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