1 /*

     2  * Copyright (c) 2001, 2016, 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.

    22  *

    23  */

    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   // Calculate and return chunk size (in number of regions) for parallel

    69   // addition of regions

    70   uint calculate_parallel_work_chunk_size(uint n_workers, uint n_regions) const;

    71 public:

    72 

    73   // Return the current candidate region to be considered for

    74   // collection without removing it from the CSet chooser.

    75   HeapRegion* peek() {

    76     HeapRegion* res = NULL;

    77     if (_front < _end) {

    78       res = regions_at(_front);

    79       assert(res != NULL, "Unexpected NULL hr in _regions at index %u", _front);

    80     }

    81     return res;

    82   }

    83 

    84   // Remove the given region from the CSet chooser and move to the

    85   // next one.

    86   HeapRegion* pop() {

    87     HeapRegion* hr = regions_at(_front);

    88     assert(hr != NULL, "pre-condition");

    89     assert(_front < _end, "pre-condition");

    90     regions_at_put(_front, NULL);

    91     assert(hr->reclaimable_bytes() <= _remaining_reclaimable_bytes,

    92            "remaining reclaimable bytes inconsistent "

    93            "from region: " SIZE_FORMAT " remaining: " SIZE_FORMAT,

    94            hr->reclaimable_bytes(), _remaining_reclaimable_bytes);

    95     _remaining_reclaimable_bytes -= hr->reclaimable_bytes();

    96     _front += 1;

    97     return hr;

    98   }

    99 

   100   void push(HeapRegion* hr);

   101 

   102   CollectionSetChooser();

   103 

   104   void sort_regions();

   105 

   106   // Determine whether to add the given region to the CSet chooser or

   107   // not. Currently, we skip pinned regions and regions whose live

   108   // bytes are over the threshold. Humongous regions may be reclaimed during cleanup.

   109   bool should_add(HeapRegion* hr) {

   110     assert(hr->is_marked(), "pre-condition");

   111     assert(!hr->is_young(), "should never consider young regions");

   112     return !hr->is_pinned() &&

   113             hr->live_bytes() < _region_live_threshold_bytes;

   114   }

   115 

   116   // Returns the number candidate old regions added

   117   uint length() { return _end; }

   118 

   119   // Serial version.

   120   void add_region(HeapRegion *hr);

   121 

   122   // Must be called before calls to claim_array_chunk().

   123   // n_regions is the number of regions, chunk_size the chunk size.

   124   void prepare_for_par_region_addition(uint n_threads, uint n_regions, uint chunk_size);

   125   // Returns the first index in a contiguous chunk of chunk_size indexes

   126   // that the calling thread has reserved.  These must be set by the

   127   // calling thread using set_region() (to NULL if necessary).

   128   uint claim_array_chunk(uint chunk_size);

   129   // Set the marked array entry at index to hr.  Careful to claim the index

   130   // first if in parallel.

   131   void set_region(uint index, HeapRegion* hr);

   132   // Atomically increment the number of added regions by region_num

   133   // and the amount of reclaimable bytes by reclaimable_bytes.

   134   void update_totals(uint region_num, size_t reclaimable_bytes);

   135 

   136   void clear();

   137 

   138   void rebuild(WorkGang* workers, uint n_regions);

   139 

   140   // Return the number of candidate regions that remain to be collected.

   141   uint remaining_regions() { return _end - _front; }

   142 

   143   // Determine whether the CSet chooser has more candidate regions or not.

   144   bool is_empty() { return remaining_regions() == 0; }

   145 

   146   // Return the reclaimable bytes that remain to be collected on

   147   // all the candidate regions in the CSet chooser.

   148   size_t remaining_reclaimable_bytes() { return _remaining_reclaimable_bytes; }

   149 

   150   // Returns true if the used portion of "_regions" is properly

   151   // sorted, otherwise asserts false.

   152   void verify() PRODUCT_RETURN;

   153 };

   154 

   155 class CSetChooserParUpdater : public StackObj {

   156 private:

   157   CollectionSetChooser* _chooser;

   158   bool _parallel;

   159   uint _chunk_size;

   160   uint _cur_chunk_idx;

   161   uint _cur_chunk_end;

   162   uint _regions_added;

   163   size_t _reclaimable_bytes_added;

   164 

   165 public:

   166   CSetChooserParUpdater(CollectionSetChooser* chooser,

   167                         bool parallel, uint chunk_size) :

   168     _chooser(chooser), _parallel(parallel), _chunk_size(chunk_size),

   169     _cur_chunk_idx(0), _cur_chunk_end(0),

   170     _regions_added(0), _reclaimable_bytes_added(0) { }

   171 

   172   ~CSetChooserParUpdater() {

   173     if (_parallel && _regions_added > 0) {

   174       _chooser->update_totals(_regions_added, _reclaimable_bytes_added);

   175     }

   176   }

   177 

   178   void add_region(HeapRegion* hr) {

   179     if (_parallel) {

   180       if (_cur_chunk_idx == _cur_chunk_end) {

   181         _cur_chunk_idx = _chooser->claim_array_chunk(_chunk_size);

   182         _cur_chunk_end = _cur_chunk_idx + _chunk_size;

   183       }

   184       assert(_cur_chunk_idx < _cur_chunk_end, "invariant");

   185       _chooser->set_region(_cur_chunk_idx, hr);

   186       _cur_chunk_idx += 1;

   187     } else {

   188       _chooser->add_region(hr);

   189     }

   190     _regions_added += 1;

   191     _reclaimable_bytes_added += hr->reclaimable_bytes();

   192   }

   193 

   194   bool should_add(HeapRegion* hr) { return _chooser->should_add(hr); }

   195 };

   196 

   197 #endif // SHARE_VM_GC_G1_COLLECTIONSETCHOOSER_HPP

   198