1 /*
2 * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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24
25 #ifndef SHARE_GC_G1_G1HEAPREGIONATTR_HPP
26 #define SHARE_GC_G1_G1HEAPREGIONATTR_HPP
27
28 #include "gc/g1/g1BiasedArray.hpp"
29 #include "gc/g1/heapRegion.hpp"
30
31 // Per-region attributes often used during garbage collection to avoid costly
32 // lookups for that information all over the place.
33 struct G1HeapRegionAttr {
34 public:
35 typedef int8_t region_type_t;
36 typedef uint8_t needs_remset_update_t;
37
38 private:
39 needs_remset_update_t _needs_remset_update;
40 region_type_t _type;
41
42 public:
43 // Selection of the values for the _type field were driven to micro-optimize the
44 // encoding and frequency of the checks.
45 // The most common check for a given reference is whether the region is in the
46 // collection set or not, and which generation this region is in.
47 // The selected encoding allows us to use a single check (> NotInCSet) for the
48 // former.
49 //
50 // The other values are used for objects in regions requiring various special handling,
51 // eager reclamation of humongous objects or optional regions.
52 static const region_type_t Optional = -3; // The region is optional not in the current collection set.
53 static const region_type_t Humongous = -2; // The region is a humongous candidate not in the current collection set.
54 static const region_type_t NotInCSet = -1; // The region is not in the collection set.
55 static const region_type_t Young = 0; // The region is in the collection set and a young region.
56 static const region_type_t Old = 1; // The region is in the collection set and an old region.
57 static const region_type_t Num = 2;
58
59 G1HeapRegionAttr(region_type_t type = NotInCSet, bool needs_remset_update = false) :
60 _needs_remset_update(needs_remset_update), _type(type) {
61
62 assert(is_valid(), "Invalid type %d", _type);
63 }
64
65 region_type_t type() const { return _type; }
66
67 const char* get_type_str() const {
68 switch (type()) {
69 case Optional: return "Optional";
70 case Humongous: return "Humongous";
71 case NotInCSet: return "NotInCSet";
72 case Young: return "Young";
73 case Old: return "Old";
74 default: ShouldNotReachHere(); return "";
75 }
76 }
77
78 bool needs_remset_update() const { return _needs_remset_update != 0; }
79
80 void set_old() { _type = Old; }
81 void clear_humongous() {
82 assert(is_humongous() || !is_in_cset(), "must be");
83 _type = NotInCSet;
84 }
85 void set_has_remset(bool value) { _needs_remset_update = value ? 1 : 0; }
86
87 bool is_in_cset_or_humongous() const { return is_in_cset() || is_humongous(); }
88 bool is_in_cset() const { return type() >= Young; }
89
90 bool is_humongous() const { return type() == Humongous; }
91 bool is_young() const { return type() == Young; }
92 bool is_old() const { return type() == Old; }
93 bool is_optional() const { return type() == Optional; }
94
95 #ifdef ASSERT
96 bool is_default() const { return type() == NotInCSet; }
97 bool is_valid() const { return (type() >= Optional && type() < Num); }
98 bool is_valid_gen() const { return (type() >= Young && type() <= Old); }
99 #endif
100 };
101
102 // Table for all regions in the heap for above.
103 //
104 // We use this to speed up reference processing during young collection and
105 // quickly reclaim humongous objects. For the latter, at the start of GC, by adding
106 // it as a humongous region we enable special handling for that region. During the
107 // reference iteration closures, when we see a humongous region, we then simply mark
108 // it as referenced, i.e. live, and remove it from this table to prevent further
109 // processing on it.
110 //
111 // This means that this does NOT completely correspond to the information stored
112 // in a HeapRegion, but only to what is interesting for the current young collection.
113 class G1HeapRegionAttrBiasedMappedArray : public G1BiasedMappedArray<G1HeapRegionAttr> {
114 protected:
115 G1HeapRegionAttr default_value() const { return G1HeapRegionAttr(G1HeapRegionAttr::NotInCSet); }
116 public:
117 void set_optional(uintptr_t index, bool needs_remset_update) {
118 assert(get_by_index(index).is_default(),
119 "Region attributes at index " INTPTR_FORMAT " should be default but is %s", index, get_by_index(index).get_type_str());
120 set_by_index(index, G1HeapRegionAttr(G1HeapRegionAttr::Optional, needs_remset_update));
121 }
122
123 void set_humongous(uintptr_t index, bool needs_remset_update) {
124 assert(get_by_index(index).is_default(),
125 "Region attributes at index " INTPTR_FORMAT " should be default but is %s", index, get_by_index(index).get_type_str());
126 set_by_index(index, G1HeapRegionAttr(G1HeapRegionAttr::Humongous, needs_remset_update));
127 }
128
129 void clear_humongous(uintptr_t index) {
130 get_ref_by_index(index)->clear_humongous();
131 }
132
133 void set_has_remset(uintptr_t index, bool needs_remset_update) {
134 get_ref_by_index(index)->set_has_remset(needs_remset_update);
135 }
136
137 void set_in_young(uintptr_t index) {
138 assert(get_by_index(index).is_default(),
139 "Region attributes at index " INTPTR_FORMAT " should be default but is %s", index, get_by_index(index).get_type_str());
140 set_by_index(index, G1HeapRegionAttr(G1HeapRegionAttr::Young, true));
141 }
142
143 void set_in_old(uintptr_t index, bool needs_remset_update) {
144 assert(get_by_index(index).is_default(),
145 "Region attributes at index " INTPTR_FORMAT " should be default but is %s", index, get_by_index(index).get_type_str());
146 set_by_index(index, G1HeapRegionAttr(G1HeapRegionAttr::Old, needs_remset_update));
147 }
148
149 bool is_in_cset_or_humongous(HeapWord* addr) const { return at(addr).is_in_cset_or_humongous(); }
150 bool is_in_cset(HeapWord* addr) const { return at(addr).is_in_cset(); }
151 bool is_in_cset(const HeapRegion* hr) const { return get_by_index(hr->hrm_index()).is_in_cset(); }
152 G1HeapRegionAttr at(HeapWord* addr) const { return get_by_address(addr); }
153 void clear() { G1BiasedMappedArray<G1HeapRegionAttr>::clear(); }
154 void clear(const HeapRegion* hr) { return set_by_index(hr->hrm_index(), G1HeapRegionAttr(G1HeapRegionAttr::NotInCSet)); }
155 };
156
157 #endif // SHARE_GC_G1_G1HEAPREGIONATTR_HPP