rev 52072 : 8211955: GC abstraction for LAB reserve

   1 /*
   2  * Copyright (c) 2001, 2018, 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/shared/collectedHeap.hpp"
  27 #include "gc/shared/plab.inline.hpp"
  28 #include "gc/shared/threadLocalAllocBuffer.hpp"
  29 #include "logging/log.hpp"
  30 #include "oops/arrayOop.hpp"
  31 #include "oops/oop.inline.hpp"
  32 
  33 size_t PLAB::min_size() {
  34   // Make sure that we return something that is larger than AlignmentReserve
  35   return align_object_size(MAX2(MinTLABSize / HeapWordSize, (size_t)oopDesc::header_size())) + AlignmentReserve;
  36 }
  37 
  38 size_t PLAB::max_size() {
  39   return ThreadLocalAllocBuffer::max_size();
  40 }
  41 
  42 PLAB::PLAB(size_t desired_plab_sz_) :
  43   _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
  44   _end(NULL), _hard_end(NULL), _allocated(0), _wasted(0), _undo_wasted(0)
  45 {
  46   // ArrayOopDesc::header_size depends on command line initialization.
  47   AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? align_object_size(arrayOopDesc::header_size(T_INT)) : 0;
  48   assert(min_size() > AlignmentReserve,
  49          "Minimum PLAB size " SIZE_FORMAT " must be larger than alignment reserve " SIZE_FORMAT " "
  50          "to be able to contain objects", min_size(), AlignmentReserve);
  51 }
  52 
  53 // If the minimum object size is greater than MinObjAlignment, we can
  54 // end up with a shard at the end of the buffer that's smaller than
  55 // the smallest object.  We can't allow that because the buffer must
  56 // look like it's full of objects when we retire it, so we make
  57 // sure we have enough space for a filler int array object.
  58 size_t PLAB::AlignmentReserve;
  59 
  60 void PLAB::flush_and_retire_stats(PLABStats* stats) {
  61   // Retire the last allocation buffer.
  62   size_t unused = retire_internal();
  63 
  64   // Now flush the statistics.
  65   stats->add_allocated(_allocated);
  66   stats->add_wasted(_wasted);
  67   stats->add_undo_wasted(_undo_wasted);
  68   stats->add_unused(unused);
  69 
  70   // Since we have flushed the stats we need to clear  the _allocated and _wasted
  71   // fields in case somebody retains an instance of this over GCs. Not doing so
  72   // will artifically inflate the values in the statistics.
  73   _allocated   = 0;
  74   _wasted      = 0;
  75   _undo_wasted = 0;
  76 }
  77 
  78 void PLAB::retire() {
  79   _wasted += retire_internal();
  80 }
  81 
  82 size_t PLAB::retire_internal() {
  83   size_t result = 0;
  84   if (_top < _hard_end) {
  85     Universe::heap()->fill_with_dummy_object(_top, _hard_end, true);
  86     result += invalidate();
  87   }
  88   return result;
  89 }
  90 
  91 void PLAB::add_undo_waste(HeapWord* obj, size_t word_sz) {
  92   Universe::heap()->fill_with_dummy_object(obj, obj + word_sz, true);
  93   _undo_wasted += word_sz;
  94 }
  95 
  96 void PLAB::undo_last_allocation(HeapWord* obj, size_t word_sz) {
  97   assert(pointer_delta(_top, _bottom) >= word_sz, "Bad undo");
  98   assert(pointer_delta(_top, obj) == word_sz, "Bad undo");
  99   _top = obj;
 100 }
 101 
 102 void PLAB::undo_allocation(HeapWord* obj, size_t word_sz) {
 103   // Is the alloc in the current alloc buffer?
 104   if (contains(obj)) {
 105     assert(contains(obj + word_sz - 1),
 106       "should contain whole object");
 107     undo_last_allocation(obj, word_sz);
 108   } else {
 109     add_undo_waste(obj, word_sz);
 110   }
 111 }
 112 
 113 void PLABStats::log_plab_allocation() {
 114   log_debug(gc, plab)("%s PLAB allocation: "
 115                       "allocated: " SIZE_FORMAT "B, "
 116                       "wasted: " SIZE_FORMAT "B, "
 117                       "unused: " SIZE_FORMAT "B, "
 118                       "used: " SIZE_FORMAT "B, "
 119                       "undo waste: " SIZE_FORMAT "B, ",
 120                       _description,
 121                       _allocated * HeapWordSize,
 122                       _wasted * HeapWordSize,
 123                       _unused * HeapWordSize,
 124                       used() * HeapWordSize,
 125                       _undo_wasted * HeapWordSize);
 126 }
 127 
 128 void PLABStats::log_sizing(size_t calculated_words, size_t net_desired_words) {
 129   log_debug(gc, plab)("%s sizing: "
 130                       "calculated: " SIZE_FORMAT "B, "
 131                       "actual: " SIZE_FORMAT "B",
 132                       _description,
 133                       calculated_words * HeapWordSize,
 134                       net_desired_words * HeapWordSize);
 135 }
 136 
 137 // Calculates plab size for current number of gc worker threads.
 138 size_t PLABStats::desired_plab_sz(uint no_of_gc_workers) {
 139   return align_object_size(MIN2(MAX2(min_size(), _desired_net_plab_sz / no_of_gc_workers), max_size()));
 140 }
 141 
 142 // Compute desired plab size for one gc worker thread and latch result for later
 143 // use. This should be called once at the end of parallel
 144 // scavenge; it clears the sensor accumulators.
 145 void PLABStats::adjust_desired_plab_sz() {
 146   log_plab_allocation();
 147 
 148   if (!ResizePLAB) {
 149     // Clear accumulators for next round.
 150     reset();
 151     return;
 152   }
 153 
 154   assert(is_object_aligned(max_size()) && min_size() <= max_size(),
 155          "PLAB clipping computation may be incorrect");
 156 
 157   assert(_allocated != 0 || _unused == 0,
 158          "Inconsistency in PLAB stats: "
 159          "_allocated: " SIZE_FORMAT ", "
 160          "_wasted: " SIZE_FORMAT ", "
 161          "_unused: " SIZE_FORMAT ", "
 162          "_undo_wasted: " SIZE_FORMAT,
 163          _allocated, _wasted, _unused, _undo_wasted);
 164 
 165   size_t plab_sz = compute_desired_plab_sz();
 166   // Take historical weighted average
 167   _filter.sample(plab_sz);
 168   _desired_net_plab_sz = MAX2(min_size(), (size_t)_filter.average());
 169 
 170   log_sizing(plab_sz, _desired_net_plab_sz);
 171   // Clear accumulators for next round
 172   reset();
 173 }
 174 
 175 size_t PLABStats::compute_desired_plab_sz() {
 176   size_t allocated      = MAX2(_allocated, size_t(1));
 177   double wasted_frac    = (double)_unused / (double)allocated;
 178   size_t target_refills = (size_t)((wasted_frac * TargetSurvivorRatio) / TargetPLABWastePct);
 179   if (target_refills == 0) {
 180     target_refills = 1;
 181   }
 182   size_t used = allocated - _wasted - _unused;
 183   // Assumed to have 1 gc worker thread
 184   size_t recent_plab_sz = used / target_refills;
 185   return recent_plab_sz;
 186 }
--- EOF ---