1 /* 2 * Copyright (C) 2013 Google Inc. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: 7 * 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above 11 * copyright notice, this list of conditions and the following disclaimer 12 * in the documentation and/or other materials provided with the 13 * distribution. 14 * * Neither the name of Google Inc. nor the names of its 15 * contributors may be used to endorse or promote products derived from 16 * this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #ifndef WTF_QuantizedAllocation_h 32 #define WTF_QuantizedAllocation_h 33 34 // DESCRIPTION 35 // QuantizedAllocation::quantizedSize() rounds up the specific size such that: 36 // 1) Granularity of allocation sizes is >1, and grows as a fraction of the 37 // allocation size. This property can be used to limit bucket fragmentation 38 // when sitting on top of a high-granularity allocator such as PartitionAlloc. 39 // 2) The sizes are likely (but not guaranteed) to correspond to exact "bucket 40 // sizes" of any underlying allocator that implements standard bucketing. 41 // This currently includes tcmalloc, Windows LFH and PartitionAlloc. 42 43 #include "wtf/WTFExport.h" 44 #include <limits.h> 45 46 namespace WTF { 47 48 class WTF_EXPORT QuantizedAllocation { 49 public: 50 // Allocations above 32k are rounded to 4k (which is typically the system 51 // page size). 52 static const size_t kMaxAllocation = 32768; 53 static const size_t kMaxRounding = 4096; 54 55 // This is the minimum granularity of allocation, currently 8 bytes. 56 static const size_t kMinRounding = 8; 57 58 // After 128 bytes, the granularity doubles, and proceeds to double again 59 // as the allocation size further doubles. 60 static const size_t kMinRoundingLimit = 128; 61 static const size_t kTableSize = kMaxAllocation / kMinRoundingLimit; 62 63 // Using "unsigned" is not a limitation because Chromium's max malloc() is 64 // 2GB even on 64-bit. 65 static const size_t kMaxUnquantizedAllocation = INT_MAX - kMaxRounding; 66 67 static void init(); 68 69 static size_t quantizedSize(size_t size) 70 { 71 size_t roundToLessOne; 72 if (UNLIKELY(size >= kMaxAllocation)) 73 roundToLessOne = kMaxRounding - 1; 74 else 75 roundToLessOne = table[size / kMinRoundingLimit]; 76 return (size + roundToLessOne) & ~roundToLessOne; 77 } 78 79 private: 80 static unsigned short table[kTableSize]; 81 }; 82 83 } // namespace WTF 84 85 #endif // WTF_QuantizedAllocation_h 86
