1 /*
2 * Copyright (c) 2001, 2009, 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 "incls/_precompiled.incl"
26 # include "incls/_parGCAllocBuffer.cpp.incl"
27
28 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :
29 _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
30 _end(NULL), _hard_end(NULL),
31 _retained(false), _retained_filler(),
32 _allocated(0), _wasted(0)
33 {
34 assert (min_size() > AlignmentReserve, "Inconsistency!");
35 // arrayOopDesc::header_size depends on command line initialization.
36 FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT));
37 AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;
38 }
39
40 size_t ParGCAllocBuffer::FillerHeaderSize;
41
42 // If the minimum object size is greater than MinObjAlignment, we can
43 // end up with a shard at the end of the buffer that's smaller than
44 // the smallest object. We can't allow that because the buffer must
45 // look like it's full of objects when we retire it, so we make
46 // sure we have enough space for a filler int array object.
47 size_t ParGCAllocBuffer::AlignmentReserve;
48
49 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {
50 assert(!retain || end_of_gc, "Can only retain at GC end.");
51 if (_retained) {
52 // If the buffer had been retained shorten the previous filler object.
53 assert(_retained_filler.end() <= _top, "INVARIANT");
54 CollectedHeap::fill_with_object(_retained_filler);
55 // Wasted space book-keeping, otherwise (normally) done in invalidate()
56 _wasted += _retained_filler.word_size();
57 _retained = false;
58 }
59 assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");
60 if (_top < _hard_end) {
61 CollectedHeap::fill_with_object(_top, _hard_end);
62 if (!retain) {
63 invalidate();
64 } else {
65 // Is there wasted space we'd like to retain for the next GC?
66 if (pointer_delta(_end, _top) > FillerHeaderSize) {
67 _retained = true;
68 _retained_filler = MemRegion(_top, FillerHeaderSize);
69 _top = _top + FillerHeaderSize;
70 } else {
71 invalidate();
72 }
73 }
74 }
75 }
76
77 void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
78 assert(ResizePLAB, "Wasted work");
79 stats->add_allocated(_allocated);
80 stats->add_wasted(_wasted);
81 stats->add_unused(pointer_delta(_end, _top));
82 }
83
84 // Compute desired plab size and latch result for later
85 // use. This should be called once at the end of parallel
86 // scavenge; it clears the sensor accumulators.
87 void PLABStats::adjust_desired_plab_sz() {
88 assert(ResizePLAB, "Not set");
89 if (_allocated == 0) {
90 assert(_unused == 0, "Inconsistency in PLAB stats");
91 _allocated = 1;
92 }
93 double wasted_frac = (double)_unused/(double)_allocated;
94 size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/
95 TargetPLABWastePct);
96 if (target_refills == 0) {
97 target_refills = 1;
98 }
99 _used = _allocated - _wasted - _unused;
100 size_t plab_sz = _used/(target_refills*ParallelGCThreads);
101 if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz);
102 // Take historical weighted average
103 _filter.sample(plab_sz);
104 // Clip from above and below, and align to object boundary
105 plab_sz = MAX2(min_size(), (size_t)_filter.average());
106 plab_sz = MIN2(max_size(), plab_sz);
107 plab_sz = align_object_size(plab_sz);
108 // Latch the result
109 if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz);
110 if (ResizePLAB) {
111 _desired_plab_sz = plab_sz;
112 }
113 // Now clear the accumulators for next round:
114 // note this needs to be fixed in the case where we
115 // are retaining across scavenges. FIX ME !!! XXX
116 _allocated = 0;
117 _wasted = 0;
118 _unused = 0;
119 }
120
121 #ifndef PRODUCT
122 void ParGCAllocBuffer::print() {
123 gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p"
124 "_retained: %c _retained_filler: [%p,%p)\n",
125 _bottom, _top, _end, _hard_end,
126 "FT"[_retained], _retained_filler.start(), _retained_filler.end());
127 }
128 #endif // !PRODUCT
129
130 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords =
131 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(),
132 ((size_t)Generation::GenGrain)/HeapWordSize);
133 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes =
134 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize,
135 (size_t)Generation::GenGrain);
136
137 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz,
138 BlockOffsetSharedArray* bsa) :
139 ParGCAllocBuffer(word_sz),
140 _bsa(bsa),
141 _bt(bsa, MemRegion(_bottom, _hard_end)),
142 _true_end(_hard_end)
143 {}
144
145 // The buffer comes with its own BOT, with a shared (obviously) underlying
146 // BlockOffsetSharedArray. We manipulate this BOT in the normal way
147 // as we would for any contiguous space. However, on accasion we
148 // need to do some buffer surgery at the extremities before we
149 // start using the body of the buffer for allocations. Such surgery
150 // (as explained elsewhere) is to prevent allocation on a card that
151 // is in the process of being walked concurrently by another GC thread.
152 // When such surgery happens at a point that is far removed (to the
153 // right of the current allocation point, top), we use the "contig"
154 // parameter below to directly manipulate the shared array without
155 // modifying the _next_threshold state in the BOT.
156 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr,
157 bool contig) {
158 CollectedHeap::fill_with_object(mr);
159 if (contig) {
160 _bt.alloc_block(mr.start(), mr.end());
161 } else {
162 _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end());
163 }
164 }
165
166 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) {
167 HeapWord* res = NULL;
168 if (_true_end > _hard_end) {
169 assert((HeapWord*)align_size_down(intptr_t(_hard_end),
170 ChunkSizeInBytes) == _hard_end,
171 "or else _true_end should be equal to _hard_end");
172 assert(_retained, "or else _true_end should be equal to _hard_end");
173 assert(_retained_filler.end() <= _top, "INVARIANT");
174 CollectedHeap::fill_with_object(_retained_filler);
175 if (_top < _hard_end) {
176 fill_region_with_block(MemRegion(_top, _hard_end), true);
177 }
178 HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords);
179 _retained_filler = MemRegion(_hard_end, FillerHeaderSize);
180 _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size());
181 _top = _retained_filler.end();
182 _hard_end = next_hard_end;
183 _end = _hard_end - AlignmentReserve;
184 res = ParGCAllocBuffer::allocate(word_sz);
185 if (res != NULL) {
186 _bt.alloc_block(res, word_sz);
187 }
188 }
189 return res;
190 }
191
192 void
193 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) {
194 ParGCAllocBuffer::undo_allocation(obj, word_sz);
195 // This may back us up beyond the previous threshold, so reset.
196 _bt.set_region(MemRegion(_top, _hard_end));
197 _bt.initialize_threshold();
198 }
199
200 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) {
201 assert(!retain || end_of_gc, "Can only retain at GC end.");
202 if (_retained) {
203 // We're about to make the retained_filler into a block.
204 _bt.BlockOffsetArray::alloc_block(_retained_filler.start(),
205 _retained_filler.end());
206 }
207 // Reset _hard_end to _true_end (and update _end)
208 if (retain && _hard_end != NULL) {
209 assert(_hard_end <= _true_end, "Invariant.");
210 _hard_end = _true_end;
211 _end = MAX2(_top, _hard_end - AlignmentReserve);
212 assert(_end <= _hard_end, "Invariant.");
213 }
214 _true_end = _hard_end;
215 HeapWord* pre_top = _top;
216
217 ParGCAllocBuffer::retire(end_of_gc, retain);
218 // Now any old _retained_filler is cut back to size, the free part is
219 // filled with a filler object, and top is past the header of that
220 // object.
221
222 if (retain && _top < _end) {
223 assert(end_of_gc && retain, "Or else retain should be false.");
224 // If the lab does not start on a card boundary, we don't want to
225 // allocate onto that card, since that might lead to concurrent
226 // allocation and card scanning, which we don't support. So we fill
227 // the first card with a garbage object.
228 size_t first_card_index = _bsa->index_for(pre_top);
229 HeapWord* first_card_start = _bsa->address_for_index(first_card_index);
230 if (first_card_start < pre_top) {
231 HeapWord* second_card_start =
232 _bsa->inc_by_region_size(first_card_start);
233
234 // Ensure enough room to fill with the smallest block
235 second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve);
236
237 // If the end is already in the first card, don't go beyond it!
238 // Or if the remainder is too small for a filler object, gobble it up.
239 if (_hard_end < second_card_start ||
240 pointer_delta(_hard_end, second_card_start) < AlignmentReserve) {
241 second_card_start = _hard_end;
242 }
243 if (pre_top < second_card_start) {
244 MemRegion first_card_suffix(pre_top, second_card_start);
245 fill_region_with_block(first_card_suffix, true);
246 }
247 pre_top = second_card_start;
248 _top = pre_top;
249 _end = MAX2(_top, _hard_end - AlignmentReserve);
250 }
251
252 // If the lab does not end on a card boundary, we don't want to
253 // allocate onto that card, since that might lead to concurrent
254 // allocation and card scanning, which we don't support. So we fill
255 // the last card with a garbage object.
256 size_t last_card_index = _bsa->index_for(_hard_end);
257 HeapWord* last_card_start = _bsa->address_for_index(last_card_index);
258 if (last_card_start < _hard_end) {
259
260 // Ensure enough room to fill with the smallest block
261 last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve);
262
263 // If the top is already in the last card, don't go back beyond it!
264 // Or if the remainder is too small for a filler object, gobble it up.
265 if (_top > last_card_start ||
266 pointer_delta(last_card_start, _top) < AlignmentReserve) {
267 last_card_start = _top;
268 }
269 if (last_card_start < _hard_end) {
270 MemRegion last_card_prefix(last_card_start, _hard_end);
271 fill_region_with_block(last_card_prefix, false);
272 }
273 _hard_end = last_card_start;
274 _end = MAX2(_top, _hard_end - AlignmentReserve);
275 _true_end = _hard_end;
276 assert(_end <= _hard_end, "Invariant.");
277 }
278
279 // At this point:
280 // 1) we had a filler object from the original top to hard_end.
281 // 2) We've filled in any partial cards at the front and back.
282 if (pre_top < _hard_end) {
283 // Now we can reset the _bt to do allocation in the given area.
284 MemRegion new_filler(pre_top, _hard_end);
285 fill_region_with_block(new_filler, false);
286 _top = pre_top + ParGCAllocBuffer::FillerHeaderSize;
287 // If there's no space left, don't retain.
288 if (_top >= _end) {
289 _retained = false;
290 invalidate();
291 return;
292 }
293 _retained_filler = MemRegion(pre_top, _top);
294 _bt.set_region(MemRegion(_top, _hard_end));
295 _bt.initialize_threshold();
296 assert(_bt.threshold() > _top, "initialize_threshold failed!");
297
298 // There may be other reasons for queries into the middle of the
299 // filler object. When such queries are done in parallel with
300 // allocation, bad things can happen, if the query involves object
301 // iteration. So we ensure that such queries do not involve object
302 // iteration, by putting another filler object on the boundaries of
303 // such queries. One such is the object spanning a parallel card
304 // chunk boundary.
305
306 // "chunk_boundary" is the address of the first chunk boundary less
307 // than "hard_end".
308 HeapWord* chunk_boundary =
309 (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes);
310 assert(chunk_boundary < _hard_end, "Or else above did not work.");
311 assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve,
312 "Consequence of last card handling above.");
313
314 if (_top <= chunk_boundary) {
315 assert(_true_end == _hard_end, "Invariant.");
316 while (_top <= chunk_boundary) {
317 assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve,
318 "Consequence of last card handling above.");
319 _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end);
320 CollectedHeap::fill_with_object(chunk_boundary, _hard_end);
321 _hard_end = chunk_boundary;
322 chunk_boundary -= ChunkSizeInWords;
323 }
324 _end = _hard_end - AlignmentReserve;
325 assert(_top <= _end, "Invariant.");
326 // Now reset the initial filler chunk so it doesn't overlap with
327 // the one(s) inserted above.
328 MemRegion new_filler(pre_top, _hard_end);
329 fill_region_with_block(new_filler, false);
330 }
331 } else {
332 _retained = false;
333 invalidate();
334 }
335 } else {
336 assert(!end_of_gc ||
337 (!_retained && _true_end == _hard_end), "Checking.");
338 }
339 assert(_end <= _hard_end, "Invariant.");
340 assert(_top < _end || _top == _hard_end, "Invariant");
341 }