8236926: Concurrently uncommit memory in G1

Reviewed-by: ayang, tschatzl

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -64,6 +64,7 @@
 #include "gc/g1/g1Trace.hpp"
 #include "gc/g1/g1YCTypes.hpp"
 #include "gc/g1/g1ServiceThread.hpp"
+#include "gc/g1/g1UncommitRegionTask.hpp"
 #include "gc/g1/g1VMOperations.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
@@ -743,7 +744,7 @@ void G1CollectedHeap::dealloc_archive_regions(MemRegion* ranges, size_t count) {
   HeapWord* prev_last_addr = NULL;
   HeapRegion* prev_last_region = NULL;
   size_t size_used = 0;
-  size_t uncommitted_regions = 0;
+  uint shrink_count = 0;
 
   // For each Memregion, free the G1 regions that constitute it, and
   // notify mark-sweep that the range is no longer to be considered 'archive.'
@@ -792,14 +793,17 @@ void G1CollectedHeap::dealloc_archive_regions(MemRegion* ranges, size_t count) {
       } else {
         curr_region = NULL;
       }
+
       _hrm.shrink_at(curr_index, 1);
-      uncommitted_regions++;
+      shrink_count++;
     }
   }
 
-  if (uncommitted_regions != 0) {
+  if (shrink_count != 0) {
-    log_debug(gc, ergo, heap)("Attempt heap shrinking (uncommitted archive regions). Total size: " SIZE_FORMAT "B",
+    log_debug(gc, ergo, heap)("Attempt heap shrinking (archive regions). Total size: " SIZE_FORMAT "B",
-                              HeapRegion::GrainWords * HeapWordSize * uncommitted_regions);
+                              HeapRegion::GrainWords * HeapWordSize * shrink_count);
+    // Explicit uncommit.
+    uncommit_regions(shrink_count);
   }
   decrease_used(size_used);
 }
@@ -1015,6 +1019,7 @@ void G1CollectedHeap::prepare_heap_for_mutators() {
   rebuild_region_sets(false /* free_list_only */);
   abort_refinement();
   resize_heap_if_necessary();
+  uncommit_regions_if_necessary();
 
   // Rebuild the strong code root lists for each region
   rebuild_strong_code_roots();
@@ -1294,6 +1299,7 @@ void G1CollectedHeap::shrink_helper(size_t shrink_bytes) {
   log_debug(gc, ergo, heap)("Shrink the heap. requested shrinking amount: " SIZE_FORMAT "B aligned shrinking amount: " SIZE_FORMAT "B attempted shrinking amount: " SIZE_FORMAT "B",
                             shrink_bytes, aligned_shrink_bytes, shrunk_bytes);
   if (num_regions_removed > 0) {
+    log_debug(gc, heap)("Uncommittable regions after shrink: %u", num_regions_removed);
     policy()->record_new_heap_size(num_regions());
   } else {
     log_debug(gc, ergo, heap)("Did not expand the heap (heap shrinking operation failed)");
@@ -2611,6 +2617,20 @@ void G1CollectedHeap::gc_epilogue(bool full) {
   _collection_pause_end = Ticks::now();
 }
 
+uint G1CollectedHeap::uncommit_regions(uint region_limit) {
+  return _hrm.uncommit_inactive_regions(region_limit);
+}
+
+bool G1CollectedHeap::has_uncommittable_regions() {
+  return _hrm.has_inactive_regions();
+}
+
+void G1CollectedHeap::uncommit_regions_if_necessary() {
+  if (has_uncommittable_regions()) {
+    G1UncommitRegionTask::enqueue();
+  }
+}
+
 void G1CollectedHeap::verify_numa_regions(const char* desc) {
   LogTarget(Trace, gc, heap, verify) lt;
 

src/hotspot/share/gc/g1/g1CollectedHeap.hpp

@@ -563,6 +563,12 @@ public:
 
   void resize_heap_if_necessary();
 
+  // Check if there is memory to uncommit and if so schedule a task to do it.
+  void uncommit_regions_if_necessary();
+  // Immediately uncommit uncommittable regions.
+  uint uncommit_regions(uint region_limit);
+  bool has_uncommittable_regions();
+
   G1NUMA* numa() const { return _numa; }
 
   // Expand the garbage-first heap by at least the given size (in bytes!).

src/hotspot/share/gc/g1/g1CommittedRegionMap.cpp

@@ -0,0 +1,249 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/g1/g1CommittedRegionMap.inline.hpp"
+#include "logging/log.hpp"
+#include "memory/universe.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/safepoint.hpp"
+#include "utilities/debug.hpp"
+
+HeapRegionRange::HeapRegionRange(uint start, uint end) :
+    _start(start),
+    _end(end) {
+  assert(start <= end, "Invariant");
+}
+
+G1CommittedRegionMap::G1CommittedRegionMap() :
+  _active(mtGC),
+  _inactive(mtGC),
+  _num_active(0),
+  _num_inactive(0) { }
+
+void G1CommittedRegionMap::initialize(uint num_regions) {
+  _active.initialize(num_regions);
+  _inactive.initialize(num_regions);
+}
+
+uint G1CommittedRegionMap::num_active() const {
+  return _num_active;
+}
+
+uint G1CommittedRegionMap::num_inactive() const {
+  return _num_inactive;
+}
+
+uint G1CommittedRegionMap::max_length() const {
+  return (uint) _active.size();
+}
+
+void G1CommittedRegionMap::activate(uint start, uint end) {
+  verify_active_count(start, end, 0);
+  verify_inactive_count(start, end, 0);
+
+  log_debug(gc, heap, region)("Activate regions [%u, %u)", start, end);
+
+  active_set_range(start, end);
+}
+
+void G1CommittedRegionMap::reactivate(uint start, uint end) {
+  verify_active_count(start, end, 0);
+  verify_inactive_count(start, end, (end - start));
+
+  log_debug(gc, heap, region)("Reactivate regions [%u, %u)", start, end);
+
+  active_set_range(start, end);
+  inactive_clear_range(start, end);
+}
+
+void G1CommittedRegionMap::deactivate(uint start, uint end) {
+  verify_active_count(start, end, (end - start));
+  verify_inactive_count(start, end, 0);
+
+  log_debug(gc, heap, region)("Deactivate regions [%u, %u)", start, end);
+
+  active_clear_range(start, end);
+  inactive_set_range(start, end);
+}
+
+void G1CommittedRegionMap::uncommit(uint start, uint end) {
+  verify_active_count(start, end, 0);
+  verify_inactive_count(start, end, (end-start));
+
+  log_debug(gc, heap, region)("Uncommit regions [%u, %u)", start, end);
+
+  inactive_clear_range(start, end);
+}
+
+HeapRegionRange G1CommittedRegionMap::next_active_range(uint offset) const {
+  // Find first active index from offset.
+  uint start = (uint) _active.get_next_one_offset(offset);
+  if (start == max_length()) {
+    // Early out when no active regions are found.
+    return HeapRegionRange(max_length(), max_length());
+  }
+
+  uint end = (uint) _active.get_next_zero_offset(start);
+  verify_active_range(start, end);
+
+  return HeapRegionRange(start, end);
+}
+
+HeapRegionRange G1CommittedRegionMap::next_committable_range(uint offset) const {
+  // We should only call this function when there are no inactive regions.
+  verify_no_inactive_regons();
+
+  // Find first free region from offset.
+  uint start = (uint) _active.get_next_zero_offset(offset);
+  if (start == max_length()) {
+    // Early out when no free regions are found.
+    return HeapRegionRange(max_length(), max_length());
+  }
+
+  uint end = (uint) _active.get_next_one_offset(start);
+  verify_free_range(start, end);
+
+  return HeapRegionRange(start, end);
+}
+
+HeapRegionRange G1CommittedRegionMap::next_inactive_range(uint offset) const {
+  // Find first inactive region from offset.
+  uint start = (uint) _inactive.get_next_one_offset(offset);
+
+  if (start == max_length()) {
+    // Early when no inactive regions are found.
+    return HeapRegionRange(max_length(), max_length());
+  }
+
+  uint end = (uint) _inactive.get_next_zero_offset(start);
+  verify_inactive_range(start, end);
+
+  return HeapRegionRange(start, end);
+}
+
+void G1CommittedRegionMap::active_set_range(uint start, uint end) {
+  guarantee_mt_safety_active();
+
+  _active.par_set_range(start, end, BitMap::unknown_range);
+  _num_active += (end - start);
+}
+
+void G1CommittedRegionMap::active_clear_range(uint start, uint end) {
+  guarantee_mt_safety_active();
+
+  _active.par_clear_range(start, end, BitMap::unknown_range);
+  _num_active -= (end - start);
+}
+
+void G1CommittedRegionMap::inactive_set_range(uint start, uint end) {
+  guarantee_mt_safety_inactive();
+
+  _inactive.par_set_range(start, end, BitMap::unknown_range);
+  _num_inactive += (end - start);
+}
+
+void G1CommittedRegionMap::inactive_clear_range(uint start, uint end) {
+  guarantee_mt_safety_inactive();
+
+  _inactive.par_clear_range(start, end, BitMap::unknown_range);
+  _num_inactive -= (end - start);
+}
+
+void G1CommittedRegionMap::guarantee_mt_safety_active() const {
+  // G1CommittedRegionMap _active-map MT safety protocol:
+  // (a) If we're at a safepoint, the caller must either be the VM thread or
+  //     hold the FreeList_lock.
+  // (b) If we're not at a safepoint, the caller must hold the Heap_lock.
+  // Protocol only applies after initialization is complete.
+
+  if (!Universe::is_fully_initialized()) {
+    return;
+  }
+
+  if (SafepointSynchronize::is_at_safepoint()) {
+    guarantee(Thread::current()->is_VM_thread() ||
+              FreeList_lock->owned_by_self(),
+              "G1CommittedRegionMap _active-map MT safety protocol at a safepoint");
+  } else {
+    guarantee(Heap_lock->owned_by_self(),
+              "G1CommittedRegionMap _active-map MT safety protocol outside a safepoint");
+  }
+}
+
+void G1CommittedRegionMap::guarantee_mt_safety_inactive() const {
+  // G1CommittedRegionMap _inactive-map MT safety protocol:
+  // (a) If we're at a safepoint, the caller must either be the VM thread or
+  //     hold the FreeList_lock.
+  // (b) If we're not at a safepoint, the caller must hold the Uncommit_lock.
+  // Protocol only applies after initialization is complete.
+
+  if (!Universe::is_fully_initialized()) {
+    return;
+  }
+
+  if (SafepointSynchronize::is_at_safepoint()) {
+    guarantee(Thread::current()->is_VM_thread() ||
+              FreeList_lock->owned_by_self(),
+              "G1CommittedRegionMap MT safety protocol at a safepoint");
+  } else {
+    guarantee(Uncommit_lock->owned_by_self(),
+              "G1CommittedRegionMap MT safety protocol outside a safepoint");
+  }
+}
+
+#ifdef ASSERT
+void G1CommittedRegionMap::verify_active_range(uint start, uint end) const {
+  assert(active(start), "First region (%u) is not active", start);
+  assert(active(end - 1), "Last region (%u) is not active", end - 1);
+  assert(end == _active.size() || !active(end), "Region (%u) is active but not included in range", end);
+}
+
+void G1CommittedRegionMap::verify_inactive_range(uint start, uint end) const {
+  assert(inactive(start), "First region (%u) is not inactive", start);
+  assert(inactive(end - 1), "Last region (%u) in range is not inactive", end - 1);
+  assert(end == _inactive.size() || !inactive(end), "Region (%u) is inactive but not included in range", end);
+}
+
+void G1CommittedRegionMap::verify_free_range(uint start, uint end) const {
+  assert(!active(start), "First region (%u) is active", start);
+  assert(!active(end - 1), "Last region (%u) in range is active", end - 1);
+}
+
+void G1CommittedRegionMap::verify_no_inactive_regons() const {
+  BitMap::idx_t first_inactive = _inactive.get_next_one_offset(0);
+  assert(first_inactive == _inactive.size(), "Should be no inactive regions, but was at index: " SIZE_FORMAT, first_inactive);
+}
+
+void G1CommittedRegionMap::verify_active_count(uint start, uint end, uint expected) const {
+  uint found = (uint) _active.count_one_bits(start, end);
+  assert(found == expected, "Unexpected number of active regions, found: %u, expected: %u", found, expected);
+}
+
+void G1CommittedRegionMap::verify_inactive_count(uint start, uint end, uint expected) const {
+  uint found = (uint) _inactive.count_one_bits(start, end);
+  assert(found == expected, "Unexpected number of inactive regions, found: %u, expected: %u", found, expected);
+}
+
+#endif //ASSERT

src/hotspot/share/gc/g1/g1CommittedRegionMap.hpp

@@ -0,0 +1,124 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_GC_G1_G1COMMITTEDREGIONMAP_HPP
+#define SHARE_GC_G1_G1COMMITTEDREGIONMAP_HPP
+
+#include "memory/allocation.hpp"
+#include "utilities/bitMap.hpp"
+#include "utilities/macros.hpp"
+
+// Helper class to define a range [start, end) of regions.
+class HeapRegionRange : public StackObj {
+  // Inclusive start of the range.
+  uint _start;
+  // Exclusive end of the range.
+  uint _end;
+ public:
+  HeapRegionRange(uint start, uint end);
+
+  uint start() const { return _start; }
+  uint end() const { return _end; }
+  uint length() const { return _end - _start; }
+};
+
+// The G1CommittedRegionMap keeps track of which regions are currently committed.
+// It tracks both regions ready for use and if there are any regions ready for
+// uncommit. We basically have three states. Uncommitted, Active, Inactive. All
+// regions that are either Active or Inactive are committed.
+//
+// State transitions:
+//   Uncommitted -> Active      (activate())
+//   Active      -> Inactive    (deactivate())
+//   Inactive    -> Active      (reactivate())
+//   Inactive    -> Uncommitted (uncommit())
+//
+class G1CommittedRegionMap : public CHeapObj<mtGC> {
+  // Each bit in this bitmap indicates that the corresponding region is active
+  // and available for allocation.
+  CHeapBitMap _active;
+  // Each bit in this bitmap indicates that the corresponding region is no longer
+  // active and it can be uncommitted.
+  CHeapBitMap _inactive;
+  // The union of these two bitmaps are the regions that are currently committed.
+
+  // The number of regions active and available for use.
+  uint _num_active;
+
+  // The number of regions ready to be uncommitted.
+  uint _num_inactive;
+
+  uint max_length() const;
+
+  // Helpers to mark and do accounting for the bitmaps. Depending on when called
+  // these helpers require to own different locks. See guarantee_mt_safety_* for
+  // details.
+  void active_set_range(uint start, uint end);
+  void active_clear_range(uint start, uint end);
+  void inactive_set_range(uint start, uint end);
+  void inactive_clear_range(uint start, uint end);
+
+public:
+  G1CommittedRegionMap();
+  void initialize(uint num_regions);
+
+  uint num_active() const;
+  uint num_inactive() const;
+
+  // Check if a region is marked active.
+  inline bool active(uint index) const;
+  // Check if a region is marked inactive.
+  inline bool inactive(uint index) const;
+
+  // Mark a range of regions as active.
+  void activate(uint start, uint end);
+  // Mark a range of regions as inactive and ready to be uncommitted.
+  void deactivate(uint start, uint end);
+  // Mark a range of regions active again and no longer ready for uncommit.
+  void reactivate(uint start, uint end);
+  // Uncommit a range of inactive regions.
+  void uncommit(uint start, uint end);
+
+  // Finds the next range of active regions starting at offset.
+  HeapRegionRange next_active_range(uint offset) const;
+  // Finds the next range of inactive regions starting at offset.
+  HeapRegionRange next_inactive_range(uint offset) const;
+  // Finds the next range of committable regions starting at offset.
+  // This function must only be called when no inactive regions are
+  // present and can be used to activate more regions.
+  HeapRegionRange next_committable_range(uint offset) const;
+
+protected:
+  virtual void guarantee_mt_safety_active() const;
+  virtual void guarantee_mt_safety_inactive() const;
+
+  void verify_active_range(uint start, uint end) const NOT_DEBUG_RETURN;
+  void verify_free_range(uint start, uint end) const NOT_DEBUG_RETURN;
+  void verify_inactive_range(uint start, uint end) const NOT_DEBUG_RETURN;
+  void verify_no_inactive_regons() const NOT_DEBUG_RETURN;
+  void verify_active_count(uint start, uint end, uint expected) const NOT_DEBUG_RETURN;
+  void verify_inactive_count(uint start, uint end, uint expected) const NOT_DEBUG_RETURN;
+};
+
+#endif // SHARE_GC_G1_G1COMMITTEDREGIONMAP_HPP

src/hotspot/share/gc/g1/g1CommittedRegionMap.inline.hpp

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_GC_G1_G1COMMITTEDREGIONMAP_INLINE_HPP
+#define SHARE_GC_G1_G1COMMITTEDREGIONMAP_INLINE_HPP
+
+#include "gc/g1/g1CommittedRegionMap.hpp"
+#include "utilities/bitMap.inline.hpp"
+
+inline bool G1CommittedRegionMap::active(uint index) const {
+  return _active.at(index);
+}
+
+inline bool G1CommittedRegionMap::inactive(uint index) const {
+  return _inactive.at(index);
+}
+
+#endif // SHARE_GC_G1_G1COMMITTEDREGIONMAP_INLINE_HPP

src/hotspot/share/gc/g1/g1ConcurrentMark.cpp

@@ -1160,6 +1160,7 @@ void G1ConcurrentMark::remark() {
     }
 
     _g1h->resize_heap_if_necessary();
+    _g1h->uncommit_regions_if_necessary();
 
     compute_new_sizes();
 

src/hotspot/share/gc/g1/g1HRPrinter.hpp

@@ -98,6 +98,18 @@ public:
     }
   }
 
+  void active(HeapRegion* hr) {
+    if (is_active()) {
+      print("ACTIVE", hr);
+    }
+  }
+
+  void inactive(HeapRegion* hr) {
+    if (is_active()) {
+      print("INACTIVE", hr);
+    }
+  }
+
   void uncommit(HeapRegion* hr) {
     if (is_active()) {
       print("UNCOMMIT", hr);

src/hotspot/share/gc/g1/g1PageBasedVirtualSpace.cpp

@@ -187,7 +187,9 @@ void G1PageBasedVirtualSpace::pretouch_internal(size_t start_page, size_t end_pa
 
 bool G1PageBasedVirtualSpace::commit(size_t start_page, size_t size_in_pages) {
   // We need to make sure to commit all pages covered by the given area.
-  guarantee(is_area_uncommitted(start_page, size_in_pages), "Specified area is not uncommitted");
+  guarantee(is_area_uncommitted(start_page, size_in_pages),
+            "Specified area is not uncommitted, start page: " SIZE_FORMAT ", page count: " SIZE_FORMAT,
+            start_page, size_in_pages);
 
   bool zero_filled = true;
   size_t end_page = start_page + size_in_pages;
@@ -196,12 +198,12 @@ bool G1PageBasedVirtualSpace::commit(size_t start_page, size_t size_in_pages) {
     // Check for dirty pages and update zero_filled if any found.
     if (_dirty.get_next_one_offset(start_page, end_page) < end_page) {
       zero_filled = false;
-      _dirty.clear_range(start_page, end_page);
+      _dirty.par_clear_range(start_page, end_page, BitMap::unknown_range);
     }
   } else {
     commit_internal(start_page, end_page);
   }
-  _committed.set_range(start_page, end_page);
+  _committed.par_set_range(start_page, end_page, BitMap::unknown_range);
 
   return zero_filled;
 }
@@ -215,18 +217,20 @@ void G1PageBasedVirtualSpace::uncommit_internal(size_t start_page, size_t end_pa
 }
 
 void G1PageBasedVirtualSpace::uncommit(size_t start_page, size_t size_in_pages) {
-  guarantee(is_area_committed(start_page, size_in_pages), "checking");
+  guarantee(is_area_committed(start_page, size_in_pages),
+            "Specified area is not committed, start page: " SIZE_FORMAT ", page count: " SIZE_FORMAT,
+            start_page, size_in_pages);
 
   size_t end_page = start_page + size_in_pages;
   if (_special) {
     // Mark that memory is dirty. If committed again the memory might
     // need to be cleared explicitly.
-    _dirty.set_range(start_page, end_page);
+    _dirty.par_set_range(start_page, end_page, BitMap::unknown_range);
   } else {
     uncommit_internal(start_page, end_page);
   }
 
-  _committed.clear_range(start_page, end_page);
+  _committed.par_clear_range(start_page, end_page, BitMap::unknown_range);
 }
 
 void G1PageBasedVirtualSpace::pretouch(size_t start_page, size_t size_in_pages, WorkGang* pretouch_gang) {

src/hotspot/share/gc/g1/g1RegionToSpaceMapper.cpp

@@ -28,6 +28,7 @@
 #include "gc/g1/g1RegionToSpaceMapper.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/virtualspace.hpp"
+#include "runtime/mutexLocker.hpp"
 #include "services/memTracker.hpp"
 #include "utilities/align.hpp"
 #include "utilities/bitMap.inline.hpp"
@@ -50,6 +51,14 @@ G1RegionToSpaceMapper::G1RegionToSpaceMapper(ReservedSpace rs,
   MemTracker::record_virtual_memory_type((address)rs.base(), type);
 }
 
+// Used to manually signal a mapper to handle a set of regions as committed.
+// Setting the 'zero_filled' parameter to false signals the mapper that the
+// regions have not been cleared by the OS and that they need to be clear
+// explicitly.
+void G1RegionToSpaceMapper::signal_mapping_changed(uint start_idx, size_t num_regions) {
+  fire_on_commit(start_idx, num_regions, false);
+}
+
 // G1RegionToSpaceMapper implementation where the region granularity is larger than
 // or the same as the commit granularity.
 // Basically, the space corresponding to one region region spans several OS pages.
@@ -70,7 +79,21 @@ class G1RegionsLargerThanCommitSizeMapper : public G1RegionToSpaceMapper {
     guarantee(alloc_granularity >= page_size, "allocation granularity smaller than commit granularity");
   }
 
+  bool is_range_committed(uint start_idx, size_t num_regions) {
+    BitMap::idx_t end = start_idx + num_regions;
+    return _region_commit_map.get_next_zero_offset(start_idx, end) == end;
+  }
+
+  bool is_range_uncommitted(uint start_idx, size_t num_regions) {
+    BitMap::idx_t end = start_idx + num_regions;
+    return _region_commit_map.get_next_one_offset(start_idx, end) == end;
+  }
+
   virtual void commit_regions(uint start_idx, size_t num_regions, WorkGang* pretouch_gang) {
+    guarantee(is_range_uncommitted(start_idx, num_regions),
+              "Range not uncommitted, start: %u, num_regions: " SIZE_FORMAT,
+              start_idx, num_regions);
+
     const size_t start_page = (size_t)start_idx * _pages_per_region;
     const size_t size_in_pages = num_regions * _pages_per_region;
     bool zero_filled = _storage.commit(start_page, size_in_pages);
@@ -84,13 +107,17 @@ class G1RegionsLargerThanCommitSizeMapper : public G1RegionToSpaceMapper {
     if (AlwaysPreTouch) {
       _storage.pretouch(start_page, size_in_pages, pretouch_gang);
     }
-    _region_commit_map.set_range(start_idx, start_idx + num_regions);
+    _region_commit_map.par_set_range(start_idx, start_idx + num_regions, BitMap::unknown_range);
     fire_on_commit(start_idx, num_regions, zero_filled);
   }
 
   virtual void uncommit_regions(uint start_idx, size_t num_regions) {
+    guarantee(is_range_committed(start_idx, num_regions),
+             "Range not committed, start: %u, num_regions: " SIZE_FORMAT,
+              start_idx, num_regions);
+
     _storage.uncommit((size_t)start_idx * _pages_per_region, num_regions * _pages_per_region);
-    _region_commit_map.clear_range(start_idx, start_idx + num_regions);
+    _region_commit_map.par_clear_range(start_idx, start_idx + num_regions, BitMap::unknown_range);
   }
 };
 
@@ -99,6 +126,17 @@ class G1RegionsLargerThanCommitSizeMapper : public G1RegionToSpaceMapper {
 // Basically, the contents of one OS page span several regions.
 class G1RegionsSmallerThanCommitSizeMapper : public G1RegionToSpaceMapper {
   size_t _regions_per_page;
+  // Lock to prevent bitmap updates and the actual underlying
+  // commit to get out of order. This can happen in the cases
+  // where one thread is expanding the heap during a humongous
+  // allocation and at the same time the service thread is
+  // doing uncommit. These operations will not operate on the
+  // same regions, but they might operate on regions sharing
+  // an underlying OS page. So we need to make sure that both
+  // those resources are in sync:
+  // - G1RegionToSpaceMapper::_region_commit_map;
+  // - G1PageBasedVirtualSpace::_committed (_storage.commit())
+  Mutex _lock;
 
   size_t region_idx_to_page_idx(uint region_idx) const {
     return region_idx / _regions_per_page;
@@ -128,7 +166,8 @@ class G1RegionsSmallerThanCommitSizeMapper : public G1RegionToSpaceMapper {
                                        size_t commit_factor,
                                        MEMFLAGS type) :
     G1RegionToSpaceMapper(rs, actual_size, page_size, alloc_granularity, commit_factor, type),
-    _regions_per_page((page_size * commit_factor) / alloc_granularity) {
+    _regions_per_page((page_size * commit_factor) / alloc_granularity),
+    _lock(Mutex::leaf, "G1 mapper lock", true, Mutex::_safepoint_check_never) {
 
     guarantee((page_size * commit_factor) >= alloc_granularity, "allocation granularity smaller than commit granularity");
   }
@@ -148,29 +187,36 @@ class G1RegionsSmallerThanCommitSizeMapper : public G1RegionToSpaceMapper {
     size_t end_page = region_idx_to_page_idx(region_limit - 1);
 
     bool all_zero_filled = true;
-    for (size_t page = start_page; page <= end_page; page++) {
-      if (!is_page_committed(page)) {
-        // Page not committed.
-        if (num_committed == 0) {
-          first_committed = page;
-        }
-        num_committed++;
 
-        if (!_storage.commit(page, 1)) {
+    // Concurrent operations might operate on regions sharing the same
-          // Found dirty region during commit.
+    // underlying OS page. See lock declaration for more details.
+    {
+      MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
+      for (size_t page = start_page; page <= end_page; page++) {
+        if (!is_page_committed(page)) {
+          // Page not committed.
+          if (num_committed == 0) {
+            first_committed = page;
+          }
+          num_committed++;
+
+          if (!_storage.commit(page, 1)) {
+            // Found dirty region during commit.
+            all_zero_filled = false;
+          }
+
+          // Move memory to correct NUMA node for the heap.
+          numa_request_on_node(page);
+        } else {
+          // Page already committed.
           all_zero_filled = false;
         }
-
-        // Move memory to correct NUMA node for the heap.
-        numa_request_on_node(page);
-      } else {
-        // Page already committed.
-        all_zero_filled = false;
       }
-    }
 
-    // Update the commit map for the given range.
+      // Update the commit map for the given range. Not using the par_set_range
-    _region_commit_map.set_range(start_idx, region_limit);
+      // since updates to _region_commit_map for this mapper is protected by _lock.
+      _region_commit_map.set_range(start_idx, region_limit, BitMap::unknown_range);
+    }
 
     if (AlwaysPreTouch && num_committed > 0) {
       _storage.pretouch(first_committed, num_committed, pretouch_gang);
@@ -188,8 +234,12 @@ class G1RegionsSmallerThanCommitSizeMapper : public G1RegionToSpaceMapper {
     size_t start_page = region_idx_to_page_idx(start_idx);
     size_t end_page = region_idx_to_page_idx(region_limit - 1);
 
-    // Clear commit map for the given range.
+    // Concurrent operations might operate on regions sharing the same
-    _region_commit_map.clear_range(start_idx, region_limit);
+    // underlying OS page. See lock declaration for more details.
+    MutexLocker ml(&_lock, Mutex::_no_safepoint_check_flag);
+    // Clear commit map for the given range. Not using the par_clear_range since
+    // updates to _region_commit_map for this mapper is protected by _lock.
+    _region_commit_map.clear_range(start_idx, region_limit, BitMap::unknown_range);
 
     for (size_t page = start_page; page <= end_page; page++) {
       // We know all pages were committed before clearing the map. If the

src/hotspot/share/gc/g1/g1RegionToSpaceMapper.hpp

@@ -66,6 +66,8 @@ class G1RegionToSpaceMapper : public CHeapObj<mtGC> {
 
   void set_mapping_changed_listener(G1MappingChangedListener* listener) { _listener = listener; }
 
+  void signal_mapping_changed(uint start_idx, size_t num_regions);
+
   virtual ~G1RegionToSpaceMapper() {}
 
   virtual void commit_regions(uint start_idx, size_t num_regions = 1, WorkGang* pretouch_workers = NULL) = 0;

src/hotspot/share/gc/g1/g1ServiceThread.cpp

@@ -205,16 +205,12 @@ void G1ServiceThread::register_task(G1ServiceTask* task, jlong delay) {
   // Associate the task with the service thread.
   task->set_service_thread(this);
 
-  // Schedule the task to run after the given delay.
+  // Schedule the task to run after the given delay. The service will be
+  // notified to check if this task is first in the queue.
   schedule_task(task, delay);
-
-  // Notify the service thread that there is a new task, thread might
-  // be waiting and the newly added task might be first in the list.
-  MonitorLocker ml(&_monitor, Mutex::_no_safepoint_check_flag);
-  ml.notify();
 }
 
-void G1ServiceThread::schedule_task(G1ServiceTask* task, jlong delay_ms) {
+void G1ServiceThread::schedule(G1ServiceTask* task, jlong delay_ms) {
   guarantee(task->is_registered(), "Must be registered before scheduled");
   guarantee(task->next() == NULL, "Task already in queue");
 
@@ -229,6 +225,11 @@ void G1ServiceThread::schedule_task(G1ServiceTask* task, jlong delay_ms) {
                       task->name(), TimeHelper::counter_to_seconds(task->time()));
 }
 
+void G1ServiceThread::schedule_task(G1ServiceTask* task, jlong delay_ms) {
+  schedule(task, delay_ms);
+  notify();
+}
+
 int64_t G1ServiceThread::time_to_next_task_ms() {
   assert(_monitor.owned_by_self(), "Must be owner of lock");
   assert(!_task_queue.is_empty(), "Should not be called for empty list");
@@ -243,6 +244,11 @@ int64_t G1ServiceThread::time_to_next_task_ms() {
   return (int64_t) TimeHelper::counter_to_millis(time_diff);
 }
 
+void G1ServiceThread::notify() {
+  MonitorLocker ml(&_monitor, Mutex::_no_safepoint_check_flag);
+  ml.notify();
+}
+
 void G1ServiceThread::sleep_before_next_cycle() {
   if (should_terminate()) {
     return;
@@ -309,8 +315,7 @@ void G1ServiceThread::run_service() {
 }
 
 void G1ServiceThread::stop_service() {
-  MonitorLocker ml(&_monitor, Mutex::_no_safepoint_check_flag);
+  notify();
-  ml.notify();
 }
 
 G1ServiceTask::G1ServiceTask(const char* name) :
@@ -328,7 +333,9 @@ bool G1ServiceTask::is_registered() {
 }
 
 void G1ServiceTask::schedule(jlong delay_ms) {
-  _service_thread->schedule_task(this, delay_ms);
+  assert(Thread::current() == _service_thread,
+         "Can only be used when already running on the service thread");
+  _service_thread->schedule(this, delay_ms);
 }
 
 const char* G1ServiceTask::name() {

src/hotspot/share/gc/g1/g1ServiceThread.hpp

@@ -61,8 +61,9 @@ public:
   virtual void execute() = 0;
 
 protected:
-  // Schedule the task on the associated service thread
+  // Schedule the task on the associated service thread using
-  // using the provided delay in milliseconds.
+  // the provided delay in milliseconds. Can only be used when
+  // currently running on the service thread.
   void schedule(jlong delay_ms);
 
   // These setters are protected for use by testing and the
@@ -122,8 +123,13 @@ class G1ServiceThread: public ConcurrentGCThread {
   G1ServiceTask* pop_due_task();
   void run_task(G1ServiceTask* task);
 
-  // Schedule a registered task to run after the given delay.
+  // Helper used by both schedule_task() and G1ServiceTask::schedule()
-  void schedule_task(G1ServiceTask* task, jlong delay);
+  // to schedule a registered task to run after the given delay.
+  void schedule(G1ServiceTask* task, jlong delay);
+
+  // Notify a change to the service thread. Used to either stop
+  // the service or to force check for new tasks.
+  void notify();
 
 public:
   G1ServiceThread();
@@ -133,6 +139,10 @@ public:
   // Register a task with the service thread and schedule it. If
   // no delay is specified the task is scheduled to run directly.
   void register_task(G1ServiceTask* task, jlong delay = 0);
+
+  // Schedule the task and notify the service thread that a new
+  // task might be ready to run.
+  void schedule_task(G1ServiceTask* task, jlong delay);
 };
 
 #endif // SHARE_GC_G1_G1SERVICETHREAD_HPP

src/hotspot/share/gc/g1/g1UncommitRegionTask.cpp

@@ -0,0 +1,136 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/g1/g1CollectedHeap.inline.hpp"
+#include "gc/g1/g1UncommitRegionTask.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
+#include "runtime/globals.hpp"
+#include "utilities/ticks.hpp"
+
+G1UncommitRegionTask* G1UncommitRegionTask::_instance = NULL;
+
+G1UncommitRegionTask::G1UncommitRegionTask() :
+    G1ServiceTask("G1 Uncommit Region Task"),
+    _active(false),
+    _summary_duration(),
+    _summary_region_count(0) { }
+
+void G1UncommitRegionTask::initialize() {
+  assert(_instance == NULL, "Already initialized");
+  _instance = new G1UncommitRegionTask();
+
+  // Register the task with the service thread. This will automatically
+  // schedule the task so we change the state to active.
+  _instance->set_active(true);
+  G1CollectedHeap::heap()->service_thread()->register_task(_instance);
+}
+
+G1UncommitRegionTask* G1UncommitRegionTask::instance() {
+  if (_instance == NULL) {
+    initialize();
+  }
+  return _instance;
+}
+
+void G1UncommitRegionTask::enqueue() {
+  assert_at_safepoint_on_vm_thread();
+
+  G1UncommitRegionTask* uncommit_task = instance();
+  if (!uncommit_task->is_active()) {
+    // Change state to active and schedule with no delay.
+    uncommit_task->set_active(true);
+    G1CollectedHeap::heap()->service_thread()->schedule_task(uncommit_task, 0);
+  }
+}
+
+bool G1UncommitRegionTask::is_active() {
+  return _active;
+}
+
+void G1UncommitRegionTask::set_active(bool state) {
+  assert(_active != state, "Must do a state change");
+  // There is no need to guard _active with a lock since the places where it
+  // is updated can never run in parallel. The state is set to true only in
+  // a safepoint and it is set to false while running on the service thread
+  // joined with the suspendible thread set.
+  _active = state;
+}
+
+void G1UncommitRegionTask::report_execution(Tickspan time, uint regions) {
+  _summary_region_count += regions;
+  _summary_duration += time;
+
+  log_trace(gc, heap)("Concurrent Uncommit: " SIZE_FORMAT "%s, %u regions, %1.3fms",
+                      byte_size_in_proper_unit(regions * HeapRegion::GrainBytes),
+                      proper_unit_for_byte_size(regions * HeapRegion::GrainBytes),
+                      regions,
+                      time.seconds() * 1000);
+}
+
+void G1UncommitRegionTask::report_summary() {
+  log_debug(gc, heap)("Concurrent Uncommit Summary: " SIZE_FORMAT "%s, %u regions, %1.3fms",
+                      byte_size_in_proper_unit(_summary_region_count * HeapRegion::GrainBytes),
+                      proper_unit_for_byte_size(_summary_region_count * HeapRegion::GrainBytes),
+                      _summary_region_count,
+                      _summary_duration.seconds() * 1000);
+}
+
+void G1UncommitRegionTask::clear_summary() {
+  _summary_duration = Tickspan();
+  _summary_region_count = 0;
+}
+
+void G1UncommitRegionTask::execute() {
+  assert(_active, "Must be active");
+
+  // Translate the size limit into a number of regions. This cannot be a
+  // compile time constant because G1HeapRegionSize is set ergonomically.
+  static const uint region_limit = (uint) (UncommitSizeLimit / G1HeapRegionSize);
+
+  // Prevent from running during a GC pause.
+  SuspendibleThreadSetJoiner sts;
+  G1CollectedHeap* g1h = G1CollectedHeap::heap();
+
+  Ticks start = Ticks::now();
+  uint uncommit_count = g1h->uncommit_regions(region_limit);
+  Tickspan uncommit_time = (Ticks::now() - start);
+
+  if (uncommit_count > 0) {
+    report_execution(uncommit_time, uncommit_count);
+  }
+
+  // Reschedule if there are more regions to uncommit, otherwise
+  // change state to inactive.
+  if (g1h->has_uncommittable_regions()) {
+    // No delay, reason to reschedule rather then to loop is to allow
+    // other tasks to run without waiting for a full uncommit cycle.
+    schedule(0);
+  } else {
+    // Nothing more to do, change state and report a summary.
+    set_active(false);
+    report_summary();
+    clear_summary();
+  }
+}

src/hotspot/share/gc/g1/g1UncommitRegionTask.hpp

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_GC_G1_G1UNCOMMITREGIONTASK_HPP
+#define SHARE_GC_G1_G1UNCOMMITREGIONTASK_HPP
+
+#include "gc/g1/g1ServiceThread.hpp"
+#include "utilities/globalDefinitions.hpp"
+#include "utilities/ticks.hpp"
+
+class G1UncommitRegionTask : public G1ServiceTask {
+  // Each execution of the uncommit task is limited to uncommit at most 256M.
+  // This limit is small enough to ensure that the duration of each invocation
+  // is short, while still making reasonable progress.
+  static const uint UncommitSizeLimit = 256 * M;
+
+  static G1UncommitRegionTask* _instance;
+  static void initialize();
+  static G1UncommitRegionTask* instance();
+
+  // The _active state is used to prevent the task from being enqueued on the
+  // service thread multiple times. If the task is active, a new requst to
+  // enqueue it will be ignored.
+  bool _active;
+
+  // Members to keep a summary of the current concurrent uncommit
+  // work. Used for printing when no more work is available.
+  Tickspan _summary_duration;
+  uint _summary_region_count;
+
+  G1UncommitRegionTask();
+  bool is_active();
+  void set_active(bool state);
+
+  void report_execution(Tickspan time, uint regions);
+  void report_summary();
+  void clear_summary();
+
+public:
+  static void enqueue();
+  virtual void execute();
+};
+
+#endif

src/hotspot/share/gc/g1/heapRegionManager.cpp

@@ -26,6 +26,7 @@
 #include "gc/g1/g1Arguments.hpp"
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1ConcurrentRefine.hpp"
+#include "gc/g1/g1CommittedRegionMap.inline.hpp"
 #include "gc/g1/g1NUMAStats.hpp"
 #include "gc/g1/heapRegion.hpp"
 #include "gc/g1/heapRegionManager.inline.hpp"
@@ -59,16 +60,11 @@ public:
   const char* get_description() { return "Free Regions"; }
 };
 
-HeapRegionRange::HeapRegionRange(uint start, uint end) : _start(start), _end(end) {
-  assert(start <= end, "Invariant");
-}
-
 HeapRegionManager::HeapRegionManager() :
   _bot_mapper(NULL),
   _cardtable_mapper(NULL),
   _card_counts_mapper(NULL),
-  _available_map(mtGC),
+  _committed_map(),
-  _num_committed(0),
   _allocated_heapregions_length(0),
   _regions(), _heap_mapper(NULL),
   _prev_bitmap_mapper(NULL),
@@ -96,11 +92,7 @@ void HeapRegionManager::initialize(G1RegionToSpaceMapper* heap_storage,
 
   _regions.initialize(heap_storage->reserved(), HeapRegion::GrainBytes);
 
-  _available_map.initialize(_regions.length());
+  _committed_map.initialize(reserved_length());
-}
-
-bool HeapRegionManager::is_available(uint region) const {
-  return _available_map.at(region);
 }
 
 HeapRegion* HeapRegionManager::allocate_free_region(HeapRegionType type, uint requested_node_index) {
@@ -174,13 +166,26 @@ HeapRegion* HeapRegionManager::new_heap_region(uint hrm_index) {
   return g1h->new_heap_region(hrm_index, mr);
 }
 
+void HeapRegionManager::expand(uint start, uint num_regions, WorkGang* pretouch_gang) {
+  commit_regions(start, num_regions, pretouch_gang);
+  for (uint i = start; i < start + num_regions; i++) {
+    HeapRegion* hr = _regions.get_by_index(i);
+    if (hr == NULL) {
+      hr = new_heap_region(i);
+      OrderAccess::storestore();
+      _regions.set_by_index(i, hr);
+      _allocated_heapregions_length = MAX2(_allocated_heapregions_length, i + 1);
+    }
+    G1CollectedHeap::heap()->hr_printer()->commit(hr);
+  }
+  activate_regions(start, num_regions);
+}
+
 void HeapRegionManager::commit_regions(uint index, size_t num_regions, WorkGang* pretouch_gang) {
   guarantee(num_regions > 0, "Must commit more than zero regions");
   guarantee(num_regions <= available(),
             "Cannot commit more than the maximum amount of regions");
 
-  _num_committed += (uint)num_regions;
-
   _heap_mapper->commit_regions(index, num_regions, pretouch_gang);
 
   // Also commit auxiliary data
@@ -193,26 +198,21 @@ void HeapRegionManager::commit_regions(uint index, size_t num_regions, WorkGang*
   _card_counts_mapper->commit_regions(index, num_regions, pretouch_gang);
 }
 
-void HeapRegionManager::uncommit_regions(uint start, size_t num_regions) {
+void HeapRegionManager::uncommit_regions(uint start, uint num_regions) {
-  guarantee(num_regions >= 1, "Need to specify at least one region to uncommit, tried to uncommit zero regions at %u", start);
+  guarantee(num_regions > 0, "No point in calling this for zero regions");
-  guarantee(_num_committed >= num_regions, "pre-condition");
 
-  // Reset node index to distinguish with committed regions.
+  uint end = start + num_regions;
-  for (uint i = start; i < start + num_regions; i++) {
+  G1HRPrinter* printer = G1CollectedHeap::heap()->hr_printer();
-    at(i)->set_node_index(G1NUMA::UnknownNodeIndex);
+  if (printer->is_active()) {
-  }
+    for (uint i = start; i < end; i++) {
-
+      // Can't use at() here since region is no longer marked available.
-  // Print before uncommitting.
+      HeapRegion* hr = _regions.get_by_index(i);
-  if (G1CollectedHeap::heap()->hr_printer()->is_active()) {
+      assert(hr != NULL, "Region should still be present");
-    for (uint i = start; i < start + num_regions; i++) {
+      printer->uncommit(hr);
-      HeapRegion* hr = at(i);
-      G1CollectedHeap::heap()->hr_printer()->uncommit(hr);
     }
   }
 
-  _num_committed -= (uint)num_regions;
+  // Uncommit heap memory
-
-  _available_map.par_clear_range(start, start + num_regions, BitMap::unknown_range);
   _heap_mapper->uncommit_regions(start, num_regions);
 
   // Also uncommit auxiliary data
@@ -223,35 +223,63 @@ void HeapRegionManager::uncommit_regions(uint start, size_t num_regions) {
   _cardtable_mapper->uncommit_regions(start, num_regions);
 
   _card_counts_mapper->uncommit_regions(start, num_regions);
+
+  _committed_map.uncommit(start, end);
 }
 
-void HeapRegionManager::make_regions_available(uint start, uint num_regions, WorkGang* pretouch_gang) {
+void HeapRegionManager::initialize_regions(uint start, uint num_regions) {
-  guarantee(num_regions > 0, "No point in calling this for zero regions");
-  commit_regions(start, num_regions, pretouch_gang);
-  for (uint i = start; i < start + num_regions; i++) {
-    if (_regions.get_by_index(i) == NULL) {
-      HeapRegion* new_hr = new_heap_region(i);
-      OrderAccess::storestore();
-      _regions.set_by_index(i, new_hr);
-      _allocated_heapregions_length = MAX2(_allocated_heapregions_length, i + 1);
-    }
-  }
-
-  _available_map.par_set_range(start, start + num_regions, BitMap::unknown_range);
-
   for (uint i = start; i < start + num_regions; i++) {
     assert(is_available(i), "Just made region %u available but is apparently not.", i);
     HeapRegion* hr = at(i);
-    if (G1CollectedHeap::heap()->hr_printer()->is_active()) {
-      G1CollectedHeap::heap()->hr_printer()->commit(hr);
-    }
 
     hr->initialize();
     hr->set_node_index(G1NUMA::numa()->index_for_region(hr));
-    insert_into_free_list(at(i));
+    insert_into_free_list(hr);
+    G1CollectedHeap::heap()->hr_printer()->active(hr);
   }
 }
 
+void HeapRegionManager::activate_regions(uint start, uint num_regions) {
+  _committed_map.activate(start, start + num_regions);
+  initialize_regions(start, num_regions);
+}
+
+void HeapRegionManager::reactivate_regions(uint start, uint num_regions) {
+  assert(num_regions > 0, "No point in calling this for zero regions");
+
+  clear_auxiliary_data_structures(start, num_regions);
+
+  _committed_map.reactivate(start, start + num_regions);
+  initialize_regions(start, num_regions);
+}
+
+void HeapRegionManager::deactivate_regions(uint start, uint num_regions) {
+  assert(num_regions > 0, "Need to specify at least one region to uncommit, tried to uncommit zero regions at %u", start);
+  assert(length() >= num_regions, "pre-condition");
+
+  // Reset NUMA index to and print state change.
+  uint end = start + num_regions;
+  for (uint i = start; i < end; i++) {
+    HeapRegion* hr = at(i);
+    hr->set_node_index(G1NUMA::UnknownNodeIndex);
+    G1CollectedHeap::heap()->hr_printer()->inactive(hr);
+  }
+
+  _committed_map.deactivate(start, end);
+}
+
+void HeapRegionManager::clear_auxiliary_data_structures(uint start, uint num_regions) {
+  // Signal marking bitmaps to clear the given regions.
+  _prev_bitmap_mapper->signal_mapping_changed(start, num_regions);
+  _next_bitmap_mapper->signal_mapping_changed(start, num_regions);
+  // Signal G1BlockOffsetTable to clear the given regions.
+  _bot_mapper->signal_mapping_changed(start, num_regions);
+  // Signal G1CardTable to clear the given regions.
+  _cardtable_mapper->signal_mapping_changed(start, num_regions);
+  // Signal G1CardCounts to clear the given regions.
+  _card_counts_mapper->signal_mapping_changed(start, num_regions);
+}
+
 MemoryUsage HeapRegionManager::get_auxiliary_data_memory_usage() const {
   size_t used_sz =
     _prev_bitmap_mapper->committed_size() +
@@ -270,31 +298,88 @@ MemoryUsage HeapRegionManager::get_auxiliary_data_memory_usage() const {
   return MemoryUsage(0, used_sz, committed_sz, committed_sz);
 }
 
-uint HeapRegionManager::expand_by(uint num_regions, WorkGang* pretouch_workers) {
+bool HeapRegionManager::has_inactive_regions() const {
-  return expand_at(0, num_regions, pretouch_workers);
+  return _committed_map.num_inactive() > 0;
 }
 
-uint HeapRegionManager::expand_at(uint start, uint num_regions, WorkGang* pretouch_workers) {
+uint HeapRegionManager::uncommit_inactive_regions(uint limit) {
-  if (num_regions == 0) {
+  assert(limit > 0, "Need to specify at least one region to uncommit");
-    return 0;
-  }
 
-  uint offset = start;
+  uint uncommitted = 0;
+  uint offset = 0;
+  do {
+    MutexLocker uc(Uncommit_lock, Mutex::_no_safepoint_check_flag);
+    HeapRegionRange range = _committed_map.next_inactive_range(offset);
+    // No more regions available for uncommit. Return the number of regions
+    // already uncommitted or 0 if there were no longer any inactive regions.
+    if (range.length() == 0) {
+      return uncommitted;
+    }
+
+    uint start = range.start();
+    uint num_regions = MIN2(range.length(), limit - uncommitted);
+    uncommitted += num_regions;
+    uncommit_regions(start, num_regions);
+  } while (uncommitted < limit);
+
+  assert(uncommitted == limit, "Invariant");
+  return uncommitted;
+}
+
+uint HeapRegionManager::expand_inactive(uint num_regions) {
+  uint offset = 0;
   uint expanded = 0;
 
   do {
-    HeapRegionRange regions = find_unavailable_from_idx(offset);
+    HeapRegionRange regions = _committed_map.next_inactive_range(offset);
     if (regions.length() == 0) {
       // No more unavailable regions.
       break;
     }
 
     uint to_expand = MIN2(num_regions - expanded, regions.length());
-    make_regions_available(regions.start(), to_expand, pretouch_workers);
+    reactivate_regions(regions.start(), to_expand);
     expanded += to_expand;
     offset = regions.end();
   } while (expanded < num_regions);
 
+  return expanded;
+}
+
+uint HeapRegionManager::expand_any(uint num_regions, WorkGang* pretouch_workers) {
+  assert(num_regions > 0, "Must expand at least 1 region");
+
+  uint offset = 0;
+  uint expanded = 0;
+
+  do {
+    HeapRegionRange regions = _committed_map.next_committable_range(offset);
+    if (regions.length() == 0) {
+      // No more unavailable regions.
+      break;
+    }
+
+    uint to_expand = MIN2(num_regions - expanded, regions.length());
+    expand(regions.start(), to_expand, pretouch_workers);
+    expanded += to_expand;
+    offset = regions.end();
+  } while (expanded < num_regions);
+
+  return expanded;
+}
+
+uint HeapRegionManager::expand_by(uint num_regions, WorkGang* pretouch_workers) {
+  assert(num_regions > 0, "Must expand at least 1 region");
+
+  // First "undo" any requests to uncommit memory concurrently by
+  // reverting such regions to being available.
+  uint expanded = expand_inactive(num_regions);
+
+  // Commit more regions if needed.
+  if (expanded < num_regions) {
+    expanded += expand_any(num_regions - expanded, pretouch_workers);
+  }
+
   verify_optional();
   return expanded;
 }
@@ -304,9 +389,24 @@ void HeapRegionManager::expand_exact(uint start, uint num_regions, WorkGang* pre
   uint end = start + num_regions;
 
   for (uint i = start; i < end; i++) {
-    if (!is_available(i)) {
+    // First check inactive. If the regions is inactive, try to reactivate it
-      make_regions_available(i, 1, pretouch_workers);
+    // before it get uncommitted by the G1SeriveThread.
+    if (_committed_map.inactive(i)) {
+      // Need to grab the lock since this can be called by a java thread
+      // doing humongous allocations.
+      MutexLocker uc(Uncommit_lock, Mutex::_no_safepoint_check_flag);
+      // State might change while getting the lock.
+      if (_committed_map.inactive(i)) {
+        reactivate_regions(i, 1);
+      }
     }
+    // Not else-if to catch the case where the inactive region was uncommited
+    // while waiting to get the lock.
+    if (!_committed_map.active(i)) {
+      expand(i, 1, pretouch_workers);
+    }
+
+    assert(at(i)->is_free(), "Region must be free at this point");
   }
 
   verify_optional();
@@ -385,15 +485,13 @@ uint HeapRegionManager::find_contiguous_in_range(uint start, uint end, uint num_
 }
 
 uint HeapRegionManager::find_contiguous_in_free_list(uint num_regions) {
-  BitMap::idx_t range_start = 0;
-  BitMap::idx_t range_end = range_start;
   uint candidate = G1_NO_HRM_INDEX;
+  HeapRegionRange range(0,0);
 
   do {
-    range_start = _available_map.get_next_one_offset(range_end);
+    range = _committed_map.next_active_range(range.end());
-    range_end = _available_map.get_next_zero_offset(range_start);
+    candidate = find_contiguous_in_range(range.start(), range.end(), num_regions);
-    candidate = find_contiguous_in_range((uint) range_start, (uint) range_end, num_regions);
+  } while (candidate == G1_NO_HRM_INDEX && range.end() < reserved_length());
-  } while (candidate == G1_NO_HRM_INDEX && range_end < reserved_length());
 
   return candidate;
 }
@@ -435,28 +533,6 @@ void HeapRegionManager::iterate(HeapRegionClosure* blk) const {
   }
 }
 
-HeapRegionRange HeapRegionManager::find_unavailable_from_idx(uint index) const {
-  guarantee(index <= reserved_length(), "checking");
-
-  // Find first unavailable region from offset.
-  BitMap::idx_t start = _available_map.get_next_zero_offset(index);
-  if (start == _available_map.size()) {
-    // No unavailable regions found.
-    return HeapRegionRange(reserved_length(), reserved_length());
-  }
-
-  // The end of the range is the next available region.
-  BitMap::idx_t end = _available_map.get_next_one_offset(start);
-
-  assert(!_available_map.at(start), "Found region (" SIZE_FORMAT ") is not unavailable", start);
-  assert(!_available_map.at(end - 1), "Last region (" SIZE_FORMAT ") in range is not unavailable", end - 1);
-  assert(end == _available_map.size() || _available_map.at(end), "Region (" SIZE_FORMAT ") is not available", end);
-
-  // Shrink returned range to number of regions left to commit if necessary.
-  end = MIN2(start + available(), end);
-  return HeapRegionRange((uint) start, (uint) end);
-}
-
 uint HeapRegionManager::find_highest_free(bool* expanded) {
   // Loop downwards from the highest region index, looking for an
   // entry which is either free or not yet committed.  If not yet
@@ -578,7 +654,8 @@ void HeapRegionManager::shrink_at(uint index, size_t num_regions) {
     assert(at(i)->is_free(), "Expected free region at index %u", i);
   }
 #endif
-  uncommit_regions(index, num_regions);
+  // Mark regions as inactive making them ready for uncommit.
+  deactivate_regions(index, (uint) num_regions);
 }
 
 uint HeapRegionManager::find_empty_from_idx_reverse(uint start_idx, uint* res_idx) const {
@@ -617,9 +694,9 @@ void HeapRegionManager::verify() {
   guarantee(_allocated_heapregions_length <= reserved_length(),
             "invariant: _allocated_length: %u _max_length: %u",
             _allocated_heapregions_length, reserved_length());
-  guarantee(_num_committed <= max_length(),
+  guarantee(length() <= max_length(),
-            "invariant: _num_committed: %u max_regions: %u",
+            "invariant: committed regions: %u max_regions: %u",
-            _num_committed, max_length());
+            length(), max_length());
 
   bool prev_committed = true;
   uint num_committed = 0;
@@ -650,7 +727,7 @@ void HeapRegionManager::verify() {
     guarantee(_regions.get_by_index(i) == NULL, "invariant i: %u", i);
   }
 
-  guarantee(num_committed == _num_committed, "Found %u committed regions, but should be %u", num_committed, _num_committed);
+  guarantee(num_committed == length(), "Found %u committed regions, but should be %u", num_committed, length());
   _free_list.verify();
 }
 

src/hotspot/share/gc/g1/heapRegionManager.hpp

@@ -26,6 +26,7 @@
 #define SHARE_GC_G1_HEAPREGIONMANAGER_HPP
 
 #include "gc/g1/g1BiasedArray.hpp"
+#include "gc/g1/g1CommittedRegionMap.hpp"
 #include "gc/g1/g1RegionToSpaceMapper.hpp"
 #include "gc/g1/heapRegionSet.hpp"
 #include "memory/allocation.hpp"
@@ -42,20 +43,6 @@ class G1HeapRegionTable : public G1BiasedMappedArray<HeapRegion*> {
   virtual HeapRegion* default_value() const { return NULL; }
 };
 
-// Helper class to define a range [start, end) of regions.
-class HeapRegionRange : public StackObj {
-  // Inclusive start of the range.
-  uint _start;
-  // Exclusive end of the range.
-  uint _end;
- public:
-  HeapRegionRange(uint start, uint end);
-
-  uint start() const { return _start; }
-  uint end() const { return _end; }
-  uint length() const { return _end - _start; }
-};
-
 // This class keeps track of the actual heap memory, auxiliary data
 // and its metadata (i.e., HeapRegion instances) and the list of free regions.
 //
@@ -91,12 +78,9 @@ class HeapRegionManager: public CHeapObj<mtGC> {
   G1RegionToSpaceMapper* _cardtable_mapper;
   G1RegionToSpaceMapper* _card_counts_mapper;
 
-  // Each bit in this bitmap indicates that the corresponding region is available
+  // Keeps track of the currently committed regions in the heap. The committed regions
-  // for allocation.
+  // can either be active (ready for use) or inactive (ready for uncommit).
-  CHeapBitMap _available_map;
+  G1CommittedRegionMap _committed_map;
-
-  // The number of regions committed in the heap.
-  uint _num_committed;
 
   // Internal only. The highest heap region +1 we allocated a HeapRegion instance for.
   uint _allocated_heapregions_length;
@@ -107,6 +91,9 @@ class HeapRegionManager: public CHeapObj<mtGC> {
   // Pass down commit calls to the VirtualSpace.
   void commit_regions(uint index, size_t num_regions = 1, WorkGang* pretouch_gang = NULL);
 
+  // Initialize the HeapRegions in the range and put them on the free list.
+  void initialize_regions(uint start, uint num_regions);
+
   // Find a contiguous set of empty or uncommitted regions of length num_regions and return
   // the index of the first region or G1_NO_HRM_INDEX if the search was unsuccessful.
   // Start and end defines the range to seek in, policy is first-fit.
@@ -120,10 +107,6 @@ class HeapRegionManager: public CHeapObj<mtGC> {
 
   void assert_contiguous_range(uint start, uint num_regions) NOT_DEBUG_RETURN;
 
-  // Finds the next sequence of unavailable regions starting at the given index. Returns the
-  // sequence found as a HeapRegionRange. If no regions can be found, both start and end of
-  // the returned range is equal to reserved_length().
-  HeapRegionRange find_unavailable_from_idx(uint index) const;
   // Finds the next sequence of empty regions starting from start_idx, going backwards in
   // the heap. Returns the length of the sequence found. If this value is zero, no
   // sequence could be found, otherwise res_idx contains the start index of this range.
@@ -132,14 +115,30 @@ class HeapRegionManager: public CHeapObj<mtGC> {
   // Checks the G1MemoryNodeManager to see if this region is on the preferred node.
   bool is_on_preferred_index(uint region_index, uint preferred_node_index);
 
+  // Clear the auxiliary data structures by notifying them that the mapping has
+  // changed. The structures that needs to be cleared will than clear. This is
+  // used to allow reuse regions scheduled for uncommit without uncommitting and
+  // then committing them.
+  void clear_auxiliary_data_structures(uint start, uint num_regions);
+
   G1HeapRegionTable _regions;
   G1RegionToSpaceMapper* _heap_mapper;
   G1RegionToSpaceMapper* _prev_bitmap_mapper;
   G1RegionToSpaceMapper* _next_bitmap_mapper;
   FreeRegionList _free_list;
 
-  void make_regions_available(uint index, uint num_regions = 1, WorkGang* pretouch_gang = NULL);
+  void expand(uint index, uint num_regions, WorkGang* pretouch_gang = NULL);
-  void uncommit_regions(uint index, size_t num_regions = 1);
+
+  // G1RegionCommittedMap helpers. These functions do the work that comes with
+  // the state changes tracked by G1CommittedRegionMap. To make sure this is
+  // safe from a multi-threading point of view there are two lock protocols in
+  // G1RegionCommittedMap::guarantee_mt_safety_* that are enforced. The lock
+  // needed should have been acquired before calling these functions.
+  void activate_regions(uint index, uint num_regions);
+  void deactivate_regions(uint start, uint num_regions);
+  void reactivate_regions(uint start, uint num_regions);
+  void uncommit_regions(uint start, uint num_regions);
+
   // Allocate a new HeapRegion for the given index.
   HeapRegion* new_heap_region(uint hrm_index);
 
@@ -149,6 +148,10 @@ class HeapRegionManager: public CHeapObj<mtGC> {
 
   // Expand helper for cases when the regions to expand are well defined.
   void expand_exact(uint start, uint num_regions, WorkGang* pretouch_workers);
+  // Expand helper activating inactive regions rather than committing new ones.
+  uint expand_inactive(uint num_regions);
+  // Expand helper finding new regions to commit.
+  uint expand_any(uint num_regions, WorkGang* pretouch_workers);
 
 #ifdef ASSERT
 public:
@@ -180,7 +183,7 @@ public:
   inline HeapRegion* at_or_null(uint index) const;
 
   // Returns whether the given region is available for allocation.
-  bool is_available(uint region) const;
+  inline bool is_available(uint region) const;
 
   // Return the next region (by index) that is part of the same
   // humongous object that hr is part of.
@@ -233,8 +236,8 @@ public:
   // Return the number of regions available (uncommitted) regions.
   uint available() const { return max_length() - length(); }
 
-  // Return the number of regions that have been committed in the heap.
+  // Return the number of regions currently active and available for use.
-  uint length() const { return _num_committed; }
+  uint length() const { return _committed_map.num_active(); }
 
   // The number of regions reserved for the heap.
   uint reserved_length() const { return (uint)_regions.length(); }
@@ -252,11 +255,6 @@ public:
   // number of regions might be smaller than what's desired.
   uint expand_by(uint num_regions, WorkGang* pretouch_workers);
 
-  // Makes sure that the regions from start to start+num_regions-1 are available
-  // for allocation. Returns the number of regions that were committed to achieve
-  // this.
-  uint expand_at(uint start, uint num_regions, WorkGang* pretouch_workers);
-
   // Try to expand on the given node index, returning the index of the new region.
   uint expand_on_preferred_node(uint node_index);
 
@@ -282,10 +280,17 @@ public:
   // Return the actual number of uncommitted regions.
   uint shrink_by(uint num_regions_to_remove);
 
-  // Uncommit a number of regions starting at the specified index, which must be available,
+  // Remove a number of regions starting at the specified index, which must be available,
-  // empty, and free.
+  // empty, and free. The regions are marked inactive and can later be uncommitted.
   void shrink_at(uint index, size_t num_regions);
 
+  // Check if there are any inactive regions that can be uncommitted.
+  bool has_inactive_regions() const;
+
+  // Uncommit inactive regions. Limit the number of regions to uncommit and return
+  // actual number uncommitted.
+  uint uncommit_inactive_regions(uint limit);
+
   void verify();
 
   // Do some sanity checking.

src/hotspot/share/gc/g1/heapRegionManager.inline.hpp

@@ -25,10 +25,15 @@
 #ifndef SHARE_GC_G1_HEAPREGIONMANAGER_INLINE_HPP
 #define SHARE_GC_G1_HEAPREGIONMANAGER_INLINE_HPP
 
+#include "gc/g1/g1CommittedRegionMap.inline.hpp"
 #include "gc/g1/heapRegion.hpp"
 #include "gc/g1/heapRegionManager.hpp"
 #include "gc/g1/heapRegionSet.inline.hpp"
 
+inline bool HeapRegionManager::is_available(uint region) const {
+  return _committed_map.active(region);
+}
+
 inline HeapRegion* HeapRegionManager::addr_to_region(HeapWord* addr) const {
   assert(addr < heap_end(),
         "addr: " PTR_FORMAT " end: " PTR_FORMAT, p2i(addr), p2i(heap_end()));

src/hotspot/share/prims/whitebox.cpp

@@ -96,6 +96,7 @@
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/g1ConcurrentMark.hpp"
 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
+#include "gc/g1/heapRegionManager.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
 #endif // INCLUDE_G1GC
 #if INCLUDE_PARALLELGC
@@ -504,6 +505,13 @@ WB_ENTRY(jint, WB_G1RegionSize(JNIEnv* env, jobject o))
   THROW_MSG_0(vmSymbols::java_lang_UnsupportedOperationException(), "WB_G1RegionSize: G1 GC is not enabled");
 WB_END
 
+WB_ENTRY(jboolean, WB_G1HasRegionsToUncommit(JNIEnv* env, jobject o))
+  if (UseG1GC) {
+    return G1CollectedHeap::heap()->has_uncommittable_regions();
+  }
+  THROW_MSG_0(vmSymbols::java_lang_UnsupportedOperationException(), "WB_G1HasRegionsToUncommit: G1 GC is not enabled");
+WB_END
+
 #endif // INCLUDE_G1GC
 
 #if INCLUDE_PARALLELGC
@@ -2302,6 +2310,7 @@ static JNINativeMethod methods[] = {
   {CC"g1NumFreeRegions",   CC"()J",                   (void*)&WB_G1NumFreeRegions  },
   {CC"g1RegionSize",       CC"()I",                   (void*)&WB_G1RegionSize      },
   {CC"g1StartConcMarkCycle",       CC"()Z",           (void*)&WB_G1StartMarkCycle  },
+  {CC"g1HasRegionsToUncommit",  CC"()Z",              (void*)&WB_G1HasRegionsToUncommit},
   {CC"g1AuxiliaryMemoryUsage", CC"()Ljava/lang/management/MemoryUsage;",
                                                       (void*)&WB_G1AuxiliaryMemoryUsage  },
   {CC"g1ActiveMemoryNodeCount", CC"()I",              (void*)&WB_G1ActiveMemoryNodeCount },

src/hotspot/share/runtime/mutexLocker.cpp

@@ -113,6 +113,7 @@ Mutex*   OopMapCacheAlloc_lock        = NULL;
 
 Mutex*   FreeList_lock                = NULL;
 Mutex*   OldSets_lock                 = NULL;
+Mutex*   Uncommit_lock                = NULL;
 Monitor* RootRegionScan_lock          = NULL;
 
 Mutex*   Management_lock              = NULL;
@@ -220,6 +221,7 @@ void mutex_init() {
 
     def(FreeList_lock              , PaddedMutex  , leaf     ,   true,  _safepoint_check_never);
     def(OldSets_lock               , PaddedMutex  , leaf     ,   true,  _safepoint_check_never);
+    def(Uncommit_lock              , PaddedMutex  , leaf + 1 ,   true,  _safepoint_check_never);
     def(RootRegionScan_lock        , PaddedMonitor, leaf     ,   true,  _safepoint_check_never);
 
     def(StringDedupQueue_lock      , PaddedMonitor, leaf,        true,  _safepoint_check_never);

src/hotspot/share/runtime/mutexLocker.hpp

@@ -108,6 +108,7 @@ extern Mutex*   OopMapCacheAlloc_lock;           // protects allocation of oop_m
 
 extern Mutex*   FreeList_lock;                   // protects the free region list during safepoints
 extern Mutex*   OldSets_lock;                    // protects the old region sets
+extern Mutex*   Uncommit_lock;                   // protects the uncommit list when not at safepoints
 extern Monitor* RootRegionScan_lock;             // used to notify that the CM threads have finished scanning the IM snapshot regions
 
 extern Mutex*   Management_lock;                 // a lock used to serialize JVM management

test/hotspot/gtest/gc/g1/test_g1RegionMap.cpp

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/g1/g1CommittedRegionMap.inline.hpp"
+#include "runtime/os.hpp"
+#include "unittest.hpp"
+
+class G1CommittedRegionMapSerial : public G1CommittedRegionMap {
+public:
+  static const uint TestRegions = 512;
+
+  void verify_counts() {
+    verify_active_count(0, TestRegions, num_active());
+    verify_inactive_count(0, TestRegions, num_inactive());
+  }
+
+protected:
+  void guarantee_mt_safety_active() const { }
+  void guarantee_mt_safety_inactive() const { }
+};
+
+static bool mutate() {
+  return os::random() % 2 == 0;
+}
+
+static void generate_random_map(G1CommittedRegionMap* map) {
+  for (uint i = 0; i < G1CommittedRegionMapSerial::TestRegions; i++) {
+    if (mutate()) {
+      map->activate(i, i+1);
+    }
+  }
+
+  if (map->num_active() == 0) {
+    // If we randomly activated 0 regions, activate the first half
+    // to have some regions to test.
+    map->activate(0, G1CommittedRegionMapSerial::TestRegions / 2);
+  }
+}
+
+static void random_deactivate(G1CommittedRegionMap* map) {
+  uint current_offset = 0;
+  do {
+    HeapRegionRange current = map->next_active_range(current_offset);
+    if (mutate()) {
+      if (current.length() < 5) {
+        // For short ranges, deactivate whole.
+        map->deactivate(current.start(), current.end());
+      } else {
+        // For larger ranges, deactivate half.
+        map->deactivate(current.start(), current.end() - (current.length() / 2));
+      }
+    }
+    current_offset = current.end();
+  } while (current_offset != G1CommittedRegionMapSerial::TestRegions);
+}
+
+static void random_uncommit_or_reactive(G1CommittedRegionMap* map) {
+  uint current_offset = 0;
+  do {
+    HeapRegionRange current = map->next_inactive_range(current_offset);
+    // Randomly either reactivate or uncommit
+    if (mutate()) {
+      map->reactivate(current.start(), current.end());
+    } else {
+      map->uncommit(current.start(), current.end());
+    }
+
+    current_offset = current.end();
+  } while (current_offset != G1CommittedRegionMapSerial::TestRegions);
+}
+
+static void random_activate_free(G1CommittedRegionMap* map) {
+  uint current_offset = 0;
+  do {
+    HeapRegionRange current = map->next_committable_range(current_offset);
+    // Randomly either reactivate or uncommit
+    if (mutate()) {
+      if (current.length() < 5) {
+        // For short ranges, deactivate whole.
+        map->activate(current.start(), current.end());
+      } else {
+        // For larger ranges, deactivate half.
+        map->activate(current.start(), current.end() - (current.length() / 2));
+      }
+    }
+
+    current_offset = current.end();
+  } while (current_offset != G1CommittedRegionMapSerial::TestRegions);
+}
+
+TEST(G1CommittedRegionMapTest, serial) {
+  G1CommittedRegionMapSerial serial_map;
+  serial_map.initialize(G1CommittedRegionMapSerial::TestRegions);
+
+  // Activate some regions
+  generate_random_map(&serial_map);
+
+  // Work through the map and mutate it
+  for (int i = 0; i < 500; i++) {
+    random_deactivate(&serial_map);
+    serial_map.verify_counts();
+    random_uncommit_or_reactive(&serial_map);
+    serial_map.verify_counts();
+    random_activate_free(&serial_map);
+    serial_map.verify_counts();
+    ASSERT_EQ(serial_map.num_inactive(), 0u);
+  }
+}

test/hotspot/gtest/gc/g1/test_stressCommitUncommit.cpp

@@ -0,0 +1,120 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/g1/g1BlockOffsetTable.hpp"
+#include "gc/g1/g1RegionToSpaceMapper.hpp"
+#include "memory/virtualspace.hpp"
+#include "gc/shared/workgroup.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/os.hpp"
+#include "unittest.hpp"
+
+class G1MapperWorkers : AllStatic {
+  static WorkGang* _work_gang;
+  static WorkGang* work_gang() {
+    if (_work_gang == NULL) {
+      _work_gang = new WorkGang("G1 Small Workers", MaxWorkers, false, false);
+      _work_gang->initialize_workers();
+      _work_gang->update_active_workers(MaxWorkers);
+    }
+    return _work_gang;
+  }
+
+public:
+  static const uint MaxWorkers = 4;
+  static void run_task(AbstractGangTask* task) {
+    work_gang()->run_task(task);
+  }
+};
+WorkGang* G1MapperWorkers::_work_gang = NULL;
+
+class G1TestCommitUncommit : public AbstractGangTask {
+  G1RegionToSpaceMapper* _mapper;
+  uint _claim_id;
+public:
+  G1TestCommitUncommit(G1RegionToSpaceMapper* mapper) :
+      AbstractGangTask("Stress mapper"),
+      _mapper(mapper),
+      _claim_id(0) { }
+
+  void work(uint worker_id) {
+    uint index = Atomic::fetch_and_add(&_claim_id, 1u);
+
+    for (int i = 0; i < 100000; i++) {
+      // Stress commit and uncommit of a single region. The same
+      // will be done for multiple adjacent region to make sure
+      // we properly handle bitmap updates as well as updates for
+      // regions sharing the same underlying OS page.
+      _mapper->commit_regions(index);
+      _mapper->uncommit_regions(index);
+    }
+  }
+};
+
+TEST_VM(G1RegionToSpaceMapper, smallStressAdjacent) {
+  // Fake a heap with 1m regions and create a BOT like mapper. This
+  // will give a G1RegionsSmallerThanCommitSizeMapper to stress.
+  uint num_regions = G1MapperWorkers::MaxWorkers;
+  size_t region_size = 1*M;
+  size_t size = G1BlockOffsetTable::compute_size(num_regions * region_size / HeapWordSize);
+  size_t page_size = os::vm_page_size();
+
+  ReservedSpace rs(size, os::vm_page_size());
+
+  G1RegionToSpaceMapper* small_mapper  =
+    G1RegionToSpaceMapper::create_mapper(rs,
+                                         size,
+                                         page_size,
+                                         region_size,
+                                         G1BlockOffsetTable::heap_map_factor(),
+                                         mtGC);
+
+
+
+  G1TestCommitUncommit task(small_mapper);
+  G1MapperWorkers::run_task(&task);
+}
+
+TEST_VM(G1RegionToSpaceMapper, largeStressAdjacent) {
+  // Fake a heap with 2m regions and create a BOT like mapper. This
+  // will give a G1RegionsLargerThanCommitSizeMapper to stress.
+  uint num_regions = G1MapperWorkers::MaxWorkers;
+  size_t region_size = 2*M;
+  size_t size = G1BlockOffsetTable::compute_size(num_regions * region_size / HeapWordSize);
+  size_t page_size = os::vm_page_size();
+
+  ReservedSpace rs(size, page_size);
+
+  G1RegionToSpaceMapper* large_mapper  =
+    G1RegionToSpaceMapper::create_mapper(rs,
+                                         size,
+                                         page_size,
+                                         region_size,
+                                         G1BlockOffsetTable::heap_map_factor(),
+                                         mtGC);
+
+  G1TestCommitUncommit task(large_mapper);
+  G1MapperWorkers::run_task(&task);
+}

test/hotspot/jtreg/gc/g1/TestShrinkAuxiliaryData.java

@@ -153,7 +153,7 @@ public class TestShrinkAuxiliaryData {
 
     static class ShrinkAuxiliaryDataTest {
 
-        public static void main(String[] args) throws IOException {
+        public static void main(String[] args) throws Exception {
 
             ShrinkAuxiliaryDataTest testCase = new ShrinkAuxiliaryDataTest();
 
@@ -220,7 +220,7 @@ public class TestShrinkAuxiliaryData {
 
         private final List<GarbageObject> garbage = new ArrayList<>();
 
-        public void test() throws IOException {
+        public void test() throws Exception {
 
             MemoryUsage muFull, muFree, muAuxDataFull, muAuxDataFree;
             float auxFull, auxFree;
@@ -242,6 +242,14 @@ public class TestShrinkAuxiliaryData {
             deallocate();
             System.gc();
 
+            if (WhiteBox.getWhiteBox().g1HasRegionsToUncommit()) {
+                System.out.println("Waiting for concurrent uncommit to complete");
+                do {
+                    Thread.sleep(1000);
+                } while(WhiteBox.getWhiteBox().g1HasRegionsToUncommit());
+                System.out.println("Concurrent uncommit done");
+            }
+
             muFree = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
             muAuxDataFree = WhiteBox.getWhiteBox().g1AuxiliaryMemoryUsage();
 

test/hotspot/jtreg/gc/stress/TestStressG1Uncommit.java

@@ -0,0 +1,149 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package gc.stress;
+
+/*
+ * @test TestStressUncommit
+ * @key stress
+ * @summary Stress uncommitting by allocating and releasing memory
+ * @requires vm.gc.G1
+ * @library /test/lib
+ * @modules java.base/jdk.internal.misc
+ * @run driver/timeout=1300 gc.stress.TestStressG1Uncommit
+ */
+
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryMXBean;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import com.sun.management.ThreadMXBean;
+
+import jdk.test.lib.Asserts;
+import jdk.test.lib.process.ProcessTools;
+import jdk.test.lib.process.OutputAnalyzer;
+
+public class TestStressG1Uncommit {
+    public static void main(String[] args) throws Exception {
+        ArrayList<String> options = new ArrayList<>();
+        Collections.addAll(options,
+            "-Xlog:gc,gc+heap+region=debug",
+            "-XX:+UseG1GC",
+            StressUncommit.class.getName()
+        );
+        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(options);
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+        output.shouldHaveExitValue(0);
+        output.shouldMatch("Uncommit regions");
+        output.outputTo(System.out);
+    }
+}
+
+class StressUncommit {
+    private static final long M = 1024 * 1024;
+    private static final long G = 1024 * M;
+    private static final Instant StartTime = Instant.now();
+
+    private static final ThreadMXBean threadBean = (ThreadMXBean) ManagementFactory.getThreadMXBean();
+    private static final MemoryMXBean memoryBean = ManagementFactory.getMemoryMXBean();
+    private static ConcurrentLinkedQueue<Object> globalKeepAlive;
+
+    public static void main(String args[]) throws InterruptedException {
+        // Leave 20% head room to try to avoid Full GCs.
+        long allocationSize = (long) (Runtime.getRuntime().maxMemory() * 0.8);
+
+        // Figure out suitable number of workers (~1 per gig).
+        int gigsOfAllocation = (int) Math.ceil((double) allocationSize / G);
+        int numWorkers = Math.min(gigsOfAllocation, Runtime.getRuntime().availableProcessors());
+        long workerAllocation = allocationSize / numWorkers;
+
+        log("Using " + numWorkers + " workers, each allocating: ~" + (workerAllocation / M) + "M");
+        ExecutorService workers = Executors.newFixedThreadPool(numWorkers);
+        try {
+            int iteration = 1;
+            // Run for 60 seconds.
+            while (uptime() < 60) {
+                log("Interation: " + iteration++);
+                globalKeepAlive = new ConcurrentLinkedQueue<>();
+                // Submit work to executor.
+                CountDownLatch workersRunning = new CountDownLatch(numWorkers);
+                for (int j = 0; j < numWorkers; j++) {
+                    // Submit worker task.
+                    workers.submit(() -> {
+                    allocateToLimit(workerAllocation);
+                    workersRunning.countDown();
+                    });
+                }
+
+                // Wait for tasks to complete.
+                workersRunning.await();
+
+                // Clear the reference holding all task allocations alive.
+                globalKeepAlive = null;
+
+                // Do a GC that should shrink the heap.
+                long committedBefore = memoryBean.getHeapMemoryUsage().getCommitted();
+                System.gc();
+                long committedAfter = memoryBean.getHeapMemoryUsage().getCommitted();
+                Asserts.assertLessThan(committedAfter, committedBefore);
+            }
+        } finally {
+            workers.shutdown();
+            workers.awaitTermination(5, TimeUnit.SECONDS);
+        }
+    }
+
+    private static void allocateToLimit(long limit) {
+        var localKeepAlive = new LinkedList<byte[]>();
+
+        long currentAllocation = threadBean.getCurrentThreadAllocatedBytes();
+        long allocationLimit = currentAllocation + limit;
+
+        while (currentAllocation < allocationLimit) {
+            // Check roughly every megabyte.
+            for (long j = 0 ; j < 1000; j++) {
+            localKeepAlive.add(new byte[1024]);
+            }
+            currentAllocation = threadBean.getCurrentThreadAllocatedBytes();
+        }
+
+        // Add to globalKeepAlive for realease by main thread.
+        globalKeepAlive.add(localKeepAlive);
+    }
+
+    private static long uptime() {
+        return Duration.between(StartTime, Instant.now()).getSeconds();
+    }
+
+    private static void log(String text) {
+        System.out.println(uptime() + "s: " + text);
+    }
+}

test/lib/sun/hotspot/WhiteBox.java

@@ -163,6 +163,7 @@ public class WhiteBox {
 
   // G1
   public native boolean g1InConcurrentMark();
+  public native boolean g1HasRegionsToUncommit();
   private native boolean g1IsHumongous0(Object o);
   public         boolean g1IsHumongous(Object o) {
     Objects.requireNonNull(o);