1//===-- sanitizer_allocator_size_class_map.h --------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// Part of the Sanitizer Allocator.
11//
12//===----------------------------------------------------------------------===//
13#ifndef SANITIZER_ALLOCATOR_H
14#error This file must be included inside sanitizer_allocator.h
15#endif
16
17// SizeClassMap maps allocation sizes into size classes and back.
18// Class 0 always corresponds to size 0.
19// The other sizes are controlled by the template parameters:
20//   kMinSizeLog: defines the class 1    as 2^kMinSizeLog.
21//   kMaxSizeLog: defines the last class as 2^kMaxSizeLog.
22//   kMidSizeLog: the classes starting from 1 increase with step
23//                2^kMinSizeLog until 2^kMidSizeLog.
24//   kNumBits: the number of non-zero bits in sizes after 2^kMidSizeLog.
25//             E.g. with kNumBits==3 all size classes after 2^kMidSizeLog
26//             look like 0b1xx0..0, where x is either 0 or 1.
27//
28// Example: kNumBits=3, kMidSizeLog=4, kMidSizeLog=8, kMaxSizeLog=17:
29//
30// Classes 1 - 16 correspond to sizes 16 to 256 (size = class_id * 16).
31// Next 4 classes: 256 + i * 64  (i = 1 to 4).
32// Next 4 classes: 512 + i * 128 (i = 1 to 4).
33// ...
34// Next 4 classes: 2^k + i * 2^(k-2) (i = 1 to 4).
35// Last class corresponds to kMaxSize = 1 << kMaxSizeLog.
36//
37// This structure of the size class map gives us:
38//   - Efficient table-free class-to-size and size-to-class functions.
39//   - Difference between two consequent size classes is between 14% and 25%
40//
41// This class also gives a hint to a thread-caching allocator about the amount
42// of chunks that need to be cached per-thread:
43//  - kMaxNumCachedHint is a hint for maximal number of chunks per size class.
44//    The actual number is computed in TransferBatch.
45//  - (1 << kMaxBytesCachedLog) is the maximal number of bytes per size class.
46//
47// Part of output of SizeClassMap::Print():
48// c00 => s: 0 diff: +0 00% l 0 cached: 0 0; id 0
49// c01 => s: 16 diff: +16 00% l 4 cached: 256 4096; id 1
50// c02 => s: 32 diff: +16 100% l 5 cached: 256 8192; id 2
51// c03 => s: 48 diff: +16 50% l 5 cached: 256 12288; id 3
52// c04 => s: 64 diff: +16 33% l 6 cached: 256 16384; id 4
53// c05 => s: 80 diff: +16 25% l 6 cached: 256 20480; id 5
54// c06 => s: 96 diff: +16 20% l 6 cached: 256 24576; id 6
55// c07 => s: 112 diff: +16 16% l 6 cached: 256 28672; id 7
56//
57// c08 => s: 128 diff: +16 14% l 7 cached: 256 32768; id 8
58// c09 => s: 144 diff: +16 12% l 7 cached: 256 36864; id 9
59// c10 => s: 160 diff: +16 11% l 7 cached: 256 40960; id 10
60// c11 => s: 176 diff: +16 10% l 7 cached: 256 45056; id 11
61// c12 => s: 192 diff: +16 09% l 7 cached: 256 49152; id 12
62// c13 => s: 208 diff: +16 08% l 7 cached: 256 53248; id 13
63// c14 => s: 224 diff: +16 07% l 7 cached: 256 57344; id 14
64// c15 => s: 240 diff: +16 07% l 7 cached: 256 61440; id 15
65//
66// c16 => s: 256 diff: +16 06% l 8 cached: 256 65536; id 16
67// c17 => s: 320 diff: +64 25% l 8 cached: 204 65280; id 17
68// c18 => s: 384 diff: +64 20% l 8 cached: 170 65280; id 18
69// c19 => s: 448 diff: +64 16% l 8 cached: 146 65408; id 19
70//
71// c20 => s: 512 diff: +64 14% l 9 cached: 128 65536; id 20
72// c21 => s: 640 diff: +128 25% l 9 cached: 102 65280; id 21
73// c22 => s: 768 diff: +128 20% l 9 cached: 85 65280; id 22
74// c23 => s: 896 diff: +128 16% l 9 cached: 73 65408; id 23
75//
76// c24 => s: 1024 diff: +128 14% l 10 cached: 64 65536; id 24
77// c25 => s: 1280 diff: +256 25% l 10 cached: 51 65280; id 25
78// c26 => s: 1536 diff: +256 20% l 10 cached: 42 64512; id 26
79// c27 => s: 1792 diff: +256 16% l 10 cached: 36 64512; id 27
80//
81// ...
82//
83// c48 => s: 65536 diff: +8192 14% l 16 cached: 1 65536; id 48
84// c49 => s: 81920 diff: +16384 25% l 16 cached: 1 81920; id 49
85// c50 => s: 98304 diff: +16384 20% l 16 cached: 1 98304; id 50
86// c51 => s: 114688 diff: +16384 16% l 16 cached: 1 114688; id 51
87//
88// c52 => s: 131072 diff: +16384 14% l 17 cached: 1 131072; id 52
89//
90//
91// Another example (kNumBits=2):
92// c00 => s: 0 diff: +0 00% l 0 cached: 0 0; id 0
93// c01 => s: 32 diff: +32 00% l 5 cached: 64 2048; id 1
94// c02 => s: 64 diff: +32 100% l 6 cached: 64 4096; id 2
95// c03 => s: 96 diff: +32 50% l 6 cached: 64 6144; id 3
96// c04 => s: 128 diff: +32 33% l 7 cached: 64 8192; id 4
97// c05 => s: 160 diff: +32 25% l 7 cached: 64 10240; id 5
98// c06 => s: 192 diff: +32 20% l 7 cached: 64 12288; id 6
99// c07 => s: 224 diff: +32 16% l 7 cached: 64 14336; id 7
100// c08 => s: 256 diff: +32 14% l 8 cached: 64 16384; id 8
101// c09 => s: 384 diff: +128 50% l 8 cached: 42 16128; id 9
102// c10 => s: 512 diff: +128 33% l 9 cached: 32 16384; id 10
103// c11 => s: 768 diff: +256 50% l 9 cached: 21 16128; id 11
104// c12 => s: 1024 diff: +256 33% l 10 cached: 16 16384; id 12
105// c13 => s: 1536 diff: +512 50% l 10 cached: 10 15360; id 13
106// c14 => s: 2048 diff: +512 33% l 11 cached: 8 16384; id 14
107// c15 => s: 3072 diff: +1024 50% l 11 cached: 5 15360; id 15
108// c16 => s: 4096 diff: +1024 33% l 12 cached: 4 16384; id 16
109// c17 => s: 6144 diff: +2048 50% l 12 cached: 2 12288; id 17
110// c18 => s: 8192 diff: +2048 33% l 13 cached: 2 16384; id 18
111// c19 => s: 12288 diff: +4096 50% l 13 cached: 1 12288; id 19
112// c20 => s: 16384 diff: +4096 33% l 14 cached: 1 16384; id 20
113// c21 => s: 24576 diff: +8192 50% l 14 cached: 1 24576; id 21
114// c22 => s: 32768 diff: +8192 33% l 15 cached: 1 32768; id 22
115// c23 => s: 49152 diff: +16384 50% l 15 cached: 1 49152; id 23
116// c24 => s: 65536 diff: +16384 33% l 16 cached: 1 65536; id 24
117// c25 => s: 98304 diff: +32768 50% l 16 cached: 1 98304; id 25
118// c26 => s: 131072 diff: +32768 33% l 17 cached: 1 131072; id 26
119
120template <uptr kNumBits, uptr kMinSizeLog, uptr kMidSizeLog, uptr kMaxSizeLog,
121          uptr kMaxNumCachedHintT, uptr kMaxBytesCachedLog>
122class SizeClassMap {
123  static const uptr kMinSize = 1 << kMinSizeLog;
124  static const uptr kMidSize = 1 << kMidSizeLog;
125  static const uptr kMidClass = kMidSize / kMinSize;
126  static const uptr S = kNumBits - 1;
127  static const uptr M = (1 << S) - 1;
128
129 public:
130  // kMaxNumCachedHintT is a power of two. It serves as a hint
131  // for the size of TransferBatch, the actual size could be a bit smaller.
132  static const uptr kMaxNumCachedHint = kMaxNumCachedHintT;
133  COMPILER_CHECK((kMaxNumCachedHint & (kMaxNumCachedHint - 1)) == 0);
134
135  static const uptr kMaxSize = 1UL << kMaxSizeLog;
136  static const uptr kNumClasses =
137      kMidClass + ((kMaxSizeLog - kMidSizeLog) << S) + 1 + 1;
138  static const uptr kLargestClassID = kNumClasses - 2;
139  static const uptr kBatchClassID = kNumClasses - 1;
140  COMPILER_CHECK(kNumClasses >= 16 && kNumClasses <= 256);
141  static const uptr kNumClassesRounded =
142      kNumClasses <= 32  ? 32 :
143      kNumClasses <= 64  ? 64 :
144      kNumClasses <= 128 ? 128 : 256;
145
146  static uptr Size(uptr class_id) {
147    // Estimate the result for kBatchClassID because this class does not know
148    // the exact size of TransferBatch. It's OK since we are using the actual
149    // sizeof(TransferBatch) where it matters.
150    if (UNLIKELY(class_id == kBatchClassID))
151      return kMaxNumCachedHint * sizeof(uptr);
152    if (class_id <= kMidClass)
153      return kMinSize * class_id;
154    class_id -= kMidClass;
155    uptr t = kMidSize << (class_id >> S);
156    return t + (t >> S) * (class_id & M);
157  }
158
159  static uptr ClassID(uptr size) {
160    if (UNLIKELY(size > kMaxSize))
161      return 0;
162    if (size <= kMidSize)
163      return (size + kMinSize - 1) >> kMinSizeLog;
164    const uptr l = MostSignificantSetBitIndex(size);
165    const uptr hbits = (size >> (l - S)) & M;
166    const uptr lbits = size & ((1U << (l - S)) - 1);
167    const uptr l1 = l - kMidSizeLog;
168    return kMidClass + (l1 << S) + hbits + (lbits > 0);
169  }
170
171  static uptr MaxCachedHint(uptr size) {
172    DCHECK_LE(size, kMaxSize);
173    if (UNLIKELY(size == 0))
174      return 0;
175    uptr n;
176    // Force a 32-bit division if the template parameters allow for it.
177    if (kMaxBytesCachedLog > 31 || kMaxSizeLog > 31)
178      n = (1UL << kMaxBytesCachedLog) / size;
179    else
180      n = (1U << kMaxBytesCachedLog) / static_cast<u32>(size);
181    return Max<uptr>(1U, Min(kMaxNumCachedHint, n));
182  }
183
184  static void Print() {
185    uptr prev_s = 0;
186    uptr total_cached = 0;
187    for (uptr i = 0; i < kNumClasses; i++) {
188      uptr s = Size(i);
189      if (s >= kMidSize / 2 && (s & (s - 1)) == 0)
190        Printf("\n");
191      uptr d = s - prev_s;
192      uptr p = prev_s ? (d * 100 / prev_s) : 0;
193      uptr l = s ? MostSignificantSetBitIndex(s) : 0;
194      uptr cached = MaxCachedHint(s) * s;
195      if (i == kBatchClassID)
196        d = p = l = 0;
197      Printf("c%02zd => s: %zd diff: +%zd %02zd%% l %zd "
198             "cached: %zd %zd; id %zd\n",
199             i, Size(i), d, p, l, MaxCachedHint(s), cached, ClassID(s));
200      total_cached += cached;
201      prev_s = s;
202    }
203    Printf("Total cached: %zd\n", total_cached);
204  }
205
206  static void Validate() {
207    for (uptr c = 1; c < kNumClasses; c++) {
208      // Printf("Validate: c%zd\n", c);
209      uptr s = Size(c);
210      CHECK_NE(s, 0U);
211      if (c == kBatchClassID)
212        continue;
213      CHECK_EQ(ClassID(s), c);
214      if (c < kLargestClassID)
215        CHECK_EQ(ClassID(s + 1), c + 1);
216      CHECK_EQ(ClassID(s - 1), c);
217      CHECK_GT(Size(c), Size(c - 1));
218    }
219    CHECK_EQ(ClassID(kMaxSize + 1), 0);
220
221    for (uptr s = 1; s <= kMaxSize; s++) {
222      uptr c = ClassID(s);
223      // Printf("s%zd => c%zd\n", s, c);
224      CHECK_LT(c, kNumClasses);
225      CHECK_GE(Size(c), s);
226      if (c > 0)
227        CHECK_LT(Size(c - 1), s);
228    }
229  }
230};
231
232typedef SizeClassMap<3, 4, 8, 17, 128, 16> DefaultSizeClassMap;
233typedef SizeClassMap<3, 4, 8, 17, 64, 14> CompactSizeClassMap;
234typedef SizeClassMap<2, 5, 9, 16, 64, 14> VeryCompactSizeClassMap;
235
236// The following SizeClassMap only holds a way small number of cached entries,
237// allowing for denser per-class arrays, smaller memory footprint and usually
238// better performances in threaded environments.
239typedef SizeClassMap<3, 4, 8, 17, 8, 10> DenseSizeClassMap;
240// Similar to VeryCompact map above, this one has a small number of different
241// size classes, and also reduced thread-local caches.
242typedef SizeClassMap<2, 5, 9, 16, 8, 10> VeryDenseSizeClassMap;
243