1 /*
2 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
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24 */
25
26 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP
27 #define SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP
28
29 #include "gc/shared/gcTrace.hpp"
30 #include "gc/shenandoah/shenandoahGC.hpp"
31 #include "gc/shenandoah/shenandoahSharedVariables.hpp"
32 #include "gc/shenandoah/shenandoahTrace.hpp"
33 #include "memory/allocation.hpp"
34 #include "utilities/ostream.hpp"
35
36 class ShenandoahCollectorPolicy : public CHeapObj<mtGC> {
37 private:
38 size_t _success_concurrent_gcs;
39 size_t _abbreviated_concurrent_gcs;
40 size_t _success_degenerated_gcs;
41 size_t _abbreviated_degenerated_gcs;
42 // Written by control thread, read by mutators
43 volatile size_t _success_full_gcs;
44 uint _consecutive_degenerated_gcs;
45 uint _consecutive_degenerated_gcs_without_progress;
46 volatile size_t _consecutive_young_gcs;
47 size_t _mixed_gcs;
48 size_t _success_old_gcs;
49 size_t _interrupted_old_gcs;
50 size_t _alloc_failure_degenerated;
51 size_t _alloc_failure_degenerated_upgrade_to_full;
52 size_t _alloc_failure_full;
53 size_t _collection_cause_counts[GCCause::_last_gc_cause];
54 size_t _degen_point_counts[ShenandoahGC::_DEGENERATED_LIMIT];
55
56 ShenandoahSharedFlag _in_shutdown;
57 ShenandoahTracer* _tracer;
58
59 void reset_consecutive_degenerated_gcs() {
60 _consecutive_degenerated_gcs = 0;
61 _consecutive_degenerated_gcs_without_progress = 0;
62 }
63
64 public:
65 // The most common scenario for lack of good progress following a degenerated GC is an accumulation of floating
66 // garbage during the most recently aborted concurrent GC effort. With generational GC, it is far more effective to
67 // reclaim this floating garbage with another degenerated cycle (which focuses on young generation and might require
68 // a pause of 200 ms) rather than a full GC cycle (which may require over 2 seconds with a 10 GB old generation).
69 //
70 // In generational mode, we'll only upgrade to full GC if we've done two degen cycles in a row and both indicated
71 // bad progress. In non-generational mode, we'll preserve the original behavior, which is to upgrade to full
72 // immediately following a degenerated cycle with bad progress. This preserves original behavior of non-generational
73 // Shenandoah to avoid introducing "surprising new behavior." It also makes less sense with non-generational
74 // Shenandoah to replace a full GC with a degenerated GC, because both have similar pause times in non-generational
75 // mode.
76 static constexpr size_t GENERATIONAL_CONSECUTIVE_BAD_DEGEN_PROGRESS_THRESHOLD = 2;
77
78 ShenandoahCollectorPolicy();
79
80 void record_mixed_cycle();
81 void record_success_old();
82 void record_interrupted_old();
83
84 // A collection cycle may be "abbreviated" if Shenandoah finds a sufficient percentage
85 // of regions that contain no live objects (ShenandoahImmediateThreshold). These cycles
86 // end after final mark, skipping the evacuation and reference-updating phases. Such
87 // cycles are very efficient and are worth tracking. Note that both degenerated and
88 // concurrent cycles can be abbreviated.
89 void record_success_concurrent(bool is_young, bool is_abbreviated);
90
91 // Record that a degenerated cycle has been completed. Note that such a cycle may or
92 // may not make "progress". We separately track the total number of degenerated cycles,
93 // the number of consecutive degenerated cycles and the number of consecutive cycles that
94 // fail to make good progress.
95 void record_degenerated(bool is_young, bool is_abbreviated, bool progress);
96 void record_success_full();
97 void record_alloc_failure_to_degenerated(ShenandoahGC::ShenandoahDegenPoint point);
98 void record_alloc_failure_to_full();
99 void record_degenerated_upgrade_to_full();
100 void record_collection_cause(GCCause::Cause cause);
101
102 void record_shutdown();
103 bool is_at_shutdown() const;
104
105 ShenandoahTracer* tracer() const {return _tracer;}
106
107 void print_gc_stats(outputStream* out) const;
108
109 size_t full_gc_count() const {
110 return _success_full_gcs + _alloc_failure_degenerated_upgrade_to_full;
111 }
112
113 // If the heuristics find that the number of consecutive degenerated cycles is above
114 // ShenandoahFullGCThreshold, then they will initiate a Full GC upon an allocation
115 // failure.
116 size_t consecutive_degenerated_gc_count() const {
117 return _consecutive_degenerated_gcs;
118 }
119
120 // Genshen will only upgrade to a full gc after the configured number of futile degenerated cycles.
121 bool generational_should_upgrade_degenerated_gc() const {
122 return _consecutive_degenerated_gcs_without_progress >= GENERATIONAL_CONSECUTIVE_BAD_DEGEN_PROGRESS_THRESHOLD;
123 }
124
125 static bool is_allocation_failure(GCCause::Cause cause);
126 static bool is_shenandoah_gc(GCCause::Cause cause);
127 static bool is_requested_gc(GCCause::Cause cause);
128 static bool is_explicit_gc(GCCause::Cause cause);
129 static bool should_run_full_gc(GCCause::Cause cause);
130 static bool should_handle_requested_gc(GCCause::Cause cause);
131
132 size_t consecutive_young_gc_count() const {
133 return _consecutive_young_gcs;
134 }
135
136 private:
137 void update_young(bool is_young);
138 };
139
140 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHCOLLECTORPOLICY_HPP