Wed, 02 Sep 2009 00:04:29 -0700
4957990: Perm heap bloat in JVM
Summary: Treat ProfileData in MDO's as a source of weak, not strong, roots. Fixes the bug for stop-world collection -- the case of concurrent collection will be fixed separately.
Reviewed-by: jcoomes, jmasa, kvn, never
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25 #include "incls/_precompiled.incl"
26 #include "incls/_g1MarkSweep.cpp.incl"
28 class HeapRegion;
30 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
31 bool clear_all_softrefs) {
32 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
34 // hook up weak ref data so it can be used during Mark-Sweep
35 assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
36 assert(rp != NULL, "should be non-NULL");
37 GenMarkSweep::_ref_processor = rp;
38 rp->setup_policy(clear_all_softrefs);
40 // When collecting the permanent generation methodOops may be moving,
41 // so we either have to flush all bcp data or convert it into bci.
42 CodeCache::gc_prologue();
43 Threads::gc_prologue();
45 // Increment the invocation count for the permanent generation, since it is
46 // implicitly collected whenever we do a full mark sweep collection.
47 SharedHeap* sh = SharedHeap::heap();
48 sh->perm_gen()->stat_record()->invocations++;
50 bool marked_for_unloading = false;
52 allocate_stacks();
54 // We should save the marks of the currently locked biased monitors.
55 // The marking doesn't preserve the marks of biased objects.
56 BiasedLocking::preserve_marks();
58 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
60 if (VerifyDuringGC) {
61 G1CollectedHeap* g1h = G1CollectedHeap::heap();
62 g1h->checkConcurrentMark();
63 }
65 mark_sweep_phase2();
67 // Don't add any more derived pointers during phase3
68 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
70 mark_sweep_phase3();
72 mark_sweep_phase4();
74 GenMarkSweep::restore_marks();
75 BiasedLocking::restore_marks();
76 GenMarkSweep::deallocate_stacks();
78 // We must invalidate the perm-gen rs, so that it gets rebuilt.
79 GenRemSet* rs = sh->rem_set();
80 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
82 // "free at last gc" is calculated from these.
83 // CHF: cheating for now!!!
84 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
85 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
87 Threads::gc_epilogue();
88 CodeCache::gc_epilogue();
90 // refs processing: clean slate
91 GenMarkSweep::_ref_processor = NULL;
92 }
95 void G1MarkSweep::allocate_stacks() {
96 GenMarkSweep::_preserved_count_max = 0;
97 GenMarkSweep::_preserved_marks = NULL;
98 GenMarkSweep::_preserved_count = 0;
99 GenMarkSweep::_preserved_mark_stack = NULL;
100 GenMarkSweep::_preserved_oop_stack = NULL;
102 GenMarkSweep::_marking_stack =
103 new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);
105 int size = SystemDictionary::number_of_classes() * 2;
106 GenMarkSweep::_revisit_klass_stack =
107 new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);
108 // (#klass/k)^2 for k ~ 10 appears a better fit, but this will have to do
109 // for now until we have a chance to work out a more optimal setting.
110 GenMarkSweep::_revisit_mdo_stack =
111 new (ResourceObj::C_HEAP) GrowableArray<DataLayout*>(size*2, true);
113 }
115 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
116 bool clear_all_softrefs) {
117 // Recursively traverse all live objects and mark them
118 EventMark m("1 mark object");
119 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
120 GenMarkSweep::trace(" 1");
122 SharedHeap* sh = SharedHeap::heap();
124 sh->process_strong_roots(true, // Collecting permanent generation.
125 SharedHeap::SO_SystemClasses,
126 &GenMarkSweep::follow_root_closure,
127 &GenMarkSweep::follow_root_closure);
129 // Process reference objects found during marking
130 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
131 rp->setup_policy(clear_all_softrefs);
132 rp->process_discovered_references(&GenMarkSweep::is_alive,
133 &GenMarkSweep::keep_alive,
134 &GenMarkSweep::follow_stack_closure,
135 NULL);
137 // Follow system dictionary roots and unload classes
138 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
139 assert(GenMarkSweep::_marking_stack->is_empty(),
140 "stack should be empty by now");
142 // Follow code cache roots (has to be done after system dictionary,
143 // assumes all live klasses are marked)
144 CodeCache::do_unloading(&GenMarkSweep::is_alive,
145 &GenMarkSweep::keep_alive,
146 purged_class);
147 GenMarkSweep::follow_stack();
149 // Update subklass/sibling/implementor links of live klasses
150 GenMarkSweep::follow_weak_klass_links();
151 assert(GenMarkSweep::_marking_stack->is_empty(),
152 "stack should be empty by now");
154 // Visit memoized MDO's and clear any unmarked weak refs
155 GenMarkSweep::follow_mdo_weak_refs();
156 assert(GenMarkSweep::_marking_stack->is_empty(), "just drained");
159 // Visit symbol and interned string tables and delete unmarked oops
160 SymbolTable::unlink(&GenMarkSweep::is_alive);
161 StringTable::unlink(&GenMarkSweep::is_alive);
163 assert(GenMarkSweep::_marking_stack->is_empty(),
164 "stack should be empty by now");
165 }
167 class G1PrepareCompactClosure: public HeapRegionClosure {
168 ModRefBarrierSet* _mrbs;
169 CompactPoint _cp;
171 void free_humongous_region(HeapRegion* hr) {
172 HeapWord* bot = hr->bottom();
173 HeapWord* end = hr->end();
174 assert(hr->startsHumongous(),
175 "Only the start of a humongous region should be freed.");
176 G1CollectedHeap::heap()->free_region(hr);
177 hr->prepare_for_compaction(&_cp);
178 // Also clear the part of the card table that will be unused after
179 // compaction.
180 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
181 }
183 public:
184 G1PrepareCompactClosure(CompactibleSpace* cs) :
185 _cp(NULL, cs, cs->initialize_threshold()),
186 _mrbs(G1CollectedHeap::heap()->mr_bs())
187 {}
188 bool doHeapRegion(HeapRegion* hr) {
189 if (hr->isHumongous()) {
190 if (hr->startsHumongous()) {
191 oop obj = oop(hr->bottom());
192 if (obj->is_gc_marked()) {
193 obj->forward_to(obj);
194 } else {
195 free_humongous_region(hr);
196 }
197 } else {
198 assert(hr->continuesHumongous(), "Invalid humongous.");
199 }
200 } else {
201 hr->prepare_for_compaction(&_cp);
202 // Also clear the part of the card table that will be unused after
203 // compaction.
204 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
205 }
206 return false;
207 }
208 };
210 // Finds the first HeapRegion.
211 class FindFirstRegionClosure: public HeapRegionClosure {
212 HeapRegion* _a_region;
213 public:
214 FindFirstRegionClosure() : _a_region(NULL) {}
215 bool doHeapRegion(HeapRegion* r) {
216 _a_region = r;
217 return true;
218 }
219 HeapRegion* result() { return _a_region; }
220 };
222 void G1MarkSweep::mark_sweep_phase2() {
223 // Now all live objects are marked, compute the new object addresses.
225 // It is imperative that we traverse perm_gen LAST. If dead space is
226 // allowed a range of dead object may get overwritten by a dead int
227 // array. If perm_gen is not traversed last a klassOop may get
228 // overwritten. This is fine since it is dead, but if the class has dead
229 // instances we have to skip them, and in order to find their size we
230 // need the klassOop!
231 //
232 // It is not required that we traverse spaces in the same order in
233 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
234 // tracking expects us to do so. See comment under phase4.
236 G1CollectedHeap* g1h = G1CollectedHeap::heap();
237 Generation* pg = g1h->perm_gen();
239 EventMark m("2 compute new addresses");
240 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
241 GenMarkSweep::trace("2");
243 FindFirstRegionClosure cl;
244 g1h->heap_region_iterate(&cl);
245 HeapRegion *r = cl.result();
246 CompactibleSpace* sp = r;
247 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
248 sp = r->next_compaction_space();
249 }
251 G1PrepareCompactClosure blk(sp);
252 g1h->heap_region_iterate(&blk);
254 CompactPoint perm_cp(pg, NULL, NULL);
255 pg->prepare_for_compaction(&perm_cp);
256 }
258 class G1AdjustPointersClosure: public HeapRegionClosure {
259 public:
260 bool doHeapRegion(HeapRegion* r) {
261 if (r->isHumongous()) {
262 if (r->startsHumongous()) {
263 // We must adjust the pointers on the single H object.
264 oop obj = oop(r->bottom());
265 debug_only(GenMarkSweep::track_interior_pointers(obj));
266 // point all the oops to the new location
267 obj->adjust_pointers();
268 debug_only(GenMarkSweep::check_interior_pointers());
269 }
270 } else {
271 // This really ought to be "as_CompactibleSpace"...
272 r->adjust_pointers();
273 }
274 return false;
275 }
276 };
278 void G1MarkSweep::mark_sweep_phase3() {
279 G1CollectedHeap* g1h = G1CollectedHeap::heap();
280 Generation* pg = g1h->perm_gen();
282 // Adjust the pointers to reflect the new locations
283 EventMark m("3 adjust pointers");
284 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
285 GenMarkSweep::trace("3");
287 SharedHeap* sh = SharedHeap::heap();
289 sh->process_strong_roots(true, // Collecting permanent generation.
290 SharedHeap::SO_AllClasses,
291 &GenMarkSweep::adjust_root_pointer_closure,
292 &GenMarkSweep::adjust_pointer_closure);
294 g1h->ref_processor()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
296 // Now adjust pointers in remaining weak roots. (All of which should
297 // have been cleared if they pointed to non-surviving objects.)
298 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
299 &GenMarkSweep::adjust_pointer_closure);
301 GenMarkSweep::adjust_marks();
303 G1AdjustPointersClosure blk;
304 g1h->heap_region_iterate(&blk);
305 pg->adjust_pointers();
306 }
308 class G1SpaceCompactClosure: public HeapRegionClosure {
309 public:
310 G1SpaceCompactClosure() {}
312 bool doHeapRegion(HeapRegion* hr) {
313 if (hr->isHumongous()) {
314 if (hr->startsHumongous()) {
315 oop obj = oop(hr->bottom());
316 if (obj->is_gc_marked()) {
317 obj->init_mark();
318 } else {
319 assert(hr->is_empty(), "Should have been cleared in phase 2.");
320 }
321 hr->reset_during_compaction();
322 }
323 } else {
324 hr->compact();
325 }
326 return false;
327 }
328 };
330 void G1MarkSweep::mark_sweep_phase4() {
331 // All pointers are now adjusted, move objects accordingly
333 // It is imperative that we traverse perm_gen first in phase4. All
334 // classes must be allocated earlier than their instances, and traversing
335 // perm_gen first makes sure that all klassOops have moved to their new
336 // location before any instance does a dispatch through it's klass!
338 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
339 // in the same order in phase2, phase3 and phase4. We don't quite do that
340 // here (perm_gen first rather than last), so we tell the validate code
341 // to use a higher index (saved from phase2) when verifying perm_gen.
342 G1CollectedHeap* g1h = G1CollectedHeap::heap();
343 Generation* pg = g1h->perm_gen();
345 EventMark m("4 compact heap");
346 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
347 GenMarkSweep::trace("4");
349 pg->compact();
351 G1SpaceCompactClosure blk;
352 g1h->heap_region_iterate(&blk);
354 }
356 // Local Variables: ***
357 // c-indentation-style: gnu ***
358 // End: ***