1/* 2 * Copyright (c) 2007, 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. 22 * 23 */ 24 25#include "precompiled.hpp" 26#include "gc/shared/cardTableModRefBS.hpp" 27#include "gc/shared/cardTableRS.hpp" 28#include "gc/shared/collectedHeap.hpp" 29#include "gc/shared/genCollectedHeap.hpp" 30#include "gc/shared/space.inline.hpp" 31#include "memory/allocation.inline.hpp" 32#include "memory/virtualspace.hpp" 33#include "oops/oop.inline.hpp" 34#include "runtime/java.hpp" 35#include "runtime/mutexLocker.hpp" 36#include "runtime/orderAccess.inline.hpp" 37#include "runtime/vmThread.hpp" 38 39void CardTableModRefBSForCTRS:: 40non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr, 41 OopsInGenClosure* cl, 42 CardTableRS* ct, 43 uint n_threads) { 44 assert(n_threads > 0, "expected n_threads > 0"); 45 assert(n_threads <= ParallelGCThreads, 46 "n_threads: %u > ParallelGCThreads: %u", n_threads, ParallelGCThreads); 47 48 // Make sure the LNC array is valid for the space. 49 jbyte** lowest_non_clean; 50 uintptr_t lowest_non_clean_base_chunk_index; 51 size_t lowest_non_clean_chunk_size; 52 get_LNC_array_for_space(sp, lowest_non_clean, 53 lowest_non_clean_base_chunk_index, 54 lowest_non_clean_chunk_size); 55 56 uint n_strides = n_threads * ParGCStridesPerThread; 57 SequentialSubTasksDone* pst = sp->par_seq_tasks(); 58 // Sets the condition for completion of the subtask (how many threads 59 // need to finish in order to be done). 60 pst->set_n_threads(n_threads); 61 pst->set_n_tasks(n_strides); 62 63 uint stride = 0; 64 while (!pst->is_task_claimed(/* reference */ stride)) { 65 process_stride(sp, mr, stride, n_strides, 66 cl, ct, 67 lowest_non_clean, 68 lowest_non_clean_base_chunk_index, 69 lowest_non_clean_chunk_size); 70 } 71 if (pst->all_tasks_completed()) { 72 // Clear lowest_non_clean array for next time. 73 intptr_t first_chunk_index = addr_to_chunk_index(mr.start()); 74 uintptr_t last_chunk_index = addr_to_chunk_index(mr.last()); 75 for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) { 76 intptr_t ind = ch - lowest_non_clean_base_chunk_index; 77 assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size, 78 "Bounds error"); 79 lowest_non_clean[ind] = NULL; 80 } 81 } 82} 83 84void 85CardTableModRefBSForCTRS:: 86process_stride(Space* sp, 87 MemRegion used, 88 jint stride, int n_strides, 89 OopsInGenClosure* cl, 90 CardTableRS* ct, 91 jbyte** lowest_non_clean, 92 uintptr_t lowest_non_clean_base_chunk_index, 93 size_t lowest_non_clean_chunk_size) { 94 // We go from higher to lower addresses here; it wouldn't help that much 95 // because of the strided parallelism pattern used here. 96 97 // Find the first card address of the first chunk in the stride that is 98 // at least "bottom" of the used region. 99 jbyte* start_card = byte_for(used.start()); 100 jbyte* end_card = byte_after(used.last()); 101 uintptr_t start_chunk = addr_to_chunk_index(used.start()); 102 uintptr_t start_chunk_stride_num = start_chunk % n_strides; 103 jbyte* chunk_card_start; 104 105 if ((uintptr_t)stride >= start_chunk_stride_num) { 106 chunk_card_start = (jbyte*)(start_card + 107 (stride - start_chunk_stride_num) * 108 ParGCCardsPerStrideChunk); 109 } else { 110 // Go ahead to the next chunk group boundary, then to the requested stride. 111 chunk_card_start = (jbyte*)(start_card + 112 (n_strides - start_chunk_stride_num + stride) * 113 ParGCCardsPerStrideChunk); 114 } 115 116 while (chunk_card_start < end_card) { 117 // Even though we go from lower to higher addresses below, the 118 // strided parallelism can interleave the actual processing of the 119 // dirty pages in various ways. For a specific chunk within this 120 // stride, we take care to avoid double scanning or missing a card 121 // by suitably initializing the "min_done" field in process_chunk_boundaries() 122 // below, together with the dirty region extension accomplished in 123 // DirtyCardToOopClosure::do_MemRegion(). 124 jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk; 125 // Invariant: chunk_mr should be fully contained within the "used" region. 126 MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start), 127 chunk_card_end >= end_card ? 128 used.end() : addr_for(chunk_card_end)); 129 assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)"); 130 assert(used.contains(chunk_mr), "chunk_mr should be subset of used"); 131 132 // This function is used by the parallel card table iteration. 133 const bool parallel = true; 134 135 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), 136 cl->gen_boundary(), 137 parallel); 138 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel); 139 140 141 // Process the chunk. 142 process_chunk_boundaries(sp, 143 dcto_cl, 144 chunk_mr, 145 used, 146 lowest_non_clean, 147 lowest_non_clean_base_chunk_index, 148 lowest_non_clean_chunk_size); 149 150 // We want the LNC array updates above in process_chunk_boundaries 151 // to be visible before any of the card table value changes as a 152 // result of the dirty card iteration below. 153 OrderAccess::storestore(); 154 155 // We want to clear the cards: clear_cl here does the work of finding 156 // contiguous dirty ranges of cards to process and clear. 157 clear_cl.do_MemRegion(chunk_mr); 158 159 // Find the next chunk of the stride. 160 chunk_card_start += ParGCCardsPerStrideChunk * n_strides; 161 } 162} 163 164void 165CardTableModRefBSForCTRS:: 166process_chunk_boundaries(Space* sp, 167 DirtyCardToOopClosure* dcto_cl, 168 MemRegion chunk_mr, 169 MemRegion used, 170 jbyte** lowest_non_clean, 171 uintptr_t lowest_non_clean_base_chunk_index, 172 size_t lowest_non_clean_chunk_size) 173{ 174 // We must worry about non-array objects that cross chunk boundaries, 175 // because such objects are both precisely and imprecisely marked: 176 // .. if the head of such an object is dirty, the entire object 177 // needs to be scanned, under the interpretation that this 178 // was an imprecise mark 179 // .. if the head of such an object is not dirty, we can assume 180 // precise marking and it's efficient to scan just the dirty 181 // cards. 182 // In either case, each scanned reference must be scanned precisely 183 // once so as to avoid cloning of a young referent. For efficiency, 184 // our closures depend on this property and do not protect against 185 // double scans. 186 187 uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start()); 188 assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error."); 189 uintptr_t cur_chunk_index = start_chunk_index - lowest_non_clean_base_chunk_index; 190 191 // First, set "our" lowest_non_clean entry, which would be 192 // used by the thread scanning an adjoining left chunk with 193 // a non-array object straddling the mutual boundary. 194 // Find the object that spans our boundary, if one exists. 195 // first_block is the block possibly straddling our left boundary. 196 HeapWord* first_block = sp->block_start(chunk_mr.start()); 197 assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()), 198 "First chunk should always have a co-initial block"); 199 // Does the block straddle the chunk's left boundary, and is it 200 // a non-array object? 201 if (first_block < chunk_mr.start() // first block straddles left bdry 202 && sp->block_is_obj(first_block) // first block is an object 203 && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied) 204 || oop(first_block)->is_typeArray())) { 205 // Find our least non-clean card, so that a left neighbor 206 // does not scan an object straddling the mutual boundary 207 // too far to the right, and attempt to scan a portion of 208 // that object twice. 209 jbyte* first_dirty_card = NULL; 210 jbyte* last_card_of_first_obj = 211 byte_for(first_block + sp->block_size(first_block) - 1); 212 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start()); 213 jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last()); 214 jbyte* last_card_to_check = 215 (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk, 216 (intptr_t) last_card_of_first_obj); 217 // Note that this does not need to go beyond our last card 218 // if our first object completely straddles this chunk. 219 for (jbyte* cur = first_card_of_cur_chunk; 220 cur <= last_card_to_check; cur++) { 221 jbyte val = *cur; 222 if (card_will_be_scanned(val)) { 223 first_dirty_card = cur; break; 224 } else { 225 assert(!card_may_have_been_dirty(val), "Error"); 226 } 227 } 228 if (first_dirty_card != NULL) { 229 assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error."); 230 assert(lowest_non_clean[cur_chunk_index] == NULL, 231 "Write exactly once : value should be stable hereafter for this round"); 232 lowest_non_clean[cur_chunk_index] = first_dirty_card; 233 } 234 } else { 235 // In this case we can help our neighbor by just asking them 236 // to stop at our first card (even though it may not be dirty). 237 assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter"); 238 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start()); 239 lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk; 240 } 241 242 // Next, set our own max_to_do, which will strictly/exclusively bound 243 // the highest address that we will scan past the right end of our chunk. 244 HeapWord* max_to_do = NULL; 245 if (chunk_mr.end() < used.end()) { 246 // This is not the last chunk in the used region. 247 // What is our last block? We check the first block of 248 // the next (right) chunk rather than strictly check our last block 249 // because it's potentially more efficient to do so. 250 HeapWord* const last_block = sp->block_start(chunk_mr.end()); 251 assert(last_block <= chunk_mr.end(), "In case this property changes."); 252 if ((last_block == chunk_mr.end()) // our last block does not straddle boundary 253 || !sp->block_is_obj(last_block) // last_block isn't an object 254 || oop(last_block)->is_objArray() // last_block is an array (precisely marked) 255 || oop(last_block)->is_typeArray()) { 256 max_to_do = chunk_mr.end(); 257 } else { 258 assert(last_block < chunk_mr.end(), "Tautology"); 259 // It is a non-array object that straddles the right boundary of this chunk. 260 // last_obj_card is the card corresponding to the start of the last object 261 // in the chunk. Note that the last object may not start in 262 // the chunk. 263 jbyte* const last_obj_card = byte_for(last_block); 264 const jbyte val = *last_obj_card; 265 if (!card_will_be_scanned(val)) { 266 assert(!card_may_have_been_dirty(val), "Error"); 267 // The card containing the head is not dirty. Any marks on 268 // subsequent cards still in this chunk must have been made 269 // precisely; we can cap processing at the end of our chunk. 270 max_to_do = chunk_mr.end(); 271 } else { 272 // The last object must be considered dirty, and extends onto the 273 // following chunk. Look for a dirty card in that chunk that will 274 // bound our processing. 275 jbyte* limit_card = NULL; 276 const size_t last_block_size = sp->block_size(last_block); 277 jbyte* const last_card_of_last_obj = 278 byte_for(last_block + last_block_size - 1); 279 jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end()); 280 // This search potentially goes a long distance looking 281 // for the next card that will be scanned, terminating 282 // at the end of the last_block, if no earlier dirty card 283 // is found. 284 assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk, 285 "last card of next chunk may be wrong"); 286 for (jbyte* cur = first_card_of_next_chunk; 287 cur <= last_card_of_last_obj; cur++) { 288 const jbyte val = *cur; 289 if (card_will_be_scanned(val)) { 290 limit_card = cur; break; 291 } else { 292 assert(!card_may_have_been_dirty(val), "Error: card can't be skipped"); 293 } 294 } 295 if (limit_card != NULL) { 296 max_to_do = addr_for(limit_card); 297 assert(limit_card != NULL && max_to_do != NULL, "Error"); 298 } else { 299 // The following is a pessimistic value, because it's possible 300 // that a dirty card on a subsequent chunk has been cleared by 301 // the time we get to look at it; we'll correct for that further below, 302 // using the LNC array which records the least non-clean card 303 // before cards were cleared in a particular chunk. 304 limit_card = last_card_of_last_obj; 305 max_to_do = last_block + last_block_size; 306 assert(limit_card != NULL && max_to_do != NULL, "Error"); 307 } 308 assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size, 309 "Bounds error."); 310 // It is possible that a dirty card for the last object may have been 311 // cleared before we had a chance to examine it. In that case, the value 312 // will have been logged in the LNC for that chunk. 313 // We need to examine as many chunks to the right as this object 314 // covers. However, we need to bound this checking to the largest 315 // entry in the LNC array: this is because the heap may expand 316 // after the LNC array has been created but before we reach this point, 317 // and the last block in our chunk may have been expanded to include 318 // the expansion delta (and possibly subsequently allocated from, so 319 // it wouldn't be sufficient to check whether that last block was 320 // or was not an object at this point). 321 uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1) 322 - lowest_non_clean_base_chunk_index; 323 const uintptr_t last_chunk_index = addr_to_chunk_index(used.last()) 324 - lowest_non_clean_base_chunk_index; 325 if (last_chunk_index_to_check > last_chunk_index) { 326 assert(last_block + last_block_size > used.end(), 327 "Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]" 328 " does not exceed used.end() = " PTR_FORMAT "," 329 " yet last_chunk_index_to_check " INTPTR_FORMAT 330 " exceeds last_chunk_index " INTPTR_FORMAT, 331 p2i(last_block), p2i(last_block + last_block_size), 332 p2i(used.end()), 333 last_chunk_index_to_check, last_chunk_index); 334 assert(sp->used_region().end() > used.end(), 335 "Expansion did not happen: " 336 "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")", 337 p2i(sp->used_region().start()), p2i(sp->used_region().end()), 338 p2i(used.start()), p2i(used.end())); 339 last_chunk_index_to_check = last_chunk_index; 340 } 341 for (uintptr_t lnc_index = cur_chunk_index + 1; 342 lnc_index <= last_chunk_index_to_check; 343 lnc_index++) { 344 jbyte* lnc_card = lowest_non_clean[lnc_index]; 345 if (lnc_card != NULL) { 346 // we can stop at the first non-NULL entry we find 347 if (lnc_card <= limit_card) { 348 limit_card = lnc_card; 349 max_to_do = addr_for(limit_card); 350 assert(limit_card != NULL && max_to_do != NULL, "Error"); 351 } 352 // In any case, we break now 353 break; 354 } // else continue to look for a non-NULL entry if any 355 } 356 assert(limit_card != NULL && max_to_do != NULL, "Error"); 357 } 358 assert(max_to_do != NULL, "OOPS 1 !"); 359 } 360 assert(max_to_do != NULL, "OOPS 2!"); 361 } else { 362 max_to_do = used.end(); 363 } 364 assert(max_to_do != NULL, "OOPS 3!"); 365 // Now we can set the closure we're using so it doesn't to beyond 366 // max_to_do. 367 dcto_cl->set_min_done(max_to_do); 368#ifndef PRODUCT 369 dcto_cl->set_last_bottom(max_to_do); 370#endif 371} 372 373void 374CardTableModRefBSForCTRS:: 375get_LNC_array_for_space(Space* sp, 376 jbyte**& lowest_non_clean, 377 uintptr_t& lowest_non_clean_base_chunk_index, 378 size_t& lowest_non_clean_chunk_size) { 379 380 int i = find_covering_region_containing(sp->bottom()); 381 MemRegion covered = _covered[i]; 382 size_t n_chunks = chunks_to_cover(covered); 383 384 // Only the first thread to obtain the lock will resize the 385 // LNC array for the covered region. Any later expansion can't affect 386 // the used_at_save_marks region. 387 // (I observed a bug in which the first thread to execute this would 388 // resize, and then it would cause "expand_and_allocate" that would 389 // increase the number of chunks in the covered region. Then a second 390 // thread would come and execute this, see that the size didn't match, 391 // and free and allocate again. So the first thread would be using a 392 // freed "_lowest_non_clean" array.) 393 394 // Do a dirty read here. If we pass the conditional then take the rare 395 // event lock and do the read again in case some other thread had already 396 // succeeded and done the resize. 397 int cur_collection = GenCollectedHeap::heap()->total_collections(); 398 // Updated _last_LNC_resizing_collection[i] must not be visible before 399 // _lowest_non_clean and friends are visible. Therefore use acquire/release 400 // to guarantee this on non TSO architecures. 401 if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) { 402 MutexLocker x(ParGCRareEvent_lock); 403 // This load_acquire is here for clarity only. The MutexLocker already fences. 404 if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) { 405 if (_lowest_non_clean[i] == NULL || 406 n_chunks != _lowest_non_clean_chunk_size[i]) { 407 408 // Should we delete the old? 409 if (_lowest_non_clean[i] != NULL) { 410 assert(n_chunks != _lowest_non_clean_chunk_size[i], 411 "logical consequence"); 412 FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]); 413 _lowest_non_clean[i] = NULL; 414 } 415 // Now allocate a new one if necessary. 416 if (_lowest_non_clean[i] == NULL) { 417 _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC); 418 _lowest_non_clean_chunk_size[i] = n_chunks; 419 _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start()); 420 for (int j = 0; j < (int)n_chunks; j++) 421 _lowest_non_clean[i][j] = NULL; 422 } 423 } 424 // Make sure this gets visible only after _lowest_non_clean* was initialized 425 OrderAccess::release_store(&_last_LNC_resizing_collection[i], cur_collection); 426 } 427 } 428 // In any case, now do the initialization. 429 lowest_non_clean = _lowest_non_clean[i]; 430 lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i]; 431 lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i]; 432} 433