summaryrefslogtreecommitdiffstats
path: root/deps/jemalloc/src/hpa.c
blob: 7e2aeba0c0ffdade00eca8266f1a20ddc2db686e (plain)
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
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
#include "jemalloc/internal/jemalloc_preamble.h"
#include "jemalloc/internal/jemalloc_internal_includes.h"

#include "jemalloc/internal/hpa.h"

#include "jemalloc/internal/fb.h"
#include "jemalloc/internal/witness.h"

#define HPA_EDEN_SIZE (128 * HUGEPAGE)

static edata_t *hpa_alloc(tsdn_t *tsdn, pai_t *self, size_t size,
    size_t alignment, bool zero, bool guarded, bool frequent_reuse,
    bool *deferred_work_generated);
static size_t hpa_alloc_batch(tsdn_t *tsdn, pai_t *self, size_t size,
    size_t nallocs, edata_list_active_t *results, bool *deferred_work_generated);
static bool hpa_expand(tsdn_t *tsdn, pai_t *self, edata_t *edata,
    size_t old_size, size_t new_size, bool zero, bool *deferred_work_generated);
static bool hpa_shrink(tsdn_t *tsdn, pai_t *self, edata_t *edata,
    size_t old_size, size_t new_size, bool *deferred_work_generated);
static void hpa_dalloc(tsdn_t *tsdn, pai_t *self, edata_t *edata,
    bool *deferred_work_generated);
static void hpa_dalloc_batch(tsdn_t *tsdn, pai_t *self,
    edata_list_active_t *list, bool *deferred_work_generated);
static uint64_t hpa_time_until_deferred_work(tsdn_t *tsdn, pai_t *self);

bool
hpa_supported() {
#ifdef _WIN32
	/*
	 * At least until the API and implementation is somewhat settled, we
	 * don't want to try to debug the VM subsystem on the hardest-to-test
	 * platform.
	 */
	return false;
#endif
	if (!pages_can_hugify) {
		return false;
	}
	/*
	 * We fundamentally rely on a address-space-hungry growth strategy for
	 * hugepages.
	 */
	if (LG_SIZEOF_PTR != 3) {
		return false;
	}
	/*
	 * If we couldn't detect the value of HUGEPAGE, HUGEPAGE_PAGES becomes
	 * this sentinel value -- see the comment in pages.h.
	 */
	if (HUGEPAGE_PAGES == 1) {
		return false;
	}
	return true;
}

static void
hpa_do_consistency_checks(hpa_shard_t *shard) {
	assert(shard->base != NULL);
}

bool
hpa_central_init(hpa_central_t *central, base_t *base, const hpa_hooks_t *hooks) {
	/* malloc_conf processing should have filtered out these cases. */
	assert(hpa_supported());
	bool err;
	err = malloc_mutex_init(&central->grow_mtx, "hpa_central_grow",
	    WITNESS_RANK_HPA_CENTRAL_GROW, malloc_mutex_rank_exclusive);
	if (err) {
		return true;
	}
	err = malloc_mutex_init(&central->mtx, "hpa_central",
	    WITNESS_RANK_HPA_CENTRAL, malloc_mutex_rank_exclusive);
	if (err) {
		return true;
	}
	central->base = base;
	central->eden = NULL;
	central->eden_len = 0;
	central->age_counter = 0;
	central->hooks = *hooks;
	return false;
}

static hpdata_t *
hpa_alloc_ps(tsdn_t *tsdn, hpa_central_t *central) {
	return (hpdata_t *)base_alloc(tsdn, central->base, sizeof(hpdata_t),
	    CACHELINE);
}

hpdata_t *
hpa_central_extract(tsdn_t *tsdn, hpa_central_t *central, size_t size,
    bool *oom) {
	/* Don't yet support big allocations; these should get filtered out. */
	assert(size <= HUGEPAGE);
	/*
	 * Should only try to extract from the central allocator if the local
	 * shard is exhausted.  We should hold the grow_mtx on that shard.
	 */
	witness_assert_positive_depth_to_rank(
	    tsdn_witness_tsdp_get(tsdn), WITNESS_RANK_HPA_SHARD_GROW);

	malloc_mutex_lock(tsdn, &central->grow_mtx);
	*oom = false;

	hpdata_t *ps = NULL;

	/* Is eden a perfect fit? */
	if (central->eden != NULL && central->eden_len == HUGEPAGE) {
		ps = hpa_alloc_ps(tsdn, central);
		if (ps == NULL) {
			*oom = true;
			malloc_mutex_unlock(tsdn, &central->grow_mtx);
			return NULL;
		}
		hpdata_init(ps, central->eden, central->age_counter++);
		central->eden = NULL;
		central->eden_len = 0;
		malloc_mutex_unlock(tsdn, &central->grow_mtx);
		return ps;
	}

	/*
	 * We're about to try to allocate from eden by splitting.  If eden is
	 * NULL, we have to allocate it too.  Otherwise, we just have to
	 * allocate an edata_t for the new psset.
	 */
	if (central->eden == NULL) {
		/*
		 * During development, we're primarily concerned with systems
		 * with overcommit.  Eventually, we should be more careful here.
		 */
		bool commit = true;
		/* Allocate address space, bailing if we fail. */
		void *new_eden = pages_map(NULL, HPA_EDEN_SIZE, HUGEPAGE,
		    &commit);
		if (new_eden == NULL) {
			*oom = true;
			malloc_mutex_unlock(tsdn, &central->grow_mtx);
			return NULL;
		}
		ps = hpa_alloc_ps(tsdn, central);
		if (ps == NULL) {
			pages_unmap(new_eden, HPA_EDEN_SIZE);
			*oom = true;
			malloc_mutex_unlock(tsdn, &central->grow_mtx);
			return NULL;
		}
		central->eden = new_eden;
		central->eden_len = HPA_EDEN_SIZE;
	} else {
		/* Eden is already nonempty; only need an edata for ps. */
		ps = hpa_alloc_ps(tsdn, central);
		if (ps == NULL) {
			*oom = true;
			malloc_mutex_unlock(tsdn, &central->grow_mtx);
			return NULL;
		}
	}
	assert(ps != NULL);
	assert(central->eden != NULL);
	assert(central->eden_len > HUGEPAGE);
	assert(central->eden_len % HUGEPAGE == 0);
	assert(HUGEPAGE_ADDR2BASE(central->eden) == central->eden);

	hpdata_init(ps, central->eden, central->age_counter++);

	char *eden_char = (char *)central->eden;
	eden_char += HUGEPAGE;
	central->eden = (void *)eden_char;
	central->eden_len -= HUGEPAGE;

	malloc_mutex_unlock(tsdn, &central->grow_mtx);

	return ps;
}

bool
hpa_shard_init(hpa_shard_t *shard, hpa_central_t *central, emap_t *emap,
    base_t *base, edata_cache_t *edata_cache, unsigned ind,
    const hpa_shard_opts_t *opts) {
	/* malloc_conf processing should have filtered out these cases. */
	assert(hpa_supported());
	bool err;
	err = malloc_mutex_init(&shard->grow_mtx, "hpa_shard_grow",
	    WITNESS_RANK_HPA_SHARD_GROW, malloc_mutex_rank_exclusive);
	if (err) {
		return true;
	}
	err = malloc_mutex_init(&shard->mtx, "hpa_shard",
	    WITNESS_RANK_HPA_SHARD, malloc_mutex_rank_exclusive);
	if (err) {
		return true;
	}

	assert(edata_cache != NULL);
	shard->central = central;
	shard->base = base;
	edata_cache_fast_init(&shard->ecf, edata_cache);
	psset_init(&shard->psset);
	shard->age_counter = 0;
	shard->ind = ind;
	shard->emap = emap;

	shard->opts = *opts;

	shard->npending_purge = 0;
	nstime_init_zero(&shard->last_purge);

	shard->stats.npurge_passes = 0;
	shard->stats.npurges = 0;
	shard->stats.nhugifies = 0;
	shard->stats.ndehugifies = 0;

	/*
	 * Fill these in last, so that if an hpa_shard gets used despite
	 * initialization failing, we'll at least crash instead of just
	 * operating on corrupted data.
	 */
	shard->pai.alloc = &hpa_alloc;
	shard->pai.alloc_batch = &hpa_alloc_batch;
	shard->pai.expand = &hpa_expand;
	shard->pai.shrink = &hpa_shrink;
	shard->pai.dalloc = &hpa_dalloc;
	shard->pai.dalloc_batch = &hpa_dalloc_batch;
	shard->pai.time_until_deferred_work = &hpa_time_until_deferred_work;

	hpa_do_consistency_checks(shard);

	return false;
}

/*
 * Note that the stats functions here follow the usual stats naming conventions;
 * "merge" obtains the stats from some live object of instance, while "accum"
 * only combines the stats from one stats objet to another.  Hence the lack of
 * locking here.
 */
static void
hpa_shard_nonderived_stats_accum(hpa_shard_nonderived_stats_t *dst,
    hpa_shard_nonderived_stats_t *src) {
	dst->npurge_passes += src->npurge_passes;
	dst->npurges += src->npurges;
	dst->nhugifies += src->nhugifies;
	dst->ndehugifies += src->ndehugifies;
}

void
hpa_shard_stats_accum(hpa_shard_stats_t *dst, hpa_shard_stats_t *src) {
	psset_stats_accum(&dst->psset_stats, &src->psset_stats);
	hpa_shard_nonderived_stats_accum(&dst->nonderived_stats,
	    &src->nonderived_stats);
}

void
hpa_shard_stats_merge(tsdn_t *tsdn, hpa_shard_t *shard,
    hpa_shard_stats_t *dst) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_lock(tsdn, &shard->grow_mtx);
	malloc_mutex_lock(tsdn, &shard->mtx);
	psset_stats_accum(&dst->psset_stats, &shard->psset.stats);
	hpa_shard_nonderived_stats_accum(&dst->nonderived_stats, &shard->stats);
	malloc_mutex_unlock(tsdn, &shard->mtx);
	malloc_mutex_unlock(tsdn, &shard->grow_mtx);
}

static bool
hpa_good_hugification_candidate(hpa_shard_t *shard, hpdata_t *ps) {
	/*
	 * Note that this needs to be >= rather than just >, because of the
	 * important special case in which the hugification threshold is exactly
	 * HUGEPAGE.
	 */
	return hpdata_nactive_get(ps) * PAGE
	    >= shard->opts.hugification_threshold;
}

static size_t
hpa_adjusted_ndirty(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	return psset_ndirty(&shard->psset) - shard->npending_purge;
}

static size_t
hpa_ndirty_max(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	if (shard->opts.dirty_mult == (fxp_t)-1) {
		return (size_t)-1;
	}
	return fxp_mul_frac(psset_nactive(&shard->psset),
	    shard->opts.dirty_mult);
}

static bool
hpa_hugify_blocked_by_ndirty(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	hpdata_t *to_hugify = psset_pick_hugify(&shard->psset);
	if (to_hugify == NULL) {
		return false;
	}
	return hpa_adjusted_ndirty(tsdn, shard)
	    + hpdata_nretained_get(to_hugify) > hpa_ndirty_max(tsdn, shard);
}

static bool
hpa_should_purge(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	if (hpa_adjusted_ndirty(tsdn, shard) > hpa_ndirty_max(tsdn, shard)) {
		return true;
	}
	if (hpa_hugify_blocked_by_ndirty(tsdn, shard)) {
		return true;
	}
	return false;
}

static void
hpa_update_purge_hugify_eligibility(tsdn_t *tsdn, hpa_shard_t *shard,
    hpdata_t *ps) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	if (hpdata_changing_state_get(ps)) {
		hpdata_purge_allowed_set(ps, false);
		hpdata_disallow_hugify(ps);
		return;
	}
	/*
	 * Hugepages are distinctly costly to purge, so try to avoid it unless
	 * they're *particularly* full of dirty pages.  Eventually, we should
	 * use a smarter / more dynamic heuristic for situations where we have
	 * to manually hugify.
	 *
	 * In situations where we don't manually hugify, this problem is
	 * reduced.  The "bad" situation we're trying to avoid is one's that's
	 * common in some Linux configurations (where both enabled and defrag
	 * are set to madvise) that can lead to long latency spikes on the first
	 * access after a hugification.  The ideal policy in such configurations
	 * is probably time-based for both purging and hugifying; only hugify a
	 * hugepage if it's met the criteria for some extended period of time,
	 * and only dehugify it if it's failed to meet the criteria for an
	 * extended period of time.  When background threads are on, we should
	 * try to take this hit on one of them, as well.
	 *
	 * I think the ideal setting is THP always enabled, and defrag set to
	 * deferred; in that case we don't need any explicit calls on the
	 * allocator's end at all; we just try to pack allocations in a
	 * hugepage-friendly manner and let the OS hugify in the background.
	 */
	hpdata_purge_allowed_set(ps, hpdata_ndirty_get(ps) > 0);
	if (hpa_good_hugification_candidate(shard, ps)
	    && !hpdata_huge_get(ps)) {
		nstime_t now;
		shard->central->hooks.curtime(&now, /* first_reading */ true);
		hpdata_allow_hugify(ps, now);
	}
	/*
	 * Once a hugepage has become eligible for hugification, we don't mark
	 * it as ineligible just because it stops meeting the criteria (this
	 * could lead to situations where a hugepage that spends most of its
	 * time meeting the criteria never quite getting hugified if there are
	 * intervening deallocations).  The idea is that the hugification delay
	 * will allow them to get purged, reseting their "hugify-allowed" bit.
	 * If they don't get purged, then the hugification isn't hurting and
	 * might help.  As an exception, we don't hugify hugepages that are now
	 * empty; it definitely doesn't help there until the hugepage gets
	 * reused, which is likely not for a while.
	 */
	if (hpdata_nactive_get(ps) == 0) {
		hpdata_disallow_hugify(ps);
	}
}

static bool
hpa_shard_has_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	hpdata_t *to_hugify = psset_pick_hugify(&shard->psset);
	return to_hugify != NULL || hpa_should_purge(tsdn, shard);
}

/* Returns whether or not we purged anything. */
static bool
hpa_try_purge(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);

	hpdata_t *to_purge = psset_pick_purge(&shard->psset);
	if (to_purge == NULL) {
		return false;
	}
	assert(hpdata_purge_allowed_get(to_purge));
	assert(!hpdata_changing_state_get(to_purge));

	/*
	 * Don't let anyone else purge or hugify this page while
	 * we're purging it (allocations and deallocations are
	 * OK).
	 */
	psset_update_begin(&shard->psset, to_purge);
	assert(hpdata_alloc_allowed_get(to_purge));
	hpdata_mid_purge_set(to_purge, true);
	hpdata_purge_allowed_set(to_purge, false);
	hpdata_disallow_hugify(to_purge);
	/*
	 * Unlike with hugification (where concurrent
	 * allocations are allowed), concurrent allocation out
	 * of a hugepage being purged is unsafe; we might hand
	 * out an extent for an allocation and then purge it
	 * (clearing out user data).
	 */
	hpdata_alloc_allowed_set(to_purge, false);
	psset_update_end(&shard->psset, to_purge);

	/* Gather all the metadata we'll need during the purge. */
	bool dehugify = hpdata_huge_get(to_purge);
	hpdata_purge_state_t purge_state;
	size_t num_to_purge = hpdata_purge_begin(to_purge, &purge_state);

	shard->npending_purge += num_to_purge;

	malloc_mutex_unlock(tsdn, &shard->mtx);

	/* Actually do the purging, now that the lock is dropped. */
	if (dehugify) {
		shard->central->hooks.dehugify(hpdata_addr_get(to_purge),
		    HUGEPAGE);
	}
	size_t total_purged = 0;
	uint64_t purges_this_pass = 0;
	void *purge_addr;
	size_t purge_size;
	while (hpdata_purge_next(to_purge, &purge_state, &purge_addr,
	    &purge_size)) {
		total_purged += purge_size;
		assert(total_purged <= HUGEPAGE);
		purges_this_pass++;
		shard->central->hooks.purge(purge_addr, purge_size);
	}

	malloc_mutex_lock(tsdn, &shard->mtx);
	/* The shard updates */
	shard->npending_purge -= num_to_purge;
	shard->stats.npurge_passes++;
	shard->stats.npurges += purges_this_pass;
	shard->central->hooks.curtime(&shard->last_purge,
	    /* first_reading */ false);
	if (dehugify) {
		shard->stats.ndehugifies++;
	}

	/* The hpdata updates. */
	psset_update_begin(&shard->psset, to_purge);
	if (dehugify) {
		hpdata_dehugify(to_purge);
	}
	hpdata_purge_end(to_purge, &purge_state);
	hpdata_mid_purge_set(to_purge, false);

	hpdata_alloc_allowed_set(to_purge, true);
	hpa_update_purge_hugify_eligibility(tsdn, shard, to_purge);

	psset_update_end(&shard->psset, to_purge);

	return true;
}

/* Returns whether or not we hugified anything. */
static bool
hpa_try_hugify(tsdn_t *tsdn, hpa_shard_t *shard) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);

	if (hpa_hugify_blocked_by_ndirty(tsdn, shard)) {
		return false;
	}

	hpdata_t *to_hugify = psset_pick_hugify(&shard->psset);
	if (to_hugify == NULL) {
		return false;
	}
	assert(hpdata_hugify_allowed_get(to_hugify));
	assert(!hpdata_changing_state_get(to_hugify));

	/* Make sure that it's been hugifiable for long enough. */
	nstime_t time_hugify_allowed = hpdata_time_hugify_allowed(to_hugify);
	uint64_t millis = shard->central->hooks.ms_since(&time_hugify_allowed);
	if (millis < shard->opts.hugify_delay_ms) {
		return false;
	}

	/*
	 * Don't let anyone else purge or hugify this page while
	 * we're hugifying it (allocations and deallocations are
	 * OK).
	 */
	psset_update_begin(&shard->psset, to_hugify);
	hpdata_mid_hugify_set(to_hugify, true);
	hpdata_purge_allowed_set(to_hugify, false);
	hpdata_disallow_hugify(to_hugify);
	assert(hpdata_alloc_allowed_get(to_hugify));
	psset_update_end(&shard->psset, to_hugify);

	malloc_mutex_unlock(tsdn, &shard->mtx);

	shard->central->hooks.hugify(hpdata_addr_get(to_hugify), HUGEPAGE);

	malloc_mutex_lock(tsdn, &shard->mtx);
	shard->stats.nhugifies++;

	psset_update_begin(&shard->psset, to_hugify);
	hpdata_hugify(to_hugify);
	hpdata_mid_hugify_set(to_hugify, false);
	hpa_update_purge_hugify_eligibility(tsdn, shard, to_hugify);
	psset_update_end(&shard->psset, to_hugify);

	return true;
}

/*
 * Execution of deferred work is forced if it's triggered by an explicit
 * hpa_shard_do_deferred_work() call.
 */
static void
hpa_shard_maybe_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard,
    bool forced) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	if (!forced && shard->opts.deferral_allowed) {
		return;
	}
	/*
	 * If we're on a background thread, do work so long as there's work to
	 * be done.  Otherwise, bound latency to not be *too* bad by doing at
	 * most a small fixed number of operations.
	 */
	bool hugified = false;
	bool purged = false;
	size_t max_ops = (forced ? (size_t)-1 : 16);
	size_t nops = 0;
	do {
		/*
		 * Always purge before hugifying, to make sure we get some
		 * ability to hit our quiescence targets.
		 */
		purged = false;
		while (hpa_should_purge(tsdn, shard) && nops < max_ops) {
			purged = hpa_try_purge(tsdn, shard);
			if (purged) {
				nops++;
			}
		}
		hugified = hpa_try_hugify(tsdn, shard);
		if (hugified) {
			nops++;
		}
		malloc_mutex_assert_owner(tsdn, &shard->mtx);
		malloc_mutex_assert_owner(tsdn, &shard->mtx);
	} while ((hugified || purged) && nops < max_ops);
}

static edata_t *
hpa_try_alloc_one_no_grow(tsdn_t *tsdn, hpa_shard_t *shard, size_t size,
    bool *oom) {
	bool err;
	edata_t *edata = edata_cache_fast_get(tsdn, &shard->ecf);
	if (edata == NULL) {
		*oom = true;
		return NULL;
	}

	hpdata_t *ps = psset_pick_alloc(&shard->psset, size);
	if (ps == NULL) {
		edata_cache_fast_put(tsdn, &shard->ecf, edata);
		return NULL;
	}

	psset_update_begin(&shard->psset, ps);

	if (hpdata_empty(ps)) {
		/*
		 * If the pageslab used to be empty, treat it as though it's
		 * brand new for fragmentation-avoidance purposes; what we're
		 * trying to approximate is the age of the allocations *in* that
		 * pageslab, and the allocations in the new pageslab are
		 * definitionally the youngest in this hpa shard.
		 */
		hpdata_age_set(ps, shard->age_counter++);
	}

	void *addr = hpdata_reserve_alloc(ps, size);
	edata_init(edata, shard->ind, addr, size, /* slab */ false,
	    SC_NSIZES, /* sn */ hpdata_age_get(ps), extent_state_active,
	    /* zeroed */ false, /* committed */ true, EXTENT_PAI_HPA,
	    EXTENT_NOT_HEAD);
	edata_ps_set(edata, ps);

	/*
	 * This could theoretically be moved outside of the critical section,
	 * but that introduces the potential for a race.  Without the lock, the
	 * (initially nonempty, since this is the reuse pathway) pageslab we
	 * allocated out of could become otherwise empty while the lock is
	 * dropped.  This would force us to deal with a pageslab eviction down
	 * the error pathway, which is a pain.
	 */
	err = emap_register_boundary(tsdn, shard->emap, edata,
	    SC_NSIZES, /* slab */ false);
	if (err) {
		hpdata_unreserve(ps, edata_addr_get(edata),
		    edata_size_get(edata));
		/*
		 * We should arguably reset dirty state here, but this would
		 * require some sort of prepare + commit functionality that's a
		 * little much to deal with for now.
		 *
		 * We don't have a do_deferred_work down this pathway, on the
		 * principle that we didn't *really* affect shard state (we
		 * tweaked the stats, but our tweaks weren't really accurate).
		 */
		psset_update_end(&shard->psset, ps);
		edata_cache_fast_put(tsdn, &shard->ecf, edata);
		*oom = true;
		return NULL;
	}

	hpa_update_purge_hugify_eligibility(tsdn, shard, ps);
	psset_update_end(&shard->psset, ps);
	return edata;
}

static size_t
hpa_try_alloc_batch_no_grow(tsdn_t *tsdn, hpa_shard_t *shard, size_t size,
    bool *oom, size_t nallocs, edata_list_active_t *results,
    bool *deferred_work_generated) {
	malloc_mutex_lock(tsdn, &shard->mtx);
	size_t nsuccess = 0;
	for (; nsuccess < nallocs; nsuccess++) {
		edata_t *edata = hpa_try_alloc_one_no_grow(tsdn, shard, size,
		    oom);
		if (edata == NULL) {
			break;
		}
		edata_list_active_append(results, edata);
	}

	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ false);
	*deferred_work_generated = hpa_shard_has_deferred_work(tsdn, shard);
	malloc_mutex_unlock(tsdn, &shard->mtx);
	return nsuccess;
}

static size_t
hpa_alloc_batch_psset(tsdn_t *tsdn, hpa_shard_t *shard, size_t size,
    size_t nallocs, edata_list_active_t *results,
    bool *deferred_work_generated) {
	assert(size <= shard->opts.slab_max_alloc);
	bool oom = false;

	size_t nsuccess = hpa_try_alloc_batch_no_grow(tsdn, shard, size, &oom,
	    nallocs, results, deferred_work_generated);

	if (nsuccess == nallocs || oom) {
		return nsuccess;
	}

	/*
	 * We didn't OOM, but weren't able to fill everything requested of us;
	 * try to grow.
	 */
	malloc_mutex_lock(tsdn, &shard->grow_mtx);
	/*
	 * Check for grow races; maybe some earlier thread expanded the psset
	 * in between when we dropped the main mutex and grabbed the grow mutex.
	 */
	nsuccess += hpa_try_alloc_batch_no_grow(tsdn, shard, size, &oom,
	    nallocs - nsuccess, results, deferred_work_generated);
	if (nsuccess == nallocs || oom) {
		malloc_mutex_unlock(tsdn, &shard->grow_mtx);
		return nsuccess;
	}

	/*
	 * Note that we don't hold shard->mtx here (while growing);
	 * deallocations (and allocations of smaller sizes) may still succeed
	 * while we're doing this potentially expensive system call.
	 */
	hpdata_t *ps = hpa_central_extract(tsdn, shard->central, size, &oom);
	if (ps == NULL) {
		malloc_mutex_unlock(tsdn, &shard->grow_mtx);
		return nsuccess;
	}

	/*
	 * We got the pageslab; allocate from it.  This does an unlock followed
	 * by a lock on the same mutex, and holds the grow mutex while doing
	 * deferred work, but this is an uncommon path; the simplicity is worth
	 * it.
	 */
	malloc_mutex_lock(tsdn, &shard->mtx);
	psset_insert(&shard->psset, ps);
	malloc_mutex_unlock(tsdn, &shard->mtx);

	nsuccess += hpa_try_alloc_batch_no_grow(tsdn, shard, size, &oom,
	    nallocs - nsuccess, results, deferred_work_generated);
	/*
	 * Drop grow_mtx before doing deferred work; other threads blocked on it
	 * should be allowed to proceed while we're working.
	 */
	malloc_mutex_unlock(tsdn, &shard->grow_mtx);

	return nsuccess;
}

static hpa_shard_t *
hpa_from_pai(pai_t *self) {
	assert(self->alloc = &hpa_alloc);
	assert(self->expand = &hpa_expand);
	assert(self->shrink = &hpa_shrink);
	assert(self->dalloc = &hpa_dalloc);
	return (hpa_shard_t *)self;
}

static size_t
hpa_alloc_batch(tsdn_t *tsdn, pai_t *self, size_t size, size_t nallocs,
    edata_list_active_t *results, bool *deferred_work_generated) {
	assert(nallocs > 0);
	assert((size & PAGE_MASK) == 0);
	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
	    WITNESS_RANK_CORE, 0);
	hpa_shard_t *shard = hpa_from_pai(self);

	if (size > shard->opts.slab_max_alloc) {
		return 0;
	}

	size_t nsuccess = hpa_alloc_batch_psset(tsdn, shard, size, nallocs,
	    results, deferred_work_generated);

	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
	    WITNESS_RANK_CORE, 0);

	/*
	 * Guard the sanity checks with config_debug because the loop cannot be
	 * proven non-circular by the compiler, even if everything within the
	 * loop is optimized away.
	 */
	if (config_debug) {
		edata_t *edata;
		ql_foreach(edata, &results->head, ql_link_active) {
			emap_assert_mapped(tsdn, shard->emap, edata);
			assert(edata_pai_get(edata) == EXTENT_PAI_HPA);
			assert(edata_state_get(edata) == extent_state_active);
			assert(edata_arena_ind_get(edata) == shard->ind);
			assert(edata_szind_get_maybe_invalid(edata) ==
			    SC_NSIZES);
			assert(!edata_slab_get(edata));
			assert(edata_committed_get(edata));
			assert(edata_base_get(edata) == edata_addr_get(edata));
			assert(edata_base_get(edata) != NULL);
		}
	}
	return nsuccess;
}

static edata_t *
hpa_alloc(tsdn_t *tsdn, pai_t *self, size_t size, size_t alignment, bool zero,
    bool guarded, bool frequent_reuse, bool *deferred_work_generated) {
	assert((size & PAGE_MASK) == 0);
	assert(!guarded);
	witness_assert_depth_to_rank(tsdn_witness_tsdp_get(tsdn),
	    WITNESS_RANK_CORE, 0);

	/* We don't handle alignment or zeroing for now. */
	if (alignment > PAGE || zero) {
		return NULL;
	}
	/*
	 * An alloc with alignment == PAGE and zero == false is equivalent to a
	 * batch alloc of 1.  Just do that, so we can share code.
	 */
	edata_list_active_t results;
	edata_list_active_init(&results);
	size_t nallocs = hpa_alloc_batch(tsdn, self, size, /* nallocs */ 1,
	    &results, deferred_work_generated);
	assert(nallocs == 0 || nallocs == 1);
	edata_t *edata = edata_list_active_first(&results);
	return edata;
}

static bool
hpa_expand(tsdn_t *tsdn, pai_t *self, edata_t *edata, size_t old_size,
    size_t new_size, bool zero, bool *deferred_work_generated) {
	/* Expand not yet supported. */
	return true;
}

static bool
hpa_shrink(tsdn_t *tsdn, pai_t *self, edata_t *edata,
    size_t old_size, size_t new_size, bool *deferred_work_generated) {
	/* Shrink not yet supported. */
	return true;
}

static void
hpa_dalloc_prepare_unlocked(tsdn_t *tsdn, hpa_shard_t *shard, edata_t *edata) {
	malloc_mutex_assert_not_owner(tsdn, &shard->mtx);

	assert(edata_pai_get(edata) == EXTENT_PAI_HPA);
	assert(edata_state_get(edata) == extent_state_active);
	assert(edata_arena_ind_get(edata) == shard->ind);
	assert(edata_szind_get_maybe_invalid(edata) == SC_NSIZES);
	assert(edata_committed_get(edata));
	assert(edata_base_get(edata) != NULL);

	/*
	 * Another thread shouldn't be trying to touch the metadata of an
	 * allocation being freed.  The one exception is a merge attempt from a
	 * lower-addressed PAC extent; in this case we have a nominal race on
	 * the edata metadata bits, but in practice the fact that the PAI bits
	 * are different will prevent any further access.  The race is bad, but
	 * benign in practice, and the long term plan is to track enough state
	 * in the rtree to prevent these merge attempts in the first place.
	 */
	edata_addr_set(edata, edata_base_get(edata));
	edata_zeroed_set(edata, false);
	emap_deregister_boundary(tsdn, shard->emap, edata);
}

static void
hpa_dalloc_locked(tsdn_t *tsdn, hpa_shard_t *shard, edata_t *edata) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);

	/*
	 * Release the metadata early, to avoid having to remember to do it
	 * while we're also doing tricky purging logic.  First, we need to grab
	 * a few bits of metadata from it.
	 *
	 * Note that the shard mutex protects ps's metadata too; it wouldn't be
	 * correct to try to read most information out of it without the lock.
	 */
	hpdata_t *ps = edata_ps_get(edata);
	/* Currently, all edatas come from pageslabs. */
	assert(ps != NULL);
	void *unreserve_addr = edata_addr_get(edata);
	size_t unreserve_size = edata_size_get(edata);
	edata_cache_fast_put(tsdn, &shard->ecf, edata);

	psset_update_begin(&shard->psset, ps);
	hpdata_unreserve(ps, unreserve_addr, unreserve_size);
	hpa_update_purge_hugify_eligibility(tsdn, shard, ps);
	psset_update_end(&shard->psset, ps);
}

static void
hpa_dalloc_batch(tsdn_t *tsdn, pai_t *self, edata_list_active_t *list,
    bool *deferred_work_generated) {
	hpa_shard_t *shard = hpa_from_pai(self);

	edata_t *edata;
	ql_foreach(edata, &list->head, ql_link_active) {
		hpa_dalloc_prepare_unlocked(tsdn, shard, edata);
	}

	malloc_mutex_lock(tsdn, &shard->mtx);
	/* Now, remove from the list. */
	while ((edata = edata_list_active_first(list)) != NULL) {
		edata_list_active_remove(list, edata);
		hpa_dalloc_locked(tsdn, shard, edata);
	}
	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ false);
	*deferred_work_generated =
	    hpa_shard_has_deferred_work(tsdn, shard);

	malloc_mutex_unlock(tsdn, &shard->mtx);
}

static void
hpa_dalloc(tsdn_t *tsdn, pai_t *self, edata_t *edata,
    bool *deferred_work_generated) {
	assert(!edata_guarded_get(edata));
	/* Just a dalloc_batch of size 1; this lets us share logic. */
	edata_list_active_t dalloc_list;
	edata_list_active_init(&dalloc_list);
	edata_list_active_append(&dalloc_list, edata);
	hpa_dalloc_batch(tsdn, self, &dalloc_list, deferred_work_generated);
}

/*
 * Calculate time until either purging or hugification ought to happen.
 * Called by background threads.
 */
static uint64_t
hpa_time_until_deferred_work(tsdn_t *tsdn, pai_t *self) {
	hpa_shard_t *shard = hpa_from_pai(self);
	uint64_t time_ns = BACKGROUND_THREAD_DEFERRED_MAX;

	malloc_mutex_lock(tsdn, &shard->mtx);

	hpdata_t *to_hugify = psset_pick_hugify(&shard->psset);
	if (to_hugify != NULL) {
		nstime_t time_hugify_allowed =
		    hpdata_time_hugify_allowed(to_hugify);
		uint64_t since_hugify_allowed_ms =
		    shard->central->hooks.ms_since(&time_hugify_allowed);
		/*
		 * If not enough time has passed since hugification was allowed,
		 * sleep for the rest.
		 */
		if (since_hugify_allowed_ms < shard->opts.hugify_delay_ms) {
			time_ns = shard->opts.hugify_delay_ms -
			    since_hugify_allowed_ms;
			time_ns *= 1000 * 1000;
		} else {
			malloc_mutex_unlock(tsdn, &shard->mtx);
			return BACKGROUND_THREAD_DEFERRED_MIN;
		}
	}

	if (hpa_should_purge(tsdn, shard)) {
		/*
		 * If we haven't purged before, no need to check interval
		 * between purges. Simply purge as soon as possible.
		 */
		if (shard->stats.npurge_passes == 0) {
			malloc_mutex_unlock(tsdn, &shard->mtx);
			return BACKGROUND_THREAD_DEFERRED_MIN;
		}
		uint64_t since_last_purge_ms = shard->central->hooks.ms_since(
		    &shard->last_purge);

		if (since_last_purge_ms < shard->opts.min_purge_interval_ms) {
			uint64_t until_purge_ns;
			until_purge_ns = shard->opts.min_purge_interval_ms -
			    since_last_purge_ms;
			until_purge_ns *= 1000 * 1000;

			if (until_purge_ns < time_ns) {
				time_ns = until_purge_ns;
			}
		} else {
			time_ns = BACKGROUND_THREAD_DEFERRED_MIN;
		}
	}
	malloc_mutex_unlock(tsdn, &shard->mtx);
	return time_ns;
}

void
hpa_shard_disable(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_lock(tsdn, &shard->mtx);
	edata_cache_fast_disable(tsdn, &shard->ecf);
	malloc_mutex_unlock(tsdn, &shard->mtx);
}

static void
hpa_shard_assert_stats_empty(psset_bin_stats_t *bin_stats) {
	assert(bin_stats->npageslabs == 0);
	assert(bin_stats->nactive == 0);
}

static void
hpa_assert_empty(tsdn_t *tsdn, hpa_shard_t *shard, psset_t *psset) {
	malloc_mutex_assert_owner(tsdn, &shard->mtx);
	for (int huge = 0; huge <= 1; huge++) {
		hpa_shard_assert_stats_empty(&psset->stats.full_slabs[huge]);
		for (pszind_t i = 0; i < PSSET_NPSIZES; i++) {
			hpa_shard_assert_stats_empty(
			    &psset->stats.nonfull_slabs[i][huge]);
		}
	}
}

void
hpa_shard_destroy(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);
	/*
	 * By the time we're here, the arena code should have dalloc'd all the
	 * active extents, which means we should have eventually evicted
	 * everything from the psset, so it shouldn't be able to serve even a
	 * 1-page allocation.
	 */
	if (config_debug) {
		malloc_mutex_lock(tsdn, &shard->mtx);
		hpa_assert_empty(tsdn, shard, &shard->psset);
		malloc_mutex_unlock(tsdn, &shard->mtx);
	}
	hpdata_t *ps;
	while ((ps = psset_pick_alloc(&shard->psset, PAGE)) != NULL) {
		/* There should be no allocations anywhere. */
		assert(hpdata_empty(ps));
		psset_remove(&shard->psset, ps);
		shard->central->hooks.unmap(hpdata_addr_get(ps), HUGEPAGE);
	}
}

void
hpa_shard_set_deferral_allowed(tsdn_t *tsdn, hpa_shard_t *shard,
    bool deferral_allowed) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_lock(tsdn, &shard->mtx);
	bool deferral_previously_allowed = shard->opts.deferral_allowed;
	shard->opts.deferral_allowed = deferral_allowed;
	if (deferral_previously_allowed && !deferral_allowed) {
		hpa_shard_maybe_do_deferred_work(tsdn, shard,
		    /* forced */ true);
	}
	malloc_mutex_unlock(tsdn, &shard->mtx);
}

void
hpa_shard_do_deferred_work(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_lock(tsdn, &shard->mtx);
	hpa_shard_maybe_do_deferred_work(tsdn, shard, /* forced */ true);
	malloc_mutex_unlock(tsdn, &shard->mtx);
}

void
hpa_shard_prefork3(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_prefork(tsdn, &shard->grow_mtx);
}

void
hpa_shard_prefork4(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_prefork(tsdn, &shard->mtx);
}

void
hpa_shard_postfork_parent(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_postfork_parent(tsdn, &shard->grow_mtx);
	malloc_mutex_postfork_parent(tsdn, &shard->mtx);
}

void
hpa_shard_postfork_child(tsdn_t *tsdn, hpa_shard_t *shard) {
	hpa_do_consistency_checks(shard);

	malloc_mutex_postfork_child(tsdn, &shard->grow_mtx);
	malloc_mutex_postfork_child(tsdn, &shard->mtx);
}