< prev index next >

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

Print this page
rev 53416 : imported patch 8217330-split-collectionsetchooser
rev 53417 : [mq]: 8217330-leo-review

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2019, 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.

@@ -26,21 +26,21 @@
 #include "gc/g1/collectionSetChooser.hpp"
 #include "gc/g1/g1CollectedHeap.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
 #include "gc/shared/space.inline.hpp"
 #include "runtime/atomic.hpp"
+#include "utilities/quickSort.hpp"
 
-// Even though we don't use the GC efficiency in our heuristics as
-// much as we used to, we still order according to GC efficiency. This
-// will cause regions with a lot of live objects and large RSets to
-// end up at the end of the array. Given that we might skip collecting
-// the last few old regions, if after a few mixed GCs the remaining
-// have reclaimable bytes under a certain threshold, the hope is that
-// the ones we'll skip are ones with both large RSets and a lot of
-// live objects, not the ones with just a lot of live objects if we
+// Order regions according to GC efficiency. This will cause regions with a lot
+// of live objects and large remembered sets to end up at the end of the array.
+// Given that we might skip collecting the last few old regions, if after a few
+// mixed GCs the remaining have reclaimable bytes under a certain threshold, the
+// hope is that the ones we'll skip are ones with both large remembered sets and
+// a lot of live objects, not the ones with just a lot of live objects if we
 // ordered according to the amount of reclaimable bytes per region.
 static int order_regions(HeapRegion* hr1, HeapRegion* hr2) {
+  // Make sure that NULL entries are moved to the end.
   if (hr1 == NULL) {
     if (hr2 == NULL) {
       return 0;
     } else {
       return 1;

@@ -49,197 +49,145 @@
     return -1;
   }
 
   double gc_eff1 = hr1->gc_efficiency();
   double gc_eff2 = hr2->gc_efficiency();
+
   if (gc_eff1 > gc_eff2) {
     return -1;
   } if (gc_eff1 < gc_eff2) {
     return 1;
   } else {
     return 0;
   }
 }
 
-static int order_regions(HeapRegion** hr1p, HeapRegion** hr2p) {
-  return order_regions(*hr1p, *hr2p);
-}
+// Determine collection set candidates: For all regions determine whether they
+// should be a collection set candidates, calculate their efficiency, sort and
+// return them as G1CollectionSetCandidates instance.
+// Threads calculate the GC efficiency of the regions they get to process, and
+// put them into some work area unsorted. At the end the array is sorted and
+// copied into the G1CollectionSetCandidates instance; the caller will be the new
+// owner of this object.
+class G1BuildCandidateRegionsTask : public AbstractGangTask {
 
-CollectionSetChooser::CollectionSetChooser() :
-  // The line below is the worst bit of C++ hackery I've ever written
-  // (Detlefs, 11/23).  You should think of it as equivalent to
-  // "_regions(100, true)": initialize the growable array and inform it
-  // that it should allocate its elem array(s) on the C heap.
-  //
-  // The first argument, however, is actually a comma expression
-  // (set_allocation_type(this, C_HEAP), 100). The purpose of the
-  // set_allocation_type() call is to replace the default allocation
-  // type for embedded objects STACK_OR_EMBEDDED with C_HEAP. It will
-  // allow to pass the assert in GenericGrowableArray() which checks
-  // that a growable array object must be on C heap if elements are.
-  //
-  // Note: containing object is allocated on C heap since it is CHeapObj.
-  //
-  _regions((ResourceObj::set_allocation_type((address) &_regions,
-                                             ResourceObj::C_HEAP),
-                  100), true /* C_Heap */),
-    _front(0), _end(0), _first_par_unreserved_idx(0),
-    _region_live_threshold_bytes(0), _remaining_reclaimable_bytes(0) {
-  _region_live_threshold_bytes = mixed_gc_live_threshold_bytes();
-}
+  // Work area for building the set of collection set candidates. Contains references
+  // to heap regions with their GC efficiencies calculated. To reduce contention
+  // on claiming array elements, worker threads claim parts of this array in chunks;
+  // Array elements may be NULL as threads might not get enough regions to fill
+  // up their chunks completely.
+  // Final sorting will remove them.
+  class G1BuildCandidateArray : public StackObj {
 
-#ifndef PRODUCT
-void CollectionSetChooser::verify() {
-  guarantee(_end <= regions_length(), "_end: %u regions length: %u", _end, regions_length());
-  guarantee(_front <= _end, "_front: %u _end: %u", _front, _end);
-  uint index = 0;
-  size_t sum_of_reclaimable_bytes = 0;
-  while (index < _front) {
-    guarantee(regions_at(index) == NULL,
-              "all entries before _front should be NULL");
-    index += 1;
-  }
-  HeapRegion *prev = NULL;
-  while (index < _end) {
-    HeapRegion *curr = regions_at(index++);
-    guarantee(curr != NULL, "Regions in _regions array cannot be NULL");
-    guarantee(!curr->is_young(), "should not be young!");
-    guarantee(!curr->is_pinned(),
-              "Pinned region should not be in collection set (index %u)", curr->hrm_index());
-    if (prev != NULL) {
-      guarantee(order_regions(prev, curr) != 1,
-                "GC eff prev: %1.4f GC eff curr: %1.4f",
-                prev->gc_efficiency(), curr->gc_efficiency());
-    }
-    sum_of_reclaimable_bytes += curr->reclaimable_bytes();
-    prev = curr;
-  }
-  guarantee(sum_of_reclaimable_bytes == _remaining_reclaimable_bytes,
-            "reclaimable bytes inconsistent, "
-            "remaining: " SIZE_FORMAT " sum: " SIZE_FORMAT,
-            _remaining_reclaimable_bytes, sum_of_reclaimable_bytes);
-}
-#endif // !PRODUCT
+    uint const _max_size;
+    uint const _chunk_size;
 
-void CollectionSetChooser::sort_regions() {
-  // First trim any unused portion of the top in the parallel case.
-  if (_first_par_unreserved_idx > 0) {
-    assert(_first_par_unreserved_idx <= regions_length(),
-           "Or we didn't reserved enough length");
-    regions_trunc_to(_first_par_unreserved_idx);
-  }
-  _regions.sort(order_regions);
-  assert(_end <= regions_length(), "Requirement");
-#ifdef ASSERT
-  for (uint i = 0; i < _end; i++) {
-    assert(regions_at(i) != NULL, "Should be true by sorting!");
-  }
-#endif // ASSERT
-  if (log_is_enabled(Trace, gc, liveness)) {
-    G1PrintRegionLivenessInfoClosure cl("Post-Sorting");
-    for (uint i = 0; i < _end; ++i) {
-      HeapRegion* r = regions_at(i);
-      cl.do_heap_region(r);
-    }
-  }
-  verify();
-}
+    HeapRegion** _data;
 
-void CollectionSetChooser::add_region(HeapRegion* hr) {
-  assert(!hr->is_pinned(),
-         "Pinned region shouldn't be added to the collection set (index %u)", hr->hrm_index());
-  assert(hr->is_old(), "should be old but is %s", hr->get_type_str());
-  assert(hr->rem_set()->is_complete(),
-         "Trying to add region %u to the collection set with incomplete remembered set", hr->hrm_index());
-  _regions.append(hr);
-  _end++;
-  _remaining_reclaimable_bytes += hr->reclaimable_bytes();
-  hr->calc_gc_efficiency();
-}
+    uint volatile _cur_claim_idx;
 
-void CollectionSetChooser::push(HeapRegion* hr) {
-  assert(hr != NULL, "Can't put back a NULL region");
-  assert(_front >= 1, "Too many regions have been put back");
-  _front--;
-  regions_at_put(_front, hr);
-  _remaining_reclaimable_bytes += hr->reclaimable_bytes();
-}
+    // Calculates the maximum array size that will be used.
+    static uint required_array_size(uint num_regions, uint num_workers, uint chunk_size) {
+      uint const max_waste = num_workers * chunk_size;
+      // The array should be aligned with respect to chunk_size.
+      uint const aligned_num_regions = ((num_regions + chunk_size - 1) / chunk_size) * chunk_size;
 
-void CollectionSetChooser::prepare_for_par_region_addition(uint n_threads,
-                                                           uint n_regions,
-                                                           uint chunk_size) {
-  _first_par_unreserved_idx = 0;
-  uint max_waste = n_threads * chunk_size;
-  // it should be aligned with respect to chunk_size
-  uint aligned_n_regions = (n_regions + chunk_size - 1) / chunk_size * chunk_size;
-  assert(aligned_n_regions % chunk_size == 0, "should be aligned");
-  regions_at_put_grow(aligned_n_regions + max_waste - 1, NULL);
-}
+      return aligned_num_regions + max_waste;
+    }
 
-uint CollectionSetChooser::claim_array_chunk(uint chunk_size) {
-  uint res = (uint) Atomic::add((jint) chunk_size,
-                                (volatile jint*) &_first_par_unreserved_idx);
-  assert(regions_length() > res + chunk_size - 1,
-         "Should already have been expanded");
-  return res - chunk_size;
-}
+  public:
+    G1BuildCandidateArray(uint max_num_regions, uint num_workers, uint chunk_size) :
+      _max_size(required_array_size(max_num_regions, num_workers, chunk_size)),
+      _chunk_size(chunk_size),
+      _data(NEW_C_HEAP_ARRAY(HeapRegion*, _max_size, mtGC)),
+      _cur_claim_idx(0) {
+      for (uint i = 0; i < _max_size; i++) {
+        _data[i] = NULL;
+      }
+    }
 
-void CollectionSetChooser::set_region(uint index, HeapRegion* hr) {
-  assert(regions_at(index) == NULL, "precondition");
-  assert(hr->is_old(), "should be old but is %s", hr->get_type_str());
-  regions_at_put(index, hr);
-  hr->calc_gc_efficiency();
-}
+    ~G1BuildCandidateArray() {
+      FREE_C_HEAP_ARRAY(HeapRegion*, _data);
+    }
 
-void CollectionSetChooser::update_totals(uint region_num,
-                                         size_t reclaimable_bytes) {
-  // Only take the lock if we actually need to update the totals.
-  if (region_num > 0) {
-    assert(reclaimable_bytes > 0, "invariant");
-    // We could have just used atomics instead of taking the
-    // lock. However, we currently don't have an atomic add for size_t.
-    MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
-    _end += region_num;
-    _remaining_reclaimable_bytes += reclaimable_bytes;
-  } else {
-    assert(reclaimable_bytes == 0, "invariant");
+    // Claim a new chunk, returning its bounds [from, to[.
+    void claim_chunk(uint& from, uint& to) {
+      uint result = Atomic::add(_chunk_size, &_cur_claim_idx);
+      assert(_max_size > result - 1,
+             "Array too small, is %u should be %u with chunk size %u.",
+             _max_size, result, _chunk_size);
+      from = result - _chunk_size;
+      to = result;
   }
-}
 
-void CollectionSetChooser::iterate(HeapRegionClosure* cl) {
-  for (uint i = _front; i < _end; i++) {
-    HeapRegion* r = regions_at(i);
-    if (cl->do_heap_region(r)) {
-      cl->set_incomplete();
-      break;
+    // Set element in array.
+    void set(uint idx, HeapRegion* hr) {
+      assert(idx < _max_size, "Index %u out of bounds %u", idx, _max_size);
+      assert(_data[idx] == NULL, "Value must not have been set.");
+      _data[idx] = hr;
     }
+
+    void sort_and_copy_into(HeapRegion** dest, uint num_regions) {
+      if (_cur_claim_idx == 0) {
+        return;
   }
-}
+      for (uint i = _cur_claim_idx; i < _max_size; i++) {
+        assert(_data[i] == NULL, "must be");
+      }
+      QuickSort::sort(_data, _cur_claim_idx, order_regions, true);
+      for (uint i = num_regions; i < _max_size; i++) {
+        assert(_data[i] == NULL, "must be");
+      }
+      for (uint i = 0; i < num_regions; i++) {
+        dest[i] = _data[i];
+      }
+    }
+  };
 
-void CollectionSetChooser::clear() {
-  _regions.clear();
-  _front = 0;
-  _end = 0;
-  _remaining_reclaimable_bytes = 0;
-}
+  // Per-region closure. In addition to determining whether a region should be
+  // added to the candidates, and calculating those regions' gc efficiencies, also
+  // gather additional statistics.
+  class G1BuildCandidateRegionsClosure : public HeapRegionClosure {
+    G1BuildCandidateArray* _array;
 
-class ParKnownGarbageHRClosure: public HeapRegionClosure {
-  G1CollectedHeap* _g1h;
-  CSetChooserParUpdater _cset_updater;
+    uint _cur_chunk_idx;
+    uint _cur_chunk_end;
 
-public:
-  ParKnownGarbageHRClosure(CollectionSetChooser* hrSorted,
-                           uint chunk_size) :
-    _g1h(G1CollectedHeap::heap()),
-    _cset_updater(hrSorted, true /* parallel */, chunk_size) { }
+    uint _regions_added;
+    size_t _reclaimable_bytes_added;
+
+    void add_region(HeapRegion* hr) {
+      if (_cur_chunk_idx == _cur_chunk_end) {
+        _array->claim_chunk(_cur_chunk_idx, _cur_chunk_end);
+      }
+      assert(_cur_chunk_idx < _cur_chunk_end, "Must be");
+
+      hr->calc_gc_efficiency();
+      _array->set(_cur_chunk_idx, hr);
+
+      _cur_chunk_idx++;
+
+      _regions_added++;
+      _reclaimable_bytes_added += hr->reclaimable_bytes();
+    }
+
+    bool should_add(HeapRegion* hr) { return CollectionSetChooser::should_add(hr); }
+
+  public:
+    G1BuildCandidateRegionsClosure(G1BuildCandidateArray* array) :
+      _array(array),
+      _cur_chunk_idx(0),
+      _cur_chunk_end(0),
+      _regions_added(0),
+      _reclaimable_bytes_added(0) { }
 
   bool do_heap_region(HeapRegion* r) {
     // We will skip any region that's currently used as an old GC
     // alloc region (we should not consider those for collection
     // before we fill them up).
-    if (_cset_updater.should_add(r) && !_g1h->is_old_gc_alloc_region(r)) {
-      _cset_updater.add_region(r);
+      if (should_add(r) && !G1CollectedHeap::heap()->is_old_gc_alloc_region(r)) {
+        add_region(r);
     } else if (r->is_old()) {
       // Keep remembered sets for humongous regions, otherwise clean out remembered
       // sets for old regions.
       r->rem_set()->clear(true /* only_cardset */);
     } else {

@@ -247,56 +195,75 @@
              "Missed to clear unused remembered set of region %u (%s) that is %s",
              r->hrm_index(), r->get_type_str(), r->rem_set()->get_state_str());
     }
     return false;
   }
-};
 
-class ParKnownGarbageTask: public AbstractGangTask {
-  CollectionSetChooser* _hrSorted;
-  uint _chunk_size;
+    uint regions_added() const { return _regions_added; }
+    size_t reclaimable_bytes_added() const { return _reclaimable_bytes_added; }
+  };
+
   G1CollectedHeap* _g1h;
   HeapRegionClaimer _hrclaimer;
 
+  uint volatile _num_regions_added;
+  size_t volatile _reclaimable_bytes_added;
+
+  G1BuildCandidateArray _result;
+
+  void update_totals(uint num_regions, size_t reclaimable_bytes) {
+    if (num_regions > 0) {
+      assert(reclaimable_bytes > 0, "invariant");
+      Atomic::add(num_regions, &_num_regions_added);
+      Atomic::add(reclaimable_bytes, &_reclaimable_bytes_added);
+    } else {
+      assert(reclaimable_bytes == 0, "invariant");
+    }
+  }
+
 public:
-  ParKnownGarbageTask(CollectionSetChooser* hrSorted, uint chunk_size, uint n_workers) :
-      AbstractGangTask("ParKnownGarbageTask"),
-      _hrSorted(hrSorted), _chunk_size(chunk_size),
-      _g1h(G1CollectedHeap::heap()), _hrclaimer(n_workers) {}
+  G1BuildCandidateRegionsTask(uint max_num_regions, uint chunk_size, uint num_workers) :
+    AbstractGangTask("G1 Build Candidate Regions"),
+    _g1h(G1CollectedHeap::heap()),
+    _hrclaimer(num_workers),
+    _num_regions_added(0),
+    _reclaimable_bytes_added(0),
+    _result(max_num_regions, chunk_size, num_workers) { }
 
   void work(uint worker_id) {
-    ParKnownGarbageHRClosure par_known_garbage_cl(_hrSorted, _chunk_size);
-    _g1h->heap_region_par_iterate_from_worker_offset(&par_known_garbage_cl, &_hrclaimer, worker_id);
+    G1BuildCandidateRegionsClosure cl(&_result);
+    _g1h->heap_region_par_iterate_from_worker_offset(&cl, &_hrclaimer, worker_id);
+    update_totals(cl.regions_added(), cl.reclaimable_bytes_added());
   }
-};
 
-uint CollectionSetChooser::calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const {
-  assert(n_workers > 0, "Active gc workers should be greater than 0");
-  const uint overpartition_factor = 4;
-  const uint min_chunk_size = MAX2(n_regions / n_workers, 1U);
-  return MAX2(n_regions / (n_workers * overpartition_factor), min_chunk_size);
-}
+  G1CollectionSetCandidates* get_sorted_candidates() {
+    HeapRegion** regions = NEW_C_HEAP_ARRAY(HeapRegion*, _num_regions_added, mtGC);
+    _result.sort_and_copy_into(regions, _num_regions_added);
+    return new G1CollectionSetCandidates(regions,
+                                         _num_regions_added,
+                                         _reclaimable_bytes_added);
+  }
+};
 
-bool CollectionSetChooser::region_occupancy_low_enough_for_evac(size_t live_bytes) {
-  return live_bytes < mixed_gc_live_threshold_bytes();
+uint CollectionSetChooser::calculate_work_chunk_size(uint num_workers, uint num_regions) {
+  assert(num_workers > 0, "Active gc workers should be greater than 0");
+  return MAX2(num_regions / num_workers, 1U);
 }
 
-bool CollectionSetChooser::should_add(HeapRegion* hr) const {
+bool CollectionSetChooser::should_add(HeapRegion* hr) {
   return !hr->is_young() &&
          !hr->is_pinned() &&
          region_occupancy_low_enough_for_evac(hr->live_bytes()) &&
          hr->rem_set()->is_complete();
 }
 
-void CollectionSetChooser::rebuild(WorkGang* workers, uint n_regions) {
-  clear();
-
-  uint n_workers = workers->active_workers();
-
-  uint chunk_size = calculate_parallel_work_chunk_size(n_workers, n_regions);
-  prepare_for_par_region_addition(n_workers, n_regions, chunk_size);
-
-  ParKnownGarbageTask par_known_garbage_task(this, chunk_size, n_workers);
-  workers->run_task(&par_known_garbage_task);
-
-  sort_regions();
+G1CollectionSetCandidates* CollectionSetChooser::build(WorkGang* workers, uint max_num_regions) {
+  uint num_workers = workers->active_workers();
+  uint chunk_size = calculate_work_chunk_size(num_workers, max_num_regions);
+
+  G1BuildCandidateRegionsTask cl(max_num_regions, chunk_size, num_workers);
+  workers->run_task(&cl, num_workers);
+
+  G1CollectionSetCandidates* result = cl.get_sorted_candidates();
+  result->verify();
+  return result;
 }
< prev index next >