src/base/fast_alloc.hh

   1 /*
   2  * Copyright (c) 2000-2001, 2003-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Steve Reinhardt
  29  */
  30
  31 /*
  32  * This code was originally written by Steve Reinhardt as part of
  33  * the Wisconsin Wind Tunnel simulator.  Relicensed as part of M5
  34  * by permission.
  35  */
  36
  37 #ifndef __FAST_ALLOC_H__
  38 #define __FAST_ALLOC_H__
  39
  40 #include <stddef.h>
  41
  42 // Fast structure allocator.  Designed for small objects that are
  43 // frequently allocated and deallocated.  This code is derived from the
  44 // 'alloc_struct' package used in WWT and Blizzard.  C++ provides a
  45 // much nicer framework for the same optimization.  The package is
  46 // implemented as a class, FastAlloc.  Allocation and deletion are
  47 // performed using FastAlloc's new and delete operators.  Any object
  48 // that derives from the FastAlloc class will transparently use this
  49 // allocation package.
  50
  51 // The static allocate() and deallocate() methods can also be called
  52 // directly if desired.
  53
  54 // In order for derived classes to call delete with the correct
  55 // structure size even when they are deallocated via a base-type
  56 // pointer, they must have a virtual destructor.  It is sufficient for
  57 // FastAlloc to declare a virtual destructor (as it does); it is not
  58 // required for derived classes to declare their own destructor.  The
  59 // compiler will automatically generate a virtual destructor for each
  60 // derived class.  However, it is more efficient if each derived class
  61 // defines an inline destructor, so that the compiler can statically
  62 // collapse the destructor call chain back up the inheritance
  63 // hierarchy.
  64
  65 // Uncomment this #define to track in-use objects
  66 // (for debugging memory leaks).
  67 //#define FAST_ALLOC_DEBUG
  68
  69 // Uncomment this #define to count news, deletes, and chunk allocations
  70 // (by bucket).
  71 // #define FAST_ALLOC_STATS
  72
  73 #include "config/no_fast_alloc.hh"
  74
  75 #if NO_FAST_ALLOC
  76
  77 class FastAlloc {
  78 };
  79
  80 #else
  81
  82 class FastAlloc {
  83   public:
  84
  85     static void *allocate(size_t);
  86     static void deallocate(void *, size_t);
  87
  88     void *operator new(size_t);
  89     void operator delete(void *, size_t);
  90
  91 #ifdef FAST_ALLOC_DEBUG
  92     FastAlloc();
  93     FastAlloc(FastAlloc*,FastAlloc*);   // for inUseHead, see below
  94     virtual ~FastAlloc();
  95 #else
  96     virtual ~FastAlloc() {}
  97 #endif
  98
  99   private:
 100
 101     // Max_Alloc_Size is the largest object that can be allocated with
 102     // this class.  There's no fundamental limit, but this limits the
 103     // size of the freeLists array.  Let's not make this really huge
 104     // like in Blizzard.
 105     static const int Max_Alloc_Size = 512;
 106
 107     // Alloc_Quantum is the difference in size between adjacent
 108     // buckets in the free list array.
 109     static const int Log2_Alloc_Quantum = 3;
 110     static const int Alloc_Quantum = (1 << Log2_Alloc_Quantum);
 111
 112     // Num_Buckets = bucketFor(Max_Alloc_Size) + 1
 113     static const int Num_Buckets =
 114         ((Max_Alloc_Size + Alloc_Quantum - 1) >> Log2_Alloc_Quantum) + 1;
 115
 116     // when we call new() for more structures, how many should we get?
 117     static const int Num_Structs_Per_New = 20;
 118
 119     static int bucketFor(size_t);
 120     static void *moreStructs(int bucket);
 121
 122     static void *freeLists[Num_Buckets];
 123
 124 #ifdef FAST_ALLOC_STATS
 125     static unsigned newCount[Num_Buckets];
 126     static unsigned deleteCount[Num_Buckets];
 127     static unsigned allocCount[Num_Buckets];
 128 #endif
 129
 130 #ifdef FAST_ALLOC_DEBUG
 131     // per-object debugging fields
 132     bool inUse;                 // in-use flag
 133     FastAlloc *inUsePrev;       // ptrs to build list of in-use objects
 134     FastAlloc *inUseNext;
 135
 136     // static (global) debugging vars
 137     static int numInUse;        // count in-use objects
 138     static FastAlloc inUseHead; // dummy head for list of in-use objects
 139
 140   public:
 141     // functions to dump debugging info (see fast_alloc.cc for C
 142     // versions that might be more agreeable to call from gdb)
 143     static void dump_summary();
 144     static void dump_oldest(int n);
 145 #endif
 146 };
 147
 148
 149 inline
 150 int FastAlloc::bucketFor(size_t sz)
 151 {
 152     return (sz + Alloc_Quantum - 1) >> Log2_Alloc_Quantum;
 153 }
 154
 155
 156 inline
 157 void *FastAlloc::allocate(size_t sz)
 158 {
 159     int b;
 160     void *p;
 161
 162     if (sz > Max_Alloc_Size)
 163         return (void *)::new char[sz];
 164
 165     b = bucketFor(sz);
 166     p = freeLists[b];
 167
 168     if (p)
 169         freeLists[b] = *(void **)p;
 170     else
 171         p = moreStructs(b);
 172
 173 #ifdef FAST_ALLOC_STATS
 174     ++newCount[b];
 175 #endif
 176
 177     return p;
 178 }
 179
 180
 181 inline
 182 void FastAlloc::deallocate(void *p, size_t sz)
 183 {
 184     int b;
 185
 186     if (sz > Max_Alloc_Size)
 187     {
 188         ::delete [] (char *)p;
 189         return;
 190     }
 191
 192     b = bucketFor(sz);
 193     *(void **)p = freeLists[b];
 194     freeLists[b] = p;
 195 #ifdef FAST_ALLOC_STATS
 196     ++deleteCount[b];
 197 #endif
 198 }
 199
 200
 201 inline
 202 void *FastAlloc::operator new(size_t sz)
 203 {
 204     return allocate(sz);
 205 }
 206
 207
 208 inline
 209 void FastAlloc::operator delete(void *p, size_t sz)
 210 {
 211     deallocate(p, sz);
 212 }
 213
 214 #endif // NO_FAST_ALLOC
 215
 216 #endif // __FAST_ALLOC_H__