1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
|
// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import (
"runtime/internal/sys"
)
// pageBits is a bitmap representing one bit per page in a palloc chunk.
type pageBits [pallocChunkPages / 64]uint64
// get returns the value of the i'th bit in the bitmap.
func (b *pageBits) get(i uint) uint {
return uint((b[i/64] >> (i % 64)) & 1)
}
// block64 returns the 64-bit aligned block of bits containing the i'th bit.
func (b *pageBits) block64(i uint) uint64 {
return b[i/64]
}
// set sets bit i of pageBits.
func (b *pageBits) set(i uint) {
b[i/64] |= 1 << (i % 64)
}
// setRange sets bits in the range [i, i+n).
func (b *pageBits) setRange(i, n uint) {
_ = b[i/64]
if n == 1 {
// Fast path for the n == 1 case.
b.set(i)
return
}
// Set bits [i, j].
j := i + n - 1
if i/64 == j/64 {
b[i/64] |= ((uint64(1) << n) - 1) << (i % 64)
return
}
_ = b[j/64]
// Set leading bits.
b[i/64] |= ^uint64(0) << (i % 64)
for k := i/64 + 1; k < j/64; k++ {
b[k] = ^uint64(0)
}
// Set trailing bits.
b[j/64] |= (uint64(1) << (j%64 + 1)) - 1
}
// setAll sets all the bits of b.
func (b *pageBits) setAll() {
for i := range b {
b[i] = ^uint64(0)
}
}
// clear clears bit i of pageBits.
func (b *pageBits) clear(i uint) {
b[i/64] &^= 1 << (i % 64)
}
// clearRange clears bits in the range [i, i+n).
func (b *pageBits) clearRange(i, n uint) {
_ = b[i/64]
if n == 1 {
// Fast path for the n == 1 case.
b.clear(i)
return
}
// Clear bits [i, j].
j := i + n - 1
if i/64 == j/64 {
b[i/64] &^= ((uint64(1) << n) - 1) << (i % 64)
return
}
_ = b[j/64]
// Clear leading bits.
b[i/64] &^= ^uint64(0) << (i % 64)
for k := i/64 + 1; k < j/64; k++ {
b[k] = 0
}
// Clear trailing bits.
b[j/64] &^= (uint64(1) << (j%64 + 1)) - 1
}
// clearAll frees all the bits of b.
func (b *pageBits) clearAll() {
for i := range b {
b[i] = 0
}
}
// popcntRange counts the number of set bits in the
// range [i, i+n).
func (b *pageBits) popcntRange(i, n uint) (s uint) {
if n == 1 {
return uint((b[i/64] >> (i % 64)) & 1)
}
_ = b[i/64]
j := i + n - 1
if i/64 == j/64 {
return uint(sys.OnesCount64((b[i/64] >> (i % 64)) & ((1 << n) - 1)))
}
_ = b[j/64]
s += uint(sys.OnesCount64(b[i/64] >> (i % 64)))
for k := i/64 + 1; k < j/64; k++ {
s += uint(sys.OnesCount64(b[k]))
}
s += uint(sys.OnesCount64(b[j/64] & ((1 << (j%64 + 1)) - 1)))
return
}
// pallocBits is a bitmap that tracks page allocations for at most one
// palloc chunk.
//
// The precise representation is an implementation detail, but for the
// sake of documentation, 0s are free pages and 1s are allocated pages.
type pallocBits pageBits
// consec8tab is a table containing the number of consecutive
// zero bits for any uint8 value.
//
// The table is generated by calling consec8(i) for each
// possible uint8 value, which is defined as:
//
// // consec8 counts the maximum number of consecutive 0 bits
// // in a uint8.
// func consec8(n uint8) int {
// n = ^n
// i := 0
// for n != 0 {
// n &= (n << 1)
// i++
// }
// return i
// }
var consec8tab = [256]uint{
8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
5, 4, 3, 3, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2,
4, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2,
6, 5, 4, 4, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
4, 3, 2, 2, 2, 1, 1, 1, 3, 2, 1, 1, 2, 1, 1, 1,
5, 4, 3, 3, 2, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 1,
4, 3, 2, 2, 2, 1, 1, 1, 3, 2, 1, 1, 2, 1, 1, 1,
7, 6, 5, 5, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 3, 3,
4, 3, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2,
5, 4, 3, 3, 2, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 1,
4, 3, 2, 2, 2, 1, 1, 1, 3, 2, 1, 1, 2, 1, 1, 1,
6, 5, 4, 4, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
4, 3, 2, 2, 2, 1, 1, 1, 3, 2, 1, 1, 2, 1, 1, 1,
5, 4, 3, 3, 2, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 1,
4, 3, 2, 2, 2, 1, 1, 1, 3, 2, 1, 1, 2, 1, 1, 0,
}
// summarize returns a packed summary of the bitmap in pallocBits.
func (b *pallocBits) summarize() pallocSum {
// TODO(mknyszek): There may be something more clever to be done
// here to make the summarize operation more efficient. For example,
// we can compute start and end with 64-bit wide operations easily,
// but max is a bit more complex. Perhaps there exists some way to
// leverage the 64-bit start and end to our advantage?
var start, max, end uint
for i := 0; i < len(b); i++ {
a := b[i]
for j := 0; j < 64; j += 8 {
k := uint8(a >> j)
// Compute start.
si := uint(sys.TrailingZeros8(k))
if start == uint(i*64+j) {
start += si
}
// Compute max.
if end+si > max {
max = end + si
}
if mi := consec8tab[k]; mi > max {
max = mi
}
// Compute end.
if k == 0 {
end += 8
} else {
end = uint(sys.LeadingZeros8(k))
}
}
}
return packPallocSum(start, max, end)
}
// find searches for npages contiguous free pages in pallocBits and returns
// the index where that run starts, as well as the index of the first free page
// it found in the search. searchIdx represents the first known free page and
// where to begin the search from.
//
// If find fails to find any free space, it returns an index of ^uint(0) and
// the new searchIdx should be ignored.
//
// Note that if npages == 1, the two returned values will always be identical.
func (b *pallocBits) find(npages uintptr, searchIdx uint) (uint, uint) {
if npages == 1 {
addr := b.find1(searchIdx)
return addr, addr
} else if npages <= 64 {
return b.findSmallN(npages, searchIdx)
}
return b.findLargeN(npages, searchIdx)
}
// find1 is a helper for find which searches for a single free page
// in the pallocBits and returns the index.
//
// See find for an explanation of the searchIdx parameter.
func (b *pallocBits) find1(searchIdx uint) uint {
for i := searchIdx / 64; i < uint(len(b)); i++ {
x := b[i]
if x == ^uint64(0) {
continue
}
return i*64 + uint(sys.TrailingZeros64(^x))
}
return ^uint(0)
}
// findSmallN is a helper for find which searches for npages contiguous free pages
// in this pallocBits and returns the index where that run of contiguous pages
// starts as well as the index of the first free page it finds in its search.
//
// See find for an explanation of the searchIdx parameter.
//
// Returns a ^uint(0) index on failure and the new searchIdx should be ignored.
//
// findSmallN assumes npages <= 64, where any such contiguous run of pages
// crosses at most one aligned 64-bit boundary in the bits.
func (b *pallocBits) findSmallN(npages uintptr, searchIdx uint) (uint, uint) {
end, newSearchIdx := uint(0), ^uint(0)
for i := searchIdx / 64; i < uint(len(b)); i++ {
bi := b[i]
if bi == ^uint64(0) {
end = 0
continue
}
// First see if we can pack our allocation in the trailing
// zeros plus the end of the last 64 bits.
start := uint(sys.TrailingZeros64(bi))
if newSearchIdx == ^uint(0) {
// The new searchIdx is going to be at these 64 bits after any
// 1s we file, so count trailing 1s.
newSearchIdx = i*64 + uint(sys.TrailingZeros64(^bi))
}
if end+start >= uint(npages) {
return i*64 - end, newSearchIdx
}
// Next, check the interior of the 64-bit chunk.
j := findBitRange64(^bi, uint(npages))
if j < 64 {
return i*64 + j, newSearchIdx
}
end = uint(sys.LeadingZeros64(bi))
}
return ^uint(0), newSearchIdx
}
// findLargeN is a helper for find which searches for npages contiguous free pages
// in this pallocBits and returns the index where that run starts, as well as the
// index of the first free page it found it its search.
//
// See alloc for an explanation of the searchIdx parameter.
//
// Returns a ^uint(0) index on failure and the new searchIdx should be ignored.
//
// findLargeN assumes npages > 64, where any such run of free pages
// crosses at least one aligned 64-bit boundary in the bits.
func (b *pallocBits) findLargeN(npages uintptr, searchIdx uint) (uint, uint) {
start, size, newSearchIdx := ^uint(0), uint(0), ^uint(0)
for i := searchIdx / 64; i < uint(len(b)); i++ {
x := b[i]
if x == ^uint64(0) {
size = 0
continue
}
if newSearchIdx == ^uint(0) {
// The new searchIdx is going to be at these 64 bits after any
// 1s we file, so count trailing 1s.
newSearchIdx = i*64 + uint(sys.TrailingZeros64(^x))
}
if size == 0 {
size = uint(sys.LeadingZeros64(x))
start = i*64 + 64 - size
continue
}
s := uint(sys.TrailingZeros64(x))
if s+size >= uint(npages) {
size += s
return start, newSearchIdx
}
if s < 64 {
size = uint(sys.LeadingZeros64(x))
start = i*64 + 64 - size
continue
}
size += 64
}
if size < uint(npages) {
return ^uint(0), newSearchIdx
}
return start, newSearchIdx
}
// allocRange allocates the range [i, i+n).
func (b *pallocBits) allocRange(i, n uint) {
(*pageBits)(b).setRange(i, n)
}
// allocAll allocates all the bits of b.
func (b *pallocBits) allocAll() {
(*pageBits)(b).setAll()
}
// free1 frees a single page in the pallocBits at i.
func (b *pallocBits) free1(i uint) {
(*pageBits)(b).clear(i)
}
// free frees the range [i, i+n) of pages in the pallocBits.
func (b *pallocBits) free(i, n uint) {
(*pageBits)(b).clearRange(i, n)
}
// freeAll frees all the bits of b.
func (b *pallocBits) freeAll() {
(*pageBits)(b).clearAll()
}
// pages64 returns a 64-bit bitmap representing a block of 64 pages aligned
// to 64 pages. The returned block of pages is the one containing the i'th
// page in this pallocBits. Each bit represents whether the page is in-use.
func (b *pallocBits) pages64(i uint) uint64 {
return (*pageBits)(b).block64(i)
}
// findBitRange64 returns the bit index of the first set of
// n consecutive 1 bits. If no consecutive set of 1 bits of
// size n may be found in c, then it returns an integer >= 64.
func findBitRange64(c uint64, n uint) uint {
i := uint(0)
cont := uint(sys.TrailingZeros64(^c))
for cont < n && i < 64 {
i += cont
i += uint(sys.TrailingZeros64(c >> i))
cont = uint(sys.TrailingZeros64(^(c >> i)))
}
return i
}
// pallocData encapsulates pallocBits and a bitmap for
// whether or not a given page is scavenged in a single
// structure. It's effectively a pallocBits with
// additional functionality.
//
// Update the comment on (*pageAlloc).chunks should this
// structure change.
type pallocData struct {
pallocBits
scavenged pageBits
}
// allocRange sets bits [i, i+n) in the bitmap to 1 and
// updates the scavenged bits appropriately.
func (m *pallocData) allocRange(i, n uint) {
// Clear the scavenged bits when we alloc the range.
m.pallocBits.allocRange(i, n)
m.scavenged.clearRange(i, n)
}
// allocAll sets every bit in the bitmap to 1 and updates
// the scavenged bits appropriately.
func (m *pallocData) allocAll() {
// Clear the scavenged bits when we alloc the range.
m.pallocBits.allocAll()
m.scavenged.clearAll()
}
|