diff a/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp b/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
--- a/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
@@ -28,88 +28,58 @@
 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
 #include "gc/shenandoah/shenandoahControlThread.hpp"
 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
 #include "gc/shenandoah/shenandoahFreeSet.hpp"
 #include "gc/shenandoah/shenandoahFullGC.hpp"
-#include "gc/shenandoah/shenandoahPhaseTimings.hpp"
+#include "gc/shenandoah/shenandoahGeneration.hpp"
 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
-#include "gc/shenandoah/shenandoahMark.inline.hpp"
 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
-#include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
-#include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
+#include "gc/shenandoah/shenandoahPacer.inline.hpp"
 #include "gc/shenandoah/shenandoahUtils.hpp"
-#include "gc/shenandoah/shenandoahVMOperations.hpp"
-#include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
-#include "memory/iterator.hpp"
+#include "gc/shenandoah/mode/shenandoahMode.hpp"
+#include "logging/log.hpp"
 #include "memory/metaspaceUtils.hpp"
 #include "memory/metaspaceStats.hpp"
-#include "memory/universe.hpp"
-#include "runtime/atomic.hpp"
 
 ShenandoahControlThread::ShenandoahControlThread() :
-  ConcurrentGCThread(),
-  _alloc_failure_waiters_lock(Mutex::safepoint-2, "ShenandoahAllocFailureGC_lock", true),
-  _gc_waiters_lock(Mutex::safepoint-2, "ShenandoahRequestedGC_lock", true),
-  _periodic_task(this),
+  ShenandoahController(),
   _requested_gc_cause(GCCause::_no_cause_specified),
-  _degen_point(ShenandoahGC::_degenerated_outside_cycle),
-  _allocs_seen(0) {
+  _degen_point(ShenandoahGC::_degenerated_outside_cycle) {
   set_name("Shenandoah Control Thread");
-  reset_gc_id();
   create_and_start();
-  _periodic_task.enroll();
-  if (ShenandoahPacing) {
-    _periodic_pacer_notify_task.enroll();
-  }
-}
-
-ShenandoahControlThread::~ShenandoahControlThread() {
-  // This is here so that super is called.
-}
-
-void ShenandoahPeriodicTask::task() {
-  _thread->handle_force_counters_update();
-  _thread->handle_counters_update();
-}
-
-void ShenandoahPeriodicPacerNotify::task() {
-  assert(ShenandoahPacing, "Should not be here otherwise");
-  ShenandoahHeap::heap()->pacer()->notify_waiters();
 }
 
 void ShenandoahControlThread::run_service() {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
+  ShenandoahHeap* const heap = ShenandoahHeap::heap();
 
-  GCMode default_mode = concurrent_normal;
-  GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
+  const GCMode default_mode = concurrent_normal;
+  const GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
   int sleep = ShenandoahControlIntervalMin;
 
   double last_shrink_time = os::elapsedTime();
   double last_sleep_adjust_time = os::elapsedTime();
 
   // Shrink period avoids constantly polling regions for shrinking.
   // Having a period 10x lower than the delay would mean we hit the
   // shrinking with lag of less than 1/10-th of true delay.
   // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
-  double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
+  const double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
 
-  ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
-  ShenandoahHeuristics* heuristics = heap->heuristics();
+  ShenandoahCollectorPolicy* const policy = heap->shenandoah_policy();
+  ShenandoahHeuristics* const heuristics = heap->heuristics();
   while (!in_graceful_shutdown() && !should_terminate()) {
     // Figure out if we have pending requests.
-    bool alloc_failure_pending = _alloc_failure_gc.is_set();
-    bool is_gc_requested = _gc_requested.is_set();
-    GCCause::Cause requested_gc_cause = _requested_gc_cause;
-    bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
-    bool implicit_gc_requested = is_gc_requested && !is_explicit_gc(requested_gc_cause);
+    const bool alloc_failure_pending = _alloc_failure_gc.is_set();
+    const bool is_gc_requested = _gc_requested.is_set();
+    const GCCause::Cause requested_gc_cause = _requested_gc_cause;
 
-    // This control loop iteration have seen this much allocations.
-    size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
+    // This control loop iteration has seen this much allocation.
+    const size_t allocs_seen = reset_allocs_seen();
 
     // Check if we have seen a new target for soft max heap size.
-    bool soft_max_changed = check_soft_max_changed();
+    const bool soft_max_changed = heap->check_soft_max_changed();
 
     // Choose which GC mode to run in. The block below should select a single mode.
     GCMode mode = none;
     GCCause::Cause cause = GCCause::_last_gc_cause;
     ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
@@ -131,41 +101,21 @@
       } else {
         heuristics->record_allocation_failure_gc();
         policy->record_alloc_failure_to_full();
         mode = stw_full;
       }
-
-    } else if (explicit_gc_requested) {
+    } else if (is_gc_requested) {
       cause = requested_gc_cause;
-      log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
-
+      log_info(gc)("Trigger: GC request (%s)", GCCause::to_string(cause));
       heuristics->record_requested_gc();
 
-      if (ExplicitGCInvokesConcurrent) {
-        policy->record_explicit_to_concurrent();
-        mode = default_mode;
-        // Unload and clean up everything
-        heap->set_unload_classes(heuristics->can_unload_classes());
-      } else {
-        policy->record_explicit_to_full();
+      if (ShenandoahCollectorPolicy::should_run_full_gc(cause)) {
         mode = stw_full;
-      }
-    } else if (implicit_gc_requested) {
-      cause = requested_gc_cause;
-      log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
-
-      heuristics->record_requested_gc();
-
-      if (ShenandoahImplicitGCInvokesConcurrent) {
-        policy->record_implicit_to_concurrent();
+      } else {
         mode = default_mode;
-
         // Unload and clean up everything
         heap->set_unload_classes(heuristics->can_unload_classes());
-      } else {
-        policy->record_implicit_to_full();
-        mode = stw_full;
       }
     } else {
       // Potential normal cycle: ask heuristics if it wants to act
       if (heuristics->should_start_gc()) {
         mode = default_mode;
@@ -176,15 +126,15 @@
       heap->set_unload_classes(heuristics->should_unload_classes());
     }
 
     // Blow all soft references on this cycle, if handling allocation failure,
     // either implicit or explicit GC request,  or we are requested to do so unconditionally.
-    if (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs) {
+    if (alloc_failure_pending || is_gc_requested || ShenandoahAlwaysClearSoftRefs) {
       heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
     }
 
-    bool gc_requested = (mode != none);
+    const bool gc_requested = (mode != none);
     assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
 
     if (gc_requested) {
       // GC is starting, bump the internal ID
       update_gc_id();
@@ -193,11 +143,11 @@
 
       MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
 
       // If GC was requested, we are sampling the counters even without actual triggers
       // from allocation machinery. This captures GC phases more accurately.
-      set_forced_counters_update(true);
+      heap->set_forced_counters_update(true);
 
       // If GC was requested, we better dump freeset data for performance debugging
       {
         ShenandoahHeapLocker locker(heap->lock());
         heap->free_set()->log_status();
@@ -216,11 +166,11 @@
         default:
           ShouldNotReachHere();
       }
 
       // If this was the requested GC cycle, notify waiters about it
-      if (explicit_gc_requested || implicit_gc_requested) {
+      if (is_gc_requested) {
         notify_gc_waiters();
       }
 
       // If this was the allocation failure GC cycle, notify waiters about it
       if (alloc_failure_pending) {
@@ -234,20 +184,20 @@
         heap->free_set()->log_status();
 
         // Notify Universe about new heap usage. This has implications for
         // global soft refs policy, and we better report it every time heap
         // usage goes down.
-        Universe::heap()->update_capacity_and_used_at_gc();
+        heap->update_capacity_and_used_at_gc();
 
         // Signal that we have completed a visit to all live objects.
-        Universe::heap()->record_whole_heap_examined_timestamp();
+        heap->record_whole_heap_examined_timestamp();
       }
 
       // Disable forced counters update, and update counters one more time
       // to capture the state at the end of GC session.
-      handle_force_counters_update();
-      set_forced_counters_update(false);
+      heap->handle_force_counters_update();
+      heap->set_forced_counters_update(false);
 
       // Retract forceful part of soft refs policy
       heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
 
       // Clear metaspace oom flag, if current cycle unloaded classes
@@ -283,40 +233,40 @@
       // GC is over, we are at idle now
       if (ShenandoahPacing) {
         heap->pacer()->setup_for_idle();
       }
     } else {
-      // Allow allocators to know we have seen this much regions
+      // Report to pacer that we have seen this many words allocated
       if (ShenandoahPacing && (allocs_seen > 0)) {
         heap->pacer()->report_alloc(allocs_seen);
       }
     }
 
-    double current = os::elapsedTime();
+    const double current = os::elapsedTime();
 
-    if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
+    if (ShenandoahUncommit && (is_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
       // Explicit GC tries to uncommit everything down to min capacity.
       // Soft max change tries to uncommit everything down to target capacity.
       // Periodic uncommit tries to uncommit suitable regions down to min capacity.
 
-      double shrink_before = (explicit_gc_requested || soft_max_changed) ?
+      double shrink_before = (is_gc_requested || soft_max_changed) ?
                              current :
                              current - (ShenandoahUncommitDelay / 1000.0);
 
       size_t shrink_until = soft_max_changed ?
                              heap->soft_max_capacity() :
                              heap->min_capacity();
 
-      service_uncommit(shrink_before, shrink_until);
+      heap->maybe_uncommit(shrink_before, shrink_until);
       heap->phase_timings()->flush_cycle_to_global();
       last_shrink_time = current;
     }
 
     // Wait before performing the next action. If allocation happened during this wait,
     // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
     // back off exponentially.
-    if (_heap_changed.try_unset()) {
+    if (heap->has_changed()) {
       sleep = ShenandoahControlIntervalMin;
     } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
       sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
       last_sleep_adjust_time = current;
     }
@@ -327,29 +277,10 @@
   while (!should_terminate()) {
     os::naked_short_sleep(ShenandoahControlIntervalMin);
   }
 }
 
-bool ShenandoahControlThread::check_soft_max_changed() const {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-  size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
-  size_t old_soft_max = heap->soft_max_capacity();
-  if (new_soft_max != old_soft_max) {
-    new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
-    new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
-    if (new_soft_max != old_soft_max) {
-      log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
-                   byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
-                   byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
-      );
-      heap->set_soft_max_capacity(new_soft_max);
-      return true;
-    }
-  }
-  return false;
-}
-
 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
   // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
   // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
   // If second allocation failure happens during Degenerated GC cycle (for example, when GC
   // tries to evac something and no memory is available), cycle degrades to Full GC.
@@ -386,22 +317,24 @@
   //
   ShenandoahHeap* heap = ShenandoahHeap::heap();
   if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
 
   GCIdMark gc_id_mark;
-  ShenandoahGCSession session(cause);
+  ShenandoahGCSession session(cause, heap->global_generation());
 
   TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
 
-  ShenandoahConcurrentGC gc;
+  ShenandoahConcurrentGC gc(heap->global_generation(), false);
   if (gc.collect(cause)) {
     // Cycle is complete
-    heap->heuristics()->record_success_concurrent();
-    heap->shenandoah_policy()->record_success_concurrent();
+    heap->global_generation()->heuristics()->record_success_concurrent();
+    heap->shenandoah_policy()->record_success_concurrent(false, gc.abbreviated());
+    heap->log_heap_status("At end of GC");
   } else {
     assert(heap->cancelled_gc(), "Must have been cancelled");
     check_cancellation_or_degen(gc.degen_point());
+    heap->log_heap_status("At end of cancelled GC");
   }
 }
 
 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
   ShenandoahHeap* heap = ShenandoahHeap::heap();
@@ -420,86 +353,45 @@
 void ShenandoahControlThread::stop_service() {
   // Nothing to do here.
 }
 
 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
+  ShenandoahHeap* const heap = ShenandoahHeap::heap();
   GCIdMark gc_id_mark;
-  ShenandoahGCSession session(cause);
+  ShenandoahGCSession session(cause, heap->global_generation());
 
   ShenandoahFullGC gc;
   gc.collect(cause);
-
-  ShenandoahHeap* const heap = ShenandoahHeap::heap();
-  heap->heuristics()->record_success_full();
-  heap->shenandoah_policy()->record_success_full();
 }
 
 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
   assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
-
+  ShenandoahHeap* const heap = ShenandoahHeap::heap();
   GCIdMark gc_id_mark;
-  ShenandoahGCSession session(cause);
+  ShenandoahGCSession session(cause, heap->global_generation());
 
-  ShenandoahDegenGC gc(point);
+  ShenandoahDegenGC gc(point, heap->global_generation());
   gc.collect(cause);
-
-  ShenandoahHeap* const heap = ShenandoahHeap::heap();
-  heap->heuristics()->record_success_degenerated();
-  heap->shenandoah_policy()->record_success_degenerated();
-}
-
-void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-
-  // Determine if there is work to do. This avoids taking heap lock if there is
-  // no work available, avoids spamming logs with superfluous logging messages,
-  // and minimises the amount of work while locks are taken.
-
-  if (heap->committed() <= shrink_until) return;
-
-  bool has_work = false;
-  for (size_t i = 0; i < heap->num_regions(); i++) {
-    ShenandoahHeapRegion *r = heap->get_region(i);
-    if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
-      has_work = true;
-      break;
-    }
-  }
-
-  if (has_work) {
-    heap->entry_uncommit(shrink_before, shrink_until);
-  }
-}
-
-bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
-  return GCCause::is_user_requested_gc(cause) ||
-         GCCause::is_serviceability_requested_gc(cause);
 }
 
 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
-  assert(GCCause::is_user_requested_gc(cause) ||
-         GCCause::is_serviceability_requested_gc(cause) ||
-         cause == GCCause::_metadata_GC_clear_soft_refs ||
-         cause == GCCause::_codecache_GC_aggressive ||
-         cause == GCCause::_codecache_GC_threshold ||
-         cause == GCCause::_full_gc_alot ||
-         cause == GCCause::_wb_young_gc ||
-         cause == GCCause::_wb_full_gc ||
-         cause == GCCause::_wb_breakpoint ||
-         cause == GCCause::_scavenge_alot,
-         "only requested GCs here: %s", GCCause::to_string(cause));
-
-  if (is_explicit_gc(cause)) {
-    if (!DisableExplicitGC) {
-      handle_requested_gc(cause);
-    }
-  } else {
+  if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
     handle_requested_gc(cause);
   }
 }
 
 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
+  // For normal requested GCs (System.gc) we want to block the caller. However,
+  // for whitebox requested GC, we want to initiate the GC and return immediately.
+  // The whitebox caller thread will arrange for itself to wait until the GC notifies
+  // it that has reached the requested breakpoint (phase in the GC).
+  if (cause == GCCause::_wb_breakpoint) {
+    _requested_gc_cause = cause;
+    _gc_requested.set();
+    return;
+  }
+
   // Make sure we have at least one complete GC cycle before unblocking
   // from the explicit GC request.
   //
   // This is especially important for weak references cleanup and/or native
   // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
@@ -515,126 +407,15 @@
     // does not take the lock. We need to enforce following order, so that read side sees
     // latest requested gc cause when the flag is set.
     _requested_gc_cause = cause;
     _gc_requested.set();
 
-    if (cause != GCCause::_wb_breakpoint) {
-      ml.wait();
-    }
-    current_gc_id = get_gc_id();
-  }
-}
-
-void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-
-  assert(current()->is_Java_thread(), "expect Java thread here");
-
-  if (try_set_alloc_failure_gc()) {
-    // Only report the first allocation failure
-    log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
-                 req.type_string(),
-                 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
-
-    // Now that alloc failure GC is scheduled, we can abort everything else
-    heap->cancel_gc(GCCause::_allocation_failure);
-  }
-
-  MonitorLocker ml(&_alloc_failure_waiters_lock);
-  while (is_alloc_failure_gc()) {
     ml.wait();
+    current_gc_id = get_gc_id();
   }
 }
 
-void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
-  ShenandoahHeap* heap = ShenandoahHeap::heap();
-
-  if (try_set_alloc_failure_gc()) {
-    // Only report the first allocation failure
-    log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
-                 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
-  }
-
-  // Forcefully report allocation failure
-  heap->cancel_gc(GCCause::_shenandoah_allocation_failure_evac);
-}
-
-void ShenandoahControlThread::notify_alloc_failure_waiters() {
-  _alloc_failure_gc.unset();
-  MonitorLocker ml(&_alloc_failure_waiters_lock);
-  ml.notify_all();
-}
-
-bool ShenandoahControlThread::try_set_alloc_failure_gc() {
-  return _alloc_failure_gc.try_set();
-}
-
-bool ShenandoahControlThread::is_alloc_failure_gc() {
-  return _alloc_failure_gc.is_set();
-}
-
 void ShenandoahControlThread::notify_gc_waiters() {
   _gc_requested.unset();
   MonitorLocker ml(&_gc_waiters_lock);
   ml.notify_all();
 }
-
-void ShenandoahControlThread::handle_counters_update() {
-  if (_do_counters_update.is_set()) {
-    _do_counters_update.unset();
-    ShenandoahHeap::heap()->monitoring_support()->update_counters();
-  }
-}
-
-void ShenandoahControlThread::handle_force_counters_update() {
-  if (_force_counters_update.is_set()) {
-    _do_counters_update.unset(); // reset these too, we do update now!
-    ShenandoahHeap::heap()->monitoring_support()->update_counters();
-  }
-}
-
-void ShenandoahControlThread::notify_heap_changed() {
-  // This is called from allocation path, and thus should be fast.
-
-  // Update monitoring counters when we took a new region. This amortizes the
-  // update costs on slow path.
-  if (_do_counters_update.is_unset()) {
-    _do_counters_update.set();
-  }
-  // Notify that something had changed.
-  if (_heap_changed.is_unset()) {
-    _heap_changed.set();
-  }
-}
-
-void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
-  assert(ShenandoahPacing, "should only call when pacing is enabled");
-  Atomic::add(&_allocs_seen, words, memory_order_relaxed);
-}
-
-void ShenandoahControlThread::set_forced_counters_update(bool value) {
-  _force_counters_update.set_cond(value);
-}
-
-void ShenandoahControlThread::reset_gc_id() {
-  Atomic::store(&_gc_id, (size_t)0);
-}
-
-void ShenandoahControlThread::update_gc_id() {
-  Atomic::inc(&_gc_id);
-}
-
-size_t ShenandoahControlThread::get_gc_id() {
-  return Atomic::load(&_gc_id);
-}
-
-void ShenandoahControlThread::start() {
-  create_and_start();
-}
-
-void ShenandoahControlThread::prepare_for_graceful_shutdown() {
-  _graceful_shutdown.set();
-}
-
-bool ShenandoahControlThread::in_graceful_shutdown() {
-  return _graceful_shutdown.is_set();
-}
