1 /*
2 * Copyright (c) 2013, 2019, Red Hat, Inc. All rights reserved.
3 * Copyright (c) 2025, Oracle and/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.
23 *
24 */
25
26 #include "gc/shenandoah/shenandoahFreeSet.hpp"
27 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
28 #include "gc/shenandoah/shenandoahHeapRegion.hpp"
29 #include "gc/shenandoah/shenandoahMetrics.hpp"
30
31 ShenandoahMetricsSnapshot::ShenandoahMetricsSnapshot() {
32 _heap = ShenandoahHeap::heap();
33 }
34
35 void ShenandoahMetricsSnapshot::snap_before() {
36 _used_before = _heap->used();
37 _if_before = _heap->free_set()->internal_fragmentation();
38 _ef_before = _heap->free_set()->external_fragmentation();
39 }
40 void ShenandoahMetricsSnapshot::snap_after() {
41 _used_after = _heap->used();
42 _if_after = _heap->free_set()->internal_fragmentation();
43 _ef_after = _heap->free_set()->external_fragmentation();
44 }
45
46 // For degenerated GC, generation is Young in generational mode, Global in non-generational mode.
47 // For full GC, generation is always Global.
48 //
49 // Note that the size of the chosen collection set is proportional to the relevant generation's collection set.
50 // Note also that the generation size may change following selection of the collection set, as a side effect
51 // of evacuation. Evacuation may promote objects, causing old to grow and young to shrink. Or this may be a
52 // mixed evacuation. When old regions are evacuated, this typically allows young to expand. In all of these
53 // various scenarios, the purpose of asking is_good_progress() is to determine if there is enough memory available
54 // within young generation to justify making an attempt to perform a concurrent collection. For this reason, we'll
55 // use the current size of the generation (which may not be different than when the collection set was chosen) to
56 // assess how much free memory we require in order to consider the most recent GC to have had good progress.
57
58 bool ShenandoahMetricsSnapshot::is_good_progress(ShenandoahGeneration* generation) {
59 // Under the critical threshold?
60 ShenandoahFreeSet* free_set = _heap->free_set();
61 size_t free_actual = free_set->available();
62 assert(free_actual != ShenandoahFreeSet::FreeSetUnderConstruction, "Avoid this race");
63
64 // ShenandoahCriticalFreeThreshold is expressed as a percentage. We multiple this percentage by 1/100th
65 // of the generation capacity to determine whether the available memory within the generation exceeds the
66 // critical threshold.
67 size_t free_expected = (ShenandoahHeap::heap()->soft_max_capacity() / 100) * ShenandoahCriticalFreeThreshold;
68
69 bool prog_free = free_actual >= free_expected;
70 log_info(gc, ergo)("%s progress for free space: %zu%s, need %zu%s",
71 prog_free ? "Good" : "Bad",
72 byte_size_in_proper_unit(free_actual), proper_unit_for_byte_size(free_actual),
73 byte_size_in_proper_unit(free_expected), proper_unit_for_byte_size(free_expected));
74 if (!prog_free) {
75 return false;
76 }
77
78 // Freed up enough?
79 size_t progress_actual = (_used_before > _used_after) ? _used_before - _used_after : 0;
80 size_t progress_expected = ShenandoahHeapRegion::region_size_bytes();
81 bool prog_used = progress_actual >= progress_expected;
82 log_info(gc, ergo)("%s progress for used space: %zu%s, need %zu%s",
83 prog_used ? "Good" : "Bad",
84 byte_size_in_proper_unit(progress_actual), proper_unit_for_byte_size(progress_actual),
85 byte_size_in_proper_unit(progress_expected), proper_unit_for_byte_size(progress_expected));
86 if (prog_used) {
87 return true;
88 }
89
90 // Internal fragmentation is down?
91 double if_actual = _if_before - _if_after;
92 double if_expected = 0.01; // 1% should be enough
93 bool prog_if = if_actual >= if_expected;
94 log_info(gc, ergo)("%s progress for internal fragmentation: %.1f%%, need %.1f%%",
95 prog_if ? "Good" : "Bad",
96 if_actual * 100, if_expected * 100);
97 if (prog_if) {
98 return true;
99 }
100
101 // External fragmentation is down?
102 double ef_actual = _ef_before - _ef_after;
103 double ef_expected = 0.01; // 1% should be enough
104 bool prog_ef = ef_actual >= ef_expected;
105 log_info(gc, ergo)("%s progress for external fragmentation: %.1f%%, need %.1f%%",
106 prog_ef ? "Good" : "Bad",
107 ef_actual * 100, ef_expected * 100);
108 if (prog_ef) {
109 return true;
110 }
111
112 // Nothing good had happened.
113 return false;
114 }