view src/hotspot/share/gc/g1/collectionSetChooser.cpp @ 50441:523c2a73a3dc

8204081: Mismatch in rebuild policy and collection set chooser causes remembered sets to be kept errorneously Summary: Due to mismatch in which region's remembered sets should be rebuilt and the ones that are looked at in the collection set chooser superfluous remembered sets might be built and kept alive until the next marking. Reviewed-by: sjohanss, kbarrett
author tschatzl
date Thu, 07 Jun 2018 11:20:30 +0200
parents 2d62570a615c
children 1906adbef2dc
line wrap: on
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/*
 * Copyright (c) 2001, 2018, 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/collectionSetChooser.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/space.inline.hpp"
#include "runtime/atomic.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
// ordered according to the amount of reclaimable bytes per region.
static int order_regions(HeapRegion* hr1, HeapRegion* hr2) {
  if (hr1 == NULL) {
    if (hr2 == NULL) {
      return 0;
    } else {
      return 1;
    }
  } else if (hr2 == NULL) {
    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);
}

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();
}

#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

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();
}

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();
}

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();
}

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);
}

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;
}

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();
}

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");
  }
}

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;
    }
  }
}

void CollectionSetChooser::clear() {
  _regions.clear();
  _front = 0;
  _end = 0;
  _remaining_reclaimable_bytes = 0;
}

class ParKnownGarbageHRClosure: public HeapRegionClosure {
  G1CollectedHeap* _g1h;
  CSetChooserParUpdater _cset_updater;

public:
  ParKnownGarbageHRClosure(CollectionSetChooser* hrSorted,
                           uint chunk_size) :
    _g1h(G1CollectedHeap::heap()),
    _cset_updater(hrSorted, true /* parallel */, chunk_size) { }

  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);
    } 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 {
      assert(!r->is_old() || !r->rem_set()->is_tracked(),
             "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;
  G1CollectedHeap* _g1h;
  HeapRegionClaimer _hrclaimer;

public:
  ParKnownGarbageTask(CollectionSetChooser* hrSorted, uint chunk_size, uint n_workers) :
      AbstractGangTask("ParKnownGarbageTask"),
      _hrSorted(hrSorted), _chunk_size(chunk_size),
      _g1h(G1CollectedHeap::heap()), _hrclaimer(n_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);
  }
};

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);
}

bool CollectionSetChooser::region_occupancy_low_enough_for_evac(size_t live_bytes) {
  return live_bytes < mixed_gc_live_threshold_bytes();
}

bool CollectionSetChooser::should_add(HeapRegion* hr) const {
  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();
}