/*

 * Copyright (c) 2016, 2018, Red Hat, Inc. 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 www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#include "precompiled.hpp"

#include "gc/shenandoah/shenandoahFreeSet.hpp"

#include "gc/shenandoah/shenandoahHeap.inline.hpp"

#include "gc/shenandoah/shenandoahHeapRegionSet.hpp"

#include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"

#include "gc/shenandoah/shenandoahTraversalGC.hpp"

#include "logging/logStream.hpp"

ShenandoahFreeSet::ShenandoahFreeSet(ShenandoahHeap* heap, size_t max_regions) :

  _heap(heap),

  _mutator_free_bitmap(max_regions, mtGC),

  _collector_free_bitmap(max_regions, mtGC),

  _max(max_regions)

{

  clear_internal();

}

void ShenandoahFreeSet::increase_used(size_t num_bytes) {

  assert_heaplock_owned_by_current_thread();

  _used += num_bytes;

  assert(_used <= _capacity, "must not use more than we have: used: " SIZE_FORMAT

         ", capacity: " SIZE_FORMAT ", num_bytes: " SIZE_FORMAT, _used, _capacity, num_bytes);

}

bool ShenandoahFreeSet::is_mutator_free(size_t idx) const {

  assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT " (left: " SIZE_FORMAT ", right: " SIZE_FORMAT ")",

          idx, _max, _mutator_leftmost, _mutator_rightmost);

  return _mutator_free_bitmap.at(idx);

}

bool ShenandoahFreeSet::is_collector_free(size_t idx) const {

  assert (idx < _max, "index is sane: " SIZE_FORMAT " < " SIZE_FORMAT " (left: " SIZE_FORMAT ", right: " SIZE_FORMAT ")",

          idx, _max, _collector_leftmost, _collector_rightmost);

  return _collector_free_bitmap.at(idx);

}

HeapWord* ShenandoahFreeSet::allocate_single(ShenandoahAllocRequest& req, bool& in_new_region) {

  // Scan the bitmap looking for a first fit.

  //

  // Leftmost and rightmost bounds provide enough caching to walk bitmap efficiently. Normally,

  // we would find the region to allocate at right away.

  //

  // Allocations are biased: new application allocs go to beginning of the heap, and GC allocs

  // go to the end. This makes application allocation faster, because we would clear lots

  // of regions from the beginning most of the time.

  //

  // Free set maintains mutator and collector views, and normally they allocate in their views only,

  // unless we special cases for stealing and mixed allocations.

  switch (req.type()) {

    case ShenandoahAllocRequest::_alloc_tlab:

    case ShenandoahAllocRequest::_alloc_shared: {

      // Try to allocate in the mutator view

      for (size_t idx = _mutator_leftmost; idx <= _mutator_rightmost; idx++) {

        if (is_mutator_free(idx)) {

          HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);

          if (result != NULL) {

            return result;

          }

        }

      }

      // There is no recovery. Mutator does not touch collector view at all.

      break;

    }

    case ShenandoahAllocRequest::_alloc_gclab:

    case ShenandoahAllocRequest::_alloc_shared_gc: {

      // size_t is unsigned, need to dodge underflow when _leftmost = 0

      // Fast-path: try to allocate in the collector view first

      for (size_t c = _collector_rightmost + 1; c > _collector_leftmost; c--) {

        size_t idx = c - 1;

        if (is_collector_free(idx)) {

          HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);

          if (result != NULL) {

            return result;

          }

        }

      }

      // No dice. Can we borrow space from mutator view?

      if (!ShenandoahEvacReserveOverflow) {

        return NULL;

      }

      // Try to steal the empty region from the mutator view

      for (size_t c = _mutator_rightmost + 1; c > _mutator_leftmost; c--) {

        size_t idx = c - 1;

        if (is_mutator_free(idx)) {

          ShenandoahHeapRegion* r = _heap->get_region(idx);

          if (is_empty_or_trash(r)) {

            flip_to_gc(r);

            HeapWord *result = try_allocate_in(r, req, in_new_region);

            if (result != NULL) {

              return result;

            }

          }

        }

      }

      // Try to mix the allocation into the mutator view:

      if (ShenandoahAllowMixedAllocs) {

        for (size_t c = _mutator_rightmost + 1; c > _mutator_leftmost; c--) {

          size_t idx = c - 1;

          if (is_mutator_free(idx)) {

            HeapWord* result = try_allocate_in(_heap->get_region(idx), req, in_new_region);

            if (result != NULL) {

              return result;

            }

          }

        }

      }

      break;

    }

    default:

      ShouldNotReachHere();

  }

  return NULL;

}

HeapWord* ShenandoahFreeSet::try_allocate_in(ShenandoahHeapRegion* r, ShenandoahAllocRequest& req, bool& in_new_region) {

  assert (!has_no_alloc_capacity(r), "Performance: should avoid full regions on this path: " SIZE_FORMAT, r->region_number());

  try_recycle_trashed(r);

  in_new_region = r->is_empty();

  HeapWord* result = NULL;

  size_t size = req.size();

  if (ShenandoahElasticTLAB && req.is_lab_alloc()) {

    size_t free = align_down(r->free() >> LogHeapWordSize, MinObjAlignment);

    if (size > free) {

      size = free;

    }

    if (size >= req.min_size()) {

      result = r->allocate(size, req.type());

      assert (result != NULL, "Allocation must succeed: free " SIZE_FORMAT ", actual " SIZE_FORMAT, free, size);

    }

  } else {

    result = r->allocate(size, req.type());

  }

  if (result != NULL) {

    // Allocation successful, bump stats:

    if (req.is_mutator_alloc()) {

      increase_used(size * HeapWordSize);

    }

    // Record actual allocation size

    req.set_actual_size(size);

    if (req.is_gc_alloc() && _heap->is_concurrent_traversal_in_progress()) {

      // Traversal needs to traverse through GC allocs. Adjust TAMS to the new top

      // so that these allocations appear below TAMS, and thus get traversed.

      // See top of shenandoahTraversal.cpp for an explanation.

      _heap->marking_context()->capture_top_at_mark_start(r);

      _heap->traversal_gc()->traversal_set()->add_region_check_for_duplicates(r);

      OrderAccess::fence();

    }

  }

  if (result == NULL || has_no_alloc_capacity(r)) {

    // Region cannot afford this or future allocations. Retire it.

    //

    // While this seems a bit harsh, especially in the case when this large allocation does not

    // fit, but the next small one would, we are risking to inflate scan times when lots of

    // almost-full regions precede the fully-empty region where we want allocate the entire TLAB.

    // TODO: Record first fully-empty region, and use that for large allocations

    // Record the remainder as allocation waste

    if (req.is_mutator_alloc()) {

      size_t waste = r->free();

      if (waste > 0) {

        increase_used(waste);

        _heap->notify_mutator_alloc_words(waste >> LogHeapWordSize, true);

      }

    }

    size_t num = r->region_number();

    _collector_free_bitmap.clear_bit(num);

    _mutator_free_bitmap.clear_bit(num);

    // Touched the bounds? Need to update:

    if (touches_bounds(num)) {

      adjust_bounds();

    }

    assert_bounds();

  }

  return result;

}

bool ShenandoahFreeSet::touches_bounds(size_t num) const {

  return num == _collector_leftmost || num == _collector_rightmost || num == _mutator_leftmost || num == _mutator_rightmost;

}

void ShenandoahFreeSet::recompute_bounds() {

  // Reset to the most pessimistic case:

  _mutator_rightmost = _max - 1;

  _mutator_leftmost = 0;

  _collector_rightmost = _max - 1;

  _collector_leftmost = 0;

  // ...and adjust from there

  adjust_bounds();

}

void ShenandoahFreeSet::adjust_bounds() {

  // Rewind both mutator bounds until the next bit.

  while (_mutator_leftmost < _max && !is_mutator_free(_mutator_leftmost)) {

    _mutator_leftmost++;

  }

  while (_mutator_rightmost > 0 && !is_mutator_free(_mutator_rightmost)) {

    _mutator_rightmost--;

  }

  // Rewind both collector bounds until the next bit.

  while (_collector_leftmost < _max && !is_collector_free(_collector_leftmost)) {

    _collector_leftmost++;

  }

  while (_collector_rightmost > 0 && !is_collector_free(_collector_rightmost)) {

    _collector_rightmost--;

  }

}

HeapWord* ShenandoahFreeSet::allocate_contiguous(ShenandoahAllocRequest& req) {

  assert_heaplock_owned_by_current_thread();

  size_t words_size = req.size();

  size_t num = ShenandoahHeapRegion::required_regions(words_size * HeapWordSize);

  // No regions left to satisfy allocation, bye.

  if (num > mutator_count()) {

    return NULL;

  }

  // Find the continuous interval of $num regions, starting from $beg and ending in $end,

  // inclusive. Contiguous allocations are biased to the beginning.

  size_t beg = _mutator_leftmost;

  size_t end = beg;

  while (true) {

    if (end >= _max) {

      // Hit the end, goodbye

      return NULL;

    }

    // If regions are not adjacent, then current [beg; end] is useless, and we may fast-forward.

    // If region is not completely free, the current [beg; end] is useless, and we may fast-forward.

    if (!is_mutator_free(end) || !is_empty_or_trash(_heap->get_region(end))) {

      end++;

      beg = end;

      continue;

    }

    if ((end - beg + 1) == num) {

      // found the match

      break;

    }

    end++;

  };

  size_t remainder = words_size & ShenandoahHeapRegion::region_size_words_mask();

  // Initialize regions:

  for (size_t i = beg; i <= end; i++) {

    ShenandoahHeapRegion* r = _heap->get_region(i);

    try_recycle_trashed(r);

    assert(i == beg || _heap->get_region(i-1)->region_number() + 1 == r->region_number(), "Should be contiguous");

    assert(r->is_empty(), "Should be empty");

    if (i == beg) {

      r->make_humongous_start();

    } else {

      r->make_humongous_cont();

    }

    // Trailing region may be non-full, record the remainder there

    size_t used_words;

    if ((i == end) && (remainder != 0)) {

      used_words = remainder;

    } else {

      used_words = ShenandoahHeapRegion::region_size_words();

    }

    r->set_top(r->bottom() + used_words);

    r->reset_alloc_metadata_to_shared();

    _mutator_free_bitmap.clear_bit(r->region_number());

  }

  // While individual regions report their true use, all humongous regions are

  // marked used in the free set.

  increase_used(ShenandoahHeapRegion::region_size_bytes() * num);

  if (remainder != 0) {

    // Record this remainder as allocation waste

    _heap->notify_mutator_alloc_words(ShenandoahHeapRegion::region_size_words() - remainder, true);

  }

  // Allocated at left/rightmost? Move the bounds appropriately.

  if (beg == _mutator_leftmost || end == _mutator_rightmost) {

    adjust_bounds();

  }

  assert_bounds();

  req.set_actual_size(words_size);

  return _heap->get_region(beg)->bottom();

}

bool ShenandoahFreeSet::is_empty_or_trash(ShenandoahHeapRegion *r) {

  return r->is_empty() || r->is_trash();

}

size_t ShenandoahFreeSet::alloc_capacity(ShenandoahHeapRegion *r) {

  if (r->is_trash()) {

    // This would be recycled on allocation path

    return ShenandoahHeapRegion::region_size_bytes();

  } else {

    return r->free();

  }

}

bool ShenandoahFreeSet::has_no_alloc_capacity(ShenandoahHeapRegion *r) {

  return alloc_capacity(r) == 0;

}

void ShenandoahFreeSet::try_recycle_trashed(ShenandoahHeapRegion *r) {

  if (r->is_trash()) {

    _heap->decrease_used(r->used());

    r->recycle();

  }

}

void ShenandoahFreeSet::recycle_trash() {

  // lock is not reentrable, check we don't have it

  assert_heaplock_not_owned_by_current_thread();

  for (size_t i = 0; i < _heap->num_regions(); i++) {

    ShenandoahHeapRegion* r = _heap->get_region(i);

    if (r->is_trash()) {

      ShenandoahHeapLocker locker(_heap->lock());

      try_recycle_trashed(r);

    }

    SpinPause(); // allow allocators to take the lock

  }

}

void ShenandoahFreeSet::flip_to_gc(ShenandoahHeapRegion* r) {

  size_t idx = r->region_number();

  assert(_mutator_free_bitmap.at(idx), "Should be in mutator view");

  assert(is_empty_or_trash(r), "Should not be allocated");

  _mutator_free_bitmap.clear_bit(idx);

  _collector_free_bitmap.set_bit(idx);

  _collector_leftmost = MIN2(idx, _collector_leftmost);

  _collector_rightmost = MAX2(idx, _collector_rightmost);

  _capacity -= alloc_capacity(r);

  if (touches_bounds(idx)) {

    adjust_bounds();

  }

  assert_bounds();

}

void ShenandoahFreeSet::clear() {

  assert_heaplock_owned_by_current_thread();

  clear_internal();

}

void ShenandoahFreeSet::clear_internal() {

  _mutator_free_bitmap.clear();

  _collector_free_bitmap.clear();

  _mutator_leftmost = _max;

  _mutator_rightmost = 0;

  _collector_leftmost = _max;

  _collector_rightmost = 0;

  _capacity = 0;

  _used = 0;

}

void ShenandoahFreeSet::rebuild() {

  assert_heaplock_owned_by_current_thread();

  clear();

  for (size_t idx = 0; idx < _heap->num_regions(); idx++) {

    ShenandoahHeapRegion* region = _heap->get_region(idx);

    if (region->is_alloc_allowed() || region->is_trash()) {

      assert(!region->is_cset(), "Shouldn't be adding those to the free set");

      // Do not add regions that would surely fail allocation

      if (has_no_alloc_capacity(region)) continue;

      _capacity += alloc_capacity(region);

      assert(_used <= _capacity, "must not use more than we have");

      assert(!is_mutator_free(idx), "We are about to add it, it shouldn't be there already");

      _mutator_free_bitmap.set_bit(idx);

    }

  }

  // Evac reserve: reserve trailing space for evacuations

  size_t to_reserve = ShenandoahEvacReserve * _heap->capacity() / 100;

  size_t reserved = 0;

  for (size_t idx = _heap->num_regions() - 1; idx > 0; idx--) {

    if (reserved >= to_reserve) break;

    ShenandoahHeapRegion* region = _heap->get_region(idx);

    if (_mutator_free_bitmap.at(idx) && is_empty_or_trash(region)) {

      _mutator_free_bitmap.clear_bit(idx);

      _collector_free_bitmap.set_bit(idx);

      size_t ac = alloc_capacity(region);

      _capacity -= ac;

      reserved += ac;

    }

  }

  recompute_bounds();

  assert_bounds();

}

void ShenandoahFreeSet::log_status() {

  assert_heaplock_owned_by_current_thread();

  LogTarget(Info, gc, ergo) lt;

  if (lt.is_enabled()) {

    ResourceMark rm;

    LogStream ls(lt);

    {

      size_t last_idx = 0;

      size_t max = 0;

      size_t max_contig = 0;

      size_t empty_contig = 0;

      size_t total_used = 0;

      size_t total_free = 0;

      for (size_t idx = _mutator_leftmost; idx <= _mutator_rightmost; idx++) {

        if (is_mutator_free(idx)) {

          ShenandoahHeapRegion *r = _heap->get_region(idx);

          size_t free = alloc_capacity(r);

          max = MAX2(max, free);

          if (r->is_empty() && (last_idx + 1 == idx)) {

            empty_contig++;

          } else {

            empty_contig = 0;

          }

          total_used += r->used();

          total_free += free;

          max_contig = MAX2(max_contig, empty_contig);

          last_idx = idx;

        }

      }

      size_t max_humongous = max_contig * ShenandoahHeapRegion::region_size_bytes();

      size_t free = capacity() - used();

      ls.print("Free: " SIZE_FORMAT "M (" SIZE_FORMAT " regions), Max regular: " SIZE_FORMAT "K, Max humongous: " SIZE_FORMAT "K, ",

               total_free / M, mutator_count(), max / K, max_humongous / K);

      size_t frag_ext;

      if (free > 0) {

        frag_ext = 100 - (100 * max_humongous / free);

      } else {

        frag_ext = 0;

      }

      ls.print("External frag: " SIZE_FORMAT "%%, ", frag_ext);

      size_t frag_int;

      if (mutator_count() > 0) {

        frag_int = (100 * (total_used / mutator_count()) / ShenandoahHeapRegion::region_size_bytes());

      } else {

        frag_int = 0;

      }

      ls.print("Internal frag: " SIZE_FORMAT "%%", frag_int);

      ls.cr();

    }

    {

      size_t max = 0;

      size_t total_free = 0;

      for (size_t idx = _collector_leftmost; idx <= _collector_rightmost; idx++) {

        if (is_collector_free(idx)) {

          ShenandoahHeapRegion *r = _heap->get_region(idx);

          size_t free = alloc_capacity(r);

          max = MAX2(max, free);

          total_free += free;

        }

      }

      ls.print_cr("Evacuation Reserve: " SIZE_FORMAT "M (" SIZE_FORMAT " regions), Max regular: " SIZE_FORMAT "K",

                  total_free / M, collector_count(), max / K);