1 /*
   2  * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
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  24 
  25 #ifndef SHARE_VM_GC_G1_COLLECTIONSETCHOOSER_HPP
  26 #define SHARE_VM_GC_G1_COLLECTIONSETCHOOSER_HPP
  27 
  28 #include "gc/g1/heapRegion.hpp"
  29 #include "utilities/growableArray.hpp"
  30 
  31 class CollectionSetChooser: public CHeapObj<mtGC> {
  32 
  33   GrowableArray<HeapRegion*> _regions;
  34 
  35   // Unfortunately, GrowableArray uses ints for length and indexes. To
  36   // avoid excessive casting in the rest of the class the following
  37   // wrapper methods are provided that use uints.
  38 
  39   uint regions_length()          { return (uint) _regions.length(); }
  40   HeapRegion* regions_at(uint i) { return _regions.at((int) i);     }
  41   void regions_at_put(uint i, HeapRegion* hr) {
  42     _regions.at_put((int) i, hr);
  43   }
  44   void regions_at_put_grow(uint i, HeapRegion* hr) {
  45     _regions.at_put_grow((int) i, hr);
  46   }
  47   void regions_trunc_to(uint i)  { _regions.trunc_to((uint) i); }
  48 
  49   // The index of the next candidate old region to be considered for
  50   // addition to the CSet.
  51   uint _front;
  52 
  53   // The index of the last candidate old region
  54   uint _end;
  55 
  56   // Keeps track of the start of the next array chunk to be claimed by
  57   // parallel GC workers.
  58   uint _first_par_unreserved_idx;
  59 
  60   // If a region has more live bytes than this threshold, it will not
  61   // be added to the CSet chooser and will not be a candidate for
  62   // collection.
  63   size_t _region_live_threshold_bytes;
  64 
  65   // The sum of reclaimable bytes over all the regions in the CSet chooser.
  66   size_t _remaining_reclaimable_bytes;
  67 
  68 public:
  69 
  70   // Return the current candidate region to be considered for
  71   // collection without removing it from the CSet chooser.
  72   HeapRegion* peek() {
  73     HeapRegion* res = NULL;
  74     if (_front < _end) {
  75       res = regions_at(_front);
  76       assert(res != NULL, "Unexpected NULL hr in _regions at index %u", _front);
  77     }
  78     return res;
  79   }
  80 
  81   // Remove the given region from the CSet chooser and move to the
  82   // next one.
  83   HeapRegion* pop() {
  84     HeapRegion* hr = regions_at(_front);
  85     assert(hr != NULL, "pre-condition");
  86     assert(_front < _end, "pre-condition");
  87     regions_at_put(_front, NULL);
  88     assert(hr->reclaimable_bytes() <= _remaining_reclaimable_bytes,
  89            "remaining reclaimable bytes inconsistent "
  90            "from region: " SIZE_FORMAT " remaining: " SIZE_FORMAT,
  91            hr->reclaimable_bytes(), _remaining_reclaimable_bytes);
  92     _remaining_reclaimable_bytes -= hr->reclaimable_bytes();
  93     _front += 1;
  94     return hr;
  95   }
  96 
  97   void push(HeapRegion* hr);
  98 
  99   CollectionSetChooser();
 100 
 101   void sort_regions();
 102 
 103   // Determine whether to add the given region to the CSet chooser or
 104   // not. Currently, we skip pinned regions and regions whose live
 105   // bytes are over the threshold. Humongous regions may be reclaimed during cleanup.
 106   bool should_add(HeapRegion* hr) {
 107     assert(hr->is_marked(), "pre-condition");
 108     assert(!hr->is_young(), "should never consider young regions");
 109     return !hr->is_pinned() &&
 110             hr->live_bytes() < _region_live_threshold_bytes;
 111   }
 112 
 113   // Returns the number candidate old regions added
 114   uint length() { return _end; }
 115 
 116   // Serial version.
 117   void add_region(HeapRegion *hr);
 118 
 119   // Must be called before calls to claim_array_chunk().
 120   // n_regions is the number of regions, chunk_size the chunk size.
 121   void prepare_for_par_region_addition(uint n_threads, uint n_regions, uint chunk_size);
 122   // Returns the first index in a contiguous chunk of chunk_size indexes
 123   // that the calling thread has reserved.  These must be set by the
 124   // calling thread using set_region() (to NULL if necessary).
 125   uint claim_array_chunk(uint chunk_size);
 126   // Set the marked array entry at index to hr.  Careful to claim the index
 127   // first if in parallel.
 128   void set_region(uint index, HeapRegion* hr);
 129   // Atomically increment the number of added regions by region_num
 130   // and the amount of reclaimable bytes by reclaimable_bytes.
 131   void update_totals(uint region_num, size_t reclaimable_bytes);
 132 
 133   void clear();
 134 
 135   // Return the number of candidate regions that remain to be collected.
 136   uint remaining_regions() { return _end - _front; }
 137 
 138   // Determine whether the CSet chooser has more candidate regions or not.
 139   bool is_empty() { return remaining_regions() == 0; }
 140 
 141   // Return the reclaimable bytes that remain to be collected on
 142   // all the candidate regions in the CSet chooser.
 143   size_t remaining_reclaimable_bytes() { return _remaining_reclaimable_bytes; }
 144 
 145   // Returns true if the used portion of "_regions" is properly
 146   // sorted, otherwise asserts false.
 147   void verify() PRODUCT_RETURN;
 148 };
 149 
 150 class CSetChooserParUpdater : public StackObj {
 151 private:
 152   CollectionSetChooser* _chooser;
 153   bool _parallel;
 154   uint _chunk_size;
 155   uint _cur_chunk_idx;
 156   uint _cur_chunk_end;
 157   uint _regions_added;
 158   size_t _reclaimable_bytes_added;
 159 
 160 public:
 161   CSetChooserParUpdater(CollectionSetChooser* chooser,
 162                         bool parallel, uint chunk_size) :
 163     _chooser(chooser), _parallel(parallel), _chunk_size(chunk_size),
 164     _cur_chunk_idx(0), _cur_chunk_end(0),
 165     _regions_added(0), _reclaimable_bytes_added(0) { }
 166 
 167   ~CSetChooserParUpdater() {
 168     if (_parallel && _regions_added > 0) {
 169       _chooser->update_totals(_regions_added, _reclaimable_bytes_added);
 170     }
 171   }
 172 
 173   void add_region(HeapRegion* hr) {
 174     if (_parallel) {
 175       if (_cur_chunk_idx == _cur_chunk_end) {
 176         _cur_chunk_idx = _chooser->claim_array_chunk(_chunk_size);
 177         _cur_chunk_end = _cur_chunk_idx + _chunk_size;
 178       }
 179       assert(_cur_chunk_idx < _cur_chunk_end, "invariant");
 180       _chooser->set_region(_cur_chunk_idx, hr);
 181       _cur_chunk_idx += 1;
 182     } else {
 183       _chooser->add_region(hr);
 184     }
 185     _regions_added += 1;
 186     _reclaimable_bytes_added += hr->reclaimable_bytes();
 187   }
 188 
 189   bool should_add(HeapRegion* hr) { return _chooser->should_add(hr); }
 190 };
 191 
 192 #endif // SHARE_VM_GC_G1_COLLECTIONSETCHOOSER_HPP
 193