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