1 /*
   2  * Copyright (c) 2014, 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.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 
  27 #include "gc/shared/blockOffsetTable.inline.hpp"
  28 #include "gc/shared/cardGeneration.inline.hpp"
  29 #include "gc/shared/cardTableRS.hpp"
  30 #include "gc/shared/gcLocker.hpp"
  31 #include "gc/shared/genOopClosures.inline.hpp"
  32 #include "gc/shared/generationSpec.hpp"
  33 #include "gc/shared/space.inline.hpp"
  34 #include "memory/iterator.hpp"
  35 #include "memory/memRegion.hpp"
  36 #include "runtime/java.hpp"
  37 
  38 CardGeneration::CardGeneration(ReservedSpace rs,
  39                                size_t initial_byte_size,
  40                                CardTableRS* remset) :
  41   Generation(rs, initial_byte_size), _rs(remset),
  42   _shrink_factor(0), _min_heap_delta_bytes(), _capacity_at_prologue(),
  43   _used_at_prologue()
  44 {
  45   HeapWord* start = (HeapWord*)rs.base();
  46   size_t reserved_byte_size = rs.size();
  47   assert((uintptr_t(start) & 3) == 0, "bad alignment");
  48   assert((reserved_byte_size & 3) == 0, "bad alignment");
  49   MemRegion reserved_mr(start, heap_word_size(reserved_byte_size));
  50   _bts = new BlockOffsetSharedArray(reserved_mr,
  51                                     heap_word_size(initial_byte_size));
  52   MemRegion committed_mr(start, heap_word_size(initial_byte_size));
  53   _rs->resize_covered_region(committed_mr);
  54   if (_bts == NULL) {
  55     vm_exit_during_initialization("Could not allocate a BlockOffsetArray");
  56   }
  57 
  58   // Verify that the start and end of this generation is the start of a card.
  59   // If this wasn't true, a single card could span more than on generation,
  60   // which would cause problems when we commit/uncommit memory, and when we
  61   // clear and dirty cards.
  62   guarantee(_rs->is_aligned(reserved_mr.start()), "generation must be card aligned");
  63   if (reserved_mr.end() != GenCollectedHeap::heap()->reserved_region().end()) {
  64     // Don't check at the very end of the heap as we'll assert that we're probing off
  65     // the end if we try.
  66     guarantee(_rs->is_aligned(reserved_mr.end()), "generation must be card aligned");
  67   }
  68   _min_heap_delta_bytes = MinHeapDeltaBytes;
  69   _capacity_at_prologue = initial_byte_size;
  70   _used_at_prologue = 0;
  71 }
  72 
  73 bool CardGeneration::grow_by(size_t bytes) {
  74   assert_correct_size_change_locking();
  75   bool result = _virtual_space.expand_by(bytes);
  76   if (result) {
  77     size_t new_word_size =
  78        heap_word_size(_virtual_space.committed_size());
  79     MemRegion mr(space()->bottom(), new_word_size);
  80     // Expand card table
  81     GenCollectedHeap::heap()->barrier_set()->resize_covered_region(mr);
  82     // Expand shared block offset array
  83     _bts->resize(new_word_size);
  84 
  85     // Fix for bug #4668531
  86     if (ZapUnusedHeapArea) {
  87       MemRegion mangle_region(space()->end(),
  88       (HeapWord*)_virtual_space.high());
  89       SpaceMangler::mangle_region(mangle_region);
  90     }
  91 
  92     // Expand space -- also expands space's BOT
  93     // (which uses (part of) shared array above)
  94     space()->set_end((HeapWord*)_virtual_space.high());
  95 
  96     // update the space and generation capacity counters
  97     update_counters();
  98 
  99     if (Verbose && PrintGC) {
 100       size_t new_mem_size = _virtual_space.committed_size();
 101       size_t old_mem_size = new_mem_size - bytes;
 102       gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by "
 103                       SIZE_FORMAT "K to " SIZE_FORMAT "K",
 104                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
 105     }
 106   }
 107   return result;
 108 }
 109 
 110 bool CardGeneration::expand(size_t bytes, size_t expand_bytes) {
 111   assert_locked_or_safepoint(Heap_lock);
 112   if (bytes == 0) {
 113     return true;  // That's what grow_by(0) would return
 114   }
 115   size_t aligned_bytes  = ReservedSpace::page_align_size_up(bytes);
 116   if (aligned_bytes == 0){
 117     // The alignment caused the number of bytes to wrap.  An expand_by(0) will
 118     // return true with the implication that an expansion was done when it
 119     // was not.  A call to expand implies a best effort to expand by "bytes"
 120     // but not a guarantee.  Align down to give a best effort.  This is likely
 121     // the most that the generation can expand since it has some capacity to
 122     // start with.
 123     aligned_bytes = ReservedSpace::page_align_size_down(bytes);
 124   }
 125   size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes);
 126   bool success = false;
 127   if (aligned_expand_bytes > aligned_bytes) {
 128     success = grow_by(aligned_expand_bytes);
 129   }
 130   if (!success) {
 131     success = grow_by(aligned_bytes);
 132   }
 133   if (!success) {
 134     success = grow_to_reserved();
 135   }
 136   if (PrintGC && Verbose) {
 137     if (success && GC_locker::is_active_and_needs_gc()) {
 138       gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead");
 139     }
 140   }
 141 
 142   return success;
 143 }
 144 
 145 bool CardGeneration::grow_to_reserved() {
 146   assert_correct_size_change_locking();
 147   bool success = true;
 148   const size_t remaining_bytes = _virtual_space.uncommitted_size();
 149   if (remaining_bytes > 0) {
 150     success = grow_by(remaining_bytes);
 151     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
 152   }
 153   return success;
 154 }
 155 
 156 void CardGeneration::shrink(size_t bytes) {
 157   assert_correct_size_change_locking();
 158 
 159   size_t size = ReservedSpace::page_align_size_down(bytes);
 160   if (size == 0) {
 161     return;
 162   }
 163 
 164   // Shrink committed space
 165   _virtual_space.shrink_by(size);
 166   // Shrink space; this also shrinks the space's BOT
 167   space()->set_end((HeapWord*) _virtual_space.high());
 168   size_t new_word_size = heap_word_size(space()->capacity());
 169   // Shrink the shared block offset array
 170   _bts->resize(new_word_size);
 171   MemRegion mr(space()->bottom(), new_word_size);
 172   // Shrink the card table
 173   GenCollectedHeap::heap()->barrier_set()->resize_covered_region(mr);
 174 
 175   if (Verbose && PrintGC) {
 176     size_t new_mem_size = _virtual_space.committed_size();
 177     size_t old_mem_size = new_mem_size + size;
 178     gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
 179                   name(), old_mem_size/K, new_mem_size/K);
 180   }
 181 }
 182 
 183 // No young generation references, clear this generation's cards.
 184 void CardGeneration::clear_remembered_set() {
 185   _rs->clear(reserved());
 186 }
 187 
 188 // Objects in this generation may have moved, invalidate this
 189 // generation's cards.
 190 void CardGeneration::invalidate_remembered_set() {
 191   _rs->invalidate(used_region());
 192 }
 193 
 194 void CardGeneration::compute_new_size() {
 195   assert(_shrink_factor <= 100, "invalid shrink factor");
 196   size_t current_shrink_factor = _shrink_factor;
 197   _shrink_factor = 0;
 198 
 199   // We don't have floating point command-line arguments
 200   // Note:  argument processing ensures that MinHeapFreeRatio < 100.
 201   const double minimum_free_percentage = MinHeapFreeRatio / 100.0;
 202   const double maximum_used_percentage = 1.0 - minimum_free_percentage;
 203 
 204   // Compute some numbers about the state of the heap.
 205   const size_t used_after_gc = used();
 206   const size_t capacity_after_gc = capacity();
 207 
 208   const double min_tmp = used_after_gc / maximum_used_percentage;
 209   size_t minimum_desired_capacity = (size_t)MIN2(min_tmp, double(max_uintx));
 210   // Don't shrink less than the initial generation size
 211   minimum_desired_capacity = MAX2(minimum_desired_capacity, initial_size());
 212   assert(used_after_gc <= minimum_desired_capacity, "sanity check");
 213 
 214   if (PrintGC && Verbose) {
 215     const size_t free_after_gc = free();
 216     const double free_percentage = ((double)free_after_gc) / capacity_after_gc;
 217     gclog_or_tty->print_cr("TenuredGeneration::compute_new_size: ");
 218     gclog_or_tty->print_cr("  "
 219                   "  minimum_free_percentage: %6.2f"
 220                   "  maximum_used_percentage: %6.2f",
 221                   minimum_free_percentage,
 222                   maximum_used_percentage);
 223     gclog_or_tty->print_cr("  "
 224                   "   free_after_gc   : %6.1fK"
 225                   "   used_after_gc   : %6.1fK"
 226                   "   capacity_after_gc   : %6.1fK",
 227                   free_after_gc / (double) K,
 228                   used_after_gc / (double) K,
 229                   capacity_after_gc / (double) K);
 230     gclog_or_tty->print_cr("  "
 231                   "   free_percentage: %6.2f",
 232                   free_percentage);
 233   }
 234 
 235   if (capacity_after_gc < minimum_desired_capacity) {
 236     // If we have less free space than we want then expand
 237     size_t expand_bytes = minimum_desired_capacity - capacity_after_gc;
 238     // Don't expand unless it's significant
 239     if (expand_bytes >= _min_heap_delta_bytes) {
 240       expand(expand_bytes, 0); // safe if expansion fails
 241     }
 242     if (PrintGC && Verbose) {
 243       gclog_or_tty->print_cr("    expanding:"
 244                     "  minimum_desired_capacity: %6.1fK"
 245                     "  expand_bytes: %6.1fK"
 246                     "  _min_heap_delta_bytes: %6.1fK",
 247                     minimum_desired_capacity / (double) K,
 248                     expand_bytes / (double) K,
 249                     _min_heap_delta_bytes / (double) K);
 250     }
 251     return;
 252   }
 253 
 254   // No expansion, now see if we want to shrink
 255   size_t shrink_bytes = 0;
 256   // We would never want to shrink more than this
 257   size_t max_shrink_bytes = capacity_after_gc - minimum_desired_capacity;
 258 
 259   if (MaxHeapFreeRatio < 100) {
 260     const double maximum_free_percentage = MaxHeapFreeRatio / 100.0;
 261     const double minimum_used_percentage = 1.0 - maximum_free_percentage;
 262     const double max_tmp = used_after_gc / minimum_used_percentage;
 263     size_t maximum_desired_capacity = (size_t)MIN2(max_tmp, double(max_uintx));
 264     maximum_desired_capacity = MAX2(maximum_desired_capacity, initial_size());
 265     if (PrintGC && Verbose) {
 266       gclog_or_tty->print_cr("  "
 267                              "  maximum_free_percentage: %6.2f"
 268                              "  minimum_used_percentage: %6.2f",
 269                              maximum_free_percentage,
 270                              minimum_used_percentage);
 271       gclog_or_tty->print_cr("  "
 272                              "  _capacity_at_prologue: %6.1fK"
 273                              "  minimum_desired_capacity: %6.1fK"
 274                              "  maximum_desired_capacity: %6.1fK",
 275                              _capacity_at_prologue / (double) K,
 276                              minimum_desired_capacity / (double) K,
 277                              maximum_desired_capacity / (double) K);
 278     }
 279     assert(minimum_desired_capacity <= maximum_desired_capacity,
 280            "sanity check");
 281 
 282     if (capacity_after_gc > maximum_desired_capacity) {
 283       // Capacity too large, compute shrinking size
 284       shrink_bytes = capacity_after_gc - maximum_desired_capacity;
 285       // We don't want shrink all the way back to initSize if people call
 286       // System.gc(), because some programs do that between "phases" and then
 287       // we'd just have to grow the heap up again for the next phase.  So we
 288       // damp the shrinking: 0% on the first call, 10% on the second call, 40%
 289       // on the third call, and 100% by the fourth call.  But if we recompute
 290       // size without shrinking, it goes back to 0%.
 291       shrink_bytes = shrink_bytes / 100 * current_shrink_factor;
 292       assert(shrink_bytes <= max_shrink_bytes, "invalid shrink size");
 293       if (current_shrink_factor == 0) {
 294         _shrink_factor = 10;
 295       } else {
 296         _shrink_factor = MIN2(current_shrink_factor * 4, (size_t) 100);
 297       }
 298       if (PrintGC && Verbose) {
 299         gclog_or_tty->print_cr("  "
 300                                "  shrinking:"
 301                                "  initSize: %.1fK"
 302                                "  maximum_desired_capacity: %.1fK",
 303                                initial_size() / (double) K,
 304                                maximum_desired_capacity / (double) K);
 305         gclog_or_tty->print_cr("  "
 306                                "  shrink_bytes: %.1fK"
 307                                "  current_shrink_factor: " SIZE_FORMAT
 308                                "  new shrink factor: " SIZE_FORMAT
 309                                "  _min_heap_delta_bytes: %.1fK",
 310                                shrink_bytes / (double) K,
 311                                current_shrink_factor,
 312                                _shrink_factor,
 313                                _min_heap_delta_bytes / (double) K);
 314       }
 315     }
 316   }
 317 
 318   if (capacity_after_gc > _capacity_at_prologue) {
 319     // We might have expanded for promotions, in which case we might want to
 320     // take back that expansion if there's room after GC.  That keeps us from
 321     // stretching the heap with promotions when there's plenty of room.
 322     size_t expansion_for_promotion = capacity_after_gc - _capacity_at_prologue;
 323     expansion_for_promotion = MIN2(expansion_for_promotion, max_shrink_bytes);
 324     // We have two shrinking computations, take the largest
 325     shrink_bytes = MAX2(shrink_bytes, expansion_for_promotion);
 326     assert(shrink_bytes <= max_shrink_bytes, "invalid shrink size");
 327     if (PrintGC && Verbose) {
 328       gclog_or_tty->print_cr("  "
 329                              "  aggressive shrinking:"
 330                              "  _capacity_at_prologue: %.1fK"
 331                              "  capacity_after_gc: %.1fK"
 332                              "  expansion_for_promotion: %.1fK"
 333                              "  shrink_bytes: %.1fK",
 334                              capacity_after_gc / (double) K,
 335                              _capacity_at_prologue / (double) K,
 336                              expansion_for_promotion / (double) K,
 337                              shrink_bytes / (double) K);
 338     }
 339   }
 340   // Don't shrink unless it's significant
 341   if (shrink_bytes >= _min_heap_delta_bytes) {
 342     shrink(shrink_bytes);
 343   }
 344 }
 345 
 346 // Currently nothing to do.
 347 void CardGeneration::prepare_for_verify() {}
 348 
 349 void CardGeneration::space_iterate(SpaceClosure* blk,
 350                                                  bool usedOnly) {
 351   blk->do_space(space());
 352 }
 353 
 354 void CardGeneration::younger_refs_iterate(OopsInGenClosure* blk, uint n_threads) {
 355   blk->set_generation(this);
 356   younger_refs_in_space_iterate(space(), blk, n_threads);
 357   blk->reset_generation();
 358 }
--- EOF ---