view hotspot/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp @ 25905:04a3d83cc752

8031323: Optionally align objects copied to survivor spaces Reviewed-by: brutisso, tschatzl
author jmasa
date Fri, 01 Aug 2014 15:40:12 -0700
parents 956dc4aa4615
children 17754211a7ab
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 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
 * 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 if you need additional information or have any
 * questions.

#include "gc_interface/collectedHeap.hpp"
#include "memory/allocation.hpp"
#include "memory/blockOffsetTable.hpp"
#include "memory/threadLocalAllocBuffer.hpp"
#include "utilities/globalDefinitions.hpp"

// Forward decl.

class PLABStats;

// A per-thread allocation buffer used during GC.
class ParGCAllocBuffer: public CHeapObj<mtGC> {
  char head[32];
  size_t _word_sz;          // in HeapWord units
  HeapWord* _bottom;
  HeapWord* _top;
  HeapWord* _end;       // last allocatable address + 1
  HeapWord* _hard_end;  // _end + AlignmentReserve
  bool      _retained;  // whether we hold a _retained_filler
  MemRegion _retained_filler;
  // In support of ergonomic sizing of PLAB's
  size_t    _allocated;     // in HeapWord units
  size_t    _wasted;        // in HeapWord units
  char tail[32];
  static size_t FillerHeaderSize;
  static size_t AlignmentReserve;

  // Flush the stats supporting ergonomic sizing of PLAB's
  // Should not be called directly
  void flush_stats(PLABStats* stats);

  // Initializes the buffer to be empty, but with the given "word_sz".
  // Must get initialized with "set_buf" for an allocation to succeed.
  ParGCAllocBuffer(size_t word_sz);
  virtual ~ParGCAllocBuffer() {}

  static const size_t min_size() {
    return ThreadLocalAllocBuffer::min_size();

  static const size_t max_size() {
    return ThreadLocalAllocBuffer::max_size();

  // If an allocation of the given "word_sz" can be satisfied within the
  // buffer, do the allocation, returning a pointer to the start of the
  // allocated block.  If the allocation request cannot be satisfied,
  // return NULL.
  HeapWord* allocate(size_t word_sz) {
    HeapWord* res = _top;
    if (pointer_delta(_end, _top) >= word_sz) {
      _top = _top + word_sz;
      return res;
    } else {
      return NULL;

  // Allocate the object aligned to "alignment_in_bytes".
  HeapWord* allocate_aligned(size_t word_sz, unsigned short alignment_in_bytes);

  // Undo the last allocation in the buffer, which is required to be of the
  // "obj" of the given "word_sz".
  void undo_allocation(HeapWord* obj, size_t word_sz) {
    assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");
    assert(pointer_delta(_top, obj)     == word_sz, "Bad undo");
    _top = obj;

  // The total (word) size of the buffer, including both allocated and
  // unallocated space.
  size_t word_sz() { return _word_sz; }

  // Should only be done if we are about to reset with a new buffer of the
  // given size.
  void set_word_size(size_t new_word_sz) {
    assert(new_word_sz > AlignmentReserve, "Too small");
    _word_sz = new_word_sz;

  // The number of words of unallocated space remaining in the buffer.
  size_t words_remaining() {
    assert(_end >= _top, "Negative buffer");
    return pointer_delta(_end, _top, HeapWordSize);

  bool contains(void* addr) {
    return (void*)_bottom <= addr && addr < (void*)_hard_end;

  // Sets the space of the buffer to be [buf, space+word_sz()).
  virtual void set_buf(HeapWord* buf) {
    _bottom   = buf;
    _top      = _bottom;
    _hard_end = _bottom + word_sz();
    _end      = _hard_end - AlignmentReserve;
    assert(_end >= _top, "Negative buffer");
    // In support of ergonomic sizing
    _allocated += word_sz();

  // Flush the stats supporting ergonomic sizing of PLAB's
  // and retire the current buffer.
  void flush_stats_and_retire(PLABStats* stats, bool end_of_gc, bool retain) {
    // We flush the stats first in order to get a reading of
    // unused space in the last buffer.
    if (ResizePLAB) {

      // Since we have flushed the stats we need to clear
      // the _allocated and _wasted fields. Not doing so
      // will artifically inflate the values in the stats
      // to which we add them.
      // The next time we flush these values, we will add
      // what we have just flushed in addition to the size
      // of the buffers allocated between now and then.
      _allocated = 0;
      _wasted = 0;
    // Retire the last allocation buffer.
    retire(end_of_gc, retain);

  // Force future allocations to fail and queries for contains()
  // to return false
  void invalidate() {
    assert(!_retained, "Shouldn't retain an invalidated buffer.");
    _end    = _hard_end;
    _wasted += pointer_delta(_end, _top);  // unused  space
    _top    = _end;      // force future allocations to fail
    _bottom = _end;      // force future contains() queries to return false

  // Fills in the unallocated portion of the buffer with a garbage object.
  // If "end_of_gc" is TRUE, is after the last use in the GC.  IF "retain"
  // is true, attempt to re-use the unused portion in the next GC.
  virtual void retire(bool end_of_gc, bool retain);

  void print() PRODUCT_RETURN;

// PLAB stats book-keeping
  size_t _allocated;      // total allocated
  size_t _wasted;         // of which wasted (internal fragmentation)
  size_t _unused;         // Unused in last buffer
  size_t _used;           // derived = allocated - wasted - unused
  size_t _desired_plab_sz;// output of filter (below), suitably trimmed and quantized
         _filter;         // integrator with decay

  PLABStats(size_t desired_plab_sz_, unsigned wt) :
  { }

  static const size_t min_size() {
    return ParGCAllocBuffer::min_size();

  static const size_t max_size() {
    return ParGCAllocBuffer::max_size();

  size_t desired_plab_sz() {
    return _desired_plab_sz;

  void adjust_desired_plab_sz(uint no_of_gc_workers);
                                 // filter computation, latches output to
                                 // _desired_plab_sz, clears sensor accumulators

  void add_allocated(size_t v) {
    Atomic::add_ptr(v, &_allocated);

  void add_unused(size_t v) {
    Atomic::add_ptr(v, &_unused);

  void add_wasted(size_t v) {
    Atomic::add_ptr(v, &_wasted);

class ParGCAllocBufferWithBOT: public ParGCAllocBuffer {
  BlockOffsetArrayContigSpace _bt;
  BlockOffsetSharedArray*     _bsa;
  HeapWord*                   _true_end;  // end of the whole ParGCAllocBuffer

  static const size_t ChunkSizeInWords;
  static const size_t ChunkSizeInBytes;
  HeapWord* allocate_slow(size_t word_sz);

  void fill_region_with_block(MemRegion mr, bool contig);

  ParGCAllocBufferWithBOT(size_t word_sz, BlockOffsetSharedArray* bsa);

  HeapWord* allocate(size_t word_sz) {
    HeapWord* res = ParGCAllocBuffer::allocate(word_sz);
    if (res != NULL) {
      _bt.alloc_block(res, word_sz);
    } else {
      res = allocate_slow(word_sz);
    return res;

  void undo_allocation(HeapWord* obj, size_t word_sz);

  virtual void set_buf(HeapWord* buf_start) {
    _true_end = _hard_end;
    _bt.set_region(MemRegion(buf_start, word_sz()));

  virtual void retire(bool end_of_gc, bool retain);

  MemRegion range() {
    return MemRegion(_top, _true_end);