1 /*
2 * Copyright (c) 2001, 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.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "jvm.h"
27 #include "gc/g1/g1CollectedHeap.inline.hpp"
28 #include "gc/g1/satbMarkQueue.hpp"
29 #include "gc/shared/collectedHeap.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/safepoint.hpp"
34 #include "runtime/thread.hpp"
35 #include "runtime/threadSMR.hpp"
36 #include "runtime/vmThread.hpp"
37
38 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
39 // SATB queues are only active during marking cycles. We create
40 // them with their active field set to false. If a thread is
41 // created during a cycle and its SATB queue needs to be activated
42 // before the thread starts running, we'll need to set its active
43 // field to true. This is done in G1SATBCardTableLoggingModRefBS::
44 // on_thread_attach().
45 PtrQueue(qset, permanent, false /* active */)
46 { }
47
48 void SATBMarkQueue::flush() {
49 // Filter now to possibly save work later. If filtering empties the
50 // buffer then flush_impl can deallocate the buffer.
51 filter();
52 flush_impl();
53 }
54
55 // Return true if a SATB buffer entry refers to an object that
56 // requires marking.
57 //
58 // The entry must point into the G1 heap. In particular, it must not
59 // be a NULL pointer. NULL pointers are pre-filtered and never
60 // inserted into a SATB buffer.
61 //
62 // An entry that is below the NTAMS pointer for the containing heap
63 // region requires marking. Such an entry must point to a valid object.
64 //
65 // An entry that is at least the NTAMS pointer for the containing heap
66 // region might be any of the following, none of which should be marked.
67 //
68 // * A reference to an object allocated since marking started.
69 // According to SATB, such objects are implicitly kept live and do
70 // not need to be dealt with via SATB buffer processing.
71 //
72 // * A reference to a young generation object. Young objects are
73 // handled separately and are not marked by concurrent marking.
74 //
75 // * A stale reference to a young generation object. If a young
76 // generation object reference is recorded and not filtered out
77 // before being moved by a young collection, the reference becomes
78 // stale.
79 //
80 // * A stale reference to an eagerly reclaimed humongous object. If a
81 // humongous object is recorded and then reclaimed, the reference
82 // becomes stale.
83 //
84 // The stale reference cases are implicitly handled by the NTAMS
85 // comparison. Because of the possibility of stale references, buffer
86 // processing must be somewhat circumspect and not assume entries
87 // in an unfiltered buffer refer to valid objects.
88
89 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
90 // Includes rejection of NULL pointers.
91 assert(heap->is_in_reserved(entry),
92 "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
93
94 HeapRegion* region = heap->heap_region_containing(entry);
95 assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
96 if (entry >= region->next_top_at_mark_start()) {
97 return false;
98 }
99
100 assert(oopDesc::is_oop(oop(entry), true /* ignore mark word */),
101 "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
102
103 return true;
104 }
105
106 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
107 return requires_marking(entry, heap) && !heap->isMarkedNext((oop)entry);
108 }
109
110 // This method removes entries from a SATB buffer that will not be
111 // useful to the concurrent marking threads. Entries are retained if
112 // they require marking and are not already marked. Retained entries
113 // are compacted toward the top of the buffer.
114
115 void SATBMarkQueue::filter() {
116 G1CollectedHeap* g1h = G1CollectedHeap::heap();
117 void** buf = _buf;
118
119 if (buf == NULL) {
120 // nothing to do
121 return;
122 }
123
124 // Two-fingered compaction toward the end.
125 void** src = &buf[index()];
126 void** dst = &buf[capacity()];
127 assert(src <= dst, "invariant");
128 for ( ; src < dst; ++src) {
129 // Search low to high for an entry to keep.
130 void* entry = *src;
131 if (retain_entry(entry, g1h)) {
132 // Found keeper. Search high to low for an entry to discard.
133 while (src < --dst) {
134 if (!retain_entry(*dst, g1h)) {
135 *dst = entry; // Replace discard with keeper.
136 break;
137 }
138 }
139 // If discard search failed (src == dst), the outer loop will also end.
140 }
141 }
142 // dst points to the lowest retained entry, or the end of the buffer
143 // if all the entries were filtered out.
144 set_index(dst - buf);
145 }
146
147 // This method will first apply the above filtering to the buffer. If
148 // post-filtering a large enough chunk of the buffer has been cleared
149 // we can re-use the buffer (instead of enqueueing it) and we can just
150 // allow the mutator to carry on executing using the same buffer
151 // instead of replacing it.
152
153 bool SATBMarkQueue::should_enqueue_buffer() {
154 assert(_lock == NULL || _lock->owned_by_self(),
155 "we should have taken the lock before calling this");
156
157 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
158
159 // This method should only be called if there is a non-NULL buffer
160 // that is full.
161 assert(index() == 0, "pre-condition");
162 assert(_buf != NULL, "pre-condition");
163
164 filter();
165
166 size_t cap = capacity();
167 size_t percent_used = ((cap - index()) * 100) / cap;
168 bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
169 return should_enqueue;
170 }
171
172 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
173 assert(SafepointSynchronize::is_at_safepoint(),
174 "SATB queues must only be processed at safepoints");
175 if (_buf != NULL) {
176 cl->do_buffer(&_buf[index()], size());
177 reset();
178 }
179 }
180
181 #ifndef PRODUCT
182 // Helpful for debugging
183
184 static void print_satb_buffer(const char* name,
185 void** buf,
186 size_t index,
187 size_t capacity) {
188 tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
189 " capacity: " SIZE_FORMAT,
190 name, p2i(buf), index, capacity);
191 }
192
193 void SATBMarkQueue::print(const char* name) {
194 print_satb_buffer(name, _buf, index(), capacity());
195 }
196
197 #endif // PRODUCT
198
199 SATBMarkQueueSet::SATBMarkQueueSet() :
200 PtrQueueSet(),
201 _shared_satb_queue(this, true /* permanent */) { }
202
203 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
204 int process_completed_threshold,
205 Mutex* lock) {
206 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
207 _shared_satb_queue.set_lock(lock);
208 }
209
210 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
211 t->satb_mark_queue().handle_zero_index();
212 }
213
214 #ifdef ASSERT
215 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
216 log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
217 log_error(gc, verify)("Actual SATB active states:");
218 log_error(gc, verify)(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
219 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
220 log_error(gc, verify)(" Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
221 }
222 log_error(gc, verify)(" Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
223 }
224
225 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
226 // Verify queue set state
227 if (is_active() != expected_active) {
228 dump_active_states(expected_active);
229 guarantee(false, "SATB queue set has an unexpected active state");
230 }
231
232 // Verify thread queue states
233 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
234 if (t->satb_mark_queue().is_active() != expected_active) {
235 dump_active_states(expected_active);
236 guarantee(false, "Thread SATB queue has an unexpected active state");
237 }
238 }
239
240 // Verify shared queue state
241 if (shared_satb_queue()->is_active() != expected_active) {
242 dump_active_states(expected_active);
243 guarantee(false, "Shared SATB queue has an unexpected active state");
244 }
245 }
246 #endif // ASSERT
247
248 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
249 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
250 #ifdef ASSERT
251 verify_active_states(expected_active);
252 #endif // ASSERT
253 _all_active = active;
254 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
255 t->satb_mark_queue().set_active(active);
256 }
257 shared_satb_queue()->set_active(active);
258 }
259
260 void SATBMarkQueueSet::filter_thread_buffers() {
261 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
262 t->satb_mark_queue().filter();
263 }
264 shared_satb_queue()->filter();
265 }
266
267 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
268 BufferNode* nd = NULL;
269 {
270 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
271 if (_completed_buffers_head != NULL) {
272 nd = _completed_buffers_head;
273 _completed_buffers_head = nd->next();
274 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
275 _n_completed_buffers--;
276 if (_n_completed_buffers == 0) _process_completed = false;
277 }
278 }
279 if (nd != NULL) {
280 void **buf = BufferNode::make_buffer_from_node(nd);
281 size_t index = nd->index();
282 size_t size = buffer_size();
283 assert(index <= size, "invariant");
284 cl->do_buffer(buf + index, size - index);
285 deallocate_buffer(nd);
286 return true;
287 } else {
288 return false;
289 }
290 }
291
292 #ifndef PRODUCT
293 // Helpful for debugging
294
295 #define SATB_PRINTER_BUFFER_SIZE 256
296
297 void SATBMarkQueueSet::print_all(const char* msg) {
298 char buffer[SATB_PRINTER_BUFFER_SIZE];
299 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
300
301 tty->cr();
302 tty->print_cr("SATB BUFFERS [%s]", msg);
303
304 BufferNode* nd = _completed_buffers_head;
305 int i = 0;
306 while (nd != NULL) {
307 void** buf = BufferNode::make_buffer_from_node(nd);
308 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
309 print_satb_buffer(buffer, buf, nd->index(), buffer_size());
310 nd = nd->next();
311 i += 1;
312 }
313
314 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
315 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
316 t->satb_mark_queue().print(buffer);
317 }
318
319 shared_satb_queue()->print("Shared");
320
321 tty->cr();
322 }
323 #endif // PRODUCT
324
325 void SATBMarkQueueSet::abandon_partial_marking() {
326 BufferNode* buffers_to_delete = NULL;
327 {
328 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
329 while (_completed_buffers_head != NULL) {
330 BufferNode* nd = _completed_buffers_head;
331 _completed_buffers_head = nd->next();
332 nd->set_next(buffers_to_delete);
333 buffers_to_delete = nd;
334 }
335 _completed_buffers_tail = NULL;
336 _n_completed_buffers = 0;
337 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
338 }
339 while (buffers_to_delete != NULL) {
340 BufferNode* nd = buffers_to_delete;
341 buffers_to_delete = nd->next();
342 deallocate_buffer(nd);
343 }
344 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
345 // So we can safely manipulate these queues.
346 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
347 t->satb_mark_queue().reset();
348 }
349 shared_satb_queue()->reset();
350 }