/
PoolChunk.java
468 lines (419 loc) · 16.3 KB
/
PoolChunk.java
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
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
/*
* Copyright 2012 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.buffer;
/**
* Description of algorithm for PageRun/PoolSubpage allocation from PoolChunk
*
* Notation: The following terms are important to understand the code
* > page - a page is the smallest unit of memory chunk that can be allocated
* > chunk - a chunk is a collection of pages
* > in this code chunkSize = 2^{maxOrder} * pageSize
*
* To begin we allocate a byte array of size = chunkSize
* Whenever a ByteBuf of given size needs to be created we search for the first position
* in the byte array that has enough empty space to accommodate the requested size and
* return a (long) handle that encodes this offset information, (this memory segment is then
* marked as reserved so it is always used by exactly one ByteBuf and no more)
*
* For simplicity all sizes are normalized according to PoolArena#normalizeCapacity method
* This ensures that when we request for memory segments of size >= pageSize the normalizedCapacity
* equals the next nearest power of 2
*
* To search for the first offset in chunk that has at least requested size available we construct a
* complete balanced binary tree and store it in an array (just like heaps) - memoryMap
*
* The tree looks like this (the size of each node being mentioned in the parenthesis)
*
* depth=0 1 node (chunkSize)
* depth=1 2 nodes (chunkSize/2)
* ..
* ..
* depth=d 2^d nodes (chunkSize/2^d)
* ..
* depth=maxOrder 2^maxOrder nodes (chunkSize/2^{maxOrder} = pageSize)
*
* depth=maxOrder is the last level and the leafs consist of pages
*
* With this tree available searching in chunkArray translates like this:
* To allocate a memory segment of size chunkSize/2^k we search for the first node (from left) at height k
* which is unused
*
* Algorithm:
* ----------
* Encode the tree in memoryMap with the notation
* memoryMap[id] = x => in the subtree rooted at id, the first node that is free to be allocated
* is at depth x (counted from depth=0) i.e., at depths [depth_of_id, x), there is no node that is free
*
* As we allocate & free nodes, we update values stored in memoryMap so that the property is maintained
*
* Initialization -
* In the beginning we construct the memoryMap array by storing the depth of a node at each node
* i.e., memoryMap[id] = depth_of_id
*
* Observations:
* -------------
* 1) memoryMap[id] = depth_of_id => it is free / unallocated
* 2) memoryMap[id] > depth_of_id => at least one of its child nodes is allocated, so we cannot allocate it, but
* some of its children can still be allocated based on their availability
* 3) memoryMap[id] = maxOrder + 1 => the node is fully allocated & thus none of its children can be allocated, it
* is thus marked as unusable
*
* Algorithm: [allocateNode(d) => we want to find the first node (from left) at height h that can be allocated]
* ----------
* 1) start at root (i.e., depth = 0 or id = 1)
* 2) if memoryMap[1] > d => cannot be allocated from this chunk
* 3) if left node value <= h; we can allocate from left subtree so move to left and repeat until found
* 4) else try in right subtree
*
* Algorithm: [allocateRun(size)]
* ----------
* 1) Compute d = log_2(chunkSize/size)
* 2) Return allocateNode(d)
*
* Algorithm: [allocateSubpage(size)]
* ----------
* 1) use allocateNode(maxOrder) to find an empty (i.e., unused) leaf (i.e., page)
* 2) use this handle to construct the PoolSubpage object or if it already exists just call init(normCapacity)
* note that this PoolSubpage object is added to subpagesPool in the PoolArena when we init() it
*
* Note:
* -----
* In the implementation for improving cache coherence,
* we store 2 pieces of information (i.e, 2 byte vals) as a short value in memoryMap
*
* memoryMap[id]= (depth_of_id, x)
* where as per convention defined above
* the second value (i.e, x) indicates that the first node which is free to be allocated is at depth x (from root)
*/
final class PoolChunk<T> implements PoolChunkMetric {
private static final int INTEGER_SIZE_MINUS_ONE = Integer.SIZE - 1;
final PoolArena<T> arena;
final T memory;
final boolean unpooled;
private final byte[] memoryMap;
private final byte[] depthMap;
private final PoolSubpage<T>[] subpages;
/** Used to determine if the requested capacity is equal to or greater than pageSize. */
private final int subpageOverflowMask;
private final int pageSize;
private final int pageShifts;
private final int maxOrder;
private final int chunkSize;
private final int log2ChunkSize;
private final int maxSubpageAllocs;
/** Used to mark memory as unusable */
private final byte unusable;
private int freeBytes;
PoolChunkList<T> parent;
PoolChunk<T> prev;
PoolChunk<T> next;
// TODO: Test if adding padding helps under contention
//private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
PoolChunk(PoolArena<T> arena, T memory, int pageSize, int maxOrder, int pageShifts, int chunkSize) {
unpooled = false;
this.arena = arena;
this.memory = memory;
this.pageSize = pageSize;
this.pageShifts = pageShifts;
this.maxOrder = maxOrder;
this.chunkSize = chunkSize;
unusable = (byte) (maxOrder + 1);
log2ChunkSize = log2(chunkSize);
subpageOverflowMask = ~(pageSize - 1);
freeBytes = chunkSize;
assert maxOrder < 30 : "maxOrder should be < 30, but is: " + maxOrder;
maxSubpageAllocs = 1 << maxOrder;
// Generate the memory map.
memoryMap = new byte[maxSubpageAllocs << 1];
depthMap = new byte[memoryMap.length];
int memoryMapIndex = 1;
for (int d = 0; d <= maxOrder; ++ d) { // move down the tree one level at a time
int depth = 1 << d;
for (int p = 0; p < depth; ++ p) {
// in each level traverse left to right and set value to the depth of subtree
memoryMap[memoryMapIndex] = (byte) d;
depthMap[memoryMapIndex] = (byte) d;
memoryMapIndex ++;
}
}
subpages = newSubpageArray(maxSubpageAllocs);
}
/** Creates a special chunk that is not pooled. */
PoolChunk(PoolArena<T> arena, T memory, int size) {
unpooled = true;
this.arena = arena;
this.memory = memory;
memoryMap = null;
depthMap = null;
subpages = null;
subpageOverflowMask = 0;
pageSize = 0;
pageShifts = 0;
maxOrder = 0;
unusable = (byte) (maxOrder + 1);
chunkSize = size;
log2ChunkSize = log2(chunkSize);
maxSubpageAllocs = 0;
}
@SuppressWarnings("unchecked")
private PoolSubpage<T>[] newSubpageArray(int size) {
return new PoolSubpage[size];
}
@Override
public int usage() {
final int freeBytes = this.freeBytes;
if (freeBytes == 0) {
return 100;
}
int freePercentage = (int) (freeBytes * 100L / chunkSize);
if (freePercentage == 0) {
return 99;
}
return 100 - freePercentage;
}
long allocate(int normCapacity) {
if ((normCapacity & subpageOverflowMask) != 0) { // >= pageSize
return allocateRun(normCapacity);
} else {
return allocateSubpage(normCapacity);
}
}
/**
* Update method used by allocate
* This is triggered only when a successor is allocated and all its predecessors
* need to update their state
* The minimal depth at which subtree rooted at id has some free space
*
* @param id id
*/
private void updateParentsAlloc(int id) {
while (id > 1) {
int parentId = id >>> 1;
byte val1 = value(id);
byte val2 = value(id ^ 1);
byte val = val1 < val2 ? val1 : val2;
setValue(parentId, val);
id = parentId;
}
}
/**
* Update method used by free
* This needs to handle the special case when both children are completely free
* in which case parent be directly allocated on request of size = child-size * 2
*
* @param id id
*/
private void updateParentsFree(int id) {
int logChild = depth(id) + 1;
while (id > 1) {
int parentId = id >>> 1;
byte val1 = value(id);
byte val2 = value(id ^ 1);
logChild -= 1; // in first iteration equals log, subsequently reduce 1 from logChild as we traverse up
if (val1 == logChild && val2 == logChild) {
setValue(parentId, (byte) (logChild - 1));
} else {
byte val = val1 < val2 ? val1 : val2;
setValue(parentId, val);
}
id = parentId;
}
}
/**
* Algorithm to allocate an index in memoryMap when we query for a free node
* at depth d
*
* @param d depth
* @return index in memoryMap
*/
private int allocateNode(int d) {
int id = 1;
int initial = - (1 << d); // has last d bits = 0 and rest all = 1
byte val = value(id);
if (val > d) { // unusable
return -1;
}
while (val < d || (id & initial) == 0) { // id & initial == 1 << d for all ids at depth d, for < d it is 0
id <<= 1;
val = value(id);
if (val > d) {
id ^= 1;
val = value(id);
}
}
byte value = value(id);
assert value == d && (id & initial) == 1 << d : String.format("val = %d, id & initial = %d, d = %d",
value, id & initial, d);
setValue(id, unusable); // mark as unusable
updateParentsAlloc(id);
return id;
}
/**
* Allocate a run of pages (>=1)
*
* @param normCapacity normalized capacity
* @return index in memoryMap
*/
private long allocateRun(int normCapacity) {
int d = maxOrder - (log2(normCapacity) - pageShifts);
int id = allocateNode(d);
if (id < 0) {
return id;
}
freeBytes -= runLength(id);
return id;
}
/**
* Create/ initialize a new PoolSubpage of normCapacity
* Any PoolSubpage created/ initialized here is added to subpage pool in the PoolArena that owns this PoolChunk
*
* @param normCapacity normalized capacity
* @return index in memoryMap
*/
private long allocateSubpage(int normCapacity) {
// Obtain the head of the PoolSubPage pool that is owned by the PoolArena and synchronize on it.
// This is need as we may add it back and so alter the linked-list structure.
PoolSubpage<T> head = arena.findSubpagePoolHead(normCapacity);
synchronized (head) {
int d = maxOrder; // subpages are only be allocated from pages i.e., leaves
int id = allocateNode(d);
if (id < 0) {
return id;
}
final PoolSubpage<T>[] subpages = this.subpages;
final int pageSize = this.pageSize;
freeBytes -= pageSize;
int subpageIdx = subpageIdx(id);
PoolSubpage<T> subpage = subpages[subpageIdx];
if (subpage == null) {
subpage = new PoolSubpage<T>(head, this, id, runOffset(id), pageSize, normCapacity);
subpages[subpageIdx] = subpage;
} else {
subpage.init(head, normCapacity);
}
return subpage.allocate();
}
}
/**
* Free a subpage or a run of pages
* When a subpage is freed from PoolSubpage, it might be added back to subpage pool of the owning PoolArena
* If the subpage pool in PoolArena has at least one other PoolSubpage of given elemSize, we can
* completely free the owning Page so it is available for subsequent allocations
*
* @param handle handle to free
*/
void free(long handle) {
int memoryMapIdx = memoryMapIdx(handle);
int bitmapIdx = bitmapIdx(handle);
if (bitmapIdx != 0) { // free a subpage
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
assert subpage != null && subpage.doNotDestroy;
// Obtain the head of the PoolSubPage pool that is owned by the PoolArena and synchronize on it.
// This is need as we may add it back and so alter the linked-list structure.
PoolSubpage<T> head = arena.findSubpagePoolHead(subpage.elemSize);
synchronized (head) {
if (subpage.free(head, bitmapIdx & 0x3FFFFFFF)) {
return;
}
}
}
freeBytes += runLength(memoryMapIdx);
setValue(memoryMapIdx, depth(memoryMapIdx));
updateParentsFree(memoryMapIdx);
}
void initBuf(PooledByteBuf<T> buf, long handle, int reqCapacity) {
int memoryMapIdx = memoryMapIdx(handle);
int bitmapIdx = bitmapIdx(handle);
if (bitmapIdx == 0) {
byte val = value(memoryMapIdx);
assert val == unusable : String.valueOf(val);
buf.init(this, handle, runOffset(memoryMapIdx), reqCapacity, runLength(memoryMapIdx),
arena.parent.threadCache());
} else {
initBufWithSubpage(buf, handle, bitmapIdx, reqCapacity);
}
}
void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int reqCapacity) {
initBufWithSubpage(buf, handle, bitmapIdx(handle), reqCapacity);
}
private void initBufWithSubpage(PooledByteBuf<T> buf, long handle, int bitmapIdx, int reqCapacity) {
assert bitmapIdx != 0;
int memoryMapIdx = memoryMapIdx(handle);
PoolSubpage<T> subpage = subpages[subpageIdx(memoryMapIdx)];
assert subpage.doNotDestroy;
assert reqCapacity <= subpage.elemSize;
buf.init(
this, handle,
runOffset(memoryMapIdx) + (bitmapIdx & 0x3FFFFFFF) * subpage.elemSize, reqCapacity, subpage.elemSize,
arena.parent.threadCache());
}
private byte value(int id) {
return memoryMap[id];
}
private void setValue(int id, byte val) {
memoryMap[id] = val;
}
private byte depth(int id) {
return depthMap[id];
}
private static int log2(int val) {
// compute the (0-based, with lsb = 0) position of highest set bit i.e, log2
return INTEGER_SIZE_MINUS_ONE - Integer.numberOfLeadingZeros(val);
}
private int runLength(int id) {
// represents the size in #bytes supported by node 'id' in the tree
return 1 << log2ChunkSize - depth(id);
}
private int runOffset(int id) {
// represents the 0-based offset in #bytes from start of the byte-array chunk
int shift = id ^ 1 << depth(id);
return shift * runLength(id);
}
private int subpageIdx(int memoryMapIdx) {
return memoryMapIdx ^ maxSubpageAllocs; // remove highest set bit, to get offset
}
private static int memoryMapIdx(long handle) {
return (int) handle;
}
private static int bitmapIdx(long handle) {
return (int) (handle >>> Integer.SIZE);
}
@Override
public int chunkSize() {
return chunkSize;
}
@Override
public int freeBytes() {
return freeBytes;
}
@Override
public String toString() {
return new StringBuilder()
.append("Chunk(")
.append(Integer.toHexString(System.identityHashCode(this)))
.append(": ")
.append(usage())
.append("%, ")
.append(chunkSize - freeBytes)
.append('/')
.append(chunkSize)
.append(')')
.toString();
}
void destroy() {
arena.destroyChunk(this);
}
}