Tue, 15 Oct 2013 14:28:51 +0200
8026391: The Metachunk header wastes memory
Reviewed-by: coleenp, jmasa
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25 #include "precompiled.hpp"
26 #include "memory/allocation.hpp"
27 #include "memory/metachunk.hpp"
28 #include "utilities/copy.hpp"
29 #include "utilities/debug.hpp"
31 class VirtualSpaceNode;
33 const size_t metadata_chunk_initialize = 0xf7f7f7f7;
35 size_t Metachunk::object_alignment() {
36 return ARENA_AMALLOC_ALIGNMENT;
37 }
39 size_t Metachunk::overhead() {
40 return align_size_up(sizeof(Metachunk), object_alignment()) / BytesPerWord;
41 }
43 // Metachunk methods
45 Metachunk::Metachunk(size_t word_size,
46 VirtualSpaceNode* container)
47 : Metabase<Metachunk>(word_size),
48 _top(NULL),
49 _container(container)
50 {
51 _top = initial_top();
52 #ifdef ASSERT
53 set_is_tagged_free(false);
54 size_t data_word_size = pointer_delta(end(),
55 _top,
56 sizeof(MetaWord));
57 Copy::fill_to_words((HeapWord*)_top,
58 data_word_size,
59 metadata_chunk_initialize);
60 #endif
61 }
63 MetaWord* Metachunk::allocate(size_t word_size) {
64 MetaWord* result = NULL;
65 // If available, bump the pointer to allocate.
66 if (free_word_size() >= word_size) {
67 result = _top;
68 _top = _top + word_size;
69 }
70 return result;
71 }
73 // _bottom points to the start of the chunk including the overhead.
74 size_t Metachunk::used_word_size() const {
75 return pointer_delta(_top, bottom(), sizeof(MetaWord));
76 }
78 size_t Metachunk::free_word_size() const {
79 return pointer_delta(end(), _top, sizeof(MetaWord));
80 }
82 void Metachunk::print_on(outputStream* st) const {
83 st->print_cr("Metachunk:"
84 " bottom " PTR_FORMAT " top " PTR_FORMAT
85 " end " PTR_FORMAT " size " SIZE_FORMAT,
86 bottom(), _top, end(), word_size());
87 if (Verbose) {
88 st->print_cr(" used " SIZE_FORMAT " free " SIZE_FORMAT,
89 used_word_size(), free_word_size());
90 }
91 }
93 #ifndef PRODUCT
94 void Metachunk::mangle() {
95 // Mangle the payload of the chunk and not the links that
96 // maintain list of chunks.
97 HeapWord* start = (HeapWord*)(bottom() + overhead());
98 size_t size = word_size() - overhead();
99 Copy::fill_to_words(start, size, metadata_chunk_initialize);
100 }
101 #endif // PRODUCT
103 void Metachunk::verify() {
104 #ifdef ASSERT
105 // Cannot walk through the blocks unless the blocks have
106 // headers with sizes.
107 assert(bottom() <= _top &&
108 _top <= (MetaWord*)end(),
109 "Chunk has been smashed");
110 #endif
111 return;
112 }
114 /////////////// Unit tests ///////////////
116 #ifndef PRODUCT
118 class TestMetachunk {
119 public:
120 static void test() {
121 size_t size = 2 * 1024 * 1024;
122 void* memory = malloc(size);
123 assert(memory != NULL, "Failed to malloc 2MB");
125 Metachunk* metachunk = ::new (memory) Metachunk(size / BytesPerWord, NULL);
127 assert(metachunk->bottom() == (MetaWord*)metachunk, "assert");
128 assert(metachunk->end() == (uintptr_t*)metachunk + metachunk->size(), "assert");
130 // Check sizes
131 assert(metachunk->size() == metachunk->word_size(), "assert");
132 assert(metachunk->word_size() == pointer_delta(metachunk->end(), metachunk->bottom(),
133 sizeof(MetaWord*)), "assert");
135 // Check usage
136 assert(metachunk->used_word_size() == metachunk->overhead(), "assert");
137 assert(metachunk->free_word_size() == metachunk->word_size() - metachunk->used_word_size(), "assert");
138 assert(metachunk->top() == metachunk->initial_top(), "assert");
139 assert(metachunk->is_empty(), "assert");
141 // Allocate
142 size_t alloc_size = 64; // Words
143 assert(is_size_aligned(alloc_size, Metachunk::object_alignment()), "assert");
145 MetaWord* mem = metachunk->allocate(alloc_size);
147 // Check post alloc
148 assert(mem == metachunk->initial_top(), "assert");
149 assert(mem + alloc_size == metachunk->top(), "assert");
150 assert(metachunk->used_word_size() == metachunk->overhead() + alloc_size, "assert");
151 assert(metachunk->free_word_size() == metachunk->word_size() - metachunk->used_word_size(), "assert");
152 assert(!metachunk->is_empty(), "assert");
154 // Clear chunk
155 metachunk->reset_empty();
157 // Check post clear
158 assert(metachunk->used_word_size() == metachunk->overhead(), "assert");
159 assert(metachunk->free_word_size() == metachunk->word_size() - metachunk->used_word_size(), "assert");
160 assert(metachunk->top() == metachunk->initial_top(), "assert");
161 assert(metachunk->is_empty(), "assert");
163 free(memory);
164 }
165 };
167 void TestMetachunk_test() {
168 TestMetachunk::test();
169 }
171 #endif