Create slab allocator for small allocs (< 512 bytes) to avoid hitting the segment allocator constantly #1049
Description
Currently, many nodeos allocations hit the segment manager. The table below shows the allocations/deallocation which occured during one hour of running nodeos.
We see that there were:
- over 12 million allocations of buffers of size less than 512 bytes
- less than 30 thousand allocations of buffers of size greater than 512 bytes
so 99.7% of allocations were of buffers less than 512 bytes.
We should have slab allocators for small buffer sizes to avoid hitting the segment manager for every small allocation/deallocation, with it heavy cost of rebalancing the avl tree of free blocks.
We propose to have 64 allocators, for each size (modulo 8 bytes) from 8 to 512.
Benefits:
- much better efficiency
- much reduced fragmentation of the segment manager heap
- memory saving (at most 7 bytes wasted per allocation, while segment manager allocations have an overhead of 16 to 23 bytes).
Shared segment allocations after loading Aug-11-2024 snapshot
Runtime 1 hour, debug build of nodeos.
| alloc size | num allocs | num free | bytes allocated | bytes freed |
|---|---|---|---|---|
| 13 | 817 | 813 | 10,621 | 10,569 |
| 14 | 41 | 40 | 574 | 560 |
| 15 | 3 | 0 | 45 | 0 |
| 17 | 60,431 | 60,359 | 1,027,327 | 1,026,103 |
| 18 | 1,770 | 1,736 | 31,860 | 31,248 |
| 21 | 3,645 | 1,252 | 76,545 | 26,292 |
| 22 | 325,077 | 324,737 | 7,151,694 | 7,144,214 |
| 23 | 95 | 95 | 2,185 | 2,185 |
| 25 | 1,111,364 | 1,063,157 | 27,784,100 | 26,578,925 |
| 26 | 3,424 | 2,944 | 89,024 | 76,544 |
| 27 | 48 | 35 | 1,296 | 945 |
| 28 | 339,294 | 338,966 | 9,500,232 | 9,491,048 |
| 29 | 410,561 | 408,336 | 11,906,269 | 11,841,744 |
| 30 | 184,333 | 478 | 5,529,990 | 14,340 |
| 32 | 229 | 171 | 7,328 | 5,472 |
| 33 | 1,516,259 | 1,514,011 | 50,036,547 | 49,962,363 |
| 34 | 3,486 | 3,189 | 118,524 | 108,426 |
| 35 | 929 | 922 | 32,515 | 32,270 |
| 37 | 992 | 899 | 36,704 | 33,263 |
| 38 | 1 | 0 | 38 | 0 |
| 39 | 5 | 1 | 195 | 39 |
| 41 | 362,791 | 331,489 | 14,874,431 | 13,591,049 |
| 42 | 5 | 3 | 210 | 126 |
| 43 | 75,987 | 75,295 | 3,267,441 | 3,237,685 |
| 44 | 13 | 7 | 572 | 308 |
| 45 | 230 | 146 | 10,350 | 6,570 |
| 46 | 11,958 | 6,009 | 550,068 | 276,414 |
| 47 | 41 | 20 | 1,927 | 940 |
| 48 | 5,110 | 2,831 | 245,280 | 135,888 |
| 49 | 217,316 | 207,617 | 10,648,484 | 10,173,233 |
| 50 | 10,917 | 9,588 | 545,850 | 479,400 |
| 51 | 11,025 | 4,721 | 562,275 | 240,771 |
| 52 | 479 | 262 | 24,908 | 13,624 |
| 53 | 18,643 | 18,069 | 988,079 | 957,657 |
| 54 | 16,457 | 16,321 | 888,678 | 881,334 |
| 55 | 220 | 107 | 12,100 | 5,885 |
| 56 | 2,218 | 1,071 | 124,208 | 59,976 |
| 57 | 125,596 | 117,037 | 7,158,972 | 6,671,109 |
| 58 | 60,582 | 32,888 | 3,513,756 | 1,907,504 |
| 59 | 1,138 | 736 | 67,142 | 43,424 |
| 60 | 5,260 | 2,007 | 315,600 | 120,420 |
| 61 | 704 | 499 | 42,944 | 30,439 |
| 62 | 413,328 | 409,032 | 25,626,336 | 25,359,984 |
| 63 | 370 | 222 | 23,310 | 13,986 |
| 64 | 7,586 | 5,186 | 485,504 | 331,904 |
| 65-72 | 227,494 | 223,404 | 16,379,568 | 16,085,088 |
| 73-80 | 17,142 | 12,995 | 1,371,360 | 1,039,600 |
| 81-88 | 22,404 | 18,508 | 1,971,552 | 1,628,704 |
| 89-96 | 127,842 | 119,441 | 12,272,832 | 11,466,336 |
| 97-104 | 72,559 | 71,439 | 7,546,136 | 7,429,656 |
| 105-112 | 7,885 | 4,253 | 883,120 | 476,336 |
| 113-120 | 107,856 | 106,671 | 12,942,720 | 12,800,520 |
| 121-128 | 14,556 | 13,644 | 1,863,168 | 1,746,432 |
| 129-136 | 49,710 | 49,203 | 6,760,560 | 6,691,608 |
| 137-144 | 136,478 | 136,213 | 19,652,832 | 19,614,672 |
| 145-152 | 20,941 | 20,548 | 3,183,032 | 3,123,296 |
| 153-160 | 4,468 | 4,224 | 714,880 | 675,840 |
| 161-168 | 340,005 | 339,595 | 57,120,840 | 57,051,960 |
| 169-176 | 4,698 | 3,988 | 826,848 | 701,888 |
| 177-184 | 730 | 628 | 134,320 | 115,552 |
| 185-192 | 1,733 | 1,554 | 332,736 | 298,368 |
| 193-200 | 896 | 451 | 179,200 | 90,200 |
| 201-208 | 299 | 262 | 62,192 | 54,496 |
| 209-216 | 843 | 610 | 182,088 | 131,760 |
| 217-224 | 1,181 | 1,129 | 264,544 | 252,896 |
| 225-232 | 1,770 | 1,635 | 410,640 | 379,320 |
| 233-240 | 217 | 180 | 52,080 | 43,200 |
| 241-248 | 682 | 376 | 169,136 | 93,248 |
| 249-256 | 10,092 | 10,063 | 2,583,552 | 2,576,128 |
| 257-264 | 80 | 40 | 21,120 | 10,560 |
| 265-272 | 250 | 236 | 68,000 | 64,192 |
| 273-280 | 606 | 145 | 169,680 | 40,600 |
| 281-288 | 114 | 103 | 32,832 | 29,664 |
| 289-296 | 253 | 236 | 74,888 | 69,856 |
| 297-304 | 236 | 210 | 71,744 | 63,840 |
| 305-312 | 1,346 | 1,320 | 419,952 | 411,840 |
| 313-320 | 1,261 | 1,193 | 403,520 | 381,760 |
| 321-328 | 566 | 550 | 185,648 | 180,400 |
| 329-336 | 11 | 8 | 3,696 | 2,688 |
| 337-344 | 968 | 930 | 332,992 | 319,920 |
| 345-352 | 418 | 352 | 147,136 | 123,904 |
| 353-360 | 113 | 112 | 40,680 | 40,320 |
| 361-368 | 11 | 10 | 4,048 | 3,680 |
| 369-376 | 116 | 109 | 43,616 | 40,984 |
| 377-384 | 207 | 140 | 79,488 | 53,760 |
| 385-392 | 236 | 219 | 92,512 | 85,848 |
| 393-400 | 75 | 57 | 30,000 | 22,800 |
| 401-408 | 3,435 | 3,434 | 1,401,480 | 1,401,072 |
| 409-416 | 5 | 4 | 2,080 | 1,664 |
| 417-424 | 663 | 560 | 281,112 | 237,440 |
| 425-432 | 19 | 17 | 8,208 | 7,344 |
| 433-440 | 178 | 173 | 78,320 | 76,120 |
| 441-448 | 22 | 17 | 9,856 | 7,616 |
| 449-456 | 35 | 33 | 15,960 | 15,048 |
| 457-464 | 2 | 1 | 928 | 464 |
| 465-472 | 145 | 142 | 68,440 | 67,024 |
| 473-480 | 12 | 10 | 5,760 | 4,800 |
| 481-488 | 651 | 552 | 317,688 | 269,376 |
| 489-496 | 21 | 16 | 10,416 | 7,936 |
| 497-504 | 3,422 | 3,387 | 1,724,688 | 1,707,048 |
| 505-512 | 6,327,397 | 6,326,835 | 3,239,627,264 | 3,239,339,520 |
| 513-1,024 | 24,618 | 24,024 | 25,208,832 | 24,600,576 |
| 1,025-2,048 | 4,638 | 4,586 | 9,498,624 | 9,392,128 |
| 2,049-4,096 | 282 | 263 | 1,155,072 | 1,077,248 |
| 4,097-8,192 | 2,565 | 280 | 21,012,480 | 2,293,760 |
| 8,193-16,384 | 469 | 456 | 7,684,096 | 7,471,104 |
| 16,385-32,768 | 930 | 924 | 30,474,240 | 30,277,632 |
| 32,769-65,536 | 1,355 | 1,354 | 88,801,280 | 88,735,744 |
| 65,537-131,072 | 1,351 | 1,350 | 177,078,272 | 176,947,200 |
| 131,073-262,144 | 277 | 273 | 72,613,888 | 71,565,312 |
total allocs: 4,010,482,510 bytes
total deallocs: 3,972,943,076 bytes
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