1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
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  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  *
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 18  *
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 20  * or visit www.oracle.com if you need additional information or have any
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 24 
 25 #ifndef SHARE_GC_SHARED_PLAB_HPP
 26 #define SHARE_GC_SHARED_PLAB_HPP
 27 
 28 #include "gc/shared/collectedHeap.hpp"
 29 #include "memory/allocation.hpp"
 30 #include "utilities/globalDefinitions.hpp"
 31 
 32 // Forward declarations.
 33 class PLABStats;
 34 
 35 // A per-thread allocation buffer used during GC.
 36 class PLAB: public CHeapObj<mtGC> {
 37 protected:
 38   char      head[32];
 39   size_t    _word_sz;          // In HeapWord units
 40   HeapWord* _bottom;
 41   HeapWord* _top;
 42   HeapWord* _end;           // Last allocatable address + 1
 43   HeapWord* _hard_end;      // _end + AlignmentReserve
 44   // In support of ergonomic sizing of PLAB's
 45   size_t    _allocated;     // in HeapWord units
 46   size_t    _wasted;        // in HeapWord units
 47   size_t    _undo_wasted;
 48   char      tail[32];
 49 
 50   // Force future allocations to fail and queries for contains()
 51   // to return false. Returns the amount of unused space in this PLAB.
 52   size_t invalidate() {
 53     _end    = _hard_end;
 54     size_t remaining = pointer_delta(_end, _top);  // Calculate remaining space.
 55     _top    = _end;      // Force future allocations to fail.
 56     _bottom = _end;      // Force future contains() queries to return false.
 57     return remaining;
 58   }
 59 
 60   // Fill in remaining space with a dummy object and invalidate the PLAB. Returns
 61   // the amount of remaining space.
 62   size_t retire_internal();
 63 
 64   void add_undo_waste(HeapWord* obj, size_t word_sz);
 65 
 66   // Undo the last allocation in the buffer, which is required to be of the
 67   // "obj" of the given "word_sz".
 68   void undo_last_allocation(HeapWord* obj, size_t word_sz);
 69 
 70 public:
 71   static void startup_initialization();
 72 
 73   // Initializes the buffer to be empty, but with the given "word_sz".
 74   // Must get initialized with "set_buf" for an allocation to succeed.
 75   PLAB(size_t word_sz);
 76 
 77   static size_t size_required_for_allocation(size_t word_size) { return word_size + CollectedHeap::lab_alignment_reserve(); }
 78 
 79   // Minimum PLAB size.
 80   static size_t min_size();
 81   // Maximum PLAB size.
 82   static size_t max_size();
 83 
 84   // If an allocation of the given "word_sz" can be satisfied within the
 85   // buffer, do the allocation, returning a pointer to the start of the
 86   // allocated block.  If the allocation request cannot be satisfied,
 87   // return NULL.
 88   HeapWord* allocate(size_t word_sz) {
 89     HeapWord* res = _top;
 90     if (pointer_delta(_end, _top) >= word_sz) {
 91       _top = _top + word_sz;
 92       return res;
 93     } else {
 94       return NULL;
 95     }
 96   }
 97 
 98   // Undo any allocation in the buffer, which is required to be of the
 99   // "obj" of the given "word_sz".
100   void undo_allocation(HeapWord* obj, size_t word_sz);
101 
102   // The total (word) size of the buffer, including both allocated and
103   // unallocated space.
104   size_t word_sz() { return _word_sz; }
105 
106   size_t waste() { return _wasted; }
107   size_t undo_waste() { return _undo_wasted; }
108 
109   // The number of words of unallocated space remaining in the buffer.
110   size_t words_remaining() {
111     assert(_end >= _top, "Negative buffer");
112     return pointer_delta(_end, _top, HeapWordSize);
113   }
114 
115   bool contains(void* addr) {
116     return (void*)_bottom <= addr && addr < (void*)_hard_end;
117   }
118 
119   // Sets the space of the buffer to be [buf, space+word_sz()).
120   void set_buf(HeapWord* buf, size_t new_word_sz) {
121     assert(new_word_sz > CollectedHeap::lab_alignment_reserve(), "Too small");
122     _word_sz = new_word_sz;
123 
124     _bottom   = buf;
125     _top      = _bottom;
126     _hard_end = _bottom + word_sz();
127     _end      = _hard_end - CollectedHeap::lab_alignment_reserve();
128     assert(_end >= _top, "Negative buffer");
129     // In support of ergonomic sizing
130     _allocated += word_sz();
131   }
132 
133   // Flush allocation statistics into the given PLABStats supporting ergonomic
134   // sizing of PLAB's and retire the current buffer. To be called at the end of
135   // GC.
136   void flush_and_retire_stats(PLABStats* stats);
137 
138   // Fills in the unallocated portion of the buffer with a garbage object and updates
139   // statistics. To be called during GC.
140   void retire();
141 
142   HeapWord* top() {
143     return _top;
144   }
145 };
146 
147 // PLAB book-keeping.
148 class PLABStats : public CHeapObj<mtGC> {
149 protected:
150   const char* _description;   // Identifying string.
151 
152   size_t _allocated;          // Total allocated
153   size_t _wasted;             // of which wasted (internal fragmentation)
154   size_t _undo_wasted;        // of which wasted on undo (is not used for calculation of PLAB size)
155   size_t _unused;             // Unused in last buffer
156 
157   virtual void reset() {
158     _allocated   = 0;
159     _wasted      = 0;
160     _undo_wasted = 0;
161     _unused      = 0;
162   }
163 
164 public:
165   PLABStats(const char* description) :
166     _description(description),
167     _allocated(0),
168     _wasted(0),
169     _undo_wasted(0),
170     _unused(0)
171   { }
172 
173   virtual ~PLABStats() { }
174 
175   size_t allocated() const { return _allocated; }
176   size_t wasted() const { return _wasted; }
177   size_t unused() const { return _unused; }
178   size_t used() const { return allocated() - (wasted() + unused()); }
179   size_t undo_wasted() const { return _undo_wasted; }
180 
181   static const size_t min_size() {
182     return PLAB::min_size();
183   }
184 
185   static const size_t max_size() {
186     return PLAB::max_size();
187   }
188 
189   inline void add_allocated(size_t v);
190 
191   inline void add_unused(size_t v);
192 
193   inline void add_wasted(size_t v);
194 
195   inline void add_undo_wasted(size_t v);
196 };
197 
198 #endif // SHARE_GC_SHARED_PLAB_HPP