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()->rem_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_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 } 140 141 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_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()->rem_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 }