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