1 /*
2 * Copyright (c) 2007, 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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "gc/cms/cmsCardTable.hpp"
27 #include "gc/cms/cmsHeap.hpp"
28 #include "gc/shared/cardTableBarrierSet.hpp"
29 #include "gc/shared/cardTableRS.hpp"
30 #include "gc/shared/collectedHeap.hpp"
31 #include "gc/shared/space.inline.hpp"
32 #include "memory/allocation.inline.hpp"
33 #include "memory/virtualspace.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/mutexLocker.hpp"
37 #include "runtime/orderAccess.inline.hpp"
38 #include "runtime/vmThread.hpp"
39
40 CMSCardTable::CMSCardTable(MemRegion whole_heap) :
41 CardTableRS(whole_heap, CMSPrecleaningEnabled /* scanned_concurrently */) {
42 }
43
44 // Returns the number of chunks necessary to cover "mr".
45 size_t CMSCardTable::chunks_to_cover(MemRegion mr) {
46 return (size_t)(addr_to_chunk_index(mr.last()) -
47 addr_to_chunk_index(mr.start()) + 1);
48 }
49
50 // Returns the index of the chunk in a stride which
51 // covers the given address.
52 uintptr_t CMSCardTable::addr_to_chunk_index(const void* addr) {
53 uintptr_t card = (uintptr_t) byte_for(addr);
54 return card / ParGCCardsPerStrideChunk;
55 }
56
57 void CMSCardTable::
58 non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
59 OopsInGenClosure* cl,
60 CardTableRS* ct,
61 uint n_threads) {
62 assert(n_threads > 0, "expected n_threads > 0");
63 assert(n_threads <= ParallelGCThreads,
64 "n_threads: %u > ParallelGCThreads: %u", n_threads, ParallelGCThreads);
65
66 // Make sure the LNC array is valid for the space.
67 jbyte** lowest_non_clean;
68 uintptr_t lowest_non_clean_base_chunk_index;
69 size_t lowest_non_clean_chunk_size;
70 get_LNC_array_for_space(sp, lowest_non_clean,
71 lowest_non_clean_base_chunk_index,
72 lowest_non_clean_chunk_size);
73
74 uint n_strides = n_threads * ParGCStridesPerThread;
75 SequentialSubTasksDone* pst = sp->par_seq_tasks();
76 // Sets the condition for completion of the subtask (how many threads
77 // need to finish in order to be done).
78 pst->set_n_threads(n_threads);
79 pst->set_n_tasks(n_strides);
80
81 uint stride = 0;
82 while (!pst->is_task_claimed(/* reference */ stride)) {
83 process_stride(sp, mr, stride, n_strides,
84 cl, ct,
85 lowest_non_clean,
86 lowest_non_clean_base_chunk_index,
87 lowest_non_clean_chunk_size);
88 }
89 if (pst->all_tasks_completed()) {
90 // Clear lowest_non_clean array for next time.
91 intptr_t first_chunk_index = addr_to_chunk_index(mr.start());
92 uintptr_t last_chunk_index = addr_to_chunk_index(mr.last());
93 for (uintptr_t ch = first_chunk_index; ch <= last_chunk_index; ch++) {
94 intptr_t ind = ch - lowest_non_clean_base_chunk_index;
95 assert(0 <= ind && ind < (intptr_t)lowest_non_clean_chunk_size,
96 "Bounds error");
97 lowest_non_clean[ind] = NULL;
98 }
99 }
100 }
101
102 void
103 CMSCardTable::
104 process_stride(Space* sp,
105 MemRegion used,
106 jint stride, int n_strides,
107 OopsInGenClosure* cl,
108 CardTableRS* ct,
109 jbyte** lowest_non_clean,
110 uintptr_t lowest_non_clean_base_chunk_index,
111 size_t lowest_non_clean_chunk_size) {
112 // We go from higher to lower addresses here; it wouldn't help that much
113 // because of the strided parallelism pattern used here.
114
115 // Find the first card address of the first chunk in the stride that is
116 // at least "bottom" of the used region.
117 jbyte* start_card = byte_for(used.start());
118 jbyte* end_card = byte_after(used.last());
119 uintptr_t start_chunk = addr_to_chunk_index(used.start());
120 uintptr_t start_chunk_stride_num = start_chunk % n_strides;
121 jbyte* chunk_card_start;
122
123 if ((uintptr_t)stride >= start_chunk_stride_num) {
124 chunk_card_start = (jbyte*)(start_card +
125 (stride - start_chunk_stride_num) *
126 ParGCCardsPerStrideChunk);
127 } else {
128 // Go ahead to the next chunk group boundary, then to the requested stride.
129 chunk_card_start = (jbyte*)(start_card +
130 (n_strides - start_chunk_stride_num + stride) *
131 ParGCCardsPerStrideChunk);
132 }
133
134 while (chunk_card_start < end_card) {
135 // Even though we go from lower to higher addresses below, the
136 // strided parallelism can interleave the actual processing of the
137 // dirty pages in various ways. For a specific chunk within this
138 // stride, we take care to avoid double scanning or missing a card
139 // by suitably initializing the "min_done" field in process_chunk_boundaries()
140 // below, together with the dirty region extension accomplished in
141 // DirtyCardToOopClosure::do_MemRegion().
142 jbyte* chunk_card_end = chunk_card_start + ParGCCardsPerStrideChunk;
143 // Invariant: chunk_mr should be fully contained within the "used" region.
144 MemRegion chunk_mr = MemRegion(addr_for(chunk_card_start),
145 chunk_card_end >= end_card ?
146 used.end() : addr_for(chunk_card_end));
147 assert(chunk_mr.word_size() > 0, "[chunk_card_start > used_end)");
148 assert(used.contains(chunk_mr), "chunk_mr should be subset of used");
149
150 // This function is used by the parallel card table iteration.
151 const bool parallel = true;
152
153 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(),
154 cl->gen_boundary(),
155 parallel);
156 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);
157
158
159 // Process the chunk.
160 process_chunk_boundaries(sp,
161 dcto_cl,
162 chunk_mr,
163 used,
164 lowest_non_clean,
165 lowest_non_clean_base_chunk_index,
166 lowest_non_clean_chunk_size);
167
168 // We want the LNC array updates above in process_chunk_boundaries
169 // to be visible before any of the card table value changes as a
170 // result of the dirty card iteration below.
171 OrderAccess::storestore();
172
173 // We want to clear the cards: clear_cl here does the work of finding
174 // contiguous dirty ranges of cards to process and clear.
175 clear_cl.do_MemRegion(chunk_mr);
176
177 // Find the next chunk of the stride.
178 chunk_card_start += ParGCCardsPerStrideChunk * n_strides;
179 }
180 }
181
182 void
183 CMSCardTable::
184 process_chunk_boundaries(Space* sp,
185 DirtyCardToOopClosure* dcto_cl,
186 MemRegion chunk_mr,
187 MemRegion used,
188 jbyte** lowest_non_clean,
189 uintptr_t lowest_non_clean_base_chunk_index,
190 size_t lowest_non_clean_chunk_size)
191 {
192 // We must worry about non-array objects that cross chunk boundaries,
193 // because such objects are both precisely and imprecisely marked:
194 // .. if the head of such an object is dirty, the entire object
195 // needs to be scanned, under the interpretation that this
196 // was an imprecise mark
197 // .. if the head of such an object is not dirty, we can assume
198 // precise marking and it's efficient to scan just the dirty
199 // cards.
200 // In either case, each scanned reference must be scanned precisely
201 // once so as to avoid cloning of a young referent. For efficiency,
202 // our closures depend on this property and do not protect against
203 // double scans.
204
205 uintptr_t start_chunk_index = addr_to_chunk_index(chunk_mr.start());
206 assert(start_chunk_index >= lowest_non_clean_base_chunk_index, "Bounds error.");
207 uintptr_t cur_chunk_index = start_chunk_index - lowest_non_clean_base_chunk_index;
208
209 // First, set "our" lowest_non_clean entry, which would be
210 // used by the thread scanning an adjoining left chunk with
211 // a non-array object straddling the mutual boundary.
212 // Find the object that spans our boundary, if one exists.
213 // first_block is the block possibly straddling our left boundary.
214 HeapWord* first_block = sp->block_start(chunk_mr.start());
215 assert((chunk_mr.start() != used.start()) || (first_block == chunk_mr.start()),
216 "First chunk should always have a co-initial block");
217 // Does the block straddle the chunk's left boundary, and is it
218 // a non-array object?
219 if (first_block < chunk_mr.start() // first block straddles left bdry
220 && sp->block_is_obj(first_block) // first block is an object
221 && !(oop(first_block)->is_objArray() // first block is not an array (arrays are precisely dirtied)
222 || oop(first_block)->is_typeArray())) {
223 // Find our least non-clean card, so that a left neighbor
224 // does not scan an object straddling the mutual boundary
225 // too far to the right, and attempt to scan a portion of
226 // that object twice.
227 jbyte* first_dirty_card = NULL;
228 jbyte* last_card_of_first_obj =
229 byte_for(first_block + sp->block_size(first_block) - 1);
230 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
231 jbyte* last_card_of_cur_chunk = byte_for(chunk_mr.last());
232 jbyte* last_card_to_check =
233 (jbyte*) MIN2((intptr_t) last_card_of_cur_chunk,
234 (intptr_t) last_card_of_first_obj);
235 // Note that this does not need to go beyond our last card
236 // if our first object completely straddles this chunk.
237 for (jbyte* cur = first_card_of_cur_chunk;
238 cur <= last_card_to_check; cur++) {
239 jbyte val = *cur;
240 if (card_will_be_scanned(val)) {
241 first_dirty_card = cur; break;
242 } else {
243 assert(!card_may_have_been_dirty(val), "Error");
244 }
245 }
246 if (first_dirty_card != NULL) {
247 assert(cur_chunk_index < lowest_non_clean_chunk_size, "Bounds error.");
248 assert(lowest_non_clean[cur_chunk_index] == NULL,
249 "Write exactly once : value should be stable hereafter for this round");
250 lowest_non_clean[cur_chunk_index] = first_dirty_card;
251 }
252 } else {
253 // In this case we can help our neighbor by just asking them
254 // to stop at our first card (even though it may not be dirty).
255 assert(lowest_non_clean[cur_chunk_index] == NULL, "Write once : value should be stable hereafter");
256 jbyte* first_card_of_cur_chunk = byte_for(chunk_mr.start());
257 lowest_non_clean[cur_chunk_index] = first_card_of_cur_chunk;
258 }
259
260 // Next, set our own max_to_do, which will strictly/exclusively bound
261 // the highest address that we will scan past the right end of our chunk.
262 HeapWord* max_to_do = NULL;
263 if (chunk_mr.end() < used.end()) {
264 // This is not the last chunk in the used region.
265 // What is our last block? We check the first block of
266 // the next (right) chunk rather than strictly check our last block
267 // because it's potentially more efficient to do so.
268 HeapWord* const last_block = sp->block_start(chunk_mr.end());
269 assert(last_block <= chunk_mr.end(), "In case this property changes.");
270 if ((last_block == chunk_mr.end()) // our last block does not straddle boundary
271 || !sp->block_is_obj(last_block) // last_block isn't an object
272 || oop(last_block)->is_objArray() // last_block is an array (precisely marked)
273 || oop(last_block)->is_typeArray()) {
274 max_to_do = chunk_mr.end();
275 } else {
276 assert(last_block < chunk_mr.end(), "Tautology");
277 // It is a non-array object that straddles the right boundary of this chunk.
278 // last_obj_card is the card corresponding to the start of the last object
279 // in the chunk. Note that the last object may not start in
280 // the chunk.
281 jbyte* const last_obj_card = byte_for(last_block);
282 const jbyte val = *last_obj_card;
283 if (!card_will_be_scanned(val)) {
284 assert(!card_may_have_been_dirty(val), "Error");
285 // The card containing the head is not dirty. Any marks on
286 // subsequent cards still in this chunk must have been made
287 // precisely; we can cap processing at the end of our chunk.
288 max_to_do = chunk_mr.end();
289 } else {
290 // The last object must be considered dirty, and extends onto the
291 // following chunk. Look for a dirty card in that chunk that will
292 // bound our processing.
293 jbyte* limit_card = NULL;
294 const size_t last_block_size = sp->block_size(last_block);
295 jbyte* const last_card_of_last_obj =
296 byte_for(last_block + last_block_size - 1);
297 jbyte* const first_card_of_next_chunk = byte_for(chunk_mr.end());
298 // This search potentially goes a long distance looking
299 // for the next card that will be scanned, terminating
300 // at the end of the last_block, if no earlier dirty card
301 // is found.
302 assert(byte_for(chunk_mr.end()) - byte_for(chunk_mr.start()) == ParGCCardsPerStrideChunk,
303 "last card of next chunk may be wrong");
304 for (jbyte* cur = first_card_of_next_chunk;
305 cur <= last_card_of_last_obj; cur++) {
306 const jbyte val = *cur;
307 if (card_will_be_scanned(val)) {
308 limit_card = cur; break;
309 } else {
310 assert(!card_may_have_been_dirty(val), "Error: card can't be skipped");
311 }
312 }
313 if (limit_card != NULL) {
314 max_to_do = addr_for(limit_card);
315 assert(limit_card != NULL && max_to_do != NULL, "Error");
316 } else {
317 // The following is a pessimistic value, because it's possible
318 // that a dirty card on a subsequent chunk has been cleared by
319 // the time we get to look at it; we'll correct for that further below,
320 // using the LNC array which records the least non-clean card
321 // before cards were cleared in a particular chunk.
322 limit_card = last_card_of_last_obj;
323 max_to_do = last_block + last_block_size;
324 assert(limit_card != NULL && max_to_do != NULL, "Error");
325 }
326 assert(0 < cur_chunk_index+1 && cur_chunk_index+1 < lowest_non_clean_chunk_size,
327 "Bounds error.");
328 // It is possible that a dirty card for the last object may have been
329 // cleared before we had a chance to examine it. In that case, the value
330 // will have been logged in the LNC for that chunk.
331 // We need to examine as many chunks to the right as this object
332 // covers. However, we need to bound this checking to the largest
333 // entry in the LNC array: this is because the heap may expand
334 // after the LNC array has been created but before we reach this point,
335 // and the last block in our chunk may have been expanded to include
336 // the expansion delta (and possibly subsequently allocated from, so
337 // it wouldn't be sufficient to check whether that last block was
338 // or was not an object at this point).
339 uintptr_t last_chunk_index_to_check = addr_to_chunk_index(last_block + last_block_size - 1)
340 - lowest_non_clean_base_chunk_index;
341 const uintptr_t last_chunk_index = addr_to_chunk_index(used.last())
342 - lowest_non_clean_base_chunk_index;
343 if (last_chunk_index_to_check > last_chunk_index) {
344 assert(last_block + last_block_size > used.end(),
345 "Inconsistency detected: last_block [" PTR_FORMAT "," PTR_FORMAT "]"
346 " does not exceed used.end() = " PTR_FORMAT ","
347 " yet last_chunk_index_to_check " INTPTR_FORMAT
348 " exceeds last_chunk_index " INTPTR_FORMAT,
349 p2i(last_block), p2i(last_block + last_block_size),
350 p2i(used.end()),
351 last_chunk_index_to_check, last_chunk_index);
352 assert(sp->used_region().end() > used.end(),
353 "Expansion did not happen: "
354 "[" PTR_FORMAT "," PTR_FORMAT ") -> [" PTR_FORMAT "," PTR_FORMAT ")",
355 p2i(sp->used_region().start()), p2i(sp->used_region().end()),
356 p2i(used.start()), p2i(used.end()));
357 last_chunk_index_to_check = last_chunk_index;
358 }
359 for (uintptr_t lnc_index = cur_chunk_index + 1;
360 lnc_index <= last_chunk_index_to_check;
361 lnc_index++) {
362 jbyte* lnc_card = lowest_non_clean[lnc_index];
363 if (lnc_card != NULL) {
364 // we can stop at the first non-NULL entry we find
365 if (lnc_card <= limit_card) {
366 limit_card = lnc_card;
367 max_to_do = addr_for(limit_card);
368 assert(limit_card != NULL && max_to_do != NULL, "Error");
369 }
370 // In any case, we break now
371 break;
372 } // else continue to look for a non-NULL entry if any
373 }
374 assert(limit_card != NULL && max_to_do != NULL, "Error");
375 }
376 assert(max_to_do != NULL, "OOPS 1 !");
377 }
378 assert(max_to_do != NULL, "OOPS 2!");
379 } else {
380 max_to_do = used.end();
381 }
382 assert(max_to_do != NULL, "OOPS 3!");
383 // Now we can set the closure we're using so it doesn't to beyond
384 // max_to_do.
385 dcto_cl->set_min_done(max_to_do);
386 #ifndef PRODUCT
387 dcto_cl->set_last_bottom(max_to_do);
388 #endif
389 }
390
391 void
392 CMSCardTable::
393 get_LNC_array_for_space(Space* sp,
394 jbyte**& lowest_non_clean,
395 uintptr_t& lowest_non_clean_base_chunk_index,
396 size_t& lowest_non_clean_chunk_size) {
397
398 int i = find_covering_region_containing(sp->bottom());
399 MemRegion covered = _covered[i];
400 size_t n_chunks = chunks_to_cover(covered);
401
402 // Only the first thread to obtain the lock will resize the
403 // LNC array for the covered region. Any later expansion can't affect
404 // the used_at_save_marks region.
405 // (I observed a bug in which the first thread to execute this would
406 // resize, and then it would cause "expand_and_allocate" that would
407 // increase the number of chunks in the covered region. Then a second
408 // thread would come and execute this, see that the size didn't match,
409 // and free and allocate again. So the first thread would be using a
410 // freed "_lowest_non_clean" array.)
411
412 // Do a dirty read here. If we pass the conditional then take the rare
413 // event lock and do the read again in case some other thread had already
414 // succeeded and done the resize.
415 int cur_collection = CMSHeap::heap()->total_collections();
416 // Updated _last_LNC_resizing_collection[i] must not be visible before
417 // _lowest_non_clean and friends are visible. Therefore use acquire/release
418 // to guarantee this on non TSO architecures.
419 if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
420 MutexLocker x(ParGCRareEvent_lock);
421 // This load_acquire is here for clarity only. The MutexLocker already fences.
422 if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
423 if (_lowest_non_clean[i] == NULL ||
424 n_chunks != _lowest_non_clean_chunk_size[i]) {
425
426 // Should we delete the old?
427 if (_lowest_non_clean[i] != NULL) {
428 assert(n_chunks != _lowest_non_clean_chunk_size[i],
429 "logical consequence");
430 FREE_C_HEAP_ARRAY(CardPtr, _lowest_non_clean[i]);
431 _lowest_non_clean[i] = NULL;
432 }
433 // Now allocate a new one if necessary.
434 if (_lowest_non_clean[i] == NULL) {
435 _lowest_non_clean[i] = NEW_C_HEAP_ARRAY(CardPtr, n_chunks, mtGC);
436 _lowest_non_clean_chunk_size[i] = n_chunks;
437 _lowest_non_clean_base_chunk_index[i] = addr_to_chunk_index(covered.start());
438 for (int j = 0; j < (int)n_chunks; j++)
439 _lowest_non_clean[i][j] = NULL;
440 }
441 }
442 // Make sure this gets visible only after _lowest_non_clean* was initialized
443 OrderAccess::release_store(&_last_LNC_resizing_collection[i], cur_collection);
444 }
445 }
446 // In any case, now do the initialization.
447 lowest_non_clean = _lowest_non_clean[i];
448 lowest_non_clean_base_chunk_index = _lowest_non_clean_base_chunk_index[i];
449 lowest_non_clean_chunk_size = _lowest_non_clean_chunk_size[i];
450 }
451
452 #ifdef ASSERT
453 void CMSCardTable::verify_used_region_at_save_marks(Space* sp) const {
454 MemRegion ur = sp->used_region();
455 MemRegion urasm = sp->used_region_at_save_marks();
456
457 if (!ur.contains(urasm)) {
458 log_warning(gc)("CMS+ParNew: Did you forget to call save_marks()? "
459 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
460 "[" PTR_FORMAT ", " PTR_FORMAT ")",
461 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
462 MemRegion ur2 = sp->used_region();
463 MemRegion urasm2 = sp->used_region_at_save_marks();
464 if (!ur.equals(ur2)) {
465 log_warning(gc)("CMS+ParNew: Flickering used_region()!!");
466 }
467 if (!urasm.equals(urasm2)) {
468 log_warning(gc)("CMS+ParNew: Flickering used_region_at_save_marks()!!");
469 }
470 ShouldNotReachHere();
471 }
472 }
473 #endif // ASSERT