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
39 void CardTableModRefBSForCTRS::
40 non_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
84 void
85 CardTableModRefBSForCTRS::
86 process_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
164
165 // If you want a talkative process_chunk_boundaries,
166 // then #define NOISY(x) x
167 #ifdef NOISY
168 #error "Encountered a global preprocessor flag, NOISY, which might clash with local definition to follow"
169 #else
170 #define NOISY(x)
171 #endif
172
173 void
174 CardTableModRefBSForCTRS::
175 process_chunk_boundaries(Space* sp,
176 DirtyCardToOopClosure* dcto_cl,
177 MemRegion chunk_mr,
178 MemRegion used,
179 jbyte** lowest_non_clean,
180 uintptr_t lowest_non_clean_base_chunk_index,
181 size_t lowest_non_clean_chunk_size)
182 {
183 // We must worry about non-array objects that cross chunk boundaries,
184 // because such objects are both precisely and imprecisely marked:
185 // .. if the head of such an object is dirty, the entire object
186 // needs to be scanned, under the interpretation that this
187 // was an imprecise mark
188 // .. if the head of such an object is not dirty, we can assume
189 // precise marking and it's efficient to scan just the dirty
190 // cards.
191 // In either case, each scanned reference must be scanned precisely
192 // once so as to avoid cloning of a young referent. For efficiency,
193 // our closures depend on this property and do not protect against
194 // double scans.
195
196 uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start());
197 assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error.");
198 uintptr_t cur_chunk_index = start_chunk_index - lowest_non_clean_base_chunk_index;
199
200 NOISY(tty->print_cr("===========================================================================");)
201 NOISY(tty->print_cr(" process_chunk_boundary: Called with [" PTR_FORMAT "," PTR_FORMAT ")",
202 chunk_mr.start(), chunk_mr.end());)
203
204 // First, set "our" lowest_non_clean entry, which would be
205 // used by the thread scanning an adjoining left chunk with
206 // a non-array object straddling the mutual boundary.
207 // Find the object that spans our boundary, if one exists.
208 // first_block is the block possibly straddling our left boundary.
209 HeapWord* first_block = sp->block_start(chunk_mr.start());
210 assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
211 "First chunk should always have a co-initial block");
212 // Does the block straddle the chunk's left boundary, and is it
213 // a non-array object?
214 if (first_block < chunk_mr.start() // first block straddles left bdry
215 && sp->block_is_obj(first_block) // first block is an object
216 && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied)
217 || oop(first_block)->is_typeArray())) {
218 // Find our least non-clean card, so that a left neighbor
219 // does not scan an object straddling the mutual boundary
220 // too far to the right, and attempt to scan a portion of
221 // that object twice.
222 jbyte* first_dirty_card = NULL;
223 jbyte* last_card_of_first_obj =
224 byte_for(first_block + sp->block_size(first_block) - 1);
225 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
226 jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
227 jbyte* last_card_to_check =
228 (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
229 (intptr_t) last_card_of_first_obj);
230 // Note that this does not need to go beyond our last card
231 // if our first object completely straddles this chunk.
232 for (jbyte* cur = first_card_of_cur_chunk;
233 cur <= last_card_to_check; cur++) {
234 jbyte val = *cur;
235 if (card_will_be_scanned(val)) {
236 first_dirty_card = cur; break;
237 } else {
238 assert(!card_may_have_been_dirty(val), "Error");
239 }
240 }
241 if (first_dirty_card != NULL) {
242 NOISY(tty->print_cr(" LNC: Found a dirty card at " PTR_FORMAT " in current chunk",
243 first_dirty_card);)
244 assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error.");
245 assert(lowest_non_clean[cur_chunk_index] == NULL,
246 "Write exactly once : value should be stable hereafter for this round");
247 lowest_non_clean[cur_chunk_index] = first_dirty_card;
248 } NOISY(else {
249 tty->print_cr(" LNC: Found no dirty card in current chunk; leaving LNC entry NULL");
250 // In the future, we could have this thread look for a non-NULL value to copy from its
251 // right neighbor (up to the end of the first object).
252 if (last_card_of_cur_chunk < last_card_of_first_obj) {
253 tty->print_cr(" LNC: BEWARE!!! first obj straddles past right end of chunk:\n"
254 " might be efficient to get value from right neighbor?");
255 }
256 })
257 } else {
258 // In this case we can help our neighbor by just asking them
259 // to stop at our first card (even though it may not be dirty).
260 NOISY(tty->print_cr(" LNC: first block is not a non-array object; setting LNC to first card of current chunk");)
261 assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
262 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
263 lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
264 }
265 NOISY(tty->print_cr(" process_chunk_boundary: lowest_non_clean[" INTPTR_FORMAT "] = " PTR_FORMAT
266 " which corresponds to the heap address " PTR_FORMAT,
267 cur_chunk_index, lowest_non_clean[cur_chunk_index],
268 (lowest_non_clean[cur_chunk_index] != NULL)
269 ? addr_for(lowest_non_clean[cur_chunk_index])
270 : NULL);)
271 NOISY(tty->print_cr("---------------------------------------------------------------------------");)
272
273 // Next, set our own max_to_do, which will strictly/exclusively bound
274 // the highest address that we will scan past the right end of our chunk.
275 HeapWord* max_to_do = NULL;
276 if (chunk_mr.end() < used.end()) {
277 // This is not the last chunk in the used region.
278 // What is our last block? We check the first block of
279 // the next (right) chunk rather than strictly check our last block
280 // because it's potentially more efficient to do so.
281 HeapWord* const last_block = sp->block_start(chunk_mr.end());
282 assert(last_block <= chunk_mr.end(), "In case this property changes.");
283 if ((last_block == chunk_mr.end()) // our last block does not straddle boundary
284 || !sp->block_is_obj(last_block) // last_block isn't an object
285 || oop(last_block)->is_objArray() // last_block is an array (precisely marked)
286 || oop(last_block)->is_typeArray()) {
287 max_to_do = chunk_mr.end();
288 NOISY(tty->print_cr(" process_chunk_boundary: Last block on this card is not a non-array object;\n"
289 " max_to_do left at " PTR_FORMAT, max_to_do);)
290 } else {
291 assert(last_block < chunk_mr.end(), "Tautology");
292 // It is a non-array object that straddles the right boundary of this chunk.
293 // last_obj_card is the card corresponding to the start of the last object
294 // in the chunk. Note that the last object may not start in
295 // the chunk.
296 jbyte* const last_obj_card = byte_for(last_block);
297 const jbyte val = *last_obj_card;
298 if (!card_will_be_scanned(val)) {
299 assert(!card_may_have_been_dirty(val), "Error");
300 // The card containing the head is not dirty. Any marks on
301 // subsequent cards still in this chunk must have been made
302 // precisely; we can cap processing at the end of our chunk.
303 max_to_do = chunk_mr.end();
304 NOISY(tty->print_cr(" process_chunk_boundary: Head of last object on this card is not dirty;\n"
305 " max_to_do left at " PTR_FORMAT,
306 max_to_do);)
307 } else {
308 // The last object must be considered dirty, and extends onto the
309 // following chunk. Look for a dirty card in that chunk that will
310 // bound our processing.
311 jbyte* limit_card = NULL;
312 const size_t last_block_size = sp->block_size(last_block);
313 jbyte* const last_card_of_last_obj =
314 byte_for(last_block + last_block_size - 1);
315 jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
316 // This search potentially goes a long distance looking
317 // for the next card that will be scanned, terminating
318 // at the end of the last_block, if no earlier dirty card
319 // is found.
320 assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
321 "last card of next chunk may be wrong");
322 for (jbyte* cur = first_card_of_next_chunk;
323 cur <= last_card_of_last_obj; cur++) {
324 const jbyte val = *cur;
325 if (card_will_be_scanned(val)) {
326 NOISY(tty->print_cr(" Found a non-clean card " PTR_FORMAT " with value 0x%x",
327 cur, (int)val);)
328 limit_card = cur; break;
329 } else {
330 assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
331 }
332 }
333 if (limit_card != NULL) {
334 max_to_do = addr_for(limit_card);
335 assert(limit_card != NULL && max_to_do != NULL, "Error");
336 NOISY(tty->print_cr(" process_chunk_boundary: Found a dirty card at " PTR_FORMAT
337 " max_to_do set at " PTR_FORMAT " which is before end of last block in chunk: "
338 PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
339 limit_card, max_to_do, last_block, last_block_size, (last_block+last_block_size));)
340 } else {
341 // The following is a pessimistic value, because it's possible
342 // that a dirty card on a subsequent chunk has been cleared by
343 // the time we get to look at it; we'll correct for that further below,
344 // using the LNC array which records the least non-clean card
345 // before cards were cleared in a particular chunk.
346 limit_card = last_card_of_last_obj;
347 max_to_do = last_block + last_block_size;
348 assert(limit_card != NULL && max_to_do != NULL, "Error");
349 NOISY(tty->print_cr(" process_chunk_boundary: Found no dirty card before end of last block in chunk\n"
350 " Setting limit_card to " PTR_FORMAT
351 " and max_to_do " PTR_FORMAT " + " PTR_FORMAT " = " PTR_FORMAT,
352 limit_card, last_block, last_block_size, max_to_do);)
353 }
354 assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
355 "Bounds error.");
356 // It is possible that a dirty card for the last object may have been
357 // cleared before we had a chance to examine it. In that case, the value
358 // will have been logged in the LNC for that chunk.
359 // We need to examine as many chunks to the right as this object
360 // covers. However, we need to bound this checking to the largest
361 // entry in the LNC array: this is because the heap may expand
362 // after the LNC array has been created but before we reach this point,
363 // and the last block in our chunk may have been expanded to include
364 // the expansion delta (and possibly subsequently allocated from, so
365 // it wouldn't be sufficient to check whether that last block was
366 // or was not an object at this point).
367 uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
368 - lowest_non_clean_base_chunk_index;
369 const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
370 - lowest_non_clean_base_chunk_index;
371 if (last_chunk_index_to_check > last_chunk_index) {
372 assert(last_block + last_block_size > used.end(),
373 "Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
374 " does not exceed used.end() = " PTR_FORMAT ","
375 " yet last_chunk_index_to_check " INTPTR_FORMAT
376 " exceeds last_chunk_index " INTPTR_FORMAT,
377 p2i(last_block), p2i(last_block + last_block_size),
378 p2i(used.end()),
379 last_chunk_index_to_check, last_chunk_index);
380 assert(sp->used_region().end() > used.end(),
381 "Expansion did not happen: "
382 "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
383 p2i(sp->used_region().start()), p2i(sp->used_region().end()),
384 p2i(used.start()), p2i(used.end()));
385 NOISY(tty->print_cr(" process_chunk_boundary: heap expanded; explicitly bounding last_chunk");)
386 last_chunk_index_to_check = last_chunk_index;
387 }
388 for (uintptr_t lnc_index = cur_chunk_index + 1;
389 lnc_index <= last_chunk_index_to_check;
390 lnc_index++) {
391 jbyte* lnc_card = lowest_non_clean[lnc_index];
392 if (lnc_card != NULL) {
393 // we can stop at the first non-NULL entry we find
394 if (lnc_card <= limit_card) {
395 NOISY(tty->print_cr(" process_chunk_boundary: LNC card " PTR_FORMAT " is lower than limit_card " PTR_FORMAT,
396 " max_to_do will be lowered to " PTR_FORMAT " from " PTR_FORMAT,
397 lnc_card, limit_card, addr_for(lnc_card), max_to_do);)
398 limit_card = lnc_card;
399 max_to_do = addr_for(limit_card);
400 assert(limit_card != NULL && max_to_do != NULL, "Error");
401 }
402 // In any case, we break now
403 break;
404 } // else continue to look for a non-NULL entry if any
405 }
406 assert(limit_card != NULL && max_to_do != NULL, "Error");
407 }
408 assert(max_to_do != NULL, "OOPS 1 !");
409 }
410 assert(max_to_do != NULL, "OOPS 2!");
411 } else {
412 max_to_do = used.end();
413 NOISY(tty->print_cr(" process_chunk_boundary: Last chunk of this space;\n"
414 " max_to_do left at " PTR_FORMAT,
415 max_to_do);)
416 }
417 assert(max_to_do != NULL, "OOPS 3!");
418 // Now we can set the closure we're using so it doesn't to beyond
419 // max_to_do.
420 dcto_cl->set_min_done(max_to_do);
421 #ifndef PRODUCT
422 dcto_cl->set_last_bottom(max_to_do);
423 #endif
424 NOISY(tty->print_cr("===========================================================================\n");)
425 }
426
427 #undef NOISY
428
429 void
430 CardTableModRefBSForCTRS::
431 get_LNC_array_for_space(Space* sp,
432 jbyte**& lowest_non_clean,
433 uintptr_t& lowest_non_clean_base_chunk_index,
434 size_t& lowest_non_clean_chunk_size) {
435
436 int i = find_covering_region_containing(sp->bottom());
437 MemRegion covered = _covered[i];
438 size_t n_chunks = chunks_to_cover(covered);
439
440 // Only the first thread to obtain the lock will resize the
441 // LNC array for the covered region. Any later expansion can't affect
442 // the used_at_save_marks region.
443 // (I observed a bug in which the first thread to execute this would
444 // resize, and then it would cause "expand_and_allocate" that would
445 // increase the number of chunks in the covered region. Then a second
446 // thread would come and execute this, see that the size didn't match,
447 // and free and allocate again. So the first thread would be using a
448 // freed "_lowest_non_clean" array.)
449
450 // Do a dirty read here. If we pass the conditional then take the rare
451 // event lock and do the read again in case some other thread had already
452 // succeeded and done the resize.
453 int cur_collection = GenCollectedHeap::heap()->total_collections();
454 if (_last_LNC_resizing_collection[i] != cur_collection) {
455 MutexLocker x(ParGCRareEvent_lock);
456 if (_last_LNC_resizing_collection[i] != cur_collection) {
457 if (_lowest_non_clean[i] == NULL ||
458 n_chunks != _lowest_non_clean_chunk_size[i]) {
459
460 // Should we delete the old?
461 if (_lowest_non_clean[i] != NULL) {
462 assert(n_chunks != _lowest_non_clean_chunk_size[i],
463 "logical consequence");
464 FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]);
465 _lowest_non_clean[i] = NULL;
466 }
467 // Now allocate a new one if necessary.
468 if (_lowest_non_clean[i] == NULL) {
469 _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
470 _lowest_non_clean_chunk_size[i] = n_chunks;
471 _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
472 for (int j = 0; j < (int)n_chunks; j++)
473 _lowest_non_clean[i][j] = NULL;
474 }
475 }
476 _last_LNC_resizing_collection[i] = cur_collection;
477 }
478 }
479 // In any case, now do the initialization.
480 lowest_non_clean = _lowest_non_clean[i];
481 lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
482 lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i];
483 }