1 /*

     2  * Copyright (c) 2001, 2010, 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 #include "precompiled.hpp"

    26 #include "gc_implementation/parNew/parGCAllocBuffer.hpp"

    27 #include "memory/sharedHeap.hpp"

    28 #include "oops/arrayOop.hpp"

    29 #include "oops/oop.inline.hpp"

    30 

    31 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :

    32   _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),

    33   _end(NULL), _hard_end(NULL),

    34   _retained(false), _retained_filler(),

    35   _allocated(0), _wasted(0)

    36 {

    37   assert (min_size() > AlignmentReserve, "Inconsistency!");

    38   // arrayOopDesc::header_size depends on command line initialization.

    39   FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT));

    40   AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;

    41 }

    42 

    43 size_t ParGCAllocBuffer::FillerHeaderSize;

    44 

    45 // If the minimum object size is greater than MinObjAlignment, we can

    46 // end up with a shard at the end of the buffer that's smaller than

    47 // the smallest object.  We can't allow that because the buffer must

    48 // look like it's full of objects when we retire it, so we make

    49 // sure we have enough space for a filler int array object.

    50 size_t ParGCAllocBuffer::AlignmentReserve;

    51 

    52 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {

    53   assert(!retain || end_of_gc, "Can only retain at GC end.");

    54   if (_retained) {

    55     // If the buffer had been retained shorten the previous filler object.

    56     assert(_retained_filler.end() <= _top, "INVARIANT");

    57     CollectedHeap::fill_with_object(_retained_filler);

    58     // Wasted space book-keeping, otherwise (normally) done in invalidate()

    59     _wasted += _retained_filler.word_size();

    60     _retained = false;

    61   }

    62   assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");

    63   if (_top < _hard_end) {

    64     CollectedHeap::fill_with_object(_top, _hard_end);

    65     if (!retain) {

    66       invalidate();

    67     } else {

    68       // Is there wasted space we'd like to retain for the next GC?

    69       if (pointer_delta(_end, _top) > FillerHeaderSize) {

    70         _retained = true;

    71         _retained_filler = MemRegion(_top, FillerHeaderSize);

    72         _top = _top + FillerHeaderSize;

    73       } else {

    74         invalidate();

    75       }

    76     }

    77   }

    78 }

    79 

    80 void ParGCAllocBuffer::flush_stats(PLABStats* stats) {

    81   assert(ResizePLAB, "Wasted work");

    82   stats->add_allocated(_allocated);

    83   stats->add_wasted(_wasted);

    84   stats->add_unused(pointer_delta(_end, _top));

    85 }

    86 

    87 // Compute desired plab size and latch result for later

    88 // use. This should be called once at the end of parallel

    89 // scavenge; it clears the sensor accumulators.

    90 void PLABStats::adjust_desired_plab_sz() {

    91   assert(ResizePLAB, "Not set");

    92   if (_allocated == 0) {

    93     assert(_unused == 0, "Inconsistency in PLAB stats");

    94     _allocated = 1;

    95   }

    96   double wasted_frac    = (double)_unused/(double)_allocated;

    97   size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/

    98                                    TargetPLABWastePct);

    99   if (target_refills == 0) {

   100     target_refills = 1;

   101   }

   102   _used = _allocated - _wasted - _unused;

   103   size_t plab_sz = _used/(target_refills*ParallelGCThreads);

   104   if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz);

   105   // Take historical weighted average

   106   _filter.sample(plab_sz);

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

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

   109   plab_sz = MIN2(max_size(), plab_sz);

   110   plab_sz = align_object_size(plab_sz);

   111   // Latch the result

   112   if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz);

   113   if (ResizePLAB) {

   114     _desired_plab_sz = plab_sz;

   115   }

   116   // Now clear the accumulators for next round:

   117   // note this needs to be fixed in the case where we

   118   // are retaining across scavenges. FIX ME !!! XXX

   119   _allocated = 0;

   120   _wasted    = 0;

   121   _unused    = 0;

   122 }

   123 

   124 #ifndef PRODUCT

   125 void ParGCAllocBuffer::print() {

   126   gclog_or_tty->print("parGCAllocBuffer: _bottom: %p  _top: %p  _end: %p  _hard_end: %p"

   127              "_retained: %c _retained_filler: [%p,%p)\n",

   128              _bottom, _top, _end, _hard_end,

   129              "FT"[_retained], _retained_filler.start(), _retained_filler.end());

   130 }

   131 #endif // !PRODUCT

   132 

   133 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords =

   134 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(),

   135      ((size_t)Generation::GenGrain)/HeapWordSize);

   136 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes =

   137 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize,

   138      (size_t)Generation::GenGrain);

   139 

   140 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz,

   141                                                  BlockOffsetSharedArray* bsa) :

   142   ParGCAllocBuffer(word_sz),

   143   _bsa(bsa),

   144   _bt(bsa, MemRegion(_bottom, _hard_end)),

   145   _true_end(_hard_end)

   146 {}

   147 

   148 // The buffer comes with its own BOT, with a shared (obviously) underlying

   149 // BlockOffsetSharedArray. We manipulate this BOT in the normal way

   150 // as we would for any contiguous space. However, on accasion we

   151 // need to do some buffer surgery at the extremities before we

   152 // start using the body of the buffer for allocations. Such surgery

   153 // (as explained elsewhere) is to prevent allocation on a card that

   154 // is in the process of being walked concurrently by another GC thread.

   155 // When such surgery happens at a point that is far removed (to the

   156 // right of the current allocation point, top), we use the "contig"

   157 // parameter below to directly manipulate the shared array without

   158 // modifying the _next_threshold state in the BOT.

   159 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr,

   160                                                      bool contig) {

   161   CollectedHeap::fill_with_object(mr);

   162   if (contig) {

   163     _bt.alloc_block(mr.start(), mr.end());

   164   } else {

   165     _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end());

   166   }

   167 }

   168 

   169 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) {

   170   HeapWord* res = NULL;

   171   if (_true_end > _hard_end) {

   172     assert((HeapWord*)align_size_down(intptr_t(_hard_end),

   173                                       ChunkSizeInBytes) == _hard_end,

   174            "or else _true_end should be equal to _hard_end");

   175     assert(_retained, "or else _true_end should be equal to _hard_end");

   176     assert(_retained_filler.end() <= _top, "INVARIANT");

   177     CollectedHeap::fill_with_object(_retained_filler);

   178     if (_top < _hard_end) {

   179       fill_region_with_block(MemRegion(_top, _hard_end), true);

   180     }

   181     HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords);

   182     _retained_filler = MemRegion(_hard_end, FillerHeaderSize);

   183     _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size());

   184     _top      = _retained_filler.end();

   185     _hard_end = next_hard_end;

   186     _end      = _hard_end - AlignmentReserve;

   187     res       = ParGCAllocBuffer::allocate(word_sz);

   188     if (res != NULL) {

   189       _bt.alloc_block(res, word_sz);

   190     }

   191   }

   192   return res;

   193 }

   194 

   195 void

   196 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) {

   197   ParGCAllocBuffer::undo_allocation(obj, word_sz);

   198   // This may back us up beyond the previous threshold, so reset.

   199   _bt.set_region(MemRegion(_top, _hard_end));

   200   _bt.initialize_threshold();

   201 }

   202 

   203 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) {

   204   assert(!retain || end_of_gc, "Can only retain at GC end.");

   205   if (_retained) {

   206     // We're about to make the retained_filler into a block.

   207     _bt.BlockOffsetArray::alloc_block(_retained_filler.start(),

   208                                       _retained_filler.end());

   209   }

   210   // Reset _hard_end to _true_end (and update _end)

   211   if (retain && _hard_end != NULL) {

   212     assert(_hard_end <= _true_end, "Invariant.");

   213     _hard_end = _true_end;

   214     _end      = MAX2(_top, _hard_end - AlignmentReserve);

   215     assert(_end <= _hard_end, "Invariant.");

   216   }

   217   _true_end = _hard_end;

   218   HeapWord* pre_top = _top;

   219 

   220   ParGCAllocBuffer::retire(end_of_gc, retain);

   221   // Now any old _retained_filler is cut back to size, the free part is

   222   // filled with a filler object, and top is past the header of that

   223   // object.

   224 

   225   if (retain && _top < _end) {

   226     assert(end_of_gc && retain, "Or else retain should be false.");

   227     // If the lab does not start on a card boundary, we don't want to

   228     // allocate onto that card, since that might lead to concurrent

   229     // allocation and card scanning, which we don't support.  So we fill

   230     // the first card with a garbage object.

   231     size_t first_card_index = _bsa->index_for(pre_top);

   232     HeapWord* first_card_start = _bsa->address_for_index(first_card_index);

   233     if (first_card_start < pre_top) {

   234       HeapWord* second_card_start =

   235         _bsa->inc_by_region_size(first_card_start);

   236 

   237       // Ensure enough room to fill with the smallest block

   238       second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve);

   239 

   240       // If the end is already in the first card, don't go beyond it!

   241       // Or if the remainder is too small for a filler object, gobble it up.

   242       if (_hard_end < second_card_start ||

   243           pointer_delta(_hard_end, second_card_start) < AlignmentReserve) {

   244         second_card_start = _hard_end;

   245       }

   246       if (pre_top < second_card_start) {

   247         MemRegion first_card_suffix(pre_top, second_card_start);

   248         fill_region_with_block(first_card_suffix, true);

   249       }

   250       pre_top = second_card_start;

   251       _top = pre_top;

   252       _end = MAX2(_top, _hard_end - AlignmentReserve);

   253     }

   254 

   255     // If the lab does not end on a card boundary, we don't want to

   256     // allocate onto that card, since that might lead to concurrent

   257     // allocation and card scanning, which we don't support.  So we fill

   258     // the last card with a garbage object.

   259     size_t last_card_index = _bsa->index_for(_hard_end);

   260     HeapWord* last_card_start = _bsa->address_for_index(last_card_index);

   261     if (last_card_start < _hard_end) {

   262 

   263       // Ensure enough room to fill with the smallest block

   264       last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve);

   265 

   266       // If the top is already in the last card, don't go back beyond it!

   267       // Or if the remainder is too small for a filler object, gobble it up.

   268       if (_top > last_card_start ||

   269           pointer_delta(last_card_start, _top) < AlignmentReserve) {

   270         last_card_start = _top;

   271       }

   272       if (last_card_start < _hard_end) {

   273         MemRegion last_card_prefix(last_card_start, _hard_end);

   274         fill_region_with_block(last_card_prefix, false);

   275       }

   276       _hard_end = last_card_start;

   277       _end      = MAX2(_top, _hard_end - AlignmentReserve);

   278       _true_end = _hard_end;

   279       assert(_end <= _hard_end, "Invariant.");

   280     }

   281 

   282     // At this point:

   283     //   1) we had a filler object from the original top to hard_end.

   284     //   2) We've filled in any partial cards at the front and back.

   285     if (pre_top < _hard_end) {

   286       // Now we can reset the _bt to do allocation in the given area.

   287       MemRegion new_filler(pre_top, _hard_end);

   288       fill_region_with_block(new_filler, false);

   289       _top = pre_top + ParGCAllocBuffer::FillerHeaderSize;

   290       // If there's no space left, don't retain.

   291       if (_top >= _end) {

   292         _retained = false;

   293         invalidate();

   294         return;

   295       }

   296       _retained_filler = MemRegion(pre_top, _top);

   297       _bt.set_region(MemRegion(_top, _hard_end));

   298       _bt.initialize_threshold();

   299       assert(_bt.threshold() > _top, "initialize_threshold failed!");

   300 

   301       // There may be other reasons for queries into the middle of the

   302       // filler object.  When such queries are done in parallel with

   303       // allocation, bad things can happen, if the query involves object

   304       // iteration.  So we ensure that such queries do not involve object

   305       // iteration, by putting another filler object on the boundaries of

   306       // such queries.  One such is the object spanning a parallel card

   307       // chunk boundary.

   308 

   309       // "chunk_boundary" is the address of the first chunk boundary less

   310       // than "hard_end".

   311       HeapWord* chunk_boundary =

   312         (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes);

   313       assert(chunk_boundary < _hard_end, "Or else above did not work.");

   314       assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve,

   315              "Consequence of last card handling above.");

   316 

   317       if (_top <= chunk_boundary) {

   318         assert(_true_end == _hard_end, "Invariant.");

   319         while (_top <= chunk_boundary) {

   320           assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve,

   321                  "Consequence of last card handling above.");

   322           _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end);

   323           CollectedHeap::fill_with_object(chunk_boundary, _hard_end);

   324           _hard_end = chunk_boundary;

   325           chunk_boundary -= ChunkSizeInWords;

   326         }

   327         _end = _hard_end - AlignmentReserve;

   328         assert(_top <= _end, "Invariant.");

   329         // Now reset the initial filler chunk so it doesn't overlap with

   330         // the one(s) inserted above.

   331         MemRegion new_filler(pre_top, _hard_end);

   332         fill_region_with_block(new_filler, false);

   333       }

   334     } else {

   335       _retained = false;

   336       invalidate();

   337     }

   338   } else {

   339     assert(!end_of_gc ||

   340            (!_retained && _true_end == _hard_end), "Checking.");

   341   }

   342   assert(_end <= _hard_end, "Invariant.");

   343   assert(_top < _end || _top == _hard_end, "Invariant");

   344 }