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).
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 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 24 
 25 #ifndef SHARE_GC_SHARED_PLAB_HPP
 26 #define SHARE_GC_SHARED_PLAB_HPP
 27 
 28 #include "gc/shared/gcUtil.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   static size_t AlignmentReserve;
 50 
 51   // Force future allocations to fail and queries for contains()
 52   // to return false. Returns the amount of unused space in this PLAB.
 53   size_t invalidate() {
 54     _end    = _hard_end;
 55     size_t remaining = pointer_delta(_end, _top);  // Calculate remaining space.
 56     _top    = _end;      // Force future allocations to fail.
 57     _bottom = _end;      // Force future contains() queries to return false.
 58     return remaining;
 59   }
 60 
 61   // Fill in remaining space with a dummy object and invalidate the PLAB. Returns
 62   // the amount of remaining space.
 63   size_t retire_internal();
 64 
 65   void add_undo_waste(HeapWord* obj, size_t word_sz);
 66 
 67   // Undo the last allocation in the buffer, which is required to be of the
 68   // "obj" of the given "word_sz".
 69   void undo_last_allocation(HeapWord* obj, size_t word_sz);
 70 
 71 public:
 72   // Initializes the buffer to be empty, but with the given "word_sz".
 73   // Must get initialized with "set_buf" for an allocation to succeed.
 74   PLAB(size_t word_sz);
 75 
 76   static size_t size_required_for_allocation(size_t word_size) { return word_size + AlignmentReserve; }
 77 
 78   // Minimum PLAB size.
 79   static size_t min_size();
 80   // Maximum PLAB size.
 81   static size_t max_size();
 82 
 83   // If an allocation of the given "word_sz" can be satisfied within the
 84   // buffer, do the allocation, returning a pointer to the start of the
 85   // allocated block.  If the allocation request cannot be satisfied,
 86   // return NULL.
 87   HeapWord* allocate(size_t word_sz) {
 88     HeapWord* res = _top;
 89     if (pointer_delta(_end, _top) >= word_sz) {
 90       _top = _top + word_sz;
 91       return res;
 92     } else {
 93       return NULL;
 94     }
 95   }
 96 
 97   // Undo any allocation in the buffer, which is required to be of the
 98   // "obj" of the given "word_sz".
 99   void undo_allocation(HeapWord* obj, size_t word_sz);
100 
101   // The total (word) size of the buffer, including both allocated and
102   // unallocated space.
103   size_t word_sz() { return _word_sz; }
104 
105   size_t waste() { return _wasted; }
106   size_t undo_waste() { return _undo_wasted; }
107 
108   // The number of words of unallocated space remaining in the buffer.
109   size_t words_remaining() {
110     assert(_end >= _top, "Negative buffer");
111     return pointer_delta(_end, _top, HeapWordSize);
112   }
113 
114   bool contains(void* addr) {
115     return (void*)_bottom <= addr && addr < (void*)_hard_end;
116   }
117 
118   // Sets the space of the buffer to be [buf, space+word_sz()).
119   void set_buf(HeapWord* buf, size_t new_word_sz) {
120     assert(new_word_sz > AlignmentReserve, "Too small");
121     _word_sz = new_word_sz;
122 
123     _bottom   = buf;
124     _top      = _bottom;
125     _hard_end = _bottom + word_sz();
126     _end      = _hard_end - AlignmentReserve;
127     assert(_end >= _top, "Negative buffer");
128     // In support of ergonomic sizing
129     _allocated += word_sz();
130   }
131 
132   // Flush allocation statistics into the given PLABStats supporting ergonomic
133   // sizing of PLAB's and retire the current buffer. To be called at the end of
134   // GC.
135   void flush_and_retire_stats(PLABStats* stats);
136 
137   // Fills in the unallocated portion of the buffer with a garbage object and updates
138   // statistics. To be called during GC.
139   void retire();
140 
141   HeapWord* top() {
142     return _top;
143   }
144 };
145 
146 // PLAB book-keeping.
147 class PLABStats : public CHeapObj<mtGC> {
148  protected:
149   const char* _description;   // Identifying string.
150 
151   size_t _allocated;          // Total allocated
152   size_t _wasted;             // of which wasted (internal fragmentation)
153   size_t _undo_wasted;        // of which wasted on undo (is not used for calculation of PLAB size)
154   size_t _unused;             // Unused in last buffer
155   size_t _default_plab_sz;
156   size_t _desired_net_plab_sz;// Output of filter (below), suitably trimmed and quantized
157   AdaptiveWeightedAverage
158          _filter;             // Integrator with decay
159 
160   virtual void reset() {
161     _allocated   = 0;
162     _wasted      = 0;
163     _undo_wasted = 0;
164     _unused      = 0;
165   }
166 
167   virtual void log_plab_allocation();
168   virtual void log_sizing(size_t calculated, size_t net_desired);
169 
170   // helper for adjust_desired_plab_sz().
171   virtual size_t compute_desired_plab_sz();
172 
173  public:
174   PLABStats(const char* description, size_t default_per_thread_plab_size, size_t desired_net_plab_sz, unsigned wt) :
175     _description(description),
176     _allocated(0),
177     _wasted(0),
178     _undo_wasted(0),
179     _unused(0),
180     _default_plab_sz(default_per_thread_plab_size),
181     _desired_net_plab_sz(desired_net_plab_sz),
182     _filter(wt)
183   { }
184 
185   virtual ~PLABStats() { }
186 
187   size_t allocated() const { return _allocated; }
188   size_t wasted() const { return _wasted; }
189   size_t unused() const { return _unused; }
190   size_t used() const { return allocated() - (wasted() + unused()); }
191   size_t undo_wasted() const { return _undo_wasted; }
192 
193   static const size_t min_size() {
194     return PLAB::min_size();
195   }
196 
197   static const size_t max_size() {
198     return PLAB::max_size();
199   }
200 
201   // Calculates plab size for current number of gc worker threads.
202   size_t desired_plab_sz(uint no_of_gc_workers);
203 
204   // Updates the current desired PLAB size. Computes the new desired PLAB size with one gc worker thread,
205   // updates _desired_plab_sz and clears sensor accumulators.
206   void adjust_desired_plab_sz();
207 
208   inline void add_allocated(size_t v);
209 
210   inline void add_unused(size_t v);
211 
212   inline void add_wasted(size_t v);
213 
214   inline void add_undo_wasted(size_t v);
215 };
216 
217 #endif // SHARE_GC_SHARED_PLAB_HPP