1 /*
  2  * Copyright (c) 2016, 2019, Red Hat, 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 
 27 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
 28 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 29 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
 30 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
 31 #include "gc/shenandoah/shenandoahUtils.hpp"
 32 #include "runtime/atomic.hpp"
 33 #include "services/memTracker.hpp"
 34 #include "utilities/copy.hpp"
 35 
 36 ShenandoahCollectionSet::ShenandoahCollectionSet(ShenandoahHeap* heap, ReservedSpace space, char* heap_base) :
 37   _map_size(heap->num_regions()),
 38   _region_size_bytes_shift(ShenandoahHeapRegion::region_size_bytes_shift()),
 39   _map_space(space),
 40   _cset_map(_map_space.base() + ((uintx)heap_base >> _region_size_bytes_shift)),
 41   _biased_cset_map(_map_space.base()),
 42   _heap(heap),
 43   _garbage(0),
 44   _used(0),
 45   _region_count(0),
 46   _current_index(0) {
 47 
 48   // The collection set map is reserved to cover the entire heap *and* zero addresses.
 49   // This is needed to accept in-cset checks for both heap oops and NULLs, freeing
 50   // high-performance code from checking for NULL first.
 51   //
 52   // Since heap_base can be far away, committing the entire map would waste memory.
 53   // Therefore, we only commit the parts that are needed to operate: the heap view,
 54   // and the zero page.
 55   //
 56   // Note: we could instead commit the entire map, and piggyback on OS virtual memory
 57   // subsystem for mapping not-yet-written-to pages to a single physical backing page,
 58   // but this is not guaranteed, and would confuse NMT and other memory accounting tools.
 59 
 60   MemTracker::record_virtual_memory_type(_map_space.base(), mtGC);
 61 
 62   size_t page_size = (size_t)os::vm_page_size();
 63 
 64   if (!_map_space.special()) {
 65     // Commit entire pages that cover the heap cset map.
 66     char* bot_addr = align_down(_cset_map, page_size);
 67     char* top_addr = align_up(_cset_map + _map_size, page_size);
 68     os::commit_memory_or_exit(bot_addr, pointer_delta(top_addr, bot_addr, 1), false,
 69                               "Unable to commit collection set bitmap: heap");
 70 
 71     // Commit the zero page, if not yet covered by heap cset map.
 72     if (bot_addr != _biased_cset_map) {
 73       os::commit_memory_or_exit(_biased_cset_map, page_size, false,
 74                                 "Unable to commit collection set bitmap: zero page");
 75     }
 76   }
 77 
 78   Copy::zero_to_bytes(_cset_map, _map_size);
 79   Copy::zero_to_bytes(_biased_cset_map, page_size);
 80 }
 81 
 82 void ShenandoahCollectionSet::add_region(ShenandoahHeapRegion* r) {
 83   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 84   assert(Thread::current()->is_VM_thread(), "Must be VMThread");
 85   assert(!is_in(r), "Already in collection set");
 86   _cset_map[r->index()] = 1;
 87   _region_count++;
 88   _garbage += r->garbage();
 89   _used += r->used();
 90 
 91   // Update the region status too. State transition would be checked internally.
 92   r->make_cset();
 93 }
 94 
 95 void ShenandoahCollectionSet::clear() {
 96   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 97   Copy::zero_to_bytes(_cset_map, _map_size);
 98 
 99 #ifdef ASSERT
100   for (size_t index = 0; index < _heap->num_regions(); index ++) {
101     assert (!_heap->get_region(index)->is_cset(), "should have been cleared before");
102   }
103 #endif
104 
105   _garbage = 0;
106   _used = 0;
107 
108   _region_count = 0;
109   _current_index = 0;
110 }
111 
112 ShenandoahHeapRegion* ShenandoahCollectionSet::claim_next() {
113   // This code is optimized for the case when collection set contains only
114   // a few regions. In this case, it is more constructive to check for is_in
115   // before hitting the (potentially contended) atomic index.
116 
117   size_t max = _heap->num_regions();
118   size_t old = Atomic::load(&_current_index);
119 
120   for (size_t index = old; index < max; index++) {
121     if (is_in(index)) {
122       size_t cur = Atomic::cmpxchg(&_current_index, old, index + 1, memory_order_relaxed);
123       assert(cur >= old, "Always move forward");
124       if (cur == old) {
125         // Successfully moved the claim index, this is our region.
126         return _heap->get_region(index);
127       } else {
128         // Somebody else moved the claim index, restart from there.
129         index = cur - 1; // adjust for loop post-increment
130         old = cur;
131       }
132     }
133   }
134   return NULL;
135 }
136 
137 ShenandoahHeapRegion* ShenandoahCollectionSet::next() {
138   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
139   assert(Thread::current()->is_VM_thread(), "Must be VMThread");
140 
141   size_t max = _heap->num_regions();
142   for (size_t index = _current_index; index < max; index++) {
143     if (is_in(index)) {
144       _current_index = index + 1;
145       return _heap->get_region(index);
146     }
147   }
148 
149   return NULL;
150 }
151 
152 void ShenandoahCollectionSet::print_on(outputStream* out) const {
153   out->print_cr("Collection Set : " SIZE_FORMAT "", count());
154 
155   debug_only(size_t regions = 0;)
156   for (size_t index = 0; index < _heap->num_regions(); index ++) {
157     if (is_in(index)) {
158       _heap->get_region(index)->print_on(out);
159       debug_only(regions ++;)
160     }
161   }
162   assert(regions == count(), "Must match");
163 }