1 //===-- sanitizer_allocator_size_class_map.h --------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Part of the Sanitizer Allocator.
10 //
11 //===----------------------------------------------------------------------===//
12 #ifndef SANITIZER_ALLOCATOR_H
13 #error This file must be included inside sanitizer_allocator.h
14 #endif
15 
16 // SizeClassMap maps allocation sizes into size classes and back.
17 // Class 0 always corresponds to size 0.
18 // The other sizes are controlled by the template parameters:
19 //   kMinSizeLog: defines the class 1    as 2^kMinSizeLog.
20 //   kMaxSizeLog: defines the last class as 2^kMaxSizeLog.
21 //   kMidSizeLog: the classes starting from 1 increase with step
22 //                2^kMinSizeLog until 2^kMidSizeLog.
23 //   kNumBits: the number of non-zero bits in sizes after 2^kMidSizeLog.
24 //             E.g. with kNumBits==3 all size classes after 2^kMidSizeLog
25 //             look like 0b1xx0..0, where x is either 0 or 1.
26 //
27 // Example: kNumBits=3, kMidSizeLog=4, kMidSizeLog=8, kMaxSizeLog=17:
28 //
29 // Classes 1 - 16 correspond to sizes 16 to 256 (size = class_id * 16).
30 // Next 4 classes: 256 + i * 64  (i = 1 to 4).
31 // Next 4 classes: 512 + i * 128 (i = 1 to 4).
32 // ...
33 // Next 4 classes: 2^k + i * 2^(k-2) (i = 1 to 4).
34 // Last class corresponds to kMaxSize = 1 << kMaxSizeLog.
35 //
36 // This structure of the size class map gives us:
37 //   - Efficient table-free class-to-size and size-to-class functions.
38 //   - Difference between two consequent size classes is between 14% and 25%
39 //
40 // This class also gives a hint to a thread-caching allocator about the amount
41 // of chunks that need to be cached per-thread:
42 //  - kMaxNumCachedHint is a hint for maximal number of chunks per size class.
43 //    The actual number is computed in TransferBatch.
44 //  - (1 << kMaxBytesCachedLog) is the maximal number of bytes per size class.
45 //
46 // Part of output of SizeClassMap::Print():
47 // c00 => s: 0 diff: +0 00% l 0 cached: 0 0; id 0
48 // c01 => s: 16 diff: +16 00% l 4 cached: 256 4096; id 1
49 // c02 => s: 32 diff: +16 100% l 5 cached: 256 8192; id 2
50 // c03 => s: 48 diff: +16 50% l 5 cached: 256 12288; id 3
51 // c04 => s: 64 diff: +16 33% l 6 cached: 256 16384; id 4
52 // c05 => s: 80 diff: +16 25% l 6 cached: 256 20480; id 5
53 // c06 => s: 96 diff: +16 20% l 6 cached: 256 24576; id 6
54 // c07 => s: 112 diff: +16 16% l 6 cached: 256 28672; id 7
55 //
56 // c08 => s: 128 diff: +16 14% l 7 cached: 256 32768; id 8
57 // c09 => s: 144 diff: +16 12% l 7 cached: 256 36864; id 9
58 // c10 => s: 160 diff: +16 11% l 7 cached: 256 40960; id 10
59 // c11 => s: 176 diff: +16 10% l 7 cached: 256 45056; id 11
60 // c12 => s: 192 diff: +16 09% l 7 cached: 256 49152; id 12
61 // c13 => s: 208 diff: +16 08% l 7 cached: 256 53248; id 13
62 // c14 => s: 224 diff: +16 07% l 7 cached: 256 57344; id 14
63 // c15 => s: 240 diff: +16 07% l 7 cached: 256 61440; id 15
64 //
65 // c16 => s: 256 diff: +16 06% l 8 cached: 256 65536; id 16
66 // c17 => s: 320 diff: +64 25% l 8 cached: 204 65280; id 17
67 // c18 => s: 384 diff: +64 20% l 8 cached: 170 65280; id 18
68 // c19 => s: 448 diff: +64 16% l 8 cached: 146 65408; id 19
69 //
70 // c20 => s: 512 diff: +64 14% l 9 cached: 128 65536; id 20
71 // c21 => s: 640 diff: +128 25% l 9 cached: 102 65280; id 21
72 // c22 => s: 768 diff: +128 20% l 9 cached: 85 65280; id 22
73 // c23 => s: 896 diff: +128 16% l 9 cached: 73 65408; id 23
74 //
75 // c24 => s: 1024 diff: +128 14% l 10 cached: 64 65536; id 24
76 // c25 => s: 1280 diff: +256 25% l 10 cached: 51 65280; id 25
77 // c26 => s: 1536 diff: +256 20% l 10 cached: 42 64512; id 26
78 // c27 => s: 1792 diff: +256 16% l 10 cached: 36 64512; id 27
79 //
80 // ...
81 //
82 // c48 => s: 65536 diff: +8192 14% l 16 cached: 1 65536; id 48
83 // c49 => s: 81920 diff: +16384 25% l 16 cached: 1 81920; id 49
84 // c50 => s: 98304 diff: +16384 20% l 16 cached: 1 98304; id 50
85 // c51 => s: 114688 diff: +16384 16% l 16 cached: 1 114688; id 51
86 //
87 // c52 => s: 131072 diff: +16384 14% l 17 cached: 1 131072; id 52
88 //
89 //
90 // Another example (kNumBits=2):
91 // c00 => s: 0 diff: +0 00% l 0 cached: 0 0; id 0
92 // c01 => s: 32 diff: +32 00% l 5 cached: 64 2048; id 1
93 // c02 => s: 64 diff: +32 100% l 6 cached: 64 4096; id 2
94 // c03 => s: 96 diff: +32 50% l 6 cached: 64 6144; id 3
95 // c04 => s: 128 diff: +32 33% l 7 cached: 64 8192; id 4
96 // c05 => s: 160 diff: +32 25% l 7 cached: 64 10240; id 5
97 // c06 => s: 192 diff: +32 20% l 7 cached: 64 12288; id 6
98 // c07 => s: 224 diff: +32 16% l 7 cached: 64 14336; id 7
99 // c08 => s: 256 diff: +32 14% l 8 cached: 64 16384; id 8
100 // c09 => s: 384 diff: +128 50% l 8 cached: 42 16128; id 9
101 // c10 => s: 512 diff: +128 33% l 9 cached: 32 16384; id 10
102 // c11 => s: 768 diff: +256 50% l 9 cached: 21 16128; id 11
103 // c12 => s: 1024 diff: +256 33% l 10 cached: 16 16384; id 12
104 // c13 => s: 1536 diff: +512 50% l 10 cached: 10 15360; id 13
105 // c14 => s: 2048 diff: +512 33% l 11 cached: 8 16384; id 14
106 // c15 => s: 3072 diff: +1024 50% l 11 cached: 5 15360; id 15
107 // c16 => s: 4096 diff: +1024 33% l 12 cached: 4 16384; id 16
108 // c17 => s: 6144 diff: +2048 50% l 12 cached: 2 12288; id 17
109 // c18 => s: 8192 diff: +2048 33% l 13 cached: 2 16384; id 18
110 // c19 => s: 12288 diff: +4096 50% l 13 cached: 1 12288; id 19
111 // c20 => s: 16384 diff: +4096 33% l 14 cached: 1 16384; id 20
112 // c21 => s: 24576 diff: +8192 50% l 14 cached: 1 24576; id 21
113 // c22 => s: 32768 diff: +8192 33% l 15 cached: 1 32768; id 22
114 // c23 => s: 49152 diff: +16384 50% l 15 cached: 1 49152; id 23
115 // c24 => s: 65536 diff: +16384 33% l 16 cached: 1 65536; id 24
116 // c25 => s: 98304 diff: +32768 50% l 16 cached: 1 98304; id 25
117 // c26 => s: 131072 diff: +32768 33% l 17 cached: 1 131072; id 26
118 
119 template <uptr kNumBits, uptr kMinSizeLog, uptr kMidSizeLog, uptr kMaxSizeLog,
120           uptr kMaxNumCachedHintT, uptr kMaxBytesCachedLog>
121 class SizeClassMap {
122   static const uptr kMinSize = 1 << kMinSizeLog;
123   static const uptr kMidSize = 1 << kMidSizeLog;
124   static const uptr kMidClass = kMidSize / kMinSize;
125   static const uptr S = kNumBits - 1;
126   static const uptr M = (1 << S) - 1;
127 
128  public:
129   // kMaxNumCachedHintT is a power of two. It serves as a hint
130   // for the size of TransferBatch, the actual size could be a bit smaller.
131   static const uptr kMaxNumCachedHint = kMaxNumCachedHintT;
132   COMPILER_CHECK((kMaxNumCachedHint & (kMaxNumCachedHint - 1)) == 0);
133 
134   static const uptr kMaxSize = 1UL << kMaxSizeLog;
135   static const uptr kNumClasses =
136       kMidClass + ((kMaxSizeLog - kMidSizeLog) << S) + 1 + 1;
137   static const uptr kLargestClassID = kNumClasses - 2;
138   static const uptr kBatchClassID = kNumClasses - 1;
139   COMPILER_CHECK(kNumClasses >= 16 && kNumClasses <= 256);
140   static const uptr kNumClassesRounded =
141       kNumClasses <= 32  ? 32 :
142       kNumClasses <= 64  ? 64 :
143       kNumClasses <= 128 ? 128 : 256;
144 
Size(uptr class_id)145   static uptr Size(uptr class_id) {
146     // Estimate the result for kBatchClassID because this class does not know
147     // the exact size of TransferBatch. It's OK since we are using the actual
148     // sizeof(TransferBatch) where it matters.
149     if (UNLIKELY(class_id == kBatchClassID))
150       return kMaxNumCachedHint * sizeof(uptr);
151     if (class_id <= kMidClass)
152       return kMinSize * class_id;
153     class_id -= kMidClass;
154     uptr t = kMidSize << (class_id >> S);
155     return t + (t >> S) * (class_id & M);
156   }
157 
ClassID(uptr size)158   static uptr ClassID(uptr size) {
159     if (UNLIKELY(size > kMaxSize))
160       return 0;
161     if (size <= kMidSize)
162       return (size + kMinSize - 1) >> kMinSizeLog;
163     const uptr l = MostSignificantSetBitIndex(size);
164     const uptr hbits = (size >> (l - S)) & M;
165     const uptr lbits = size & ((1U << (l - S)) - 1);
166     const uptr l1 = l - kMidSizeLog;
167     return kMidClass + (l1 << S) + hbits + (lbits > 0);
168   }
169 
MaxCachedHint(uptr size)170   static uptr MaxCachedHint(uptr size) {
171     DCHECK_LE(size, kMaxSize);
172     if (UNLIKELY(size == 0))
173       return 0;
174     uptr n;
175     // Force a 32-bit division if the template parameters allow for it.
176     if (kMaxBytesCachedLog > 31 || kMaxSizeLog > 31)
177       n = (1UL << kMaxBytesCachedLog) / size;
178     else
179       n = (1U << kMaxBytesCachedLog) / static_cast<u32>(size);
180     return Max<uptr>(1U, Min(kMaxNumCachedHint, n));
181   }
182 
Print()183   static void Print() {
184     uptr prev_s = 0;
185     uptr total_cached = 0;
186     for (uptr i = 0; i < kNumClasses; i++) {
187       uptr s = Size(i);
188       if (s >= kMidSize / 2 && (s & (s - 1)) == 0)
189         Printf("\n");
190       uptr d = s - prev_s;
191       uptr p = prev_s ? (d * 100 / prev_s) : 0;
192       uptr l = s ? MostSignificantSetBitIndex(s) : 0;
193       uptr cached = MaxCachedHint(s) * s;
194       if (i == kBatchClassID)
195         d = p = l = 0;
196       Printf("c%02zd => s: %zd diff: +%zd %02zd%% l %zd "
197              "cached: %zd %zd; id %zd\n",
198              i, Size(i), d, p, l, MaxCachedHint(s), cached, ClassID(s));
199       total_cached += cached;
200       prev_s = s;
201     }
202     Printf("Total cached: %zd\n", total_cached);
203   }
204 
Validate()205   static void Validate() {
206     for (uptr c = 1; c < kNumClasses; c++) {
207       // Printf("Validate: c%zd\n", c);
208       uptr s = Size(c);
209       CHECK_NE(s, 0U);
210       if (c == kBatchClassID)
211         continue;
212       CHECK_EQ(ClassID(s), c);
213       if (c < kLargestClassID)
214         CHECK_EQ(ClassID(s + 1), c + 1);
215       CHECK_EQ(ClassID(s - 1), c);
216       CHECK_GT(Size(c), Size(c - 1));
217     }
218     CHECK_EQ(ClassID(kMaxSize + 1), 0);
219 
220     for (uptr s = 1; s <= kMaxSize; s++) {
221       uptr c = ClassID(s);
222       // Printf("s%zd => c%zd\n", s, c);
223       CHECK_LT(c, kNumClasses);
224       CHECK_GE(Size(c), s);
225       if (c > 0)
226         CHECK_LT(Size(c - 1), s);
227     }
228   }
229 };
230 
231 typedef SizeClassMap<3, 4, 8, 17, 128, 16> DefaultSizeClassMap;
232 typedef SizeClassMap<3, 4, 8, 17, 64, 14> CompactSizeClassMap;
233 typedef SizeClassMap<2, 5, 9, 16, 64, 14> VeryCompactSizeClassMap;
234 
235 // The following SizeClassMap only holds a way small number of cached entries,
236 // allowing for denser per-class arrays, smaller memory footprint and usually
237 // better performances in threaded environments.
238 typedef SizeClassMap<3, 4, 8, 17, 8, 10> DenseSizeClassMap;
239 // Similar to VeryCompact map above, this one has a small number of different
240 // size classes, and also reduced thread-local caches.
241 typedef SizeClassMap<2, 5, 9, 16, 8, 10> VeryDenseSizeClassMap;
242