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_implementation/g1/g1CollectedHeap.inline.hpp"
27 #include "gc_implementation/g1/satbQueue.hpp"
28 #include "memory/allocation.inline.hpp"
29 #include "memory/sharedHeap.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/mutexLocker.hpp"
32 #include "runtime/safepoint.hpp"
33 #include "runtime/thread.hpp"
34 #include "runtime/vmThread.hpp"
35
36 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
37
38 void ObjPtrQueue::flush() {
39 // Filter now to possibly save work later. If filtering empties the
40 // buffer then flush_impl can deallocate the buffer.
41 filter();
42 flush_impl();
43 }
44
45 // Return true if a SATB buffer entry refers to an object that
46 // requires marking.
47 //
59 // According to SATB, such objects are implicitly kept live and do
60 // not need to be dealt with via SATB buffer processing.
61 //
62 // * A reference to a young generation object. Young objects are
63 // handled separately and are not marked by concurrent marking.
64 //
65 // * A stale reference to a young generation object. If a young
66 // generation object reference is recorded and not filtered out
67 // before being moved by a young collection, the reference becomes
68 // stale.
69 //
70 // * A stale reference to an eagerly reclaimed humongous object. If a
71 // humongous object is recorded and then reclaimed, the reference
72 // becomes stale.
73 //
74 // The stale reference cases are implicitly handled by the NTAMS
75 // comparison. Because of the possibility of stale references, buffer
76 // processing must be somewhat circumspect and not assume entries
77 // in an unfiltered buffer refer to valid objects.
78
79 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
80 // Includes rejection of NULL pointers.
81 assert(heap->is_in_reserved(entry),
82 err_msg("Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry)));
83
84 HeapRegion* region = heap->heap_region_containing_raw(entry);
85 assert(region != NULL, err_msg("No region for " PTR_FORMAT, p2i(entry)));
86 if (entry >= region->next_top_at_mark_start()) {
87 return false;
88 }
89
90 assert(((oop)entry)->is_oop(true /* ignore mark word */),
91 err_msg("Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry)));
92
93 return true;
94 }
95
96 // This method removes entries from a SATB buffer that will not be
97 // useful to the concurrent marking threads. Entries are retained if
98 // they require marking and are not already marked. Retained entries
99 // are compacted toward the top of the buffer.
100
101 void ObjPtrQueue::filter() {
102 G1CollectedHeap* g1h = G1CollectedHeap::heap();
103 void** buf = _buf;
104 size_t sz = _sz;
105
106 if (buf == NULL) {
107 // nothing to do
108 return;
109 }
110
111 // Used for sanity checking at the end of the loop.
112 debug_only(size_t entries = 0; size_t retained = 0;)
113
114 size_t i = sz;
115 size_t new_index = sz;
116
117 while (i > _index) {
118 assert(i > 0, "we should have at least one more entry to process");
119 i -= oopSize;
120 debug_only(entries += 1;)
121 void** p = &buf[byte_index_to_index((int) i)];
122 void* entry = *p;
123 // NULL the entry so that unused parts of the buffer contain NULLs
124 // at the end. If we are going to retain it we will copy it to its
125 // final place. If we have retained all entries we have visited so
126 // far, we'll just end up copying it to the same place.
127 *p = NULL;
128
129 if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {
130 assert(new_index > 0, "we should not have already filled up the buffer");
131 new_index -= oopSize;
132 assert(new_index >= i,
133 "new_index should never be below i, as we alwaysr compact 'up'");
134 void** new_p = &buf[byte_index_to_index((int) new_index)];
135 assert(new_p >= p, "the destination location should never be below "
136 "the source as we always compact 'up'");
137 assert(*new_p == NULL,
138 "we should have already cleared the destination location");
139 *new_p = entry;
140 debug_only(retained += 1;)
141 }
142 }
143
144 #ifdef ASSERT
145 size_t entries_calc = (sz - _index) / oopSize;
146 assert(entries == entries_calc, "the number of entries we counted "
147 "should match the number of entries we calculated");
148 size_t retained_calc = (sz - new_index) / oopSize;
149 assert(retained == retained_calc, "the number of retained entries we counted "
160 // instead of replacing it.
161
162 bool ObjPtrQueue::should_enqueue_buffer() {
163 assert(_lock == NULL || _lock->owned_by_self(),
164 "we should have taken the lock before calling this");
165
166 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
167
168 // This method should only be called if there is a non-NULL buffer
169 // that is full.
170 assert(_index == 0, "pre-condition");
171 assert(_buf != NULL, "pre-condition");
172
173 filter();
174
175 size_t sz = _sz;
176 size_t all_entries = sz / oopSize;
177 size_t retained_entries = (sz - _index) / oopSize;
178 size_t perc = retained_entries * 100 / all_entries;
179 bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
180 return should_enqueue;
181 }
182
183 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
184 assert(SafepointSynchronize::is_at_safepoint(),
185 "SATB queues must only be processed at safepoints");
186 if (_buf != NULL) {
187 assert(_index % sizeof(void*) == 0, "invariant");
188 assert(_sz % sizeof(void*) == 0, "invariant");
189 assert(_index <= _sz, "invariant");
190 cl->do_buffer(_buf + byte_index_to_index((int)_index),
191 byte_index_to_index((int)(_sz - _index)));
192 _index = _sz;
193 }
194 }
195
196 #ifndef PRODUCT
197 // Helpful for debugging
198
199 void ObjPtrQueue::print(const char* name) {
|
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_implementation/g1/g1CollectedHeap.inline.hpp"
27 #include "gc_implementation/g1/satbQueue.hpp"
28 #include "gc_implementation/shenandoah/shenandoahHeap.inline.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "memory/sharedHeap.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/vmThread.hpp"
36
37 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
38
39 void ObjPtrQueue::flush() {
40 // Filter now to possibly save work later. If filtering empties the
41 // buffer then flush_impl can deallocate the buffer.
42 filter();
43 flush_impl();
44 }
45
46 // Return true if a SATB buffer entry refers to an object that
47 // requires marking.
48 //
60 // According to SATB, such objects are implicitly kept live and do
61 // not need to be dealt with via SATB buffer processing.
62 //
63 // * A reference to a young generation object. Young objects are
64 // handled separately and are not marked by concurrent marking.
65 //
66 // * A stale reference to a young generation object. If a young
67 // generation object reference is recorded and not filtered out
68 // before being moved by a young collection, the reference becomes
69 // stale.
70 //
71 // * A stale reference to an eagerly reclaimed humongous object. If a
72 // humongous object is recorded and then reclaimed, the reference
73 // becomes stale.
74 //
75 // The stale reference cases are implicitly handled by the NTAMS
76 // comparison. Because of the possibility of stale references, buffer
77 // processing must be somewhat circumspect and not assume entries
78 // in an unfiltered buffer refer to valid objects.
79
80 template <class HeapType>
81 inline bool requires_marking(const void* entry, HeapType* heap) {
82 return heap->requires_marking(entry);
83 }
84
85 void ObjPtrQueue::filter() {
86 if (UseG1GC) {
87 filter_impl<G1CollectedHeap>();
88 } else if (UseShenandoahGC) {
89 filter_impl<ShenandoahHeap>();
90 } else {
91 ShouldNotReachHere();
92 }
93 }
94
95 // This method removes entries from a SATB buffer that will not be
96 // useful to the concurrent marking threads. Entries are retained if
97 // they require marking and are not already marked. Retained entries
98 // are compacted toward the top of the buffer.
99
100 template <class HeapType>
101 void ObjPtrQueue::filter_impl() {
102 HeapType* heap = (HeapType*) Universe::heap();
103 void** buf = _buf;
104 size_t sz = _sz;
105
106 if (buf == NULL) {
107 // nothing to do
108 return;
109 }
110
111 // Used for sanity checking at the end of the loop.
112 debug_only(size_t entries = 0; size_t retained = 0;)
113
114 size_t i = sz;
115 size_t new_index = sz;
116
117 while (i > _index) {
118 assert(i > 0, "we should have at least one more entry to process");
119 i -= oopSize;
120 debug_only(entries += 1;)
121 void** p = &buf[byte_index_to_index((int) i)];
122 void* entry = *p;
123 // NULL the entry so that unused parts of the buffer contain NULLs
124 // at the end. If we are going to retain it we will copy it to its
125 // final place. If we have retained all entries we have visited so
126 // far, we'll just end up copying it to the same place.
127 *p = NULL;
128
129 if (requires_marking(entry, heap)) {
130 assert(new_index > 0, "we should not have already filled up the buffer");
131 new_index -= oopSize;
132 assert(new_index >= i,
133 "new_index should never be below i, as we alwaysr compact 'up'");
134 void** new_p = &buf[byte_index_to_index((int) new_index)];
135 assert(new_p >= p, "the destination location should never be below "
136 "the source as we always compact 'up'");
137 assert(*new_p == NULL,
138 "we should have already cleared the destination location");
139 *new_p = entry;
140 debug_only(retained += 1;)
141 }
142 }
143
144 #ifdef ASSERT
145 size_t entries_calc = (sz - _index) / oopSize;
146 assert(entries == entries_calc, "the number of entries we counted "
147 "should match the number of entries we calculated");
148 size_t retained_calc = (sz - new_index) / oopSize;
149 assert(retained == retained_calc, "the number of retained entries we counted "
160 // instead of replacing it.
161
162 bool ObjPtrQueue::should_enqueue_buffer() {
163 assert(_lock == NULL || _lock->owned_by_self(),
164 "we should have taken the lock before calling this");
165
166 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
167
168 // This method should only be called if there is a non-NULL buffer
169 // that is full.
170 assert(_index == 0, "pre-condition");
171 assert(_buf != NULL, "pre-condition");
172
173 filter();
174
175 size_t sz = _sz;
176 size_t all_entries = sz / oopSize;
177 size_t retained_entries = (sz - _index) / oopSize;
178 size_t perc = retained_entries * 100 / all_entries;
179 bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
180
181 if (UseShenandoahGC) {
182 Thread* t = Thread::current();
183 if (t->is_force_satb_flush()) {
184 if (!should_enqueue && sz != _index) {
185 // Non-empty buffer is compacted, and we decided not to enqueue it.
186 // Shenandoah still wants to know about leftover work in that buffer eventually.
187 // This avoid dealing with these leftovers during the final-mark, after the buffers
188 // are drained completely.
189 // TODO: This can be extended to handle G1 too
190 should_enqueue = true;
191 }
192 t->set_force_satb_flush(false);
193 }
194 }
195
196 return should_enqueue;
197 }
198
199 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
200 assert(SafepointSynchronize::is_at_safepoint(),
201 "SATB queues must only be processed at safepoints");
202 if (_buf != NULL) {
203 assert(_index % sizeof(void*) == 0, "invariant");
204 assert(_sz % sizeof(void*) == 0, "invariant");
205 assert(_index <= _sz, "invariant");
206 cl->do_buffer(_buf + byte_index_to_index((int)_index),
207 byte_index_to_index((int)(_sz - _index)));
208 _index = _sz;
209 }
210 }
211
212 #ifndef PRODUCT
213 // Helpful for debugging
214
215 void ObjPtrQueue::print(const char* name) {
|