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