
   notproduct(bool, LogSweeper, false,                                       \
             "Keep a ring buffer of sweeper activity")                       \
                                                                             \
@@ -3239,15 +3243,6 @@ class CommandLineFlags {
   product(bool, UseCodeCacheFlushing, true,                                 \
           "Attempt to clean the code cache before shutting off compiler")   \
                                                                             \
-  product(intx,  MinCodeCacheFlushingInterval, 30,                          \
-          "Min number of seconds between code cache cleaning sessions")     \
-                                                                            \
-  product(uintx,  CodeCacheFlushingMinimumFreeSpace, 1500*K,                \
-          "When less than X space left, start code cache cleaning")         \
-                                                                            \
-  product(uintx, CodeCacheFlushingFraction, 2,                              \
-          "Fraction of the code cache that is flushed when full")           \
-                                                                            \
   /* interpreter debugging */                                               \
   develop(intx, BinarySwitchThreshold, 5,                                   \
           "Minimal number of lookupswitch entries for rewriting to binary " \
diff --git a/src/share/vm/runtime/safepoint.cpp b/src/share/vm/runtime/safepoint.cpp
index f3191e524..95c395fad 100644
--- a/src/share/vm/runtime/safepoint.cpp
+++ b/src/share/vm/runtime/safepoint.cpp
@@ -519,8 +519,8 @@ void SafepointSynchronize::do_cleanup_tasks() {
   }
 
   {
-    TraceTime t4("sweeping nmethods", TraceSafepointCleanupTime);
-    NMethodSweeper::scan_stacks();
+    TraceTime t4("mark nmethods", TraceSafepointCleanupTime);
+    NMethodSweeper::mark_active_nmethods();
   }
 
   if (SymbolTable::needs_rehashing()) {
diff --git a/src/share/vm/runtime/sweeper.cpp b/src/share/vm/runtime/sweeper.cpp
index 37315aec3..eab7636fa 100644
--- a/src/share/vm/runtime/sweeper.cpp
+++ b/src/share/vm/runtime/sweeper.cpp
@@ -127,64 +127,79 @@ void NMethodSweeper::record_sweep(nmethod* nm, int line) {
 #define SWEEP(nm)
 #endif
 
-
-long      NMethodSweeper::_traversals = 0;   // No. of stack traversals performed
-nmethod*  NMethodSweeper::_current = NULL;   // Current nmethod
-int       NMethodSweeper::_seen = 0 ;        // No. of nmethods we have currently processed in current pass of CodeCache
-int       NMethodSweeper::_flushed_count = 0;   // Nof. nmethods flushed in current sweep
-int       NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep
-int       NMethodSweeper::_marked_count = 0;    // Nof. nmethods marked for reclaim in current sweep
-
-volatile int NMethodSweeper::_invocations = 0;   // No. of invocations left until we are completed with this pass
+nmethod*  NMethodSweeper::_current         = NULL; // Current nmethod
+long      NMethodSweeper::_traversals      = 0;    // Nof. stack traversals performed
+int       NMethodSweeper::_seen            = 0;    // Nof. nmethods we have currently processed in current pass of CodeCache
+int       NMethodSweeper::_flushed_count   = 0;    // Nof. nmethods flushed in current sweep
+int       NMethodSweeper::_zombified_count = 0;    // Nof. nmethods made zombie in current sweep
+int       NMethodSweeper::_marked_count    = 0;    // Nof. nmethods marked for reclaim in current sweep
+
+volatile int NMethodSweeper::_invocations   = 0; // Nof. invocations left until we are completed with this pass
 volatile int NMethodSweeper::_sweep_started = 0; // Whether a sweep is in progress.
 
-jint      NMethodSweeper::_locked_seen = 0;
+jint      NMethodSweeper::_locked_seen               = 0;
 jint      NMethodSweeper::_not_entrant_seen_on_stack = 0;
-bool      NMethodSweeper::_resweep = false;
-jint      NMethodSweeper::_flush_token = 0;
-jlong     NMethodSweeper::_last_full_flush_time = 0;
-int       NMethodSweeper::_highest_marked = 0;
-int       NMethodSweeper::_dead_compile_ids = 0;
-long      NMethodSweeper::_last_flush_traversal_id = 0;
-
-int       NMethodSweeper::_number_of_flushes = 0; // Total of full traversals caused by full cache
+bool      NMethodSweeper::_request_mark_phase        = false;
+
 int       NMethodSweeper::_total_nof_methods_reclaimed = 0;
-jlong     NMethodSweeper::_total_time_sweeping = 0;
-jlong     NMethodSweeper::_total_time_this_sweep = 0;
-jlong     NMethodSweeper::_peak_sweep_time = 0;
-jlong     NMethodSweeper::_peak_sweep_fraction_time = 0;
-jlong     NMethodSweeper::_total_disconnect_time = 0;
-jlong     NMethodSweeper::_peak_disconnect_time = 0;
+jlong     NMethodSweeper::_total_time_sweeping         = 0;
+jlong     NMethodSweeper::_total_time_this_sweep       = 0;
+jlong     NMethodSweeper::_peak_sweep_time             = 0;
+jlong     NMethodSweeper::_peak_sweep_fraction_time    = 0;
+int       NMethodSweeper::_hotness_counter_reset_val   = 0;
+
 
 class MarkActivationClosure: public CodeBlobClosure {
 public:
   virtual void do_code_blob(CodeBlob* cb) {
-    // If we see an activation belonging to a non_entrant nmethod, we mark it.
-    if (cb->is_nmethod() && ((nmethod*)cb)->is_not_entrant()) {
-      ((nmethod*)cb)->mark_as_seen_on_stack();
+    if (cb->is_nmethod()) {
+      nmethod* nm = (nmethod*)cb;
+      nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
+      // If we see an activation belonging to a non_entrant nmethod, we mark it.
+      if (nm->is_not_entrant()) {
+        nm->mark_as_seen_on_stack();
+      }
     }
   }
 };
 static MarkActivationClosure mark_activation_closure;
 
+class SetHotnessClosure: public CodeBlobClosure {
+public:
+  virtual void do_code_blob(CodeBlob* cb) {
+    if (cb->is_nmethod()) {
+      nmethod* nm = (nmethod*)cb;
+      nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
+    }
+  }
+};
+static SetHotnessClosure set_hotness_closure;
+
+
+int NMethodSweeper::hotness_counter_reset_val() {
+  if (_hotness_counter_reset_val == 0) {
+    _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
+  }
+  return _hotness_counter_reset_val;
+}
 bool NMethodSweeper::sweep_in_progress() {
   return (_current != NULL);
 }
 
-void NMethodSweeper::scan_stacks() {
+// Scans the stacks of all Java threads and marks activations of not-entrant methods.
+// No need to synchronize access, since 'mark_active_nmethods' is always executed at a
+// safepoint.
+void NMethodSweeper::mark_active_nmethods() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
-  if (!MethodFlushing) return;
-
-  // No need to synchronize access, since this is always executed at a
-  // safepoint.
-
-  // Make sure CompiledIC_lock in unlocked, since we might update some
-  // inline caches. If it is, we just bail-out and try later.
-  if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return;
+  // If we do not want to reclaim not-entrant or zombie methods there is no need
+  // to scan stacks
+  if (!MethodFlushing) {
+    return;
+  }
 
   // Check for restart
   assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
-  if (!sweep_in_progress() && _resweep) {
+  if (!sweep_in_progress() && need_marking_phase()) {
     _seen        = 0;
     _invocations = NmethodSweepFraction;
     _current     = CodeCache::first_nmethod();
@@ -197,30 +212,22 @@ void NMethodSweeper::scan_stacks() {
     Threads::nmethods_do(&mark_activation_closure);
 
     // reset the flags since we started a scan from the beginning.
-    _resweep = false;
+    reset_nmethod_marking();
     _locked_seen = 0;
     _not_entrant_seen_on_stack = 0;
+  } else {
+    // Only set hotness counter
+    Threads::nmethods_do(&set_hotness_closure);
   }
 
-  if (UseCodeCacheFlushing) {
-    // only allow new flushes after the interval is complete.
-    jlong now           = os::javaTimeMillis();
-    jlong max_interval  = (jlong)MinCodeCacheFlushingInterval * (jlong)1000;
-    jlong curr_interval = now - _last_full_flush_time;
-    if (curr_interval > max_interval) {
-      _flush_token = 0;
-    }
-
-    if (!CodeCache::needs_flushing() && !CompileBroker::should_compile_new_jobs()) {
-      CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
-      log_sweep("restart_compiler");
-    }
-  }
+  OrderAccess::storestore();
 }
 
 void NMethodSweeper::possibly_sweep() {
   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
-  if (!MethodFlushing || !sweep_in_progress()) return;
+  if (!MethodFlushing || !sweep_in_progress()) {
+    return;
+  }
 
   if (_invocations > 0) {
     // Only one thread at a time will sweep
@@ -258,8 +265,7 @@ void NMethodSweeper::sweep_code_cache() {
   if (!CompileBroker::should_compile_new_jobs()) {
     // If we have turned off compilations we might as well do full sweeps
     // in order to reach the clean state faster. Otherwise the sleeping compiler
-    // threads will slow down sweeping. After a few iterations the cache
-    // will be clean and sweeping stops (_resweep will not be set)
+    // threads will slow down sweeping.
     _invocations = 1;
   }
 
@@ -271,9 +277,11 @@ void NMethodSweeper::sweep_code_cache() {
   int todo = (CodeCache::nof_nmethods() - _seen) / _invocations;
   int swept_count = 0;
 
+
   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
   assert(!CodeCache_lock->owned_by_self(), "just checking");
 
+  int freed_memory = 0;
   {
     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 
@@ -299,7 +307,7 @@ void NMethodSweeper::sweep_code_cache() {
       // Now ready to process nmethod and give up CodeCache_lock
       {
         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
-        process_nmethod(_current);
+        freed_memory += process_nmethod(_current);
       }
       _seen++;
       _current = next;
@@ -308,11 +316,11 @@ void NMethodSweeper::sweep_code_cache() {
 
   assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache");
 
-  if (!sweep_in_progress() && !_resweep && (_locked_seen || _not_entrant_seen_on_stack)) {
+  if (!sweep_in_progress() && !need_marking_phase() && (_locked_seen || _not_entrant_seen_on_stack)) {
     // we've completed a scan without making progress but there were
     // nmethods we were unable to process either because they were
-    // locked or were still on stack.  We don't have to aggresively
-    // clean them up so just stop scanning.  We could scan once more
+    // locked or were still on stack. We don't have to aggressively
+    // clean them up so just stop scanning. We could scan once more
     // but that complicates the control logic and it's unlikely to
     // matter much.
     if (PrintMethodFlushing) {
@@ -351,9 +359,16 @@ void NMethodSweeper::sweep_code_cache() {
     log_sweep("finished");
   }
 
-  // Sweeper is the only case where memory is released,
-  // check here if it is time to restart the compiler.
-  if (UseCodeCacheFlushing && !CompileBroker::should_compile_new_jobs() && !CodeCache::needs_flushing()) {
+  // Sweeper is the only case where memory is released, check here if it
+  // is time to restart the compiler. Only checking if there is a certain
+  // amount of free memory in the code cache might lead to re-enabling
+  // compilation although no memory has been released. For example, there are
+  // cases when compilation was disabled although there is 4MB (or more) free
+  // memory in the code cache. The reason is code cache fragmentation. Therefore,
+  // it only makes sense to re-enable compilation if we have actually freed memory.
+  // Note that typically several kB are released for sweeping 16MB of the code
+  // cache. As a result, 'freed_memory' > 0 to restart the compiler.
+  if (UseCodeCacheFlushing && (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0))) {
     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
     log_sweep("restart_compiler");
   }
@@ -367,8 +382,8 @@ class NMethodMarker: public StackObj {
     _thread = CompilerThread::current();
     if (!nm->is_zombie() && !nm->is_unloaded()) {
       // Only expose live nmethods for scanning
-    _thread->set_scanned_nmethod(nm);
-  }
+      _thread->set_scanned_nmethod(nm);
+    }
   }
   ~NMethodMarker() {
     _thread->set_scanned_nmethod(NULL);
@@ -392,20 +407,20 @@ void NMethodSweeper::release_nmethod(nmethod *nm) {
   nm->flush();
 }
 
-void NMethodSweeper::process_nmethod(nmethod *nm) {
+int NMethodSweeper::process_nmethod(nmethod *nm) {
   assert(!CodeCache_lock->owned_by_self(), "just checking");
 
+  int freed_memory = 0;
   // Make sure this nmethod doesn't get unloaded during the scan,
-  // since the locks acquired below might safepoint.
+  // since safepoints may happen during acquired below locks.
   NMethodMarker nmm(nm);
-
   SWEEP(nm);
 
   // Skip methods that are currently referenced by the VM
   if (nm->is_locked_by_vm()) {
     // But still remember to clean-up inline caches for alive nmethods
     if (nm->is_alive()) {
-      // Clean-up all inline caches that points to zombie/non-reentrant methods
+      // Clean inline caches that point to zombie/non-entrant methods
       MutexLocker cl(CompiledIC_lock);
       nm->cleanup_inline_caches();
       SWEEP(nm);
@@ -413,18 +428,19 @@ void NMethodSweeper::process_nmethod(nmethod *nm) {
       _locked_seen++;
       SWEEP(nm);
     }
-    return;
+    return freed_memory;
   }
 
   if (nm->is_zombie()) {
-    // If it is first time, we see nmethod then we mark it. Otherwise,
-    // we reclame it. When we have seen a zombie method twice, we know that
+    // If it is the first time we see nmethod then we mark it. Otherwise,
+    // we reclaim it. When we have seen a zombie method twice, we know that
     // there are no inline caches that refer to it.
     if (nm->is_marked_for_reclamation()) {
       assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
       if (PrintMethodFlushing && Verbose) {
         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
       }
+      freed_memory = nm->total_size();
       release_nmethod(nm);
       _flushed_count++;
     } else {
@@ -432,19 +448,19 @@ void NMethodSweeper::process_nmethod(nmethod *nm) {
         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
       }
       nm->mark_for_reclamation();
-      _resweep = true;
+      request_nmethod_marking();
       _marked_count++;
       SWEEP(nm);
     }
   } else if (nm->is_not_entrant()) {
-    // If there is no current activations of this method on the
+    // If there are no current activations of this method on the
     // stack we can safely convert it to a zombie method
     if (nm->can_not_entrant_be_converted()) {
       if (PrintMethodFlushing && Verbose) {
         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
       }
       nm->make_zombie();
-      _resweep = true;
+      request_nmethod_marking();
       _zombified_count++;
       SWEEP(nm);
     } else {
@@ -459,159 +475,57 @@ void NMethodSweeper::process_nmethod(nmethod *nm) {
     }
   } else if (nm->is_unloaded()) {
     // Unloaded code, just make it a zombie
-    if (PrintMethodFlushing && Verbose)
+    if (PrintMethodFlushing && Verbose) {
       tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
-
+    }
     if (nm->is_osr_method()) {
       SWEEP(nm);
       // No inline caches will ever point to osr methods, so we can just remove it
+      freed_memory = nm->total_size();
       release_nmethod(nm);
       _flushed_count++;
     } else {
       nm->make_zombie();
-      _resweep = true;
+      request_nmethod_marking();
       _zombified_count++;
       SWEEP(nm);
     }
   } else {
-    assert(nm->is_alive(), "should be alive");
-
     if (UseCodeCacheFlushing) {
-      if (nm->is_speculatively_disconnected() && !nm->is_locked_by_vm() && !nm->is_osr_method() &&
-          (_traversals > _last_flush_traversal_id + 2) && (nm->compile_id() < _highest_marked)) {
-        // This method has not been called since the forced cleanup happened
-        nm->make_not_entrant();
+      if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
+        // Do not make native methods and OSR-methods not-entrant
+        nm->dec_hotness_counter();
+        // Get the initial value of the hotness counter. This value depends on the
+        // ReservedCodeCacheSize
+        int reset_val = hotness_counter_reset_val();
+        int time_since_reset = reset_val - nm->hotness_counter();
+        double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity);
+        // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
+        // I.e., 'threshold' increases with lower available space in the code cache and a higher
+        // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
+        // value until it is reset by stack walking - is smaller than the computed threshold, the
+        // corresponding nmethod is considered for removal.
+        if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) {
+          // A method is marked as not-entrant if the method is
+          // 1) 'old enough': nm->hotness_counter() < threshold
+          // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10)
+          //    The second condition is necessary if we are dealing with very small code cache
+          //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
+          //    The second condition ensures that methods are not immediately made not-entrant
+          //    after compilation.
+          nm->make_not_entrant();
+          request_nmethod_marking();
+        }
       }
     }
-
-    // Clean-up all inline caches that points to zombie/non-reentrant methods
+    // Clean-up all inline caches that point to zombie/non-reentrant methods
     MutexLocker cl(CompiledIC_lock);
     nm->cleanup_inline_caches();
     SWEEP(nm);
   }
+  return freed_memory;
 }
 
-// Code cache unloading: when compilers notice the code cache is getting full,
-// they will call a vm op that comes here. This code attempts to speculatively
-// unload the oldest half of the nmethods (based on the compile job id) by
-// saving the old code in a list in the CodeCache. Then
-// execution resumes. If a method so marked is not called by the second sweeper
-// stack traversal after the current one, the nmethod will be marked non-entrant and
-// got rid of by normal sweeping. If the method is called, the Method*'s
-// _code field is restored and the Method*/nmethod
-// go back to their normal state.
-void NMethodSweeper::handle_full_code_cache(bool is_full) {
-
-  if (is_full) {
-    // Since code cache is full, immediately stop new compiles
-    if (CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation)) {
-      log_sweep("disable_compiler");
-    }
-  }
-
-  // Make sure only one thread can flush
-  // The token is reset after CodeCacheMinimumFlushInterval in scan stacks,
-  // no need to check the timeout here.
-  jint old = Atomic::cmpxchg( 1, &_flush_token, 0 );
-  if (old != 0) {
-    return;
-  }
-
-  VM_HandleFullCodeCache op(is_full);
-  VMThread::execute(&op);
-
-  // resweep again as soon as possible
-  _resweep = true;
-}
-
-void NMethodSweeper::speculative_disconnect_nmethods(bool is_full) {
-  // If there was a race in detecting full code cache, only run
-  // one vm op for it or keep the compiler shut off
-
-  jlong disconnect_start_counter = os::elapsed_counter();
-
-  // Traverse the code cache trying to dump the oldest nmethods
-  int curr_max_comp_id = CompileBroker::get_compilation_id();
-  int flush_target = ((curr_max_comp_id - _dead_compile_ids) / CodeCacheFlushingFraction) + _dead_compile_ids;
-
-  log_sweep("start_cleaning");
-
-  nmethod* nm = CodeCache::alive_nmethod(CodeCache::first());
-  jint disconnected = 0;
-  jint made_not_entrant  = 0;
-  jint nmethod_count = 0;
-
-  while ((nm != NULL)){
-    int curr_comp_id = nm->compile_id();
-
-    // OSR methods cannot be flushed like this. Also, don't flush native methods
-    // since they are part of the JDK in most cases
-    if (!nm->is_osr_method() && !nm->is_locked_by_vm() && !nm->is_native_method()) {
-
-      // only count methods that can be speculatively disconnected
-      nmethod_count++;
-
-      if (nm->is_in_use() && (curr_comp_id < flush_target)) {
-        if ((nm->method()->code() == nm)) {
-          // This method has not been previously considered for
-          // unloading or it was restored already
-          CodeCache::speculatively_disconnect(nm);
-          disconnected++;
-        } else if (nm->is_speculatively_disconnected()) {
-          // This method was previously considered for preemptive unloading and was not called since then
-          CompilationPolicy::policy()->delay_compilation(nm->method());
-          nm->make_not_entrant();
-          made_not_entrant++;
-        }
-
-        if (curr_comp_id > _highest_marked) {
-          _highest_marked = curr_comp_id;
-        }
-      }
-    }
-    nm = CodeCache::alive_nmethod(CodeCache::next(nm));
-  }
-
-  // remember how many compile_ids wheren't seen last flush.
-  _dead_compile_ids = curr_max_comp_id - nmethod_count;
-
-  log_sweep("stop_cleaning",
-                       "disconnected='" UINT32_FORMAT "' made_not_entrant='" UINT32_FORMAT "'",
-                       disconnected, made_not_entrant);
-
-  // Shut off compiler. Sweeper will start over with a new stack scan and
-  // traversal cycle and turn it back on if it clears enough space.
-  if (is_full) {
-    _last_full_flush_time = os::javaTimeMillis();
-  }
-
-  jlong disconnect_end_counter = os::elapsed_counter();
-  jlong disconnect_time = disconnect_end_counter - disconnect_start_counter;
-  _total_disconnect_time += disconnect_time;
-  _peak_disconnect_time = MAX2(disconnect_time, _peak_disconnect_time);
-
-  EventCleanCodeCache event(UNTIMED);
-  if (event.should_commit()) {
-    event.set_starttime(disconnect_start_counter);
-    event.set_endtime(disconnect_end_counter);
-    event.set_disconnectedCount(disconnected);
-    event.set_madeNonEntrantCount(made_not_entrant);
-    event.commit();
-  }
-  _number_of_flushes++;
-
-  // After two more traversals the sweeper will get rid of unrestored nmethods
-  _last_flush_traversal_id = _traversals;
-  _resweep = true;
-#ifdef ASSERT
-
-  if(PrintMethodFlushing && Verbose) {
-    tty->print_cr("### sweeper: unload time: " INT64_FORMAT, (jlong)disconnect_time);
-  }
-#endif
-}
-
-
 // Print out some state information about the current sweep and the
 // state of the code cache if it's requested.
 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
diff --git a/src/share/vm/runtime/sweeper.hpp b/src/share/vm/runtime/sweeper.hpp
index da4a13adc..bd3517607 100644
--- a/src/share/vm/runtime/sweeper.hpp
+++ b/src/share/vm/runtime/sweeper.hpp
@@ -27,8 +27,30 @@
 
 // An NmethodSweeper is an incremental cleaner for:
 //    - cleanup inline caches
-//    - reclamation of unreferences zombie nmethods
-//
+//    - reclamation of nmethods
+// Removing nmethods from the code cache includes two operations
+//  1) mark active nmethods
+//     Is done in 'mark_active_nmethods()'. This function is called at a
+//     safepoint and marks all nmethods that are active on a thread's stack.
+//  2) sweep nmethods
+//     Is done in sweep_code_cache(). This function is the only place in the
+//     sweeper where memory is reclaimed. Note that sweep_code_cache() is not
+//     called at a safepoint. However, sweep_code_cache() stops executing if
+//     another thread requests a safepoint. Consequently, 'mark_active_nmethods()'
+//     and sweep_code_cache() cannot execute at the same time.
+//     To reclaim memory, nmethods are first marked as 'not-entrant'. Methods can
+//     be made not-entrant by (i) the sweeper, (ii) deoptimization, (iii) dependency
+//     invalidation, and (iv) being replaced be a different method version (tiered
+//     compilation). Not-entrant nmethod cannot be called by Java threads, but they
+//     can still be active on the stack. To ensure that active nmethod are not reclaimed,
+//     we have to wait until the next marking phase has completed. If a not-entrant
+//     nmethod was NOT marked as active, it can be converted to 'zombie' state. To safely
+//     remove the nmethod, all inline caches (IC) that point to the the nmethod must be
+//     cleared. After that, the nmethod can be evicted from the code cache. Each nmethod's
+//     state change happens during separate sweeps. It may take at least 3 sweeps before an
+//     nmethod's space is freed. Sweeping is currently done by compiler threads between
+//     compilations or at least each 5 sec (NmethodSweepCheckInterval) when the code cache
+//     is full.
 
 class NMethodSweeper : public AllStatic {
   static long      _traversals;      // Stack scan count, also sweep ID.
@@ -41,46 +63,38 @@ class NMethodSweeper : public AllStatic {
   static volatile int  _invocations;   // No. of invocations left until we are completed with this pass
   static volatile int  _sweep_started; // Flag to control conc sweeper
 
-  //The following are reset in scan_stacks and synchronized by the safepoint
-  static bool      _resweep;           // Indicates that a change has happend and we want another sweep,
-                                       // always checked and reset at a safepoint so memory will be in sync.
-  static int       _locked_seen;       // Number of locked nmethods encountered during the scan
+  //The following are reset in mark_active_nmethods and synchronized by the safepoint
+  static bool      _request_mark_phase;        // Indicates that a change has happend and we need another mark pahse,
+                                               // always checked and reset at a safepoint so memory will be in sync.
+  static int       _locked_seen;               // Number of locked nmethods encountered during the scan
   static int       _not_entrant_seen_on_stack; // Number of not entrant nmethod were are still on stack
-  static jint      _flush_token;       // token that guards method flushing, making sure it is executed only once.
-
-  // These are set during a flush, a VM-operation
-  static long      _last_flush_traversal_id; // trav number at last flush unloading
-  static jlong     _last_full_flush_time;    // timestamp of last emergency unloading
-
-  // These are synchronized by the _sweep_started token
-  static int       _highest_marked;   // highest compile id dumped at last emergency unloading
-  static int       _dead_compile_ids; // number of compile ids that where not in the cache last flush
 
   // Stat counters
-  static int       _number_of_flushes;            // Total of full traversals caused by full cache
   static int       _total_nof_methods_reclaimed;  // Accumulated nof methods flushed
   static jlong     _total_time_sweeping;          // Accumulated time sweeping
   static jlong     _total_time_this_sweep;        // Total time this sweep
   static jlong     _peak_sweep_time;              // Peak time for a full sweep
   static jlong     _peak_sweep_fraction_time;     // Peak time sweeping one fraction
-  static jlong     _total_disconnect_time;        // Total time cleaning code mem
-  static jlong     _peak_disconnect_time;         // Peak time cleaning code mem
 
-  static void process_nmethod(nmethod *nm);
+  static int  process_nmethod(nmethod *nm);
   static void release_nmethod(nmethod* nm);
 
-  static void log_sweep(const char* msg, const char* format = NULL, ...);
   static bool sweep_in_progress();
+  static void sweep_code_cache();
+  static void request_nmethod_marking() { _request_mark_phase = true; }
+  static void reset_nmethod_marking()   { _request_mark_phase = false; }
+  static bool need_marking_phase()      { return _request_mark_phase; }
+
+  static int _hotness_counter_reset_val;
 
  public:
   static long traversal_count()              { return _traversals; }
-  static int  number_of_flushes()            { return _number_of_flushes; }
   static int  total_nof_methods_reclaimed()  { return _total_nof_methods_reclaimed; }
   static jlong total_time_sweeping()         { return _total_time_sweeping; }
   static jlong peak_sweep_time()             { return _peak_sweep_time; }
   static jlong peak_sweep_fraction_time()    { return _peak_sweep_fraction_time; }
-  static jlong total_disconnect_time()       { return _total_disconnect_time; }
-  static jlong peak_disconnect_time()        { return _peak_disconnect_time; }
+  static void log_sweep(const char* msg, const char* format = NULL, ...);
+
 
 #ifdef ASSERT
   static bool is_sweeping(nmethod* which) { return _current == which; }
@@ -90,19 +104,18 @@ class NMethodSweeper : public AllStatic {
   static void report_events();
 #endif
 
-  static void scan_stacks();      // Invoked at the end of each safepoint
-  static void sweep_code_cache(); // Concurrent part of sweep job
-  static void possibly_sweep();   // Compiler threads call this to sweep
+  static void mark_active_nmethods();      // Invoked at the end of each safepoint
+  static void possibly_sweep();            // Compiler threads call this to sweep
 
-  static void notify(nmethod* nm) {
+  static int sort_nmethods_by_hotness(nmethod** nm1, nmethod** nm2);
+  static int hotness_counter_reset_val();
+
+  static void notify() {
     // Request a new sweep of the code cache from the beginning. No
     // need to synchronize the setting of this flag since it only
     // changes to false at safepoint so we can never overwrite it with false.
-     _resweep = true;
+     request_nmethod_marking();
   }
-
-  static void handle_full_code_cache(bool is_full); // Called by compilers who fail to allocate
-  static void speculative_disconnect_nmethods(bool was_full);   // Called by vm op to deal with alloc failure
 };
 
 #endif // SHARE_VM_RUNTIME_SWEEPER_HPP
diff --git a/src/share/vm/runtime/vmStructs.cpp b/src/share/vm/runtime/vmStructs.cpp
index e526c7607..e274b9034 100644
--- a/src/share/vm/runtime/vmStructs.cpp
+++ b/src/share/vm/runtime/vmStructs.cpp
@@ -842,7 +842,7 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
   nonstatic_field(nmethod,             _osr_link,                                     nmethod*)                              \
   nonstatic_field(nmethod,             _scavenge_root_link,                           nmethod*)                              \
   nonstatic_field(nmethod,             _scavenge_root_state,                          jbyte)                                 \
-  nonstatic_field(nmethod,             _state,                                        unsigned char)                         \
+  nonstatic_field(nmethod,             _state,                                        volatile unsigned char)                \
   nonstatic_field(nmethod,             _exception_offset,                             int)                                   \
   nonstatic_field(nmethod,             _deoptimize_offset,                            int)                                   \
   nonstatic_field(nmethod,             _deoptimize_mh_offset,                         int)                                   \
@@ -1360,6 +1360,7 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
   declare_integer_type(long)                                              \
   declare_integer_type(char)                                              \
   declare_unsigned_integer_type(unsigned char)                            \
+  declare_unsigned_integer_type(volatile unsigned char)                   \
   declare_unsigned_integer_type(u_char)                                   \
   declare_unsigned_integer_type(unsigned int)                             \
   declare_unsigned_integer_type(uint)                                     \
@@ -1382,6 +1383,7 @@ typedef BinaryTreeDictionary<Metablock, FreeList> MetablockTreeDictionary;
   declare_toplevel_type(char**)                                           \
   declare_toplevel_type(u_char*)                                          \
   declare_toplevel_type(unsigned char*)                                   \
+  declare_toplevel_type(volatile unsigned char*)                          \
                                                                           \
   /*******************************************************************/   \
   /* Types which it will be handy to have available over in the SA   */   \
diff --git a/src/share/vm/runtime/vm_operations.cpp b/src/share/vm/runtime/vm_operations.cpp
index 5166cfdaa..e26c3938b 100644
--- a/src/share/vm/runtime/vm_operations.cpp
+++ b/src/share/vm/runtime/vm_operations.cpp
@@ -173,10 +173,6 @@ void VM_UnlinkSymbols::doit() {
   SymbolTable::unlink();
 }
 
-void VM_HandleFullCodeCache::doit() {
-  NMethodSweeper::speculative_disconnect_nmethods(_is_full);
-}
-
 void VM_Verify::doit() {
   Universe::heap()->prepare_for_verify();
   Universe::verify(_silent);
diff --git a/src/share/vm/runtime/vm_operations.hpp b/src/share/vm/runtime/vm_operations.hpp
index b6555b457..ca616a52c 100644
--- a/src/share/vm/runtime/vm_operations.hpp
+++ b/src/share/vm/runtime/vm_operations.hpp
@@ -51,7 +51,6 @@
   template(DeoptimizeAll)                         \
   template(ZombieAll)                             \
   template(UnlinkSymbols)                         \
-  template(HandleFullCodeCache)                   \
   template(Verify)                                \
   template(PrintJNI)                              \
   template(HeapDumper)                            \
@@ -261,16 +260,6 @@ class VM_DeoptimizeFrame: public VM_Operation {
   bool allow_nested_vm_operations() const        { return true;  }
 };
 
-class VM_HandleFullCodeCache: public VM_Operation {
- private:
-  bool  _is_full;
- public:
-  VM_HandleFullCodeCache(bool is_full)           { _is_full = is_full; }
-  VMOp_Type type() const                         { return VMOp_HandleFullCodeCache; }
-  void doit();
-  bool allow_nested_vm_operations() const        { return true; }
-};
-
 #ifndef PRODUCT
 class VM_DeoptimizeAll: public VM_Operation {
  private:
diff --git a/src/share/vm/trace/trace.xml b/src/share/vm/trace/trace.xml
index 6b1d9a885..a4286116a 100644
--- a/src/share/vm/trace/trace.xml
+++ b/src/share/vm/trace/trace.xml
@@ -313,13 +313,6 @@ Declares a structure type that can be used in other events.
       <value type="UINT" field="zombifiedCount" label="Methods Zombified"/>
     </event>
 
-    <event id="CleanCodeCache" path="vm/code_sweeper/clean" label="Clean Code Cache"
-             description="Clean code cache from oldest methods"
-             has_thread="true" is_requestable="false" is_constant="false">
-      <value type="UINT" field="disconnectedCount" label="Methods Disconnected"/>
-      <value type="UINT" field="madeNonEntrantCount" label="Methods Made Non-Entrant"/>
-    </event>
-
     <!-- Code cache events -->
 
     <event id="CodeCacheFull" path="vm/code_cache/full" label="Code Cache Full"