Thu, 22 Sep 2011 10:57:37 -0700
6484982: G1: process references during evacuation pauses
Summary: G1 now uses two reference processors - one is used by concurrent marking and the other is used by STW GCs (both full and incremental evacuation pauses). In an evacuation pause, the reference processor is embedded into the closures used to scan objects. Doing so causes causes reference objects to be 'discovered' by the reference processor. At the end of the evacuation pause, these discovered reference objects are processed - preserving (and copying) referent objects (and their reachable graphs) as appropriate.
Reviewed-by: ysr, jwilhelm, brutisso, stefank, tonyp
1 /*
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25 #include "precompiled.hpp"
26 #include "gc_implementation/parallelScavenge/objectStartArray.hpp"
27 #include "memory/allocation.inline.hpp"
28 #include "memory/cardTableModRefBS.hpp"
29 #include "oops/oop.inline.hpp"
30 #include "runtime/java.hpp"
32 void ObjectStartArray::initialize(MemRegion reserved_region) {
33 // We're based on the assumption that we use the same
34 // size blocks as the card table.
35 assert((int)block_size == (int)CardTableModRefBS::card_size, "Sanity");
36 assert((int)block_size <= 512, "block_size must be less than or equal to 512");
38 // Calculate how much space must be reserved
39 _reserved_region = reserved_region;
41 size_t bytes_to_reserve = reserved_region.word_size() / block_size_in_words;
42 assert(bytes_to_reserve > 0, "Sanity");
44 bytes_to_reserve =
45 align_size_up(bytes_to_reserve, os::vm_allocation_granularity());
47 // Do not use large-pages for the backing store. The one large page region
48 // will be used for the heap proper.
49 ReservedSpace backing_store(bytes_to_reserve);
50 if (!backing_store.is_reserved()) {
51 vm_exit_during_initialization("Could not reserve space for ObjectStartArray");
52 }
54 // We do not commit any memory initially
55 if (!_virtual_space.initialize(backing_store, 0)) {
56 vm_exit_during_initialization("Could not commit space for ObjectStartArray");
57 }
59 _raw_base = (jbyte*)_virtual_space.low_boundary();
60 if (_raw_base == NULL) {
61 vm_exit_during_initialization("Could not get raw_base address");
62 }
64 _offset_base = _raw_base - (size_t(reserved_region.start()) >> block_shift);
66 _covered_region.set_start(reserved_region.start());
67 _covered_region.set_word_size(0);
69 _blocks_region.set_start((HeapWord*)_raw_base);
70 _blocks_region.set_word_size(0);
71 }
73 void ObjectStartArray::set_covered_region(MemRegion mr) {
74 assert(_reserved_region.contains(mr), "MemRegion outside of reserved space");
75 assert(_reserved_region.start() == mr.start(), "Attempt to move covered region");
77 HeapWord* low_bound = mr.start();
78 HeapWord* high_bound = mr.end();
79 assert((uintptr_t(low_bound) & (block_size - 1)) == 0, "heap must start at block boundary");
80 assert((uintptr_t(high_bound) & (block_size - 1)) == 0, "heap must end at block boundary");
82 size_t requested_blocks_size_in_bytes = mr.word_size() / block_size_in_words;
84 // Only commit memory in page sized chunks
85 requested_blocks_size_in_bytes =
86 align_size_up(requested_blocks_size_in_bytes, os::vm_page_size());
88 _covered_region = mr;
90 size_t current_blocks_size_in_bytes = _blocks_region.byte_size();
92 if (requested_blocks_size_in_bytes > current_blocks_size_in_bytes) {
93 // Expand
94 size_t expand_by = requested_blocks_size_in_bytes - current_blocks_size_in_bytes;
95 if (!_virtual_space.expand_by(expand_by)) {
96 vm_exit_out_of_memory(expand_by, "object start array expansion");
97 }
98 // Clear *only* the newly allocated region
99 memset(_blocks_region.end(), clean_block, expand_by);
100 }
102 if (requested_blocks_size_in_bytes < current_blocks_size_in_bytes) {
103 // Shrink
104 size_t shrink_by = current_blocks_size_in_bytes - requested_blocks_size_in_bytes;
105 _virtual_space.shrink_by(shrink_by);
106 }
108 _blocks_region.set_word_size(requested_blocks_size_in_bytes / sizeof(HeapWord));
110 assert(requested_blocks_size_in_bytes % sizeof(HeapWord) == 0, "Block table not expanded in word sized increment");
111 assert(requested_blocks_size_in_bytes == _blocks_region.byte_size(), "Sanity");
112 assert(block_for_addr(low_bound) == &_raw_base[0], "Checking start of map");
113 assert(block_for_addr(high_bound-1) <= &_raw_base[_blocks_region.byte_size()-1], "Checking end of map");
114 }
116 void ObjectStartArray::reset() {
117 memset(_blocks_region.start(), clean_block, _blocks_region.byte_size());
118 }
121 bool ObjectStartArray::object_starts_in_range(HeapWord* start_addr,
122 HeapWord* end_addr) const {
123 assert(start_addr <= end_addr, "range is wrong");
124 if (start_addr > end_addr) {
125 return false;
126 }
128 jbyte* start_block = block_for_addr(start_addr);
129 jbyte* end_block = block_for_addr(end_addr);
131 for (jbyte* block = start_block; block <= end_block; block++) {
132 if (*block != clean_block) {
133 return true;
134 }
135 }
136 // No object starts in this slice; verify this using
137 // more traditional methods:
138 assert(object_start(end_addr - 1) <= start_addr,
139 "Oops an object does start in this slice?");
140 return false;
141 }