cardGeneration.cpp revision 8413:92457dfb91bd 
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.
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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/gcLocker.hpp"
30#include "gc/shared/genOopClosures.inline.hpp"
31#include "gc/shared/genRemSet.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
38CardGeneration::CardGeneration(ReservedSpace rs, size_t initial_byte_size,
39                               int level,
40                               GenRemSet* remset) :
41  Generation(rs, initial_byte_size, level), _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
73bool 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
110bool 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
145bool 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
156void 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.
184void CardGeneration::clear_remembered_set() {
185  _rs->clear(reserved());
186}
187
188// Objects in this generation may have moved, invalidate this
189// generation's cards.
190void CardGeneration::invalidate_remembered_set() {
191  _rs->invalidate(used_region());
192}
193
194void 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,
212                                  spec()->init_size());
213  assert(used_after_gc <= minimum_desired_capacity, "sanity check");
214
215  if (PrintGC && Verbose) {
216    const size_t free_after_gc = free();
217    const double free_percentage = ((double)free_after_gc) / capacity_after_gc;
218    gclog_or_tty->print_cr("TenuredGeneration::compute_new_size: ");
219    gclog_or_tty->print_cr("  "
220                  "  minimum_free_percentage: %6.2f"
221                  "  maximum_used_percentage: %6.2f",
222                  minimum_free_percentage,
223                  maximum_used_percentage);
224    gclog_or_tty->print_cr("  "
225                  "   free_after_gc   : %6.1fK"
226                  "   used_after_gc   : %6.1fK"
227                  "   capacity_after_gc   : %6.1fK",
228                  free_after_gc / (double) K,
229                  used_after_gc / (double) K,
230                  capacity_after_gc / (double) K);
231    gclog_or_tty->print_cr("  "
232                  "   free_percentage: %6.2f",
233                  free_percentage);
234  }
235
236  if (capacity_after_gc < minimum_desired_capacity) {
237    // If we have less free space than we want then expand
238    size_t expand_bytes = minimum_desired_capacity - capacity_after_gc;
239    // Don't expand unless it's significant
240    if (expand_bytes >= _min_heap_delta_bytes) {
241      expand(expand_bytes, 0); // safe if expansion fails
242    }
243    if (PrintGC && Verbose) {
244      gclog_or_tty->print_cr("    expanding:"
245                    "  minimum_desired_capacity: %6.1fK"
246                    "  expand_bytes: %6.1fK"
247                    "  _min_heap_delta_bytes: %6.1fK",
248                    minimum_desired_capacity / (double) K,
249                    expand_bytes / (double) K,
250                    _min_heap_delta_bytes / (double) K);
251    }
252    return;
253  }
254
255  // No expansion, now see if we want to shrink
256  size_t shrink_bytes = 0;
257  // We would never want to shrink more than this
258  size_t max_shrink_bytes = capacity_after_gc - minimum_desired_capacity;
259
260  if (MaxHeapFreeRatio < 100) {
261    const double maximum_free_percentage = MaxHeapFreeRatio / 100.0;
262    const double minimum_used_percentage = 1.0 - maximum_free_percentage;
263    const double max_tmp = used_after_gc / minimum_used_percentage;
264    size_t maximum_desired_capacity = (size_t)MIN2(max_tmp, double(max_uintx));
265    maximum_desired_capacity = MAX2(maximum_desired_capacity,
266                                    spec()->init_size());
267    if (PrintGC && Verbose) {
268      gclog_or_tty->print_cr("  "
269                             "  maximum_free_percentage: %6.2f"
270                             "  minimum_used_percentage: %6.2f",
271                             maximum_free_percentage,
272                             minimum_used_percentage);
273      gclog_or_tty->print_cr("  "
274                             "  _capacity_at_prologue: %6.1fK"
275                             "  minimum_desired_capacity: %6.1fK"
276                             "  maximum_desired_capacity: %6.1fK",
277                             _capacity_at_prologue / (double) K,
278                             minimum_desired_capacity / (double) K,
279                             maximum_desired_capacity / (double) K);
280    }
281    assert(minimum_desired_capacity <= maximum_desired_capacity,
282           "sanity check");
283
284    if (capacity_after_gc > maximum_desired_capacity) {
285      // Capacity too large, compute shrinking size
286      shrink_bytes = capacity_after_gc - maximum_desired_capacity;
287      // We don't want shrink all the way back to initSize if people call
288      // System.gc(), because some programs do that between "phases" and then
289      // we'd just have to grow the heap up again for the next phase.  So we
290      // damp the shrinking: 0% on the first call, 10% on the second call, 40%
291      // on the third call, and 100% by the fourth call.  But if we recompute
292      // size without shrinking, it goes back to 0%.
293      shrink_bytes = shrink_bytes / 100 * current_shrink_factor;
294      assert(shrink_bytes <= max_shrink_bytes, "invalid shrink size");
295      if (current_shrink_factor == 0) {
296        _shrink_factor = 10;
297      } else {
298        _shrink_factor = MIN2(current_shrink_factor * 4, (size_t) 100);
299      }
300      if (PrintGC && Verbose) {
301        gclog_or_tty->print_cr("  "
302                      "  shrinking:"
303                      "  initSize: %.1fK"
304                      "  maximum_desired_capacity: %.1fK",
305                      spec()->init_size() / (double) K,
306                      maximum_desired_capacity / (double) K);
307        gclog_or_tty->print_cr("  "
308                      "  shrink_bytes: %.1fK"
309                      "  current_shrink_factor: " SIZE_FORMAT
310                      "  new shrink factor: " SIZE_FORMAT
311                      "  _min_heap_delta_bytes: %.1fK",
312                      shrink_bytes / (double) K,
313                      current_shrink_factor,
314                      _shrink_factor,
315                      _min_heap_delta_bytes / (double) K);
316      }
317    }
318  }
319
320  if (capacity_after_gc > _capacity_at_prologue) {
321    // We might have expanded for promotions, in which case we might want to
322    // take back that expansion if there's room after GC.  That keeps us from
323    // stretching the heap with promotions when there's plenty of room.
324    size_t expansion_for_promotion = capacity_after_gc - _capacity_at_prologue;
325    expansion_for_promotion = MIN2(expansion_for_promotion, max_shrink_bytes);
326    // We have two shrinking computations, take the largest
327    shrink_bytes = MAX2(shrink_bytes, expansion_for_promotion);
328    assert(shrink_bytes <= max_shrink_bytes, "invalid shrink size");
329    if (PrintGC && Verbose) {
330      gclog_or_tty->print_cr("  "
331                             "  aggressive shrinking:"
332                             "  _capacity_at_prologue: %.1fK"
333                             "  capacity_after_gc: %.1fK"
334                             "  expansion_for_promotion: %.1fK"
335                             "  shrink_bytes: %.1fK",
336                             capacity_after_gc / (double) K,
337                             _capacity_at_prologue / (double) K,
338                             expansion_for_promotion / (double) K,
339                             shrink_bytes / (double) K);
340    }
341  }
342  // Don't shrink unless it's significant
343  if (shrink_bytes >= _min_heap_delta_bytes) {
344    shrink(shrink_bytes);
345  }
346}
347
348// Currently nothing to do.
349void CardGeneration::prepare_for_verify() {}
350
351void CardGeneration::space_iterate(SpaceClosure* blk,
352                                                 bool usedOnly) {
353  blk->do_space(space());
354}
355
356void CardGeneration::younger_refs_iterate(OopsInGenClosure* blk) {
357  blk->set_generation(this);
358  younger_refs_in_space_iterate(space(), blk);
359  blk->reset_generation();
360}
361