1 /*
2 * Copyright (c) 2001, 2012, 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 "gc_implementation/shared/parGCAllocBuffer.hpp"
27 #include "memory/sharedHeap.hpp"
28 #include "oops/arrayOop.hpp"
29 #include "oops/oop.inline.hpp"
30
31 ParGCAllocBuffer::ParGCAllocBuffer(size_t desired_plab_sz_) :
32 _word_sz(desired_plab_sz_), _bottom(NULL), _top(NULL),
33 _end(NULL), _hard_end(NULL),
34 _retained(false), _retained_filler(),
35 _allocated(0), _wasted(0)
36 {
37 assert (min_size() > AlignmentReserve, "Inconsistency!");
38 // arrayOopDesc::header_size depends on command line initialization.
39 FillerHeaderSize = align_object_size(arrayOopDesc::header_size(T_INT));
40 AlignmentReserve = oopDesc::header_size() > MinObjAlignment ? FillerHeaderSize : 0;
41 }
42
43 size_t ParGCAllocBuffer::FillerHeaderSize;
44
45 // If the minimum object size is greater than MinObjAlignment, we can
46 // end up with a shard at the end of the buffer that's smaller than
47 // the smallest object. We can't allow that because the buffer must
48 // look like it's full of objects when we retire it, so we make
49 // sure we have enough space for a filler int array object.
50 size_t ParGCAllocBuffer::AlignmentReserve;
51
52 void ParGCAllocBuffer::retire(bool end_of_gc, bool retain) {
53 assert(!retain || end_of_gc, "Can only retain at GC end.");
54 if (_retained) {
55 // If the buffer had been retained shorten the previous filler object.
56 assert(_retained_filler.end() <= _top, "INVARIANT");
57 CollectedHeap::fill_with_object(_retained_filler);
58 // Wasted space book-keeping, otherwise (normally) done in invalidate()
59 _wasted += _retained_filler.word_size();
60 _retained = false;
61 }
62 assert(!end_of_gc || !_retained, "At this point, end_of_gc ==> !_retained.");
63 if (_top < _hard_end) {
64 CollectedHeap::fill_with_object(_top, _hard_end);
65 if (!retain) {
66 invalidate();
67 } else {
68 // Is there wasted space we'd like to retain for the next GC?
69 if (pointer_delta(_end, _top) > FillerHeaderSize) {
70 _retained = true;
71 _retained_filler = MemRegion(_top, FillerHeaderSize);
72 _top = _top + FillerHeaderSize;
73 } else {
74 invalidate();
75 }
76 }
77 }
78 }
79
80 void ParGCAllocBuffer::flush_stats(PLABStats* stats) {
81 assert(ResizePLAB, "Wasted work");
82 stats->add_allocated(_allocated);
83 stats->add_wasted(_wasted);
84 stats->add_unused(pointer_delta(_end, _top));
85 }
86
87 // Compute desired plab size and latch result for later
88 // use. This should be called once at the end of parallel
89 // scavenge; it clears the sensor accumulators.
90 void PLABStats::adjust_desired_plab_sz(uint no_of_gc_workers) {
91 assert(ResizePLAB, "Not set");
92 if (_allocated == 0) {
93 assert(_unused == 0,
94 err_msg("Inconsistency in PLAB stats: "
95 "_allocated: "SIZE_FORMAT", "
96 "_wasted: "SIZE_FORMAT", "
97 "_unused: "SIZE_FORMAT", "
98 "_used : "SIZE_FORMAT,
99 _allocated, _wasted, _unused, _used));
100
101 _allocated = 1;
102 }
103 double wasted_frac = (double)_unused/(double)_allocated;
104 size_t target_refills = (size_t)((wasted_frac*TargetSurvivorRatio)/
105 TargetPLABWastePct);
106 if (target_refills == 0) {
107 target_refills = 1;
108 }
109 _used = _allocated - _wasted - _unused;
110 size_t plab_sz = _used/(target_refills*no_of_gc_workers);
111 if (PrintPLAB) gclog_or_tty->print(" (plab_sz = %d ", plab_sz);
112 // Take historical weighted average
113 _filter.sample(plab_sz);
114 // Clip from above and below, and align to object boundary
115 plab_sz = MAX2(min_size(), (size_t)_filter.average());
116 plab_sz = MIN2(max_size(), plab_sz);
117 plab_sz = align_object_size(plab_sz);
118 // Latch the result
119 if (PrintPLAB) gclog_or_tty->print(" desired_plab_sz = %d) ", plab_sz);
120 _desired_plab_sz = plab_sz;
121 // Now clear the accumulators for next round:
122 // note this needs to be fixed in the case where we
123 // are retaining across scavenges. FIX ME !!! XXX
124 _allocated = 0;
125 _wasted = 0;
126 _unused = 0;
127 }
128
129 #ifndef PRODUCT
130 void ParGCAllocBuffer::print() {
131 gclog_or_tty->print("parGCAllocBuffer: _bottom: %p _top: %p _end: %p _hard_end: %p"
132 "_retained: %c _retained_filler: [%p,%p)\n",
133 _bottom, _top, _end, _hard_end,
134 "FT"[_retained], _retained_filler.start(), _retained_filler.end());
135 }
136 #endif // !PRODUCT
137
138 const size_t ParGCAllocBufferWithBOT::ChunkSizeInWords =
139 MIN2(CardTableModRefBS::par_chunk_heapword_alignment(),
140 ((size_t)Generation::GenGrain)/HeapWordSize);
141 const size_t ParGCAllocBufferWithBOT::ChunkSizeInBytes =
142 MIN2(CardTableModRefBS::par_chunk_heapword_alignment() * HeapWordSize,
143 (size_t)Generation::GenGrain);
144
145 ParGCAllocBufferWithBOT::ParGCAllocBufferWithBOT(size_t word_sz,
146 BlockOffsetSharedArray* bsa) :
147 ParGCAllocBuffer(word_sz),
148 _bsa(bsa),
149 _bt(bsa, MemRegion(_bottom, _hard_end)),
150 _true_end(_hard_end)
151 {}
152
153 // The buffer comes with its own BOT, with a shared (obviously) underlying
154 // BlockOffsetSharedArray. We manipulate this BOT in the normal way
155 // as we would for any contiguous space. However, on accasion we
156 // need to do some buffer surgery at the extremities before we
157 // start using the body of the buffer for allocations. Such surgery
158 // (as explained elsewhere) is to prevent allocation on a card that
159 // is in the process of being walked concurrently by another GC thread.
160 // When such surgery happens at a point that is far removed (to the
161 // right of the current allocation point, top), we use the "contig"
162 // parameter below to directly manipulate the shared array without
163 // modifying the _next_threshold state in the BOT.
164 void ParGCAllocBufferWithBOT::fill_region_with_block(MemRegion mr,
165 bool contig) {
166 CollectedHeap::fill_with_object(mr);
167 if (contig) {
168 _bt.alloc_block(mr.start(), mr.end());
169 } else {
170 _bt.BlockOffsetArray::alloc_block(mr.start(), mr.end());
171 }
172 }
173
174 HeapWord* ParGCAllocBufferWithBOT::allocate_slow(size_t word_sz) {
175 HeapWord* res = NULL;
176 if (_true_end > _hard_end) {
177 assert((HeapWord*)align_size_down(intptr_t(_hard_end),
178 ChunkSizeInBytes) == _hard_end,
179 "or else _true_end should be equal to _hard_end");
180 assert(_retained, "or else _true_end should be equal to _hard_end");
181 assert(_retained_filler.end() <= _top, "INVARIANT");
182 CollectedHeap::fill_with_object(_retained_filler);
183 if (_top < _hard_end) {
184 fill_region_with_block(MemRegion(_top, _hard_end), true);
185 }
186 HeapWord* next_hard_end = MIN2(_true_end, _hard_end + ChunkSizeInWords);
187 _retained_filler = MemRegion(_hard_end, FillerHeaderSize);
188 _bt.alloc_block(_retained_filler.start(), _retained_filler.word_size());
189 _top = _retained_filler.end();
190 _hard_end = next_hard_end;
191 _end = _hard_end - AlignmentReserve;
192 res = ParGCAllocBuffer::allocate(word_sz);
193 if (res != NULL) {
194 _bt.alloc_block(res, word_sz);
195 }
196 }
197 return res;
198 }
199
200 void
201 ParGCAllocBufferWithBOT::undo_allocation(HeapWord* obj, size_t word_sz) {
202 ParGCAllocBuffer::undo_allocation(obj, word_sz);
203 // This may back us up beyond the previous threshold, so reset.
204 _bt.set_region(MemRegion(_top, _hard_end));
205 _bt.initialize_threshold();
206 }
207
208 void ParGCAllocBufferWithBOT::retire(bool end_of_gc, bool retain) {
209 assert(!retain || end_of_gc, "Can only retain at GC end.");
210 if (_retained) {
211 // We're about to make the retained_filler into a block.
212 _bt.BlockOffsetArray::alloc_block(_retained_filler.start(),
213 _retained_filler.end());
214 }
215 // Reset _hard_end to _true_end (and update _end)
216 if (retain && _hard_end != NULL) {
217 assert(_hard_end <= _true_end, "Invariant.");
218 _hard_end = _true_end;
219 _end = MAX2(_top, _hard_end - AlignmentReserve);
220 assert(_end <= _hard_end, "Invariant.");
221 }
222 _true_end = _hard_end;
223 HeapWord* pre_top = _top;
224
225 ParGCAllocBuffer::retire(end_of_gc, retain);
226 // Now any old _retained_filler is cut back to size, the free part is
227 // filled with a filler object, and top is past the header of that
228 // object.
229
230 if (retain && _top < _end) {
231 assert(end_of_gc && retain, "Or else retain should be false.");
232 // If the lab does not start on a card boundary, we don't want to
233 // allocate onto that card, since that might lead to concurrent
234 // allocation and card scanning, which we don't support. So we fill
235 // the first card with a garbage object.
236 size_t first_card_index = _bsa->index_for(pre_top);
237 HeapWord* first_card_start = _bsa->address_for_index(first_card_index);
238 if (first_card_start < pre_top) {
239 HeapWord* second_card_start =
240 _bsa->inc_by_region_size(first_card_start);
241
242 // Ensure enough room to fill with the smallest block
243 second_card_start = MAX2(second_card_start, pre_top + AlignmentReserve);
244
245 // If the end is already in the first card, don't go beyond it!
246 // Or if the remainder is too small for a filler object, gobble it up.
247 if (_hard_end < second_card_start ||
248 pointer_delta(_hard_end, second_card_start) < AlignmentReserve) {
249 second_card_start = _hard_end;
250 }
251 if (pre_top < second_card_start) {
252 MemRegion first_card_suffix(pre_top, second_card_start);
253 fill_region_with_block(first_card_suffix, true);
254 }
255 pre_top = second_card_start;
256 _top = pre_top;
257 _end = MAX2(_top, _hard_end - AlignmentReserve);
258 }
259
260 // If the lab does not end on a card boundary, we don't want to
261 // allocate onto that card, since that might lead to concurrent
262 // allocation and card scanning, which we don't support. So we fill
263 // the last card with a garbage object.
264 size_t last_card_index = _bsa->index_for(_hard_end);
265 HeapWord* last_card_start = _bsa->address_for_index(last_card_index);
266 if (last_card_start < _hard_end) {
267
268 // Ensure enough room to fill with the smallest block
269 last_card_start = MIN2(last_card_start, _hard_end - AlignmentReserve);
270
271 // If the top is already in the last card, don't go back beyond it!
272 // Or if the remainder is too small for a filler object, gobble it up.
273 if (_top > last_card_start ||
274 pointer_delta(last_card_start, _top) < AlignmentReserve) {
275 last_card_start = _top;
276 }
277 if (last_card_start < _hard_end) {
278 MemRegion last_card_prefix(last_card_start, _hard_end);
279 fill_region_with_block(last_card_prefix, false);
280 }
281 _hard_end = last_card_start;
282 _end = MAX2(_top, _hard_end - AlignmentReserve);
283 _true_end = _hard_end;
284 assert(_end <= _hard_end, "Invariant.");
285 }
286
287 // At this point:
288 // 1) we had a filler object from the original top to hard_end.
289 // 2) We've filled in any partial cards at the front and back.
290 if (pre_top < _hard_end) {
291 // Now we can reset the _bt to do allocation in the given area.
292 MemRegion new_filler(pre_top, _hard_end);
293 fill_region_with_block(new_filler, false);
294 _top = pre_top + ParGCAllocBuffer::FillerHeaderSize;
295 // If there's no space left, don't retain.
296 if (_top >= _end) {
297 _retained = false;
298 invalidate();
299 return;
300 }
301 _retained_filler = MemRegion(pre_top, _top);
302 _bt.set_region(MemRegion(_top, _hard_end));
303 _bt.initialize_threshold();
304 assert(_bt.threshold() > _top, "initialize_threshold failed!");
305
306 // There may be other reasons for queries into the middle of the
307 // filler object. When such queries are done in parallel with
308 // allocation, bad things can happen, if the query involves object
309 // iteration. So we ensure that such queries do not involve object
310 // iteration, by putting another filler object on the boundaries of
311 // such queries. One such is the object spanning a parallel card
312 // chunk boundary.
313
314 // "chunk_boundary" is the address of the first chunk boundary less
315 // than "hard_end".
316 HeapWord* chunk_boundary =
317 (HeapWord*)align_size_down(intptr_t(_hard_end-1), ChunkSizeInBytes);
318 assert(chunk_boundary < _hard_end, "Or else above did not work.");
319 assert(pointer_delta(_true_end, chunk_boundary) >= AlignmentReserve,
320 "Consequence of last card handling above.");
321
322 if (_top <= chunk_boundary) {
323 assert(_true_end == _hard_end, "Invariant.");
324 while (_top <= chunk_boundary) {
325 assert(pointer_delta(_hard_end, chunk_boundary) >= AlignmentReserve,
326 "Consequence of last card handling above.");
327 _bt.BlockOffsetArray::alloc_block(chunk_boundary, _hard_end);
328 CollectedHeap::fill_with_object(chunk_boundary, _hard_end);
329 _hard_end = chunk_boundary;
330 chunk_boundary -= ChunkSizeInWords;
331 }
332 _end = _hard_end - AlignmentReserve;
333 assert(_top <= _end, "Invariant.");
334 // Now reset the initial filler chunk so it doesn't overlap with
335 // the one(s) inserted above.
336 MemRegion new_filler(pre_top, _hard_end);
337 fill_region_with_block(new_filler, false);
338 }
339 } else {
340 _retained = false;
341 invalidate();
342 }
343 } else {
344 assert(!end_of_gc ||
345 (!_retained && _true_end == _hard_end), "Checking.");
346 }
347 assert(_end <= _hard_end, "Invariant.");
348 assert(_top < _end || _top == _hard_end, "Invariant");
349 }