aboutsummaryrefslogtreecommitdiffstats
path: root/module/os/linux/spl/spl-kmem-cache.c
blob: 6b3d559ffc1c3933eea241da618e41aa2c87e7ba (plain) (blame)
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
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
/*
 *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
 *  Copyright (C) 2007 The Regents of the University of California.
 *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
 *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
 *  UCRL-CODE-235197
 *
 *  This file is part of the SPL, Solaris Porting Layer.
 *
 *  The SPL is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the
 *  Free Software Foundation; either version 2 of the License, or (at your
 *  option) any later version.
 *
 *  The SPL is distributed in the hope that it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/percpu_compat.h>
#include <sys/kmem.h>
#include <sys/kmem_cache.h>
#include <sys/taskq.h>
#include <sys/timer.h>
#include <sys/vmem.h>
#include <sys/wait.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/prefetch.h>

/*
 * Within the scope of spl-kmem.c file the kmem_cache_* definitions
 * are removed to allow access to the real Linux slab allocator.
 */
#undef kmem_cache_destroy
#undef kmem_cache_create
#undef kmem_cache_alloc
#undef kmem_cache_free


/*
 * Linux 3.16 replaced smp_mb__{before,after}_{atomic,clear}_{dec,inc,bit}()
 * with smp_mb__{before,after}_atomic() because they were redundant. This is
 * only used inside our SLAB allocator, so we implement an internal wrapper
 * here to give us smp_mb__{before,after}_atomic() on older kernels.
 */
#ifndef smp_mb__before_atomic
#define	smp_mb__before_atomic(x) smp_mb__before_clear_bit(x)
#endif

#ifndef smp_mb__after_atomic
#define	smp_mb__after_atomic(x) smp_mb__after_clear_bit(x)
#endif

/* BEGIN CSTYLED */

/*
 * Cache magazines are an optimization designed to minimize the cost of
 * allocating memory.  They do this by keeping a per-cpu cache of recently
 * freed objects, which can then be reallocated without taking a lock. This
 * can improve performance on highly contended caches.  However, because
 * objects in magazines will prevent otherwise empty slabs from being
 * immediately released this may not be ideal for low memory machines.
 *
 * For this reason spl_kmem_cache_magazine_size can be used to set a maximum
 * magazine size.  When this value is set to 0 the magazine size will be
 * automatically determined based on the object size.  Otherwise magazines
 * will be limited to 2-256 objects per magazine (i.e per cpu).  Magazines
 * may never be entirely disabled in this implementation.
 */
unsigned int spl_kmem_cache_magazine_size = 0;
module_param(spl_kmem_cache_magazine_size, uint, 0444);
MODULE_PARM_DESC(spl_kmem_cache_magazine_size,
	"Default magazine size (2-256), set automatically (0)");

/*
 * The default behavior is to report the number of objects remaining in the
 * cache.  This allows the Linux VM to repeatedly reclaim objects from the
 * cache when memory is low satisfy other memory allocations.  Alternately,
 * setting this value to KMC_RECLAIM_ONCE limits how aggressively the cache
 * is reclaimed.  This may increase the likelihood of out of memory events.
 */
unsigned int spl_kmem_cache_reclaim = 0 /* KMC_RECLAIM_ONCE */;
module_param(spl_kmem_cache_reclaim, uint, 0644);
MODULE_PARM_DESC(spl_kmem_cache_reclaim, "Single reclaim pass (0x1)");

unsigned int spl_kmem_cache_obj_per_slab = SPL_KMEM_CACHE_OBJ_PER_SLAB;
module_param(spl_kmem_cache_obj_per_slab, uint, 0644);
MODULE_PARM_DESC(spl_kmem_cache_obj_per_slab, "Number of objects per slab");

unsigned int spl_kmem_cache_max_size = SPL_KMEM_CACHE_MAX_SIZE;
module_param(spl_kmem_cache_max_size, uint, 0644);
MODULE_PARM_DESC(spl_kmem_cache_max_size, "Maximum size of slab in MB");

/*
 * For small objects the Linux slab allocator should be used to make the most
 * efficient use of the memory.  However, large objects are not supported by
 * the Linux slab and therefore the SPL implementation is preferred.  A cutoff
 * of 16K was determined to be optimal for architectures using 4K pages.
 */
#if PAGE_SIZE == 4096
unsigned int spl_kmem_cache_slab_limit = 16384;
#else
unsigned int spl_kmem_cache_slab_limit = 0;
#endif
module_param(spl_kmem_cache_slab_limit, uint, 0644);
MODULE_PARM_DESC(spl_kmem_cache_slab_limit,
	"Objects less than N bytes use the Linux slab");

/*
 * The number of threads available to allocate new slabs for caches.  This
 * should not need to be tuned but it is available for performance analysis.
 */
unsigned int spl_kmem_cache_kmem_threads = 4;
module_param(spl_kmem_cache_kmem_threads, uint, 0444);
MODULE_PARM_DESC(spl_kmem_cache_kmem_threads,
	"Number of spl_kmem_cache threads");
/* END CSTYLED */

/*
 * Slab allocation interfaces
 *
 * While the Linux slab implementation was inspired by the Solaris
 * implementation I cannot use it to emulate the Solaris APIs.  I
 * require two features which are not provided by the Linux slab.
 *
 * 1) Constructors AND destructors.  Recent versions of the Linux
 *    kernel have removed support for destructors.  This is a deal
 *    breaker for the SPL which contains particularly expensive
 *    initializers for mutex's, condition variables, etc.  We also
 *    require a minimal level of cleanup for these data types unlike
 *    many Linux data types which do need to be explicitly destroyed.
 *
 * 2) Virtual address space backed slab.  Callers of the Solaris slab
 *    expect it to work well for both small are very large allocations.
 *    Because of memory fragmentation the Linux slab which is backed
 *    by kmalloc'ed memory performs very badly when confronted with
 *    large numbers of large allocations.  Basing the slab on the
 *    virtual address space removes the need for contiguous pages
 *    and greatly improve performance for large allocations.
 *
 * For these reasons, the SPL has its own slab implementation with
 * the needed features.  It is not as highly optimized as either the
 * Solaris or Linux slabs, but it should get me most of what is
 * needed until it can be optimized or obsoleted by another approach.
 *
 * One serious concern I do have about this method is the relatively
 * small virtual address space on 32bit arches.  This will seriously
 * constrain the size of the slab caches and their performance.
 */

struct list_head spl_kmem_cache_list;   /* List of caches */
struct rw_semaphore spl_kmem_cache_sem; /* Cache list lock */
taskq_t *spl_kmem_cache_taskq;		/* Task queue for aging / reclaim */

static void spl_cache_shrink(spl_kmem_cache_t *skc, void *obj);

static void *
kv_alloc(spl_kmem_cache_t *skc, int size, int flags)
{
	gfp_t lflags = kmem_flags_convert(flags);
	void *ptr;

	ptr = spl_vmalloc(size, lflags | __GFP_HIGHMEM);

	/* Resulting allocated memory will be page aligned */
	ASSERT(IS_P2ALIGNED(ptr, PAGE_SIZE));

	return (ptr);
}

static void
kv_free(spl_kmem_cache_t *skc, void *ptr, int size)
{
	ASSERT(IS_P2ALIGNED(ptr, PAGE_SIZE));

	/*
	 * The Linux direct reclaim path uses this out of band value to
	 * determine if forward progress is being made.  Normally this is
	 * incremented by kmem_freepages() which is part of the various
	 * Linux slab implementations.  However, since we are using none
	 * of that infrastructure we are responsible for incrementing it.
	 */
	if (current->reclaim_state)
		current->reclaim_state->reclaimed_slab += size >> PAGE_SHIFT;

	vfree(ptr);
}

/*
 * Required space for each aligned sks.
 */
static inline uint32_t
spl_sks_size(spl_kmem_cache_t *skc)
{
	return (P2ROUNDUP_TYPED(sizeof (spl_kmem_slab_t),
	    skc->skc_obj_align, uint32_t));
}

/*
 * Required space for each aligned object.
 */
static inline uint32_t
spl_obj_size(spl_kmem_cache_t *skc)
{
	uint32_t align = skc->skc_obj_align;

	return (P2ROUNDUP_TYPED(skc->skc_obj_size, align, uint32_t) +
	    P2ROUNDUP_TYPED(sizeof (spl_kmem_obj_t), align, uint32_t));
}

uint64_t
spl_kmem_cache_inuse(kmem_cache_t *cache)
{
	return (cache->skc_obj_total);
}
EXPORT_SYMBOL(spl_kmem_cache_inuse);

uint64_t
spl_kmem_cache_entry_size(kmem_cache_t *cache)
{
	return (cache->skc_obj_size);
}
EXPORT_SYMBOL(spl_kmem_cache_entry_size);

/*
 * Lookup the spl_kmem_object_t for an object given that object.
 */
static inline spl_kmem_obj_t *
spl_sko_from_obj(spl_kmem_cache_t *skc, void *obj)
{
	return (obj + P2ROUNDUP_TYPED(skc->skc_obj_size,
	    skc->skc_obj_align, uint32_t));
}

/*
 * It's important that we pack the spl_kmem_obj_t structure and the
 * actual objects in to one large address space to minimize the number
 * of calls to the allocator.  It is far better to do a few large
 * allocations and then subdivide it ourselves.  Now which allocator
 * we use requires balancing a few trade offs.
 *
 * For small objects we use kmem_alloc() because as long as you are
 * only requesting a small number of pages (ideally just one) its cheap.
 * However, when you start requesting multiple pages with kmem_alloc()
 * it gets increasingly expensive since it requires contiguous pages.
 * For this reason we shift to vmem_alloc() for slabs of large objects
 * which removes the need for contiguous pages.  We do not use
 * vmem_alloc() in all cases because there is significant locking
 * overhead in __get_vm_area_node().  This function takes a single
 * global lock when acquiring an available virtual address range which
 * serializes all vmem_alloc()'s for all slab caches.  Using slightly
 * different allocation functions for small and large objects should
 * give us the best of both worlds.
 *
 * +------------------------+
 * | spl_kmem_slab_t --+-+  |
 * | skc_obj_size    <-+ |  |
 * | spl_kmem_obj_t      |  |
 * | skc_obj_size    <---+  |
 * | spl_kmem_obj_t      |  |
 * | ...                 v  |
 * +------------------------+
 */
static spl_kmem_slab_t *
spl_slab_alloc(spl_kmem_cache_t *skc, int flags)
{
	spl_kmem_slab_t *sks;
	void *base;
	uint32_t obj_size;

	base = kv_alloc(skc, skc->skc_slab_size, flags);
	if (base == NULL)
		return (NULL);

	sks = (spl_kmem_slab_t *)base;
	sks->sks_magic = SKS_MAGIC;
	sks->sks_objs = skc->skc_slab_objs;
	sks->sks_age = jiffies;
	sks->sks_cache = skc;
	INIT_LIST_HEAD(&sks->sks_list);
	INIT_LIST_HEAD(&sks->sks_free_list);
	sks->sks_ref = 0;
	obj_size = spl_obj_size(skc);

	for (int i = 0; i < sks->sks_objs; i++) {
		void *obj = base + spl_sks_size(skc) + (i * obj_size);

		ASSERT(IS_P2ALIGNED(obj, skc->skc_obj_align));
		spl_kmem_obj_t *sko = spl_sko_from_obj(skc, obj);
		sko->sko_addr = obj;
		sko->sko_magic = SKO_MAGIC;
		sko->sko_slab = sks;
		INIT_LIST_HEAD(&sko->sko_list);
		list_add_tail(&sko->sko_list, &sks->sks_free_list);
	}

	return (sks);
}

/*
 * Remove a slab from complete or partial list, it must be called with
 * the 'skc->skc_lock' held but the actual free must be performed
 * outside the lock to prevent deadlocking on vmem addresses.
 */
static void
spl_slab_free(spl_kmem_slab_t *sks,
    struct list_head *sks_list, struct list_head *sko_list)
{
	spl_kmem_cache_t *skc;

	ASSERT(sks->sks_magic == SKS_MAGIC);
	ASSERT(sks->sks_ref == 0);

	skc = sks->sks_cache;
	ASSERT(skc->skc_magic == SKC_MAGIC);

	/*
	 * Update slab/objects counters in the cache, then remove the
	 * slab from the skc->skc_partial_list.  Finally add the slab
	 * and all its objects in to the private work lists where the
	 * destructors will be called and the memory freed to the system.
	 */
	skc->skc_obj_total -= sks->sks_objs;
	skc->skc_slab_total--;
	list_del(&sks->sks_list);
	list_add(&sks->sks_list, sks_list);
	list_splice_init(&sks->sks_free_list, sko_list);
}

/*
 * Reclaim empty slabs at the end of the partial list.
 */
static void
spl_slab_reclaim(spl_kmem_cache_t *skc)
{
	spl_kmem_slab_t *sks = NULL, *m = NULL;
	spl_kmem_obj_t *sko = NULL, *n = NULL;
	LIST_HEAD(sks_list);
	LIST_HEAD(sko_list);

	/*
	 * Empty slabs and objects must be moved to a private list so they
	 * can be safely freed outside the spin lock.  All empty slabs are
	 * at the end of skc->skc_partial_list, therefore once a non-empty
	 * slab is found we can stop scanning.
	 */
	spin_lock(&skc->skc_lock);
	list_for_each_entry_safe_reverse(sks, m,
	    &skc->skc_partial_list, sks_list) {

		if (sks->sks_ref > 0)
			break;

		spl_slab_free(sks, &sks_list, &sko_list);
	}
	spin_unlock(&skc->skc_lock);

	/*
	 * The following two loops ensure all the object destructors are run,
	 * and the slabs themselves are freed.  This is all done outside the
	 * skc->skc_lock since this allows the destructor to sleep, and
	 * allows us to perform a conditional reschedule when a freeing a
	 * large number of objects and slabs back to the system.
	 */

	list_for_each_entry_safe(sko, n, &sko_list, sko_list) {
		ASSERT(sko->sko_magic == SKO_MAGIC);
	}

	list_for_each_entry_safe(sks, m, &sks_list, sks_list) {
		ASSERT(sks->sks_magic == SKS_MAGIC);
		kv_free(skc, sks, skc->skc_slab_size);
	}
}

static spl_kmem_emergency_t *
spl_emergency_search(struct rb_root *root, void *obj)
{
	struct rb_node *node = root->rb_node;
	spl_kmem_emergency_t *ske;
	unsigned long address = (unsigned long)obj;

	while (node) {
		ske = container_of(node, spl_kmem_emergency_t, ske_node);

		if (address < ske->ske_obj)
			node = node->rb_left;
		else if (address > ske->ske_obj)
			node = node->rb_right;
		else
			return (ske);
	}

	return (NULL);
}

static int
spl_emergency_insert(struct rb_root *root, spl_kmem_emergency_t *ske)
{
	struct rb_node **new = &(root->rb_node), *parent = NULL;
	spl_kmem_emergency_t *ske_tmp;
	unsigned long address = ske->ske_obj;

	while (*new) {
		ske_tmp = container_of(*new, spl_kmem_emergency_t, ske_node);

		parent = *new;
		if (address < ske_tmp->ske_obj)
			new = &((*new)->rb_left);
		else if (address > ske_tmp->ske_obj)
			new = &((*new)->rb_right);
		else
			return (0);
	}

	rb_link_node(&ske->ske_node, parent, new);
	rb_insert_color(&ske->ske_node, root);

	return (1);
}

/*
 * Allocate a single emergency object and track it in a red black tree.
 */
static int
spl_emergency_alloc(spl_kmem_cache_t *skc, int flags, void **obj)
{
	gfp_t lflags = kmem_flags_convert(flags);
	spl_kmem_emergency_t *ske;
	int order = get_order(skc->skc_obj_size);
	int empty;

	/* Last chance use a partial slab if one now exists */
	spin_lock(&skc->skc_lock);
	empty = list_empty(&skc->skc_partial_list);
	spin_unlock(&skc->skc_lock);
	if (!empty)
		return (-EEXIST);

	ske = kmalloc(sizeof (*ske), lflags);
	if (ske == NULL)
		return (-ENOMEM);

	ske->ske_obj = __get_free_pages(lflags, order);
	if (ske->ske_obj == 0) {
		kfree(ske);
		return (-ENOMEM);
	}

	spin_lock(&skc->skc_lock);
	empty = spl_emergency_insert(&skc->skc_emergency_tree, ske);
	if (likely(empty)) {
		skc->skc_obj_total++;
		skc->skc_obj_emergency++;
		if (skc->skc_obj_emergency > skc->skc_obj_emergency_max)
			skc->skc_obj_emergency_max = skc->skc_obj_emergency;
	}
	spin_unlock(&skc->skc_lock);

	if (unlikely(!empty)) {
		free_pages(ske->ske_obj, order);
		kfree(ske);
		return (-EINVAL);
	}

	*obj = (void *)ske->ske_obj;

	return (0);
}

/*
 * Locate the passed object in the red black tree and free it.
 */
static int
spl_emergency_free(spl_kmem_cache_t *skc, void *obj)
{
	spl_kmem_emergency_t *ske;
	int order = get_order(skc->skc_obj_size);

	spin_lock(&skc->skc_lock);
	ske = spl_emergency_search(&skc->skc_emergency_tree, obj);
	if (ske) {
		rb_erase(&ske->ske_node, &skc->skc_emergency_tree);
		skc->skc_obj_emergency--;
		skc->skc_obj_total--;
	}
	spin_unlock(&skc->skc_lock);

	if (ske == NULL)
		return (-ENOENT);

	free_pages(ske->ske_obj, order);
	kfree(ske);

	return (0);
}

/*
 * Release objects from the per-cpu magazine back to their slab.  The flush
 * argument contains the max number of entries to remove from the magazine.
 */
static void
spl_cache_flush(spl_kmem_cache_t *skc, spl_kmem_magazine_t *skm, int flush)
{
	spin_lock(&skc->skc_lock);

	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(skm->skm_magic == SKM_MAGIC);

	int count = MIN(flush, skm->skm_avail);
	for (int i = 0; i < count; i++)
		spl_cache_shrink(skc, skm->skm_objs[i]);

	skm->skm_avail -= count;
	memmove(skm->skm_objs, &(skm->skm_objs[count]),
	    sizeof (void *) * skm->skm_avail);

	spin_unlock(&skc->skc_lock);
}

/*
 * Size a slab based on the size of each aligned object plus spl_kmem_obj_t.
 * When on-slab we want to target spl_kmem_cache_obj_per_slab.  However,
 * for very small objects we may end up with more than this so as not
 * to waste space in the minimal allocation of a single page.  Also for
 * very large objects we may use as few as spl_kmem_cache_obj_per_slab_min,
 * lower than this and we will fail.
 */
static int
spl_slab_size(spl_kmem_cache_t *skc, uint32_t *objs, uint32_t *size)
{
	uint32_t sks_size, obj_size, max_size, tgt_size, tgt_objs;

	sks_size = spl_sks_size(skc);
	obj_size = spl_obj_size(skc);
	max_size = (spl_kmem_cache_max_size * 1024 * 1024);
	tgt_size = (spl_kmem_cache_obj_per_slab * obj_size + sks_size);

	if (tgt_size <= max_size) {
		tgt_objs = (tgt_size - sks_size) / obj_size;
	} else {
		tgt_objs = (max_size - sks_size) / obj_size;
		tgt_size = (tgt_objs * obj_size) + sks_size;
	}

	if (tgt_objs == 0)
		return (-ENOSPC);

	*objs = tgt_objs;
	*size = tgt_size;

	return (0);
}

/*
 * Make a guess at reasonable per-cpu magazine size based on the size of
 * each object and the cost of caching N of them in each magazine.  Long
 * term this should really adapt based on an observed usage heuristic.
 */
static int
spl_magazine_size(spl_kmem_cache_t *skc)
{
	uint32_t obj_size = spl_obj_size(skc);
	int size;

	if (spl_kmem_cache_magazine_size > 0)
		return (MAX(MIN(spl_kmem_cache_magazine_size, 256), 2));

	/* Per-magazine sizes below assume a 4Kib page size */
	if (obj_size > (PAGE_SIZE * 256))
		size = 4;  /* Minimum 4Mib per-magazine */
	else if (obj_size > (PAGE_SIZE * 32))
		size = 16; /* Minimum 2Mib per-magazine */
	else if (obj_size > (PAGE_SIZE))
		size = 64; /* Minimum 256Kib per-magazine */
	else if (obj_size > (PAGE_SIZE / 4))
		size = 128; /* Minimum 128Kib per-magazine */
	else
		size = 256;

	return (size);
}

/*
 * Allocate a per-cpu magazine to associate with a specific core.
 */
static spl_kmem_magazine_t *
spl_magazine_alloc(spl_kmem_cache_t *skc, int cpu)
{
	spl_kmem_magazine_t *skm;
	int size = sizeof (spl_kmem_magazine_t) +
	    sizeof (void *) * skc->skc_mag_size;

	skm = kmalloc_node(size, GFP_KERNEL, cpu_to_node(cpu));
	if (skm) {
		skm->skm_magic = SKM_MAGIC;
		skm->skm_avail = 0;
		skm->skm_size = skc->skc_mag_size;
		skm->skm_refill = skc->skc_mag_refill;
		skm->skm_cache = skc;
		skm->skm_cpu = cpu;
	}

	return (skm);
}

/*
 * Free a per-cpu magazine associated with a specific core.
 */
static void
spl_magazine_free(spl_kmem_magazine_t *skm)
{
	ASSERT(skm->skm_magic == SKM_MAGIC);
	ASSERT(skm->skm_avail == 0);
	kfree(skm);
}

/*
 * Create all pre-cpu magazines of reasonable sizes.
 */
static int
spl_magazine_create(spl_kmem_cache_t *skc)
{
	int i = 0;

	ASSERT((skc->skc_flags & KMC_SLAB) == 0);

	skc->skc_mag = kzalloc(sizeof (spl_kmem_magazine_t *) *
	    num_possible_cpus(), kmem_flags_convert(KM_SLEEP));
	skc->skc_mag_size = spl_magazine_size(skc);
	skc->skc_mag_refill = (skc->skc_mag_size + 1) / 2;

	for_each_possible_cpu(i) {
		skc->skc_mag[i] = spl_magazine_alloc(skc, i);
		if (!skc->skc_mag[i]) {
			for (i--; i >= 0; i--)
				spl_magazine_free(skc->skc_mag[i]);

			kfree(skc->skc_mag);
			return (-ENOMEM);
		}
	}

	return (0);
}

/*
 * Destroy all pre-cpu magazines.
 */
static void
spl_magazine_destroy(spl_kmem_cache_t *skc)
{
	spl_kmem_magazine_t *skm;
	int i = 0;

	ASSERT((skc->skc_flags & KMC_SLAB) == 0);

	for_each_possible_cpu(i) {
		skm = skc->skc_mag[i];
		spl_cache_flush(skc, skm, skm->skm_avail);
		spl_magazine_free(skm);
	}

	kfree(skc->skc_mag);
}

/*
 * Create a object cache based on the following arguments:
 * name		cache name
 * size		cache object size
 * align	cache object alignment
 * ctor		cache object constructor
 * dtor		cache object destructor
 * reclaim	cache object reclaim
 * priv		cache private data for ctor/dtor/reclaim
 * vmp		unused must be NULL
 * flags
 *	KMC_KVMEM       Force kvmem backed SPL cache
 *	KMC_SLAB        Force Linux slab backed cache
 *	KMC_NODEBUG	Disable debugging (unsupported)
 */
spl_kmem_cache_t *
spl_kmem_cache_create(char *name, size_t size, size_t align,
    spl_kmem_ctor_t ctor, spl_kmem_dtor_t dtor, void *reclaim,
    void *priv, void *vmp, int flags)
{
	gfp_t lflags = kmem_flags_convert(KM_SLEEP);
	spl_kmem_cache_t *skc;
	int rc;

	/*
	 * Unsupported flags
	 */
	ASSERT(vmp == NULL);
	ASSERT(reclaim == NULL);

	might_sleep();

	skc = kzalloc(sizeof (*skc), lflags);
	if (skc == NULL)
		return (NULL);

	skc->skc_magic = SKC_MAGIC;
	skc->skc_name_size = strlen(name) + 1;
	skc->skc_name = (char *)kmalloc(skc->skc_name_size, lflags);
	if (skc->skc_name == NULL) {
		kfree(skc);
		return (NULL);
	}
	strncpy(skc->skc_name, name, skc->skc_name_size);

	skc->skc_ctor = ctor;
	skc->skc_dtor = dtor;
	skc->skc_private = priv;
	skc->skc_vmp = vmp;
	skc->skc_linux_cache = NULL;
	skc->skc_flags = flags;
	skc->skc_obj_size = size;
	skc->skc_obj_align = SPL_KMEM_CACHE_ALIGN;
	atomic_set(&skc->skc_ref, 0);

	INIT_LIST_HEAD(&skc->skc_list);
	INIT_LIST_HEAD(&skc->skc_complete_list);
	INIT_LIST_HEAD(&skc->skc_partial_list);
	skc->skc_emergency_tree = RB_ROOT;
	spin_lock_init(&skc->skc_lock);
	init_waitqueue_head(&skc->skc_waitq);
	skc->skc_slab_fail = 0;
	skc->skc_slab_create = 0;
	skc->skc_slab_destroy = 0;
	skc->skc_slab_total = 0;
	skc->skc_slab_alloc = 0;
	skc->skc_slab_max = 0;
	skc->skc_obj_total = 0;
	skc->skc_obj_alloc = 0;
	skc->skc_obj_max = 0;
	skc->skc_obj_deadlock = 0;
	skc->skc_obj_emergency = 0;
	skc->skc_obj_emergency_max = 0;

	rc = percpu_counter_init_common(&skc->skc_linux_alloc, 0,
	    GFP_KERNEL);
	if (rc != 0) {
		kfree(skc);
		return (NULL);
	}

	/*
	 * Verify the requested alignment restriction is sane.
	 */
	if (align) {
		VERIFY(ISP2(align));
		VERIFY3U(align, >=, SPL_KMEM_CACHE_ALIGN);
		VERIFY3U(align, <=, PAGE_SIZE);
		skc->skc_obj_align = align;
	}

	/*
	 * When no specific type of slab is requested (kmem, vmem, or
	 * linuxslab) then select a cache type based on the object size
	 * and default tunables.
	 */
	if (!(skc->skc_flags & (KMC_SLAB | KMC_KVMEM))) {
		if (spl_kmem_cache_slab_limit &&
		    size <= (size_t)spl_kmem_cache_slab_limit) {
			/*
			 * Objects smaller than spl_kmem_cache_slab_limit can
			 * use the Linux slab for better space-efficiency.
			 */
			skc->skc_flags |= KMC_SLAB;
		} else {
			/*
			 * All other objects are considered large and are
			 * placed on kvmem backed slabs.
			 */
			skc->skc_flags |= KMC_KVMEM;
		}
	}

	/*
	 * Given the type of slab allocate the required resources.
	 */
	if (skc->skc_flags & KMC_KVMEM) {
		rc = spl_slab_size(skc,
		    &skc->skc_slab_objs, &skc->skc_slab_size);
		if (rc)
			goto out;

		rc = spl_magazine_create(skc);
		if (rc)
			goto out;
	} else {
		unsigned long slabflags = 0;

		if (size > (SPL_MAX_KMEM_ORDER_NR_PAGES * PAGE_SIZE)) {
			rc = EINVAL;
			goto out;
		}

#if defined(SLAB_USERCOPY)
		/*
		 * Required for PAX-enabled kernels if the slab is to be
		 * used for copying between user and kernel space.
		 */
		slabflags |= SLAB_USERCOPY;
#endif

#if defined(HAVE_KMEM_CACHE_CREATE_USERCOPY)
		/*
		 * Newer grsec patchset uses kmem_cache_create_usercopy()
		 * instead of SLAB_USERCOPY flag
		 */
		skc->skc_linux_cache = kmem_cache_create_usercopy(
		    skc->skc_name, size, align, slabflags, 0, size, NULL);
#else
		skc->skc_linux_cache = kmem_cache_create(
		    skc->skc_name, size, align, slabflags, NULL);
#endif
		if (skc->skc_linux_cache == NULL) {
			rc = ENOMEM;
			goto out;
		}
	}

	down_write(&spl_kmem_cache_sem);
	list_add_tail(&skc->skc_list, &spl_kmem_cache_list);
	up_write(&spl_kmem_cache_sem);

	return (skc);
out:
	kfree(skc->skc_name);
	percpu_counter_destroy(&skc->skc_linux_alloc);
	kfree(skc);
	return (NULL);
}
EXPORT_SYMBOL(spl_kmem_cache_create);

/*
 * Register a move callback for cache defragmentation.
 * XXX: Unimplemented but harmless to stub out for now.
 */
void
spl_kmem_cache_set_move(spl_kmem_cache_t *skc,
    kmem_cbrc_t (move)(void *, void *, size_t, void *))
{
	ASSERT(move != NULL);
}
EXPORT_SYMBOL(spl_kmem_cache_set_move);

/*
 * Destroy a cache and all objects associated with the cache.
 */
void
spl_kmem_cache_destroy(spl_kmem_cache_t *skc)
{
	DECLARE_WAIT_QUEUE_HEAD(wq);
	taskqid_t id;

	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(skc->skc_flags & (KMC_KVMEM | KMC_SLAB));

	down_write(&spl_kmem_cache_sem);
	list_del_init(&skc->skc_list);
	up_write(&spl_kmem_cache_sem);

	/* Cancel any and wait for any pending delayed tasks */
	VERIFY(!test_and_set_bit(KMC_BIT_DESTROY, &skc->skc_flags));

	spin_lock(&skc->skc_lock);
	id = skc->skc_taskqid;
	spin_unlock(&skc->skc_lock);

	taskq_cancel_id(spl_kmem_cache_taskq, id);

	/*
	 * Wait until all current callers complete, this is mainly
	 * to catch the case where a low memory situation triggers a
	 * cache reaping action which races with this destroy.
	 */
	wait_event(wq, atomic_read(&skc->skc_ref) == 0);

	if (skc->skc_flags & KMC_KVMEM) {
		spl_magazine_destroy(skc);
		spl_slab_reclaim(skc);
	} else {
		ASSERT(skc->skc_flags & KMC_SLAB);
		kmem_cache_destroy(skc->skc_linux_cache);
	}

	spin_lock(&skc->skc_lock);

	/*
	 * Validate there are no objects in use and free all the
	 * spl_kmem_slab_t, spl_kmem_obj_t, and object buffers.
	 */
	ASSERT3U(skc->skc_slab_alloc, ==, 0);
	ASSERT3U(skc->skc_obj_alloc, ==, 0);
	ASSERT3U(skc->skc_slab_total, ==, 0);
	ASSERT3U(skc->skc_obj_total, ==, 0);
	ASSERT3U(skc->skc_obj_emergency, ==, 0);
	ASSERT(list_empty(&skc->skc_complete_list));

	ASSERT3U(percpu_counter_sum(&skc->skc_linux_alloc), ==, 0);
	percpu_counter_destroy(&skc->skc_linux_alloc);

	spin_unlock(&skc->skc_lock);

	kfree(skc->skc_name);
	kfree(skc);
}
EXPORT_SYMBOL(spl_kmem_cache_destroy);

/*
 * Allocate an object from a slab attached to the cache.  This is used to
 * repopulate the per-cpu magazine caches in batches when they run low.
 */
static void *
spl_cache_obj(spl_kmem_cache_t *skc, spl_kmem_slab_t *sks)
{
	spl_kmem_obj_t *sko;

	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(sks->sks_magic == SKS_MAGIC);

	sko = list_entry(sks->sks_free_list.next, spl_kmem_obj_t, sko_list);
	ASSERT(sko->sko_magic == SKO_MAGIC);
	ASSERT(sko->sko_addr != NULL);

	/* Remove from sks_free_list */
	list_del_init(&sko->sko_list);

	sks->sks_age = jiffies;
	sks->sks_ref++;
	skc->skc_obj_alloc++;

	/* Track max obj usage statistics */
	if (skc->skc_obj_alloc > skc->skc_obj_max)
		skc->skc_obj_max = skc->skc_obj_alloc;

	/* Track max slab usage statistics */
	if (sks->sks_ref == 1) {
		skc->skc_slab_alloc++;

		if (skc->skc_slab_alloc > skc->skc_slab_max)
			skc->skc_slab_max = skc->skc_slab_alloc;
	}

	return (sko->sko_addr);
}

/*
 * Generic slab allocation function to run by the global work queues.
 * It is responsible for allocating a new slab, linking it in to the list
 * of partial slabs, and then waking any waiters.
 */
static int
__spl_cache_grow(spl_kmem_cache_t *skc, int flags)
{
	spl_kmem_slab_t *sks;

	fstrans_cookie_t cookie = spl_fstrans_mark();
	sks = spl_slab_alloc(skc, flags);
	spl_fstrans_unmark(cookie);

	spin_lock(&skc->skc_lock);
	if (sks) {
		skc->skc_slab_total++;
		skc->skc_obj_total += sks->sks_objs;
		list_add_tail(&sks->sks_list, &skc->skc_partial_list);

		smp_mb__before_atomic();
		clear_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags);
		smp_mb__after_atomic();
	}
	spin_unlock(&skc->skc_lock);

	return (sks == NULL ? -ENOMEM : 0);
}

static void
spl_cache_grow_work(void *data)
{
	spl_kmem_alloc_t *ska = (spl_kmem_alloc_t *)data;
	spl_kmem_cache_t *skc = ska->ska_cache;

	int error = __spl_cache_grow(skc, ska->ska_flags);

	atomic_dec(&skc->skc_ref);
	smp_mb__before_atomic();
	clear_bit(KMC_BIT_GROWING, &skc->skc_flags);
	smp_mb__after_atomic();
	if (error == 0)
		wake_up_all(&skc->skc_waitq);

	kfree(ska);
}

/*
 * Returns non-zero when a new slab should be available.
 */
static int
spl_cache_grow_wait(spl_kmem_cache_t *skc)
{
	return (!test_bit(KMC_BIT_GROWING, &skc->skc_flags));
}

/*
 * No available objects on any slabs, create a new slab.  Note that this
 * functionality is disabled for KMC_SLAB caches which are backed by the
 * Linux slab.
 */
static int
spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj)
{
	int remaining, rc = 0;

	ASSERT0(flags & ~KM_PUBLIC_MASK);
	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT((skc->skc_flags & KMC_SLAB) == 0);
	might_sleep();
	*obj = NULL;

	/*
	 * Before allocating a new slab wait for any reaping to complete and
	 * then return so the local magazine can be rechecked for new objects.
	 */
	if (test_bit(KMC_BIT_REAPING, &skc->skc_flags)) {
		rc = spl_wait_on_bit(&skc->skc_flags, KMC_BIT_REAPING,
		    TASK_UNINTERRUPTIBLE);
		return (rc ? rc : -EAGAIN);
	}

	/*
	 * Note: It would be nice to reduce the overhead of context switch
	 * and improve NUMA locality, by trying to allocate a new slab in the
	 * current process context with KM_NOSLEEP flag.
	 *
	 * However, this can't be applied to vmem/kvmem due to a bug that
	 * spl_vmalloc() doesn't honor gfp flags in page table allocation.
	 */

	/*
	 * This is handled by dispatching a work request to the global work
	 * queue.  This allows us to asynchronously allocate a new slab while
	 * retaining the ability to safely fall back to a smaller synchronous
	 * allocations to ensure forward progress is always maintained.
	 */
	if (test_and_set_bit(KMC_BIT_GROWING, &skc->skc_flags) == 0) {
		spl_kmem_alloc_t *ska;

		ska = kmalloc(sizeof (*ska), kmem_flags_convert(flags));
		if (ska == NULL) {
			clear_bit_unlock(KMC_BIT_GROWING, &skc->skc_flags);
			smp_mb__after_atomic();
			wake_up_all(&skc->skc_waitq);
			return (-ENOMEM);
		}

		atomic_inc(&skc->skc_ref);
		ska->ska_cache = skc;
		ska->ska_flags = flags;
		taskq_init_ent(&ska->ska_tqe);
		taskq_dispatch_ent(spl_kmem_cache_taskq,
		    spl_cache_grow_work, ska, 0, &ska->ska_tqe);
	}

	/*
	 * The goal here is to only detect the rare case where a virtual slab
	 * allocation has deadlocked.  We must be careful to minimize the use
	 * of emergency objects which are more expensive to track.  Therefore,
	 * we set a very long timeout for the asynchronous allocation and if
	 * the timeout is reached the cache is flagged as deadlocked.  From
	 * this point only new emergency objects will be allocated until the
	 * asynchronous allocation completes and clears the deadlocked flag.
	 */
	if (test_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags)) {
		rc = spl_emergency_alloc(skc, flags, obj);
	} else {
		remaining = wait_event_timeout(skc->skc_waitq,
		    spl_cache_grow_wait(skc), HZ / 10);

		if (!remaining) {
			spin_lock(&skc->skc_lock);
			if (test_bit(KMC_BIT_GROWING, &skc->skc_flags)) {
				set_bit(KMC_BIT_DEADLOCKED, &skc->skc_flags);
				skc->skc_obj_deadlock++;
			}
			spin_unlock(&skc->skc_lock);
		}

		rc = -ENOMEM;
	}

	return (rc);
}

/*
 * Refill a per-cpu magazine with objects from the slabs for this cache.
 * Ideally the magazine can be repopulated using existing objects which have
 * been released, however if we are unable to locate enough free objects new
 * slabs of objects will be created.  On success NULL is returned, otherwise
 * the address of a single emergency object is returned for use by the caller.
 */
static void *
spl_cache_refill(spl_kmem_cache_t *skc, spl_kmem_magazine_t *skm, int flags)
{
	spl_kmem_slab_t *sks;
	int count = 0, rc, refill;
	void *obj = NULL;

	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(skm->skm_magic == SKM_MAGIC);

	refill = MIN(skm->skm_refill, skm->skm_size - skm->skm_avail);
	spin_lock(&skc->skc_lock);

	while (refill > 0) {
		/* No slabs available we may need to grow the cache */
		if (list_empty(&skc->skc_partial_list)) {
			spin_unlock(&skc->skc_lock);

			local_irq_enable();
			rc = spl_cache_grow(skc, flags, &obj);
			local_irq_disable();

			/* Emergency object for immediate use by caller */
			if (rc == 0 && obj != NULL)
				return (obj);

			if (rc)
				goto out;

			/* Rescheduled to different CPU skm is not local */
			if (skm != skc->skc_mag[smp_processor_id()])
				goto out;

			/*
			 * Potentially rescheduled to the same CPU but
			 * allocations may have occurred from this CPU while
			 * we were sleeping so recalculate max refill.
			 */
			refill = MIN(refill, skm->skm_size - skm->skm_avail);

			spin_lock(&skc->skc_lock);
			continue;
		}

		/* Grab the next available slab */
		sks = list_entry((&skc->skc_partial_list)->next,
		    spl_kmem_slab_t, sks_list);
		ASSERT(sks->sks_magic == SKS_MAGIC);
		ASSERT(sks->sks_ref < sks->sks_objs);
		ASSERT(!list_empty(&sks->sks_free_list));

		/*
		 * Consume as many objects as needed to refill the requested
		 * cache.  We must also be careful not to overfill it.
		 */
		while (sks->sks_ref < sks->sks_objs && refill-- > 0 &&
		    ++count) {
			ASSERT(skm->skm_avail < skm->skm_size);
			ASSERT(count < skm->skm_size);
			skm->skm_objs[skm->skm_avail++] =
			    spl_cache_obj(skc, sks);
		}

		/* Move slab to skc_complete_list when full */
		if (sks->sks_ref == sks->sks_objs) {
			list_del(&sks->sks_list);
			list_add(&sks->sks_list, &skc->skc_complete_list);
		}
	}

	spin_unlock(&skc->skc_lock);
out:
	return (NULL);
}

/*
 * Release an object back to the slab from which it came.
 */
static void
spl_cache_shrink(spl_kmem_cache_t *skc, void *obj)
{
	spl_kmem_slab_t *sks = NULL;
	spl_kmem_obj_t *sko = NULL;

	ASSERT(skc->skc_magic == SKC_MAGIC);

	sko = spl_sko_from_obj(skc, obj);
	ASSERT(sko->sko_magic == SKO_MAGIC);
	sks = sko->sko_slab;
	ASSERT(sks->sks_magic == SKS_MAGIC);
	ASSERT(sks->sks_cache == skc);
	list_add(&sko->sko_list, &sks->sks_free_list);

	sks->sks_age = jiffies;
	sks->sks_ref--;
	skc->skc_obj_alloc--;

	/*
	 * Move slab to skc_partial_list when no longer full.  Slabs
	 * are added to the head to keep the partial list is quasi-full
	 * sorted order.  Fuller at the head, emptier at the tail.
	 */
	if (sks->sks_ref == (sks->sks_objs - 1)) {
		list_del(&sks->sks_list);
		list_add(&sks->sks_list, &skc->skc_partial_list);
	}

	/*
	 * Move empty slabs to the end of the partial list so
	 * they can be easily found and freed during reclamation.
	 */
	if (sks->sks_ref == 0) {
		list_del(&sks->sks_list);
		list_add_tail(&sks->sks_list, &skc->skc_partial_list);
		skc->skc_slab_alloc--;
	}
}

/*
 * Allocate an object from the per-cpu magazine, or if the magazine
 * is empty directly allocate from a slab and repopulate the magazine.
 */
void *
spl_kmem_cache_alloc(spl_kmem_cache_t *skc, int flags)
{
	spl_kmem_magazine_t *skm;
	void *obj = NULL;

	ASSERT0(flags & ~KM_PUBLIC_MASK);
	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));

	/*
	 * Allocate directly from a Linux slab.  All optimizations are left
	 * to the underlying cache we only need to guarantee that KM_SLEEP
	 * callers will never fail.
	 */
	if (skc->skc_flags & KMC_SLAB) {
		struct kmem_cache *slc = skc->skc_linux_cache;
		do {
			obj = kmem_cache_alloc(slc, kmem_flags_convert(flags));
		} while ((obj == NULL) && !(flags & KM_NOSLEEP));

		if (obj != NULL) {
			/*
			 * Even though we leave everything up to the
			 * underlying cache we still keep track of
			 * how many objects we've allocated in it for
			 * better debuggability.
			 */
			percpu_counter_inc(&skc->skc_linux_alloc);
		}
		goto ret;
	}

	local_irq_disable();

restart:
	/*
	 * Safe to update per-cpu structure without lock, but
	 * in the restart case we must be careful to reacquire
	 * the local magazine since this may have changed
	 * when we need to grow the cache.
	 */
	skm = skc->skc_mag[smp_processor_id()];
	ASSERT(skm->skm_magic == SKM_MAGIC);

	if (likely(skm->skm_avail)) {
		/* Object available in CPU cache, use it */
		obj = skm->skm_objs[--skm->skm_avail];
	} else {
		obj = spl_cache_refill(skc, skm, flags);
		if ((obj == NULL) && !(flags & KM_NOSLEEP))
			goto restart;

		local_irq_enable();
		goto ret;
	}

	local_irq_enable();
	ASSERT(obj);
	ASSERT(IS_P2ALIGNED(obj, skc->skc_obj_align));

ret:
	/* Pre-emptively migrate object to CPU L1 cache */
	if (obj) {
		if (obj && skc->skc_ctor)
			skc->skc_ctor(obj, skc->skc_private, flags);
		else
			prefetchw(obj);
	}

	return (obj);
}
EXPORT_SYMBOL(spl_kmem_cache_alloc);

/*
 * Free an object back to the local per-cpu magazine, there is no
 * guarantee that this is the same magazine the object was originally
 * allocated from.  We may need to flush entire from the magazine
 * back to the slabs to make space.
 */
void
spl_kmem_cache_free(spl_kmem_cache_t *skc, void *obj)
{
	spl_kmem_magazine_t *skm;
	unsigned long flags;
	int do_reclaim = 0;
	int do_emergency = 0;

	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));

	/*
	 * Run the destructor
	 */
	if (skc->skc_dtor)
		skc->skc_dtor(obj, skc->skc_private);

	/*
	 * Free the object from the Linux underlying Linux slab.
	 */
	if (skc->skc_flags & KMC_SLAB) {
		kmem_cache_free(skc->skc_linux_cache, obj);
		percpu_counter_dec(&skc->skc_linux_alloc);
		return;
	}

	/*
	 * While a cache has outstanding emergency objects all freed objects
	 * must be checked.  However, since emergency objects will never use
	 * a virtual address these objects can be safely excluded as an
	 * optimization.
	 */
	if (!is_vmalloc_addr(obj)) {
		spin_lock(&skc->skc_lock);
		do_emergency = (skc->skc_obj_emergency > 0);
		spin_unlock(&skc->skc_lock);

		if (do_emergency && (spl_emergency_free(skc, obj) == 0))
			return;
	}

	local_irq_save(flags);

	/*
	 * Safe to update per-cpu structure without lock, but
	 * no remote memory allocation tracking is being performed
	 * it is entirely possible to allocate an object from one
	 * CPU cache and return it to another.
	 */
	skm = skc->skc_mag[smp_processor_id()];
	ASSERT(skm->skm_magic == SKM_MAGIC);

	/*
	 * Per-CPU cache full, flush it to make space for this object,
	 * this may result in an empty slab which can be reclaimed once
	 * interrupts are re-enabled.
	 */
	if (unlikely(skm->skm_avail >= skm->skm_size)) {
		spl_cache_flush(skc, skm, skm->skm_refill);
		do_reclaim = 1;
	}

	/* Available space in cache, use it */
	skm->skm_objs[skm->skm_avail++] = obj;

	local_irq_restore(flags);

	if (do_reclaim)
		spl_slab_reclaim(skc);
}
EXPORT_SYMBOL(spl_kmem_cache_free);

/*
 * Depending on how many and which objects are released it may simply
 * repopulate the local magazine which will then need to age-out.  Objects
 * which cannot fit in the magazine will be released back to their slabs
 * which will also need to age out before being released.  This is all just
 * best effort and we do not want to thrash creating and destroying slabs.
 */
void
spl_kmem_cache_reap_now(spl_kmem_cache_t *skc)
{
	ASSERT(skc->skc_magic == SKC_MAGIC);
	ASSERT(!test_bit(KMC_BIT_DESTROY, &skc->skc_flags));

	if (skc->skc_flags & KMC_SLAB)
		return;

	atomic_inc(&skc->skc_ref);

	/*
	 * Prevent concurrent cache reaping when contended.
	 */
	if (test_and_set_bit(KMC_BIT_REAPING, &skc->skc_flags))
		goto out;

	/* Reclaim from the magazine and free all now empty slabs. */
	unsigned long irq_flags;
	local_irq_save(irq_flags);
	spl_kmem_magazine_t *skm = skc->skc_mag[smp_processor_id()];
	spl_cache_flush(skc, skm, skm->skm_avail);
	local_irq_restore(irq_flags);

	spl_slab_reclaim(skc);
	clear_bit_unlock(KMC_BIT_REAPING, &skc->skc_flags);
	smp_mb__after_atomic();
	wake_up_bit(&skc->skc_flags, KMC_BIT_REAPING);
out:
	atomic_dec(&skc->skc_ref);
}
EXPORT_SYMBOL(spl_kmem_cache_reap_now);

/*
 * This is stubbed out for code consistency with other platforms.  There
 * is existing logic to prevent concurrent reaping so while this is ugly
 * it should do no harm.
 */
int
spl_kmem_cache_reap_active()
{
	return (0);
}
EXPORT_SYMBOL(spl_kmem_cache_reap_active);

/*
 * Reap all free slabs from all registered caches.
 */
void
spl_kmem_reap(void)
{
	spl_kmem_cache_t *skc = NULL;

	down_read(&spl_kmem_cache_sem);
	list_for_each_entry(skc, &spl_kmem_cache_list, skc_list) {
		spl_kmem_cache_reap_now(skc);
	}
	up_read(&spl_kmem_cache_sem);
}
EXPORT_SYMBOL(spl_kmem_reap);

int
spl_kmem_cache_init(void)
{
	init_rwsem(&spl_kmem_cache_sem);
	INIT_LIST_HEAD(&spl_kmem_cache_list);
	spl_kmem_cache_taskq = taskq_create("spl_kmem_cache",
	    spl_kmem_cache_kmem_threads, maxclsyspri,
	    spl_kmem_cache_kmem_threads * 8, INT_MAX,
	    TASKQ_PREPOPULATE | TASKQ_DYNAMIC);

	return (0);
}

void
spl_kmem_cache_fini(void)
{
	taskq_destroy(spl_kmem_cache_taskq);
}