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
39CardGeneration::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
74bool 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
108bool 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_size_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_size_down(bytes);
122  }
123  size_t aligned_expand_bytes = ReservedSpace::page_align_size_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
141bool 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
152void CardGeneration::shrink(size_t bytes) {
153  assert_correct_size_change_locking();
154
155  size_t size = ReservedSpace::page_align_size_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.
178void CardGeneration::clear_remembered_set() {
179  _rs->clear(reserved());
180}
181
182// Objects in this generation may have moved, invalidate this
183// generation's cards.
184void CardGeneration::invalidate_remembered_set() {
185  _rs->invalidate(used_region());
186}
187
188void 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.
305void CardGeneration::prepare_for_verify() {}
306
307void CardGeneration::space_iterate(SpaceClosure* blk,
308                                                 bool usedOnly) {
309  blk->do_space(space());
310}
311
312void 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}
317