Training courses

Kernel and Embedded Linux

Bootlin training courses

Embedded Linux, kernel,
Yocto Project, Buildroot, real-time,
graphics, boot time, debugging...

Bootlin logo

Elixir Cross Referencer

  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
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
/*
 *******************************************************************************
 * Implementation of (2^1+,2) cuckoo hashing, where 2^1+ indicates that each
 * hash bucket contains 2^n cells, for n >= 1, and 2 indicates that two hash
 * functions are employed.  The original cuckoo hashing algorithm was described
 * in:
 *
 *   Pagh, R., F.F. Rodler (2004) Cuckoo Hashing.  Journal of Algorithms
 *     51(2):122-144.
 *
 * Generalization of cuckoo hashing was discussed in:
 *
 *   Erlingsson, U., M. Manasse, F. McSherry (2006) A cool and practical
 *     alternative to traditional hash tables.  In Proceedings of the 7th
 *     Workshop on Distributed Data and Structures (WDAS'06), Santa Clara, CA,
 *     January 2006.
 *
 * This implementation uses precisely two hash functions because that is the
 * fewest that can work, and supporting multiple hashes is an implementation
 * burden.  Here is a reproduction of Figure 1 from Erlingsson et al. (2006)
 * that shows approximate expected maximum load factors for various
 * configurations:
 *
 *           |         #cells/bucket         |
 *   #hashes |   1   |   2   |   4   |   8   |
 *   --------+-------+-------+-------+-------+
 *         1 | 0.006 | 0.006 | 0.03  | 0.12  |
 *         2 | 0.49  | 0.86  |>0.93< |>0.96< |
 *         3 | 0.91  | 0.97  | 0.98  | 0.999 |
 *         4 | 0.97  | 0.99  | 0.999 |       |
 *
 * The number of cells per bucket is chosen such that a bucket fits in one cache
 * line.  So, on 32- and 64-bit systems, we use (8,2) and (4,2) cuckoo hashing,
 * respectively.
 *
 ******************************************************************************/
#define JEMALLOC_CKH_C_
#include "jemalloc/internal/jemalloc_preamble.h"

#include "jemalloc/internal/ckh.h"

#include "jemalloc/internal/jemalloc_internal_includes.h"

#include "jemalloc/internal/assert.h"
#include "jemalloc/internal/hash.h"
#include "jemalloc/internal/malloc_io.h"
#include "jemalloc/internal/prng.h"
#include "jemalloc/internal/util.h"

/******************************************************************************/
/* Function prototypes for non-inline static functions. */

static bool	ckh_grow(tsd_t *tsd, ckh_t *ckh);
static void	ckh_shrink(tsd_t *tsd, ckh_t *ckh);

/******************************************************************************/

/*
 * Search bucket for key and return the cell number if found; SIZE_T_MAX
 * otherwise.
 */
static size_t
ckh_bucket_search(ckh_t *ckh, size_t bucket, const void *key) {
	ckhc_t *cell;
	unsigned i;

	for (i = 0; i < (ZU(1) << LG_CKH_BUCKET_CELLS); i++) {
		cell = &ckh->tab[(bucket << LG_CKH_BUCKET_CELLS) + i];
		if (cell->key != NULL && ckh->keycomp(key, cell->key)) {
			return (bucket << LG_CKH_BUCKET_CELLS) + i;
		}
	}

	return SIZE_T_MAX;
}

/*
 * Search table for key and return cell number if found; SIZE_T_MAX otherwise.
 */
static size_t
ckh_isearch(ckh_t *ckh, const void *key) {
	size_t hashes[2], bucket, cell;

	assert(ckh != NULL);

	ckh->hash(key, hashes);

	/* Search primary bucket. */
	bucket = hashes[0] & ((ZU(1) << ckh->lg_curbuckets) - 1);
	cell = ckh_bucket_search(ckh, bucket, key);
	if (cell != SIZE_T_MAX) {
		return cell;
	}

	/* Search secondary bucket. */
	bucket = hashes[1] & ((ZU(1) << ckh->lg_curbuckets) - 1);
	cell = ckh_bucket_search(ckh, bucket, key);
	return cell;
}

static bool
ckh_try_bucket_insert(ckh_t *ckh, size_t bucket, const void *key,
    const void *data) {
	ckhc_t *cell;
	unsigned offset, i;

	/*
	 * Cycle through the cells in the bucket, starting at a random position.
	 * The randomness avoids worst-case search overhead as buckets fill up.
	 */
	offset = (unsigned)prng_lg_range_u64(&ckh->prng_state,
	    LG_CKH_BUCKET_CELLS);
	for (i = 0; i < (ZU(1) << LG_CKH_BUCKET_CELLS); i++) {
		cell = &ckh->tab[(bucket << LG_CKH_BUCKET_CELLS) +
		    ((i + offset) & ((ZU(1) << LG_CKH_BUCKET_CELLS) - 1))];
		if (cell->key == NULL) {
			cell->key = key;
			cell->data = data;
			ckh->count++;
			return false;
		}
	}

	return true;
}

/*
 * No space is available in bucket.  Randomly evict an item, then try to find an
 * alternate location for that item.  Iteratively repeat this
 * eviction/relocation procedure until either success or detection of an
 * eviction/relocation bucket cycle.
 */
static bool
ckh_evict_reloc_insert(ckh_t *ckh, size_t argbucket, void const **argkey,
    void const **argdata) {
	const void *key, *data, *tkey, *tdata;
	ckhc_t *cell;
	size_t hashes[2], bucket, tbucket;
	unsigned i;

	bucket = argbucket;
	key = *argkey;
	data = *argdata;
	while (true) {
		/*
		 * Choose a random item within the bucket to evict.  This is
		 * critical to correct function, because without (eventually)
		 * evicting all items within a bucket during iteration, it
		 * would be possible to get stuck in an infinite loop if there
		 * were an item for which both hashes indicated the same
		 * bucket.
		 */
		i = (unsigned)prng_lg_range_u64(&ckh->prng_state,
		    LG_CKH_BUCKET_CELLS);
		cell = &ckh->tab[(bucket << LG_CKH_BUCKET_CELLS) + i];
		assert(cell->key != NULL);

		/* Swap cell->{key,data} and {key,data} (evict). */
		tkey = cell->key; tdata = cell->data;
		cell->key = key; cell->data = data;
		key = tkey; data = tdata;

#ifdef CKH_COUNT
		ckh->nrelocs++;
#endif

		/* Find the alternate bucket for the evicted item. */
		ckh->hash(key, hashes);
		tbucket = hashes[1] & ((ZU(1) << ckh->lg_curbuckets) - 1);
		if (tbucket == bucket) {
			tbucket = hashes[0] & ((ZU(1) << ckh->lg_curbuckets)
			    - 1);
			/*
			 * It may be that (tbucket == bucket) still, if the
			 * item's hashes both indicate this bucket.  However,
			 * we are guaranteed to eventually escape this bucket
			 * during iteration, assuming pseudo-random item
			 * selection (true randomness would make infinite
			 * looping a remote possibility).  The reason we can
			 * never get trapped forever is that there are two
			 * cases:
			 *
			 * 1) This bucket == argbucket, so we will quickly
			 *    detect an eviction cycle and terminate.
			 * 2) An item was evicted to this bucket from another,
			 *    which means that at least one item in this bucket
			 *    has hashes that indicate distinct buckets.
			 */
		}
		/* Check for a cycle. */
		if (tbucket == argbucket) {
			*argkey = key;
			*argdata = data;
			return true;
		}

		bucket = tbucket;
		if (!ckh_try_bucket_insert(ckh, bucket, key, data)) {
			return false;
		}
	}
}

static bool
ckh_try_insert(ckh_t *ckh, void const**argkey, void const**argdata) {
	size_t hashes[2], bucket;
	const void *key = *argkey;
	const void *data = *argdata;

	ckh->hash(key, hashes);

	/* Try to insert in primary bucket. */
	bucket = hashes[0] & ((ZU(1) << ckh->lg_curbuckets) - 1);
	if (!ckh_try_bucket_insert(ckh, bucket, key, data)) {
		return false;
	}

	/* Try to insert in secondary bucket. */
	bucket = hashes[1] & ((ZU(1) << ckh->lg_curbuckets) - 1);
	if (!ckh_try_bucket_insert(ckh, bucket, key, data)) {
		return false;
	}

	/*
	 * Try to find a place for this item via iterative eviction/relocation.
	 */
	return ckh_evict_reloc_insert(ckh, bucket, argkey, argdata);
}

/*
 * Try to rebuild the hash table from scratch by inserting all items from the
 * old table into the new.
 */
static bool
ckh_rebuild(ckh_t *ckh, ckhc_t *aTab) {
	size_t count, i, nins;
	const void *key, *data;

	count = ckh->count;
	ckh->count = 0;
	for (i = nins = 0; nins < count; i++) {
		if (aTab[i].key != NULL) {
			key = aTab[i].key;
			data = aTab[i].data;
			if (ckh_try_insert(ckh, &key, &data)) {
				ckh->count = count;
				return true;
			}
			nins++;
		}
	}

	return false;
}

static bool
ckh_grow(tsd_t *tsd, ckh_t *ckh) {
	bool ret;
	ckhc_t *tab, *ttab;
	unsigned lg_prevbuckets, lg_curcells;

#ifdef CKH_COUNT
	ckh->ngrows++;
#endif

	/*
	 * It is possible (though unlikely, given well behaved hashes) that the
	 * table will have to be doubled more than once in order to create a
	 * usable table.
	 */
	lg_prevbuckets = ckh->lg_curbuckets;
	lg_curcells = ckh->lg_curbuckets + LG_CKH_BUCKET_CELLS;
	while (true) {
		size_t usize;

		lg_curcells++;
		usize = sz_sa2u(sizeof(ckhc_t) << lg_curcells, CACHELINE);
		if (unlikely(usize == 0
		    || usize > SC_LARGE_MAXCLASS)) {
			ret = true;
			goto label_return;
		}
		tab = (ckhc_t *)ipallocztm(tsd_tsdn(tsd), usize, CACHELINE,
		    true, NULL, true, arena_ichoose(tsd, NULL));
		if (tab == NULL) {
			ret = true;
			goto label_return;
		}
		/* Swap in new table. */
		ttab = ckh->tab;
		ckh->tab = tab;
		tab = ttab;
		ckh->lg_curbuckets = lg_curcells - LG_CKH_BUCKET_CELLS;

		if (!ckh_rebuild(ckh, tab)) {
			idalloctm(tsd_tsdn(tsd), tab, NULL, NULL, true, true);
			break;
		}

		/* Rebuilding failed, so back out partially rebuilt table. */
		idalloctm(tsd_tsdn(tsd), ckh->tab, NULL, NULL, true, true);
		ckh->tab = tab;
		ckh->lg_curbuckets = lg_prevbuckets;
	}

	ret = false;
label_return:
	return ret;
}

static void
ckh_shrink(tsd_t *tsd, ckh_t *ckh) {
	ckhc_t *tab, *ttab;
	size_t usize;
	unsigned lg_prevbuckets, lg_curcells;

	/*
	 * It is possible (though unlikely, given well behaved hashes) that the
	 * table rebuild will fail.
	 */
	lg_prevbuckets = ckh->lg_curbuckets;
	lg_curcells = ckh->lg_curbuckets + LG_CKH_BUCKET_CELLS - 1;
	usize = sz_sa2u(sizeof(ckhc_t) << lg_curcells, CACHELINE);
	if (unlikely(usize == 0 || usize > SC_LARGE_MAXCLASS)) {
		return;
	}
	tab = (ckhc_t *)ipallocztm(tsd_tsdn(tsd), usize, CACHELINE, true, NULL,
	    true, arena_ichoose(tsd, NULL));
	if (tab == NULL) {
		/*
		 * An OOM error isn't worth propagating, since it doesn't
		 * prevent this or future operations from proceeding.
		 */
		return;
	}
	/* Swap in new table. */
	ttab = ckh->tab;
	ckh->tab = tab;
	tab = ttab;
	ckh->lg_curbuckets = lg_curcells - LG_CKH_BUCKET_CELLS;

	if (!ckh_rebuild(ckh, tab)) {
		idalloctm(tsd_tsdn(tsd), tab, NULL, NULL, true, true);
#ifdef CKH_COUNT
		ckh->nshrinks++;
#endif
		return;
	}

	/* Rebuilding failed, so back out partially rebuilt table. */
	idalloctm(tsd_tsdn(tsd), ckh->tab, NULL, NULL, true, true);
	ckh->tab = tab;
	ckh->lg_curbuckets = lg_prevbuckets;
#ifdef CKH_COUNT
	ckh->nshrinkfails++;
#endif
}

bool
ckh_new(tsd_t *tsd, ckh_t *ckh, size_t minitems, ckh_hash_t *hash,
    ckh_keycomp_t *keycomp) {
	bool ret;
	size_t mincells, usize;
	unsigned lg_mincells;

	assert(minitems > 0);
	assert(hash != NULL);
	assert(keycomp != NULL);

#ifdef CKH_COUNT
	ckh->ngrows = 0;
	ckh->nshrinks = 0;
	ckh->nshrinkfails = 0;
	ckh->ninserts = 0;
	ckh->nrelocs = 0;
#endif
	ckh->prng_state = 42; /* Value doesn't really matter. */
	ckh->count = 0;

	/*
	 * Find the minimum power of 2 that is large enough to fit minitems
	 * entries.  We are using (2+,2) cuckoo hashing, which has an expected
	 * maximum load factor of at least ~0.86, so 0.75 is a conservative load
	 * factor that will typically allow mincells items to fit without ever
	 * growing the table.
	 */
	assert(LG_CKH_BUCKET_CELLS > 0);
	mincells = ((minitems + (3 - (minitems % 3))) / 3) << 2;
	for (lg_mincells = LG_CKH_BUCKET_CELLS;
	    (ZU(1) << lg_mincells) < mincells;
	    lg_mincells++) {
		/* Do nothing. */
	}
	ckh->lg_minbuckets = lg_mincells - LG_CKH_BUCKET_CELLS;
	ckh->lg_curbuckets = lg_mincells - LG_CKH_BUCKET_CELLS;
	ckh->hash = hash;
	ckh->keycomp = keycomp;

	usize = sz_sa2u(sizeof(ckhc_t) << lg_mincells, CACHELINE);
	if (unlikely(usize == 0 || usize > SC_LARGE_MAXCLASS)) {
		ret = true;
		goto label_return;
	}
	ckh->tab = (ckhc_t *)ipallocztm(tsd_tsdn(tsd), usize, CACHELINE, true,
	    NULL, true, arena_ichoose(tsd, NULL));
	if (ckh->tab == NULL) {
		ret = true;
		goto label_return;
	}

	ret = false;
label_return:
	return ret;
}

void
ckh_delete(tsd_t *tsd, ckh_t *ckh) {
	assert(ckh != NULL);

#ifdef CKH_VERBOSE
	malloc_printf(
	    "%s(%p): ngrows: %"FMTu64", nshrinks: %"FMTu64","
	    " nshrinkfails: %"FMTu64", ninserts: %"FMTu64","
	    " nrelocs: %"FMTu64"\n", __func__, ckh,
	    (unsigned long long)ckh->ngrows,
	    (unsigned long long)ckh->nshrinks,
	    (unsigned long long)ckh->nshrinkfails,
	    (unsigned long long)ckh->ninserts,
	    (unsigned long long)ckh->nrelocs);
#endif

	idalloctm(tsd_tsdn(tsd), ckh->tab, NULL, NULL, true, true);
	if (config_debug) {
		memset(ckh, JEMALLOC_FREE_JUNK, sizeof(ckh_t));
	}
}

size_t
ckh_count(ckh_t *ckh) {
	assert(ckh != NULL);

	return ckh->count;
}

bool
ckh_iter(ckh_t *ckh, size_t *tabind, void **key, void **data) {
	size_t i, ncells;

	for (i = *tabind, ncells = (ZU(1) << (ckh->lg_curbuckets +
	    LG_CKH_BUCKET_CELLS)); i < ncells; i++) {
		if (ckh->tab[i].key != NULL) {
			if (key != NULL) {
				*key = (void *)ckh->tab[i].key;
			}
			if (data != NULL) {
				*data = (void *)ckh->tab[i].data;
			}
			*tabind = i + 1;
			return false;
		}
	}

	return true;
}

bool
ckh_insert(tsd_t *tsd, ckh_t *ckh, const void *key, const void *data) {
	bool ret;

	assert(ckh != NULL);
	assert(ckh_search(ckh, key, NULL, NULL));

#ifdef CKH_COUNT
	ckh->ninserts++;
#endif

	while (ckh_try_insert(ckh, &key, &data)) {
		if (ckh_grow(tsd, ckh)) {
			ret = true;
			goto label_return;
		}
	}

	ret = false;
label_return:
	return ret;
}

bool
ckh_remove(tsd_t *tsd, ckh_t *ckh, const void *searchkey, void **key,
    void **data) {
	size_t cell;

	assert(ckh != NULL);

	cell = ckh_isearch(ckh, searchkey);
	if (cell != SIZE_T_MAX) {
		if (key != NULL) {
			*key = (void *)ckh->tab[cell].key;
		}
		if (data != NULL) {
			*data = (void *)ckh->tab[cell].data;
		}
		ckh->tab[cell].key = NULL;
		ckh->tab[cell].data = NULL; /* Not necessary. */

		ckh->count--;
		/* Try to halve the table if it is less than 1/4 full. */
		if (ckh->count < (ZU(1) << (ckh->lg_curbuckets
		    + LG_CKH_BUCKET_CELLS - 2)) && ckh->lg_curbuckets
		    > ckh->lg_minbuckets) {
			/* Ignore error due to OOM. */
			ckh_shrink(tsd, ckh);
		}

		return false;
	}

	return true;
}

bool
ckh_search(ckh_t *ckh, const void *searchkey, void **key, void **data) {
	size_t cell;

	assert(ckh != NULL);

	cell = ckh_isearch(ckh, searchkey);
	if (cell != SIZE_T_MAX) {
		if (key != NULL) {
			*key = (void *)ckh->tab[cell].key;
		}
		if (data != NULL) {
			*data = (void *)ckh->tab[cell].data;
		}
		return false;
	}

	return true;
}

void
ckh_string_hash(const void *key, size_t r_hash[2]) {
	hash(key, strlen((const char *)key), 0x94122f33U, r_hash);
}

bool
ckh_string_keycomp(const void *k1, const void *k2) {
	assert(k1 != NULL);
	assert(k2 != NULL);

	return !strcmp((char *)k1, (char *)k2);
}

void
ckh_pointer_hash(const void *key, size_t r_hash[2]) {
	union {
		const void	*v;
		size_t		i;
	} u;

	assert(sizeof(u.v) == sizeof(u.i));
	u.v = key;
	hash(&u.i, sizeof(u.i), 0xd983396eU, r_hash);
}

bool
ckh_pointer_keycomp(const void *k1, const void *k2) {
	return (k1 == k2);
}