/*

 * Copyright (c) 2015, 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

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 */

#include "precompiled.hpp"

#include "gc/g1/g1EvacStats.hpp"

#include "gc/shared/gcId.hpp"

#include "trace/tracing.hpp"

void G1EvacStats::adjust_desired_plab_sz() {

  if (PrintPLAB) {

    gclog_or_tty->print(" (allocated = " SIZE_FORMAT " wasted = " SIZE_FORMAT " "

                        "unused = " SIZE_FORMAT " used = " SIZE_FORMAT " "

                        "undo_waste = " SIZE_FORMAT " region_end_waste = " SIZE_FORMAT " "

                        "regions filled = %u direct_allocated = " SIZE_FORMAT " "

                        "failure_used = " SIZE_FORMAT " failure_waste = " SIZE_FORMAT ") ",

                        _allocated, _wasted, _unused, used(), _undo_wasted, _region_end_waste,

                        _regions_filled, _direct_allocated, _failure_used, _failure_waste);

  }

  if (ResizePLAB) {

    assert(is_object_aligned(max_size()) && min_size() <= max_size(),

           "PLAB clipping computation may be incorrect");

    if (_allocated == 0) {

      assert((_unused == 0),

      _allocated = 1;

    }

    // The size of the PLAB caps the amount of space that can be wasted at the

    // end of the collection. In the worst case the last PLAB could be completely

    // empty.

    // This allows us to calculate the new PLAB size to achieve the

    // TargetPLABWastePct given the latest memory usage and that the last buffer

    // will be G1LastPLABAverageOccupancy full.

    //

    // E.g. assume that if in the current GC 100 words were allocated and a

    // TargetPLABWastePct of 10 had been set.

    //

    // So we could waste up to 10 words to meet that percentage. Given that we

    // also assume that that buffer is typically half-full, the new desired PLAB

    // size is set to 20 words.

    //

    // The amount of allocation performed should be independent of the number of

    // threads, so should the maximum waste we can spend in total. So if

    // we used n threads to allocate, each of them can spend maximum waste/n words in

    // a first rough approximation. The number of threads only comes into play later

    // when actually retrieving the actual desired PLAB size.

    //

    // After calculating this optimal PLAB size the algorithm applies the usual

    // exponential decaying average over this value to guess the next PLAB size.

    //

    // We account region end waste fully to PLAB allocation (in the calculation of

    // what we consider as "used_for_waste_calculation" below). This is not

    // completely fair, but is a conservative assumption because PLABs may be sized

    // flexibly while we cannot adjust inline allocations.

    // Allocation during GC will try to minimize region end waste so this impact

    // should be minimal.

    //

    // We need to cover overflow when calculating the amount of space actually used

    // by objects in PLABs when subtracting the region end waste.

    // Region end waste may be higher than actual allocation. This may occur if many

    // threads do not allocate anything but a few rather large objects. In this

    // degenerate case the PLAB size would simply quickly tend to minimum PLAB size,

    // which is an okay reaction.

    size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0;

    size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct;

    size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy);

    // Take historical weighted average

    _filter.sample(cur_plab_sz);

    // Clip from above and below, and align to object boundary

    size_t plab_sz;

    plab_sz = MAX2(min_size(), (size_t)_filter.average());

    plab_sz = MIN2(max_size(), plab_sz);

    plab_sz = align_object_size(plab_sz);

    // Latch the result

    _desired_net_plab_sz = plab_sz;

    if (PrintPLAB) {

      gclog_or_tty->print_cr(" (plab_sz = " SIZE_FORMAT " desired_plab_sz = " SIZE_FORMAT ") ", cur_plab_sz, plab_sz);

    }

  }

  // Clear accumulators for next round.

  reset();

}