heapRegionSeq.cpp

/*
 * Copyright (c) 2001, 2010, 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_implementation/g1/g1CollectedHeap.inline.hpp"
#include "gc_implementation/g1/heapRegionSeq.hpp"
#include "memory/allocation.hpp"

// Local to this file.

static int orderRegions(HeapRegion** hr1p, HeapRegion** hr2p) {
  if ((*hr1p)->end() <= (*hr2p)->bottom()) return -1;
  else if ((*hr2p)->end() <= (*hr1p)->bottom()) return 1;
  else if (*hr1p == *hr2p) return 0;
  else {
    assert(false, "We should never compare distinct overlapping regions.");
  }
  return 0;
}

HeapRegionSeq::HeapRegionSeq(const size_t max_size) :
  _alloc_search_start(0),
  // 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),
            (int)max_size),
           true),
  _next_rr_candidate(0),
  _seq_bottom(NULL)
{}

// Private methods.

HeapWord*
HeapRegionSeq::alloc_obj_from_region_index(int ind, size_t word_size) {
  assert(G1CollectedHeap::isHumongous(word_size),
         "Allocation size should be humongous");
  int cur = ind;
  int first = cur;
  size_t sumSizes = 0;
  while (cur < _regions.length() && sumSizes < word_size) {
    // Loop invariant:
    //  For all i in [first, cur):
    //       _regions.at(i)->is_empty()
    //    && _regions.at(i) is contiguous with its predecessor, if any
    //  && sumSizes is the sum of the sizes of the regions in the interval
    //       [first, cur)
    HeapRegion* curhr = _regions.at(cur);
    if (curhr->is_empty()
        && (first == cur
            || (_regions.at(cur-1)->end() ==
                curhr->bottom()))) {
      sumSizes += curhr->capacity() / HeapWordSize;
    } else {
      first = cur + 1;
      sumSizes = 0;
    }
    cur++;
  }
  if (sumSizes >= word_size) {
    _alloc_search_start = cur;

    // We need to initialize the region(s) we just discovered. This is
    // a bit tricky given that it can happen concurrently with
    // refinement threads refining cards on these regions and
    // potentially wanting to refine the BOT as they are scanning
    // those cards (this can happen shortly after a cleanup; see CR
    // 6991377). So we have to set up the region(s) carefully and in
    // a specific order.

    // Currently, allocs_are_zero_filled() returns false. The zero
    // filling infrastructure will be going away soon (see CR 6977804).
    // So no need to do anything else here.
    bool zf = G1CollectedHeap::heap()->allocs_are_zero_filled();
    assert(!zf, "not supported");

    // This will be the "starts humongous" region.
    HeapRegion* first_hr = _regions.at(first);
    {
      MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);
      first_hr->set_zero_fill_allocated();
    }
    // The header of the new object will be placed at the bottom of
    // the first region.
    HeapWord* new_obj = first_hr->bottom();
    // This will be the new end of the first region in the series that
    // should also match the end of the last region in the seriers.
    // (Note: sumSizes = "region size" x "number of regions we found").
    HeapWord* new_end = new_obj + sumSizes;
    // This will be the new top of the first region that will reflect
    // this allocation.
    HeapWord* new_top = new_obj + word_size;

    // First, we need to zero the header of the space that we will be
    // allocating. When we update top further down, some refinement
    // threads might try to scan the region. By zeroing the header we
    // ensure that any thread that will try to scan the region will
    // come across the zero klass word and bail out.
    //
    // NOTE: It would not have been correct to have used
    // CollectedHeap::fill_with_object() and make the space look like
    // an int array. The thread that is doing the allocation will
    // later update the object header to a potentially different array
    // type and, for a very short period of time, the klass and length
    // fields will be inconsistent. This could cause a refinement
    // thread to calculate the object size incorrectly.
    Copy::fill_to_words(new_obj, oopDesc::header_size(), 0);

    // We will set up the first region as "starts humongous". This
    // will also update the BOT covering all the regions to reflect
    // that there is a single object that starts at the bottom of the
    // first region.
    first_hr->set_startsHumongous(new_end);

    // Then, if there are any, we will set up the "continues
    // humongous" regions.
    HeapRegion* hr = NULL;
    for (int i = first + 1; i < cur; ++i) {
      hr = _regions.at(i);
      {
        MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);
        hr->set_zero_fill_allocated();
      }
      hr->set_continuesHumongous(first_hr);
    }
    // If we have "continues humongous" regions (hr != NULL), then the
    // end of the last one should match new_end.
    assert(hr == NULL || hr->end() == new_end, "sanity");

    // Up to this point no concurrent thread would have been able to
    // do any scanning on any region in this series. All the top
    // fields still point to bottom, so the intersection between
    // [bottom,top] and [card_start,card_end] will be empty. Before we
    // update the top fields, we'll do a storestore to make sure that
    // no thread sees the update to top before the zeroing of the
    // object header and the BOT initialization.
    OrderAccess::storestore();

    // Now that the BOT and the object header have been initialized,
    // we can update top of the "starts humongous" region.
    assert(first_hr->bottom() < new_top && new_top <= first_hr->end(),
           "new_top should be in this region");
    first_hr->set_top(new_top);

    // Now, we will update the top fields of the "continues humongous"
    // regions. The reason we need to do this is that, otherwise,
    // these regions would look empty and this will confuse parts of
    // G1. For example, the code that looks for a consecutive number
    // of empty regions will consider them empty and try to
    // re-allocate them. We can extend is_empty() to also include
    // !continuesHumongous(), but it is easier to just update the top
    // fields here.
    hr = NULL;
    for (int i = first + 1; i < cur; ++i) {
      hr = _regions.at(i);
      if ((i + 1) == cur) {
        // last continues humongous region
        assert(hr->bottom() < new_top && new_top <= hr->end(),
               "new_top should fall on this region");
        hr->set_top(new_top);
      } else {
        // not last one
        assert(new_top > hr->end(), "new_top should be above this region");
        hr->set_top(hr->end());
      }
    }
    // If we have continues humongous regions (hr != NULL), then the
    // end of the last one should match new_end and its top should
    // match new_top.
    assert(hr == NULL ||
           (hr->end() == new_end && hr->top() == new_top), "sanity");

    return new_obj;
  } else {
    // If we started from the beginning, we want to know why we can't alloc.
    return NULL;
  }
}

void HeapRegionSeq::print_empty_runs() {
  int empty_run = 0;
  int n_empty = 0;
  int empty_run_start;
  for (int i = 0; i < _regions.length(); i++) {
    HeapRegion* r = _regions.at(i);
    if (r->continuesHumongous()) continue;
    if (r->is_empty()) {
      assert(!r->isHumongous(), "H regions should not be empty.");
      if (empty_run == 0) empty_run_start = i;
      empty_run++;
      n_empty++;
    } else {
      if (empty_run > 0) {
        gclog_or_tty->print("  %d:%d", empty_run_start, empty_run);
        empty_run = 0;
      }
    }
  }
  if (empty_run > 0) {
    gclog_or_tty->print(" %d:%d", empty_run_start, empty_run);
  }
  gclog_or_tty->print_cr(" [tot = %d]", n_empty);
}

int HeapRegionSeq::find(HeapRegion* hr) {
  // FIXME: optimized for adjacent regions of fixed size.
  int ind = hr->hrs_index();
  if (ind != -1) {
    assert(_regions.at(ind) == hr, "Mismatch");
  }
  return ind;
}


// Public methods.

void HeapRegionSeq::insert(HeapRegion* hr) {
  assert(!_regions.is_full(), "Too many elements in HeapRegionSeq");
  if (_regions.length() == 0
      || _regions.top()->end() <= hr->bottom()) {
    hr->set_hrs_index(_regions.length());
    _regions.append(hr);
  } else {
    _regions.append(hr);
    _regions.sort(orderRegions);
    for (int i = 0; i < _regions.length(); i++) {
      _regions.at(i)->set_hrs_index(i);
    }
  }
  char* bot = (char*)_regions.at(0)->bottom();
  if (_seq_bottom == NULL || bot < _seq_bottom) _seq_bottom = bot;
}

size_t HeapRegionSeq::length() {
  return _regions.length();
}

size_t HeapRegionSeq::free_suffix() {
  size_t res = 0;
  int first = _regions.length() - 1;
  int cur = first;
  while (cur >= 0 &&
         (_regions.at(cur)->is_empty()
          && (first == cur
              || (_regions.at(cur+1)->bottom() ==
                  _regions.at(cur)->end())))) {
      res++;
      cur--;
  }
  return res;
}

HeapWord* HeapRegionSeq::obj_allocate(size_t word_size) {
  int cur = _alloc_search_start;
  // Make sure "cur" is a valid index.
  assert(cur >= 0, "Invariant.");
  HeapWord* res = alloc_obj_from_region_index(cur, word_size);
  if (res == NULL)
    res = alloc_obj_from_region_index(0, word_size);
  return res;
}

void HeapRegionSeq::iterate(HeapRegionClosure* blk) {
  iterate_from((HeapRegion*)NULL, blk);
}

// The first argument r is the heap region at which iteration begins.
// This operation runs fastest when r is NULL, or the heap region for
// which a HeapRegionClosure most recently returned true, or the
// heap region immediately to its right in the sequence.  In all
// other cases a linear search is required to find the index of r.

void HeapRegionSeq::iterate_from(HeapRegion* r, HeapRegionClosure* blk) {

  // :::: FIXME ::::
  // Static cache value is bad, especially when we start doing parallel
  // remembered set update. For now just don't cache anything (the
  // code in the def'd out blocks).

#if 0
  static int cached_j = 0;
#endif
  int len = _regions.length();
  int j = 0;
  // Find the index of r.
  if (r != NULL) {
#if 0
    assert(cached_j >= 0, "Invariant.");
    if ((cached_j < len) && (r == _regions.at(cached_j))) {
      j = cached_j;
    } else if ((cached_j + 1 < len) && (r == _regions.at(cached_j + 1))) {
      j = cached_j + 1;
    } else {
      j = find(r);
#endif
      if (j < 0) {
        j = 0;
      }
#if 0
    }
#endif
  }
  int i;
  for (i = j; i < len; i += 1) {
    int res = blk->doHeapRegion(_regions.at(i));
    if (res) {
#if 0
      cached_j = i;
#endif
      blk->incomplete();
      return;
    }
  }
  for (i = 0; i < j; i += 1) {
    int res = blk->doHeapRegion(_regions.at(i));
    if (res) {
#if 0
      cached_j = i;
#endif
      blk->incomplete();
      return;
    }
  }
}

void HeapRegionSeq::iterate_from(int idx, HeapRegionClosure* blk) {
  int len = _regions.length();
  int i;
  for (i = idx; i < len; i++) {
    if (blk->doHeapRegion(_regions.at(i))) {
      blk->incomplete();
      return;
    }
  }
  for (i = 0; i < idx; i++) {
    if (blk->doHeapRegion(_regions.at(i))) {
      blk->incomplete();
      return;
    }
  }
}

MemRegion HeapRegionSeq::shrink_by(size_t shrink_bytes,
                                   size_t& num_regions_deleted) {
  assert(shrink_bytes % os::vm_page_size() == 0, "unaligned");
  assert(shrink_bytes % HeapRegion::GrainBytes == 0, "unaligned");

  if (_regions.length() == 0) {
    num_regions_deleted = 0;
    return MemRegion();
  }
  int j = _regions.length() - 1;
  HeapWord* end = _regions.at(j)->end();
  HeapWord* last_start = end;
  while (j >= 0 && shrink_bytes > 0) {
    HeapRegion* cur = _regions.at(j);
    // We have to leave humongous regions where they are,
    // and work around them.
    if (cur->isHumongous()) {
      return MemRegion(last_start, end);
    }
    assert(cur == _regions.top(), "Should be top");
    if (!cur->is_empty()) break;
    cur->reset_zero_fill();
    shrink_bytes -= cur->capacity();
    num_regions_deleted++;
    _regions.pop();
    last_start = cur->bottom();
    // We need to delete these somehow, but can't currently do so here: if
    // we do, the ZF thread may still access the deleted region.  We'll
    // leave this here as a reminder that we have to do something about
    // this.
    // delete cur;
    j--;
  }
  return MemRegion(last_start, end);
}


class PrintHeapRegionClosure : public  HeapRegionClosure {
public:
  bool doHeapRegion(HeapRegion* r) {
    gclog_or_tty->print(PTR_FORMAT ":", r);
    r->print();
    return false;
  }
};

void HeapRegionSeq::print() {
  PrintHeapRegionClosure cl;
  iterate(&cl);
}