Tue, 13 Apr 2010 13:52:10 -0700
6858496: Clear all SoftReferences before an out-of-memory due to GC overhead limit.
Summary: Ensure a full GC that clears SoftReferences before throwing an out-of-memory
Reviewed-by: ysr, jcoomes
1 /*
2 * Copyright 2001-2009 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 // Remembered set for a heap region. Represent a set of "cards" that
26 // contain pointers into the owner heap region. Cards are defined somewhat
27 // abstractly, in terms of what the "BlockOffsetTable" in use can parse.
29 class G1CollectedHeap;
30 class G1BlockOffsetSharedArray;
31 class HeapRegion;
32 class HeapRegionRemSetIterator;
33 class PosParPRT;
34 class SparsePRT;
37 // The "_coarse_map" is a bitmap with one bit for each region, where set
38 // bits indicate that the corresponding region may contain some pointer
39 // into the owning region.
41 // The "_fine_grain_entries" array is an open hash table of PerRegionTables
42 // (PRTs), indicating regions for which we're keeping the RS as a set of
43 // cards. The strategy is to cap the size of the fine-grain table,
44 // deleting an entry and setting the corresponding coarse-grained bit when
45 // we would overflow this cap.
47 // We use a mixture of locking and lock-free techniques here. We allow
48 // threads to locate PRTs without locking, but threads attempting to alter
49 // a bucket list obtain a lock. This means that any failing attempt to
50 // find a PRT must be retried with the lock. It might seem dangerous that
51 // a read can find a PRT that is concurrently deleted. This is all right,
52 // because:
53 //
54 // 1) We only actually free PRT's at safe points (though we reuse them at
55 // other times).
56 // 2) We find PRT's in an attempt to add entries. If a PRT is deleted,
57 // it's _coarse_map bit is set, so the that we were attempting to add
58 // is represented. If a deleted PRT is re-used, a thread adding a bit,
59 // thinking the PRT is for a different region, does no harm.
61 class OtherRegionsTable VALUE_OBJ_CLASS_SPEC {
62 friend class HeapRegionRemSetIterator;
64 G1CollectedHeap* _g1h;
65 Mutex _m;
66 HeapRegion* _hr;
68 // These are protected by "_m".
69 BitMap _coarse_map;
70 size_t _n_coarse_entries;
71 static jint _n_coarsenings;
73 PosParPRT** _fine_grain_regions;
74 size_t _n_fine_entries;
76 #define SAMPLE_FOR_EVICTION 1
77 #if SAMPLE_FOR_EVICTION
78 size_t _fine_eviction_start;
79 static size_t _fine_eviction_stride;
80 static size_t _fine_eviction_sample_size;
81 #endif
83 SparsePRT _sparse_table;
85 // These are static after init.
86 static size_t _max_fine_entries;
87 static size_t _mod_max_fine_entries_mask;
89 // Requires "prt" to be the first element of the bucket list appropriate
90 // for "hr". If this list contains an entry for "hr", return it,
91 // otherwise return "NULL".
92 PosParPRT* find_region_table(size_t ind, HeapRegion* hr) const;
94 // Find, delete, and return a candidate PosParPRT, if any exists,
95 // adding the deleted region to the coarse bitmap. Requires the caller
96 // to hold _m, and the fine-grain table to be full.
97 PosParPRT* delete_region_table();
99 // If a PRT for "hr" is in the bucket list indicated by "ind" (which must
100 // be the correct index for "hr"), delete it and return true; else return
101 // false.
102 bool del_single_region_table(size_t ind, HeapRegion* hr);
104 static jint _cache_probes;
105 static jint _cache_hits;
107 // Indexed by thread X heap region, to minimize thread contention.
108 static int** _from_card_cache;
109 static size_t _from_card_cache_max_regions;
110 static size_t _from_card_cache_mem_size;
112 public:
113 OtherRegionsTable(HeapRegion* hr);
115 HeapRegion* hr() const { return _hr; }
117 // For now. Could "expand" some tables in the future, so that this made
118 // sense.
119 void add_reference(OopOrNarrowOopStar from, int tid);
121 void add_reference(OopOrNarrowOopStar from) {
122 return add_reference(from, 0);
123 }
125 // Removes any entries shown by the given bitmaps to contain only dead
126 // objects.
127 void scrub(CardTableModRefBS* ctbs, BitMap* region_bm, BitMap* card_bm);
129 // Not const because it takes a lock.
130 size_t occupied() const;
131 size_t occ_fine() const;
132 size_t occ_coarse() const;
133 size_t occ_sparse() const;
135 static jint n_coarsenings() { return _n_coarsenings; }
137 // Returns size in bytes.
138 // Not const because it takes a lock.
139 size_t mem_size() const;
140 static size_t static_mem_size();
141 static size_t fl_mem_size();
143 bool contains_reference(OopOrNarrowOopStar from) const;
144 bool contains_reference_locked(OopOrNarrowOopStar from) const;
146 void clear();
148 // Specifically clear the from_card_cache.
149 void clear_fcc();
151 // "from_hr" is being cleared; remove any entries from it.
152 void clear_incoming_entry(HeapRegion* from_hr);
154 // Declare the heap size (in # of regions) to the OtherRegionsTable.
155 // (Uses it to initialize from_card_cache).
156 static void init_from_card_cache(size_t max_regions);
158 // Declares that only regions i s.t. 0 <= i < new_n_regs are in use.
159 // Make sure any entries for higher regions are invalid.
160 static void shrink_from_card_cache(size_t new_n_regs);
162 static void print_from_card_cache();
164 };
167 class HeapRegionRemSet : public CHeapObj {
168 friend class VMStructs;
169 friend class HeapRegionRemSetIterator;
171 public:
172 enum Event {
173 Event_EvacStart, Event_EvacEnd, Event_RSUpdateEnd
174 };
176 private:
177 G1BlockOffsetSharedArray* _bosa;
178 G1BlockOffsetSharedArray* bosa() const { return _bosa; }
180 OtherRegionsTable _other_regions;
182 // One set bit for every region that has an entry for this one.
183 BitMap _outgoing_region_map;
185 // Clear entries for the current region in any rem sets named in
186 // the _outgoing_region_map.
187 void clear_outgoing_entries();
189 enum ParIterState { Unclaimed, Claimed, Complete };
190 volatile ParIterState _iter_state;
191 volatile jlong _iter_claimed;
193 // Unused unless G1RecordHRRSOops is true.
195 static const int MaxRecorded = 1000000;
196 static OopOrNarrowOopStar* _recorded_oops;
197 static HeapWord** _recorded_cards;
198 static HeapRegion** _recorded_regions;
199 static int _n_recorded;
201 static const int MaxRecordedEvents = 1000;
202 static Event* _recorded_events;
203 static int* _recorded_event_index;
204 static int _n_recorded_events;
206 static void print_event(outputStream* str, Event evnt);
208 public:
209 HeapRegionRemSet(G1BlockOffsetSharedArray* bosa,
210 HeapRegion* hr);
212 static int num_par_rem_sets();
213 static void setup_remset_size();
215 HeapRegion* hr() const {
216 return _other_regions.hr();
217 }
219 size_t occupied() const {
220 return _other_regions.occupied();
221 }
222 size_t occ_fine() const {
223 return _other_regions.occ_fine();
224 }
225 size_t occ_coarse() const {
226 return _other_regions.occ_coarse();
227 }
228 size_t occ_sparse() const {
229 return _other_regions.occ_sparse();
230 }
232 static jint n_coarsenings() { return OtherRegionsTable::n_coarsenings(); }
234 /* Used in the sequential case. Returns "true" iff this addition causes
235 the size limit to be reached. */
236 void add_reference(OopOrNarrowOopStar from) {
237 _other_regions.add_reference(from);
238 }
240 /* Used in the parallel case. Returns "true" iff this addition causes
241 the size limit to be reached. */
242 void add_reference(OopOrNarrowOopStar from, int tid) {
243 _other_regions.add_reference(from, tid);
244 }
246 // Records the fact that the current region contains an outgoing
247 // reference into "to_hr".
248 void add_outgoing_reference(HeapRegion* to_hr);
250 // Removes any entries shown by the given bitmaps to contain only dead
251 // objects.
252 void scrub(CardTableModRefBS* ctbs, BitMap* region_bm, BitMap* card_bm);
254 // The region is being reclaimed; clear its remset, and any mention of
255 // entries for this region in other remsets.
256 void clear();
258 // Forget any entries due to pointers from "from_hr".
259 void clear_incoming_entry(HeapRegion* from_hr) {
260 _other_regions.clear_incoming_entry(from_hr);
261 }
263 #if 0
264 virtual void cleanup() = 0;
265 #endif
267 // Should be called from single-threaded code.
268 void init_for_par_iteration();
269 // Attempt to claim the region. Returns true iff this call caused an
270 // atomic transition from Unclaimed to Claimed.
271 bool claim_iter();
272 // Sets the iteration state to "complete".
273 void set_iter_complete();
274 // Returns "true" iff the region's iteration is complete.
275 bool iter_is_complete();
277 // Support for claiming blocks of cards during iteration
278 void set_iter_claimed(size_t x) { _iter_claimed = (jlong)x; }
279 size_t iter_claimed() const { return (size_t)_iter_claimed; }
280 // Claim the next block of cards
281 size_t iter_claimed_next(size_t step) {
282 size_t current, next;
283 do {
284 current = iter_claimed();
285 next = current + step;
286 } while (Atomic::cmpxchg((jlong)next, &_iter_claimed, (jlong)current) != (jlong)current);
287 return current;
288 }
290 // Initialize the given iterator to iterate over this rem set.
291 void init_iterator(HeapRegionRemSetIterator* iter) const;
293 #if 0
294 // Apply the "do_card" method to the start address of every card in the
295 // rem set. Returns false if some application of the closure aborted.
296 virtual bool card_iterate(CardClosure* iter) = 0;
297 #endif
299 // The actual # of bytes this hr_remset takes up.
300 size_t mem_size() {
301 return _other_regions.mem_size()
302 // This correction is necessary because the above includes the second
303 // part.
304 + sizeof(this) - sizeof(OtherRegionsTable);
305 }
307 // Returns the memory occupancy of all static data structures associated
308 // with remembered sets.
309 static size_t static_mem_size() {
310 return OtherRegionsTable::static_mem_size();
311 }
313 // Returns the memory occupancy of all free_list data structures associated
314 // with remembered sets.
315 static size_t fl_mem_size() {
316 return OtherRegionsTable::fl_mem_size();
317 }
319 bool contains_reference(OopOrNarrowOopStar from) const {
320 return _other_regions.contains_reference(from);
321 }
322 void print() const;
324 // Called during a stop-world phase to perform any deferred cleanups.
325 // The second version may be called by parallel threads after then finish
326 // collection work.
327 static void cleanup();
328 static void par_cleanup();
330 // Declare the heap size (in # of regions) to the HeapRegionRemSet(s).
331 // (Uses it to initialize from_card_cache).
332 static void init_heap(size_t max_regions) {
333 OtherRegionsTable::init_from_card_cache(max_regions);
334 }
336 // Declares that only regions i s.t. 0 <= i < new_n_regs are in use.
337 static void shrink_heap(size_t new_n_regs) {
338 OtherRegionsTable::shrink_from_card_cache(new_n_regs);
339 }
341 #ifndef PRODUCT
342 static void print_from_card_cache() {
343 OtherRegionsTable::print_from_card_cache();
344 }
345 #endif
347 static void record(HeapRegion* hr, OopOrNarrowOopStar f);
348 static void print_recorded();
349 static void record_event(Event evnt);
351 // Run unit tests.
352 #ifndef PRODUCT
353 static void test();
354 #endif
356 };
358 class HeapRegionRemSetIterator : public CHeapObj {
360 // The region over which we're iterating.
361 const HeapRegionRemSet* _hrrs;
363 // Local caching of HRRS fields.
364 const BitMap* _coarse_map;
365 PosParPRT** _fine_grain_regions;
367 G1BlockOffsetSharedArray* _bosa;
368 G1CollectedHeap* _g1h;
370 // The number yielded since initialization.
371 size_t _n_yielded_fine;
372 size_t _n_yielded_coarse;
373 size_t _n_yielded_sparse;
375 // If true we're iterating over the coarse table; if false the fine
376 // table.
377 enum IterState {
378 Sparse,
379 Fine,
380 Coarse
381 };
382 IterState _is;
384 // In both kinds of iteration, heap offset of first card of current
385 // region.
386 size_t _cur_region_card_offset;
387 // Card offset within cur region.
388 size_t _cur_region_cur_card;
390 // Coarse table iteration fields:
392 // Current region index;
393 int _coarse_cur_region_index;
394 int _coarse_cur_region_cur_card;
396 bool coarse_has_next(size_t& card_index);
398 // Fine table iteration fields:
400 // Index of bucket-list we're working on.
401 int _fine_array_index;
402 // Per Region Table we're doing within current bucket list.
403 PosParPRT* _fine_cur_prt;
405 /* SparsePRT::*/ SparsePRTIter _sparse_iter;
407 void fine_find_next_non_null_prt();
409 bool fine_has_next();
410 bool fine_has_next(size_t& card_index);
412 public:
413 // We require an iterator to be initialized before use, so the
414 // constructor does little.
415 HeapRegionRemSetIterator();
417 void initialize(const HeapRegionRemSet* hrrs);
419 // If there remains one or more cards to be yielded, returns true and
420 // sets "card_index" to one of those cards (which is then considered
421 // yielded.) Otherwise, returns false (and leaves "card_index"
422 // undefined.)
423 bool has_next(size_t& card_index);
425 size_t n_yielded_fine() { return _n_yielded_fine; }
426 size_t n_yielded_coarse() { return _n_yielded_coarse; }
427 size_t n_yielded_sparse() { return _n_yielded_sparse; }
428 size_t n_yielded() {
429 return n_yielded_fine() + n_yielded_coarse() + n_yielded_sparse();
430 }
431 };
433 #if 0
434 class CardClosure: public Closure {
435 public:
436 virtual void do_card(HeapWord* card_start) = 0;
437 };
439 #endif