1 /*
2 * Copyright (c) 2015, 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 "memory/allocation.inline.hpp"
27 #include "gc/g1/g1EvacStats.hpp"
28 #include "gc/shared/gcId.hpp"
29 #include "trace/tracing.hpp"
30
31 void G1EvacStats::adjust_desired_plab_sz() {
32 if (PrintPLAB) {
33 gclog_or_tty->print(" (allocated = " SIZE_FORMAT " wasted = " SIZE_FORMAT " "
34 "unused = " SIZE_FORMAT " used = " SIZE_FORMAT " "
35 "undo_waste = " SIZE_FORMAT " region_end_waste = " SIZE_FORMAT " "
36 "regions filled = %u direct_allocated = " SIZE_FORMAT " "
37 "failure_used = " SIZE_FORMAT " failure_waste = " SIZE_FORMAT ") ",
38 _allocated, _wasted, _unused, used(), _undo_wasted, _region_end_waste,
39 _regions_filled, _direct_allocated, _failure_used, _failure_waste);
40 }
41
42 if (ResizePLAB) {
43
44 assert(is_object_aligned(max_size()) && min_size() <= max_size(),
45 "PLAB clipping computation may be incorrect");
46
47 if (_allocated == 0) {
48 assert((_unused == 0),
49 "Inconsistency in PLAB stats: "
50 "_allocated: " SIZE_FORMAT ", "
51 "_wasted: " SIZE_FORMAT ", "
52 "_region_end_waste: " SIZE_FORMAT ", "
53 "_unused: " SIZE_FORMAT ", "
54 "_used : " SIZE_FORMAT,
55 _allocated, _wasted, _region_end_waste, _unused, used());
56 _allocated = 1;
57 }
58 // The size of the PLAB caps the amount of space that can be wasted at the
59 // end of the collection. In the worst case the last PLAB could be completely
60 // empty.
61 // This allows us to calculate the new PLAB size to achieve the
62 // TargetPLABWastePct given the latest memory usage and that the last buffer
63 // will be G1LastPLABAverageOccupancy full.
64 //
65 // E.g. assume that if in the current GC 100 words were allocated and a
66 // TargetPLABWastePct of 10 had been set.
67 //
68 // So we could waste up to 10 words to meet that percentage. Given that we
69 // also assume that that buffer is typically half-full, the new desired PLAB
70 // size is set to 20 words.
71 //
72 // The amount of allocation performed should be independent of the number of
73 // threads, so should the maximum waste we can spend in total. So if
74 // we used n threads to allocate, each of them can spend maximum waste/n words in
75 // a first rough approximation. The number of threads only comes into play later
76 // when actually retrieving the actual desired PLAB size.
77 //
78 // After calculating this optimal PLAB size the algorithm applies the usual
79 // exponential decaying average over this value to guess the next PLAB size.
80 //
81 // We account region end waste fully to PLAB allocation (in the calculation of
82 // what we consider as "used_for_waste_calculation" below). This is not
83 // completely fair, but is a conservative assumption because PLABs may be sized
84 // flexibly while we cannot adjust inline allocations.
85 // Allocation during GC will try to minimize region end waste so this impact
86 // should be minimal.
87 //
88 // We need to cover overflow when calculating the amount of space actually used
89 // by objects in PLABs when subtracting the region end waste.
90 // Region end waste may be higher than actual allocation. This may occur if many
91 // threads do not allocate anything but a few rather large objects. In this
92 // degenerate case the PLAB size would simply quickly tend to minimum PLAB size,
93 // which is an okay reaction.
94 size_t const used_for_waste_calculation = used() > _region_end_waste ? used() - _region_end_waste : 0;
95
96 size_t const total_waste_allowed = used_for_waste_calculation * TargetPLABWastePct;
97 size_t const cur_plab_sz = (size_t)((double)total_waste_allowed / G1LastPLABAverageOccupancy);
98 // Take historical weighted average
99 _filter.sample(cur_plab_sz);
100 // Clip from above and below, and align to object boundary
101 size_t plab_sz;
102 plab_sz = MAX2(min_size(), (size_t)_filter.average());
103 plab_sz = MIN2(max_size(), plab_sz);
104 plab_sz = align_object_size(plab_sz);
105 // Latch the result
106 _desired_net_plab_sz = plab_sz;
107 if (PrintPLAB) {
108 gclog_or_tty->print(" (plab_sz = " SIZE_FORMAT " desired_plab_sz = " SIZE_FORMAT ") ", cur_plab_sz, plab_sz);
109 }
110 }
111 if (PrintPLAB) {
112 gclog_or_tty->cr();
113 }
114 // Clear accumulators for next round.
115 reset();
116 }
117
118 G1EvacStats::~G1EvacStats() { }