summaryrefslogtreecommitdiff
path: root/mm/zswap.c
blob: e1e621d0b6a0289b6e7ef5193b108e7b15a80bc0 (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
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
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * zswap.c - zswap driver file
 *
 * zswap is a backend for frontswap that takes pages that are in the process
 * of being swapped out and attempts to compress and store them in a
 * RAM-based memory pool.  This can result in a significant I/O reduction on
 * the swap device and, in the case where decompressing from RAM is faster
 * than reading from the swap device, can also improve workload performance.
 *
 * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/frontswap.h>
#include <linux/rbtree.h>
#include <linux/swap.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <linux/mempool.h>
#include <linux/zpool.h>
#include <crypto/acompress.h>

#include <linux/mm_types.h>
#include <linux/page-flags.h>
#include <linux/swapops.h>
#include <linux/writeback.h>
#include <linux/pagemap.h>
#include <linux/workqueue.h>

#include "swap.h"

/*********************************
* statistics
**********************************/
/* Total bytes used by the compressed storage */
u64 zswap_pool_total_size;
/* The number of compressed pages currently stored in zswap */
atomic_t zswap_stored_pages = ATOMIC_INIT(0);
/* The number of same-value filled pages currently stored in zswap */
static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);

/*
 * The statistics below are not protected from concurrent access for
 * performance reasons so they may not be a 100% accurate.  However,
 * they do provide useful information on roughly how many times a
 * certain event is occurring.
*/

/* Pool limit was hit (see zswap_max_pool_percent) */
static u64 zswap_pool_limit_hit;
/* Pages written back when pool limit was reached */
static u64 zswap_written_back_pages;
/* Store failed due to a reclaim failure after pool limit was reached */
static u64 zswap_reject_reclaim_fail;
/* Compressed page was too big for the allocator to (optimally) store */
static u64 zswap_reject_compress_poor;
/* Store failed because underlying allocator could not get memory */
static u64 zswap_reject_alloc_fail;
/* Store failed because the entry metadata could not be allocated (rare) */
static u64 zswap_reject_kmemcache_fail;
/* Duplicate store was encountered (rare) */
static u64 zswap_duplicate_entry;

/* Shrinker work queue */
static struct workqueue_struct *shrink_wq;
/* Pool limit was hit, we need to calm down */
static bool zswap_pool_reached_full;

/*********************************
* tunables
**********************************/

#define ZSWAP_PARAM_UNSET ""

static int zswap_setup(void);

/* Enable/disable zswap */
static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
static int zswap_enabled_param_set(const char *,
				   const struct kernel_param *);
static const struct kernel_param_ops zswap_enabled_param_ops = {
	.set =		zswap_enabled_param_set,
	.get =		param_get_bool,
};
module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);

/* Crypto compressor to use */
static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
static int zswap_compressor_param_set(const char *,
				      const struct kernel_param *);
static const struct kernel_param_ops zswap_compressor_param_ops = {
	.set =		zswap_compressor_param_set,
	.get =		param_get_charp,
	.free =		param_free_charp,
};
module_param_cb(compressor, &zswap_compressor_param_ops,
		&zswap_compressor, 0644);

/* Compressed storage zpool to use */
static char *zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
static int zswap_zpool_param_set(const char *, const struct kernel_param *);
static const struct kernel_param_ops zswap_zpool_param_ops = {
	.set =		zswap_zpool_param_set,
	.get =		param_get_charp,
	.free =		param_free_charp,
};
module_param_cb(zpool, &zswap_zpool_param_ops, &zswap_zpool_type, 0644);

/* The maximum percentage of memory that the compressed pool can occupy */
static unsigned int zswap_max_pool_percent = 20;
module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);

/* The threshold for accepting new pages after the max_pool_percent was hit */
static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
		   uint, 0644);

/*
 * Enable/disable handling same-value filled pages (enabled by default).
 * If disabled every page is considered non-same-value filled.
 */
static bool zswap_same_filled_pages_enabled = true;
module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
		   bool, 0644);

/* Enable/disable handling non-same-value filled pages (enabled by default) */
static bool zswap_non_same_filled_pages_enabled = true;
module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
		   bool, 0644);

/*********************************
* data structures
**********************************/

struct crypto_acomp_ctx {
	struct crypto_acomp *acomp;
	struct acomp_req *req;
	struct crypto_wait wait;
	u8 *dstmem;
	struct mutex *mutex;
};

struct zswap_pool {
	struct zpool *zpool;
	struct crypto_acomp_ctx __percpu *acomp_ctx;
	struct kref kref;
	struct list_head list;
	struct work_struct release_work;
	struct work_struct shrink_work;
	struct hlist_node node;
	char tfm_name[CRYPTO_MAX_ALG_NAME];
};

/*
 * struct zswap_entry
 *
 * This structure contains the metadata for tracking a single compressed
 * page within zswap.
 *
 * rbnode - links the entry into red-black tree for the appropriate swap type
 * offset - the swap offset for the entry.  Index into the red-black tree.
 * refcount - the number of outstanding reference to the entry. This is needed
 *            to protect against premature freeing of the entry by code
 *            concurrent calls to load, invalidate, and writeback.  The lock
 *            for the zswap_tree structure that contains the entry must
 *            be held while changing the refcount.  Since the lock must
 *            be held, there is no reason to also make refcount atomic.
 * length - the length in bytes of the compressed page data.  Needed during
 *          decompression. For a same value filled page length is 0.
 * pool - the zswap_pool the entry's data is in
 * handle - zpool allocation handle that stores the compressed page data
 * value - value of the same-value filled pages which have same content
 */
struct zswap_entry {
	struct rb_node rbnode;
	pgoff_t offset;
	int refcount;
	unsigned int length;
	struct zswap_pool *pool;
	union {
		unsigned long handle;
		unsigned long value;
	};
	struct obj_cgroup *objcg;
};

struct zswap_header {
	swp_entry_t swpentry;
};

/*
 * The tree lock in the zswap_tree struct protects a few things:
 * - the rbtree
 * - the refcount field of each entry in the tree
 */
struct zswap_tree {
	struct rb_root rbroot;
	spinlock_t lock;
};

static struct zswap_tree *zswap_trees[MAX_SWAPFILES];

/* RCU-protected iteration */
static LIST_HEAD(zswap_pools);
/* protects zswap_pools list modification */
static DEFINE_SPINLOCK(zswap_pools_lock);
/* pool counter to provide unique names to zpool */
static atomic_t zswap_pools_count = ATOMIC_INIT(0);

enum zswap_init_type {
	ZSWAP_UNINIT,
	ZSWAP_INIT_SUCCEED,
	ZSWAP_INIT_FAILED
};

static enum zswap_init_type zswap_init_state;

/* used to ensure the integrity of initialization */
static DEFINE_MUTEX(zswap_init_lock);

/* init completed, but couldn't create the initial pool */
static bool zswap_has_pool;

/*********************************
* helpers and fwd declarations
**********************************/

#define zswap_pool_debug(msg, p)				\
	pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,		\
		 zpool_get_type((p)->zpool))

static int zswap_writeback_entry(struct zpool *pool, unsigned long handle);
static int zswap_pool_get(struct zswap_pool *pool);
static void zswap_pool_put(struct zswap_pool *pool);

static const struct zpool_ops zswap_zpool_ops = {
	.evict = zswap_writeback_entry
};

static bool zswap_is_full(void)
{
	return totalram_pages() * zswap_max_pool_percent / 100 <
			DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
}

static bool zswap_can_accept(void)
{
	return totalram_pages() * zswap_accept_thr_percent / 100 *
				zswap_max_pool_percent / 100 >
			DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
}

static void zswap_update_total_size(void)
{
	struct zswap_pool *pool;
	u64 total = 0;

	rcu_read_lock();

	list_for_each_entry_rcu(pool, &zswap_pools, list)
		total += zpool_get_total_size(pool->zpool);

	rcu_read_unlock();

	zswap_pool_total_size = total;
}

/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *zswap_entry_cache;

static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
{
	struct zswap_entry *entry;
	entry = kmem_cache_alloc(zswap_entry_cache, gfp);
	if (!entry)
		return NULL;
	entry->refcount = 1;
	RB_CLEAR_NODE(&entry->rbnode);
	return entry;
}

static void zswap_entry_cache_free(struct zswap_entry *entry)
{
	kmem_cache_free(zswap_entry_cache, entry);
}

/*********************************
* rbtree functions
**********************************/
static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
{
	struct rb_node *node = root->rb_node;
	struct zswap_entry *entry;

	while (node) {
		entry = rb_entry(node, struct zswap_entry, rbnode);
		if (entry->offset > offset)
			node = node->rb_left;
		else if (entry->offset < offset)
			node = node->rb_right;
		else
			return entry;
	}
	return NULL;
}

/*
 * In the case that a entry with the same offset is found, a pointer to
 * the existing entry is stored in dupentry and the function returns -EEXIST
 */
static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
			struct zswap_entry **dupentry)
{
	struct rb_node **link = &root->rb_node, *parent = NULL;
	struct zswap_entry *myentry;

	while (*link) {
		parent = *link;
		myentry = rb_entry(parent, struct zswap_entry, rbnode);
		if (myentry->offset > entry->offset)
			link = &(*link)->rb_left;
		else if (myentry->offset < entry->offset)
			link = &(*link)->rb_right;
		else {
			*dupentry = myentry;
			return -EEXIST;
		}
	}
	rb_link_node(&entry->rbnode, parent, link);
	rb_insert_color(&entry->rbnode, root);
	return 0;
}

static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
{
	if (!RB_EMPTY_NODE(&entry->rbnode)) {
		rb_erase(&entry->rbnode, root);
		RB_CLEAR_NODE(&entry->rbnode);
	}
}

/*
 * Carries out the common pattern of freeing and entry's zpool allocation,
 * freeing the entry itself, and decrementing the number of stored pages.
 */
static void zswap_free_entry(struct zswap_entry *entry)
{
	if (entry->objcg) {
		obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
		obj_cgroup_put(entry->objcg);
	}
	if (!entry->length)
		atomic_dec(&zswap_same_filled_pages);
	else {
		zpool_free(entry->pool->zpool, entry->handle);
		zswap_pool_put(entry->pool);
	}
	zswap_entry_cache_free(entry);
	atomic_dec(&zswap_stored_pages);
	zswap_update_total_size();
}

/* caller must hold the tree lock */
static void zswap_entry_get(struct zswap_entry *entry)
{
	entry->refcount++;
}

/* caller must hold the tree lock
* remove from the tree and free it, if nobody reference the entry
*/
static void zswap_entry_put(struct zswap_tree *tree,
			struct zswap_entry *entry)
{
	int refcount = --entry->refcount;

	BUG_ON(refcount < 0);
	if (refcount == 0) {
		zswap_rb_erase(&tree->rbroot, entry);
		zswap_free_entry(entry);
	}
}

/* caller must hold the tree lock */
static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
				pgoff_t offset)
{
	struct zswap_entry *entry;

	entry = zswap_rb_search(root, offset);
	if (entry)
		zswap_entry_get(entry);

	return entry;
}

/*********************************
* per-cpu code
**********************************/
static DEFINE_PER_CPU(u8 *, zswap_dstmem);
/*
 * If users dynamically change the zpool type and compressor at runtime, i.e.
 * zswap is running, zswap can have more than one zpool on one cpu, but they
 * are sharing dtsmem. So we need this mutex to be per-cpu.
 */
static DEFINE_PER_CPU(struct mutex *, zswap_mutex);

static int zswap_dstmem_prepare(unsigned int cpu)
{
	struct mutex *mutex;
	u8 *dst;

	dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
	if (!dst)
		return -ENOMEM;

	mutex = kmalloc_node(sizeof(*mutex), GFP_KERNEL, cpu_to_node(cpu));
	if (!mutex) {
		kfree(dst);
		return -ENOMEM;
	}

	mutex_init(mutex);
	per_cpu(zswap_dstmem, cpu) = dst;
	per_cpu(zswap_mutex, cpu) = mutex;
	return 0;
}

static int zswap_dstmem_dead(unsigned int cpu)
{
	struct mutex *mutex;
	u8 *dst;

	mutex = per_cpu(zswap_mutex, cpu);
	kfree(mutex);
	per_cpu(zswap_mutex, cpu) = NULL;

	dst = per_cpu(zswap_dstmem, cpu);
	kfree(dst);
	per_cpu(zswap_dstmem, cpu) = NULL;

	return 0;
}

static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
{
	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
	struct crypto_acomp *acomp;
	struct acomp_req *req;

	acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
	if (IS_ERR(acomp)) {
		pr_err("could not alloc crypto acomp %s : %ld\n",
				pool->tfm_name, PTR_ERR(acomp));
		return PTR_ERR(acomp);
	}
	acomp_ctx->acomp = acomp;

	req = acomp_request_alloc(acomp_ctx->acomp);
	if (!req) {
		pr_err("could not alloc crypto acomp_request %s\n",
		       pool->tfm_name);
		crypto_free_acomp(acomp_ctx->acomp);
		return -ENOMEM;
	}
	acomp_ctx->req = req;

	crypto_init_wait(&acomp_ctx->wait);
	/*
	 * if the backend of acomp is async zip, crypto_req_done() will wakeup
	 * crypto_wait_req(); if the backend of acomp is scomp, the callback
	 * won't be called, crypto_wait_req() will return without blocking.
	 */
	acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
				   crypto_req_done, &acomp_ctx->wait);

	acomp_ctx->mutex = per_cpu(zswap_mutex, cpu);
	acomp_ctx->dstmem = per_cpu(zswap_dstmem, cpu);

	return 0;
}

static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
{
	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);

	if (!IS_ERR_OR_NULL(acomp_ctx)) {
		if (!IS_ERR_OR_NULL(acomp_ctx->req))
			acomp_request_free(acomp_ctx->req);
		if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
			crypto_free_acomp(acomp_ctx->acomp);
	}

	return 0;
}

/*********************************
* pool functions
**********************************/

static struct zswap_pool *__zswap_pool_current(void)
{
	struct zswap_pool *pool;

	pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
	WARN_ONCE(!pool && zswap_has_pool,
		  "%s: no page storage pool!\n", __func__);

	return pool;
}

static struct zswap_pool *zswap_pool_current(void)
{
	assert_spin_locked(&zswap_pools_lock);

	return __zswap_pool_current();
}

static struct zswap_pool *zswap_pool_current_get(void)
{
	struct zswap_pool *pool;

	rcu_read_lock();

	pool = __zswap_pool_current();
	if (!zswap_pool_get(pool))
		pool = NULL;

	rcu_read_unlock();

	return pool;
}

static struct zswap_pool *zswap_pool_last_get(void)
{
	struct zswap_pool *pool, *last = NULL;

	rcu_read_lock();

	list_for_each_entry_rcu(pool, &zswap_pools, list)
		last = pool;
	WARN_ONCE(!last && zswap_has_pool,
		  "%s: no page storage pool!\n", __func__);
	if (!zswap_pool_get(last))
		last = NULL;

	rcu_read_unlock();

	return last;
}

/* type and compressor must be null-terminated */
static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
{
	struct zswap_pool *pool;

	assert_spin_locked(&zswap_pools_lock);

	list_for_each_entry_rcu(pool, &zswap_pools, list) {
		if (strcmp(pool->tfm_name, compressor))
			continue;
		if (strcmp(zpool_get_type(pool->zpool), type))
			continue;
		/* if we can't get it, it's about to be destroyed */
		if (!zswap_pool_get(pool))
			continue;
		return pool;
	}

	return NULL;
}

static void shrink_worker(struct work_struct *w)
{
	struct zswap_pool *pool = container_of(w, typeof(*pool),
						shrink_work);

	if (zpool_shrink(pool->zpool, 1, NULL))
		zswap_reject_reclaim_fail++;
	zswap_pool_put(pool);
}

static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
{
	struct zswap_pool *pool;
	char name[38]; /* 'zswap' + 32 char (max) num + \0 */
	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
	int ret;

	if (!zswap_has_pool) {
		/* if either are unset, pool initialization failed, and we
		 * need both params to be set correctly before trying to
		 * create a pool.
		 */
		if (!strcmp(type, ZSWAP_PARAM_UNSET))
			return NULL;
		if (!strcmp(compressor, ZSWAP_PARAM_UNSET))
			return NULL;
	}

	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
	if (!pool)
		return NULL;

	/* unique name for each pool specifically required by zsmalloc */
	snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));

	pool->zpool = zpool_create_pool(type, name, gfp, &zswap_zpool_ops);
	if (!pool->zpool) {
		pr_err("%s zpool not available\n", type);
		goto error;
	}
	pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));

	strscpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));

	pool->acomp_ctx = alloc_percpu(*pool->acomp_ctx);
	if (!pool->acomp_ctx) {
		pr_err("percpu alloc failed\n");
		goto error;
	}

	ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
				       &pool->node);
	if (ret)
		goto error;
	pr_debug("using %s compressor\n", pool->tfm_name);

	/* being the current pool takes 1 ref; this func expects the
	 * caller to always add the new pool as the current pool
	 */
	kref_init(&pool->kref);
	INIT_LIST_HEAD(&pool->list);
	INIT_WORK(&pool->shrink_work, shrink_worker);

	zswap_pool_debug("created", pool);

	return pool;

error:
	if (pool->acomp_ctx)
		free_percpu(pool->acomp_ctx);
	if (pool->zpool)
		zpool_destroy_pool(pool->zpool);
	kfree(pool);
	return NULL;
}

static struct zswap_pool *__zswap_pool_create_fallback(void)
{
	bool has_comp, has_zpool;

	has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
	if (!has_comp && strcmp(zswap_compressor,
				CONFIG_ZSWAP_COMPRESSOR_DEFAULT)) {
		pr_err("compressor %s not available, using default %s\n",
		       zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT);
		param_free_charp(&zswap_compressor);
		zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
		has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
	}
	if (!has_comp) {
		pr_err("default compressor %s not available\n",
		       zswap_compressor);
		param_free_charp(&zswap_compressor);
		zswap_compressor = ZSWAP_PARAM_UNSET;
	}

	has_zpool = zpool_has_pool(zswap_zpool_type);
	if (!has_zpool && strcmp(zswap_zpool_type,
				 CONFIG_ZSWAP_ZPOOL_DEFAULT)) {
		pr_err("zpool %s not available, using default %s\n",
		       zswap_zpool_type, CONFIG_ZSWAP_ZPOOL_DEFAULT);
		param_free_charp(&zswap_zpool_type);
		zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
		has_zpool = zpool_has_pool(zswap_zpool_type);
	}
	if (!has_zpool) {
		pr_err("default zpool %s not available\n",
		       zswap_zpool_type);
		param_free_charp(&zswap_zpool_type);
		zswap_zpool_type = ZSWAP_PARAM_UNSET;
	}

	if (!has_comp || !has_zpool)
		return NULL;

	return zswap_pool_create(zswap_zpool_type, zswap_compressor);
}

static void zswap_pool_destroy(struct zswap_pool *pool)
{
	zswap_pool_debug("destroying", pool);

	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
	free_percpu(pool->acomp_ctx);
	zpool_destroy_pool(pool->zpool);
	kfree(pool);
}

static int __must_check zswap_pool_get(struct zswap_pool *pool)
{
	if (!pool)
		return 0;

	return kref_get_unless_zero(&pool->kref);
}

static void __zswap_pool_release(struct work_struct *work)
{
	struct zswap_pool *pool = container_of(work, typeof(*pool),
						release_work);

	synchronize_rcu();

	/* nobody should have been able to get a kref... */
	WARN_ON(kref_get_unless_zero(&pool->kref));

	/* pool is now off zswap_pools list and has no references. */
	zswap_pool_destroy(pool);
}

static void __zswap_pool_empty(struct kref *kref)
{
	struct zswap_pool *pool;

	pool = container_of(kref, typeof(*pool), kref);

	spin_lock(&zswap_pools_lock);

	WARN_ON(pool == zswap_pool_current());

	list_del_rcu(&pool->list);

	INIT_WORK(&pool->release_work, __zswap_pool_release);
	schedule_work(&pool->release_work);

	spin_unlock(&zswap_pools_lock);
}

static void zswap_pool_put(struct zswap_pool *pool)
{
	kref_put(&pool->kref, __zswap_pool_empty);
}

/*********************************
* param callbacks
**********************************/

static bool zswap_pool_changed(const char *s, const struct kernel_param *kp)
{
	/* no change required */
	if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
		return false;
	return true;
}

/* val must be a null-terminated string */
static int __zswap_param_set(const char *val, const struct kernel_param *kp,
			     char *type, char *compressor)
{
	struct zswap_pool *pool, *put_pool = NULL;
	char *s = strstrip((char *)val);
	int ret = 0;
	bool new_pool = false;

	mutex_lock(&zswap_init_lock);
	switch (zswap_init_state) {
	case ZSWAP_UNINIT:
		/* if this is load-time (pre-init) param setting,
		 * don't create a pool; that's done during init.
		 */
		ret = param_set_charp(s, kp);
		break;
	case ZSWAP_INIT_SUCCEED:
		new_pool = zswap_pool_changed(s, kp);
		break;
	case ZSWAP_INIT_FAILED:
		pr_err("can't set param, initialization failed\n");
		ret = -ENODEV;
	}
	mutex_unlock(&zswap_init_lock);

	/* no need to create a new pool, return directly */
	if (!new_pool)
		return ret;

	if (!type) {
		if (!zpool_has_pool(s)) {
			pr_err("zpool %s not available\n", s);
			return -ENOENT;
		}
		type = s;
	} else if (!compressor) {
		if (!crypto_has_acomp(s, 0, 0)) {
			pr_err("compressor %s not available\n", s);
			return -ENOENT;
		}
		compressor = s;
	} else {
		WARN_ON(1);
		return -EINVAL;
	}

	spin_lock(&zswap_pools_lock);

	pool = zswap_pool_find_get(type, compressor);
	if (pool) {
		zswap_pool_debug("using existing", pool);
		WARN_ON(pool == zswap_pool_current());
		list_del_rcu(&pool->list);
	}

	spin_unlock(&zswap_pools_lock);

	if (!pool)
		pool = zswap_pool_create(type, compressor);

	if (pool)
		ret = param_set_charp(s, kp);
	else
		ret = -EINVAL;

	spin_lock(&zswap_pools_lock);

	if (!ret) {
		put_pool = zswap_pool_current();
		list_add_rcu(&pool->list, &zswap_pools);
		zswap_has_pool = true;
	} else if (pool) {
		/* add the possibly pre-existing pool to the end of the pools
		 * list; if it's new (and empty) then it'll be removed and
		 * destroyed by the put after we drop the lock
		 */
		list_add_tail_rcu(&pool->list, &zswap_pools);
		put_pool = pool;
	}

	spin_unlock(&zswap_pools_lock);

	if (!zswap_has_pool && !pool) {
		/* if initial pool creation failed, and this pool creation also
		 * failed, maybe both compressor and zpool params were bad.
		 * Allow changing this param, so pool creation will succeed
		 * when the other param is changed. We already verified this
		 * param is ok in the zpool_has_pool() or crypto_has_acomp()
		 * checks above.
		 */
		ret = param_set_charp(s, kp);
	}

	/* drop the ref from either the old current pool,
	 * or the new pool we failed to add
	 */
	if (put_pool)
		zswap_pool_put(put_pool);

	return ret;
}

static int zswap_compressor_param_set(const char *val,
				      const struct kernel_param *kp)
{
	return __zswap_param_set(val, kp, zswap_zpool_type, NULL);
}

static int zswap_zpool_param_set(const char *val,
				 const struct kernel_param *kp)
{
	return __zswap_param_set(val, kp, NULL, zswap_compressor);
}

static int zswap_enabled_param_set(const char *val,
				   const struct kernel_param *kp)
{
	int ret = -ENODEV;

	/* if this is load-time (pre-init) param setting, only set param. */
	if (system_state != SYSTEM_RUNNING)
		return param_set_bool(val, kp);

	mutex_lock(&zswap_init_lock);
	switch (zswap_init_state) {
	case ZSWAP_UNINIT:
		if (zswap_setup())
			break;
		fallthrough;
	case ZSWAP_INIT_SUCCEED:
		if (!zswap_has_pool)
			pr_err("can't enable, no pool configured\n");
		else
			ret = param_set_bool(val, kp);
		break;
	case ZSWAP_INIT_FAILED:
		pr_err("can't enable, initialization failed\n");
	}
	mutex_unlock(&zswap_init_lock);

	return ret;
}

/*********************************
* writeback code
**********************************/
/* return enum for zswap_get_swap_cache_page */
enum zswap_get_swap_ret {
	ZSWAP_SWAPCACHE_NEW,
	ZSWAP_SWAPCACHE_EXIST,
	ZSWAP_SWAPCACHE_FAIL,
};

/*
 * zswap_get_swap_cache_page
 *
 * This is an adaption of read_swap_cache_async()
 *
 * This function tries to find a page with the given swap entry
 * in the swapper_space address space (the swap cache).  If the page
 * is found, it is returned in retpage.  Otherwise, a page is allocated,
 * added to the swap cache, and returned in retpage.
 *
 * If success, the swap cache page is returned in retpage
 * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
 * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
 *     the new page is added to swapcache and locked
 * Returns ZSWAP_SWAPCACHE_FAIL on error
 */
static int zswap_get_swap_cache_page(swp_entry_t entry,
				struct page **retpage)
{
	bool page_was_allocated;

	*retpage = __read_swap_cache_async(entry, GFP_KERNEL,
			NULL, 0, &page_was_allocated);
	if (page_was_allocated)
		return ZSWAP_SWAPCACHE_NEW;
	if (!*retpage)
		return ZSWAP_SWAPCACHE_FAIL;
	return ZSWAP_SWAPCACHE_EXIST;
}

/*
 * Attempts to free an entry by adding a page to the swap cache,
 * decompressing the entry data into the page, and issuing a
 * bio write to write the page back to the swap device.
 *
 * This can be thought of as a "resumed writeback" of the page
 * to the swap device.  We are basically resuming the same swap
 * writeback path that was intercepted with the frontswap_store()
 * in the first place.  After the page has been decompressed into
 * the swap cache, the compressed version stored by zswap can be
 * freed.
 */
static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
{
	struct zswap_header *zhdr;
	swp_entry_t swpentry;
	struct zswap_tree *tree;
	pgoff_t offset;
	struct zswap_entry *entry;
	struct page *page;
	struct scatterlist input, output;
	struct crypto_acomp_ctx *acomp_ctx;

	u8 *src, *tmp = NULL;
	unsigned int dlen;
	int ret;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_NONE,
	};

	if (!zpool_can_sleep_mapped(pool)) {
		tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
		if (!tmp)
			return -ENOMEM;
	}

	/* extract swpentry from data */
	zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
	swpentry = zhdr->swpentry; /* here */
	tree = zswap_trees[swp_type(swpentry)];
	offset = swp_offset(swpentry);
	zpool_unmap_handle(pool, handle);

	/* find and ref zswap entry */
	spin_lock(&tree->lock);
	entry = zswap_entry_find_get(&tree->rbroot, offset);
	if (!entry) {
		/* entry was invalidated */
		spin_unlock(&tree->lock);
		kfree(tmp);
		return 0;
	}
	spin_unlock(&tree->lock);
	BUG_ON(offset != entry->offset);

	/* try to allocate swap cache page */
	switch (zswap_get_swap_cache_page(swpentry, &page)) {
	case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
		ret = -ENOMEM;
		goto fail;

	case ZSWAP_SWAPCACHE_EXIST:
		/* page is already in the swap cache, ignore for now */
		put_page(page);
		ret = -EEXIST;
		goto fail;

	case ZSWAP_SWAPCACHE_NEW: /* page is locked */
		/* decompress */
		acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
		dlen = PAGE_SIZE;

		zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
		src = (u8 *)zhdr + sizeof(struct zswap_header);
		if (!zpool_can_sleep_mapped(pool)) {
			memcpy(tmp, src, entry->length);
			src = tmp;
			zpool_unmap_handle(pool, handle);
		}

		mutex_lock(acomp_ctx->mutex);
		sg_init_one(&input, src, entry->length);
		sg_init_table(&output, 1);
		sg_set_page(&output, page, PAGE_SIZE, 0);
		acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
		ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
		dlen = acomp_ctx->req->dlen;
		mutex_unlock(acomp_ctx->mutex);

		if (!zpool_can_sleep_mapped(pool))
			kfree(tmp);
		else
			zpool_unmap_handle(pool, handle);

		BUG_ON(ret);
		BUG_ON(dlen != PAGE_SIZE);

		/* page is up to date */
		SetPageUptodate(page);
	}

	/* move it to the tail of the inactive list after end_writeback */
	SetPageReclaim(page);

	/* start writeback */
	__swap_writepage(page, &wbc);
	put_page(page);
	zswap_written_back_pages++;

	spin_lock(&tree->lock);
	/* drop local reference */
	zswap_entry_put(tree, entry);

	/*
	* There are two possible situations for entry here:
	* (1) refcount is 1(normal case),  entry is valid and on the tree
	* (2) refcount is 0, entry is freed and not on the tree
	*     because invalidate happened during writeback
	*  search the tree and free the entry if find entry
	*/
	if (entry == zswap_rb_search(&tree->rbroot, offset))
		zswap_entry_put(tree, entry);
	spin_unlock(&tree->lock);

	return ret;

fail:
	if (!zpool_can_sleep_mapped(pool))
		kfree(tmp);

	/*
	* if we get here due to ZSWAP_SWAPCACHE_EXIST
	* a load may be happening concurrently.
	* it is safe and okay to not free the entry.
	* if we free the entry in the following put
	* it is also okay to return !0
	*/
	spin_lock(&tree->lock);
	zswap_entry_put(tree, entry);
	spin_unlock(&tree->lock);

	return ret;
}

static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
{
	unsigned long *page;
	unsigned long val;
	unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;

	page = (unsigned long *)ptr;
	val = page[0];

	if (val != page[last_pos])
		return 0;

	for (pos = 1; pos < last_pos; pos++) {
		if (val != page[pos])
			return 0;
	}

	*value = val;

	return 1;
}

static void zswap_fill_page(void *ptr, unsigned long value)
{
	unsigned long *page;

	page = (unsigned long *)ptr;
	memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
}

/*********************************
* frontswap hooks
**********************************/
/* attempts to compress and store an single page */
static int zswap_frontswap_store(unsigned type, pgoff_t offset,
				struct page *page)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry, *dupentry;
	struct scatterlist input, output;
	struct crypto_acomp_ctx *acomp_ctx;
	struct obj_cgroup *objcg = NULL;
	struct zswap_pool *pool;
	int ret;
	unsigned int hlen, dlen = PAGE_SIZE;
	unsigned long handle, value;
	char *buf;
	u8 *src, *dst;
	struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) };
	gfp_t gfp;

	/* THP isn't supported */
	if (PageTransHuge(page)) {
		ret = -EINVAL;
		goto reject;
	}

	if (!zswap_enabled || !tree) {
		ret = -ENODEV;
		goto reject;
	}

	objcg = get_obj_cgroup_from_page(page);
	if (objcg && !obj_cgroup_may_zswap(objcg))
		goto shrink;

	/* reclaim space if needed */
	if (zswap_is_full()) {
		zswap_pool_limit_hit++;
		zswap_pool_reached_full = true;
		goto shrink;
	}

	if (zswap_pool_reached_full) {
	       if (!zswap_can_accept()) {
			ret = -ENOMEM;
			goto reject;
		} else
			zswap_pool_reached_full = false;
	}

	/* allocate entry */
	entry = zswap_entry_cache_alloc(GFP_KERNEL);
	if (!entry) {
		zswap_reject_kmemcache_fail++;
		ret = -ENOMEM;
		goto reject;
	}

	if (zswap_same_filled_pages_enabled) {
		src = kmap_atomic(page);
		if (zswap_is_page_same_filled(src, &value)) {
			kunmap_atomic(src);
			entry->offset = offset;
			entry->length = 0;
			entry->value = value;
			atomic_inc(&zswap_same_filled_pages);
			goto insert_entry;
		}
		kunmap_atomic(src);
	}

	if (!zswap_non_same_filled_pages_enabled) {
		ret = -EINVAL;
		goto freepage;
	}

	/* if entry is successfully added, it keeps the reference */
	entry->pool = zswap_pool_current_get();
	if (!entry->pool) {
		ret = -EINVAL;
		goto freepage;
	}

	/* compress */
	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);

	mutex_lock(acomp_ctx->mutex);

	dst = acomp_ctx->dstmem;
	sg_init_table(&input, 1);
	sg_set_page(&input, page, PAGE_SIZE, 0);

	/* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */
	sg_init_one(&output, dst, PAGE_SIZE * 2);
	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
	/*
	 * it maybe looks a little bit silly that we send an asynchronous request,
	 * then wait for its completion synchronously. This makes the process look
	 * synchronous in fact.
	 * Theoretically, acomp supports users send multiple acomp requests in one
	 * acomp instance, then get those requests done simultaneously. but in this
	 * case, frontswap actually does store and load page by page, there is no
	 * existing method to send the second page before the first page is done
	 * in one thread doing frontswap.
	 * but in different threads running on different cpu, we have different
	 * acomp instance, so multiple threads can do (de)compression in parallel.
	 */
	ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
	dlen = acomp_ctx->req->dlen;

	if (ret) {
		ret = -EINVAL;
		goto put_dstmem;
	}

	/* store */
	hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
	if (zpool_malloc_support_movable(entry->pool->zpool))
		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
	ret = zpool_malloc(entry->pool->zpool, hlen + dlen, gfp, &handle);
	if (ret == -ENOSPC) {
		zswap_reject_compress_poor++;
		goto put_dstmem;
	}
	if (ret) {
		zswap_reject_alloc_fail++;
		goto put_dstmem;
	}
	buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_WO);
	memcpy(buf, &zhdr, hlen);
	memcpy(buf + hlen, dst, dlen);
	zpool_unmap_handle(entry->pool->zpool, handle);
	mutex_unlock(acomp_ctx->mutex);

	/* populate entry */
	entry->offset = offset;
	entry->handle = handle;
	entry->length = dlen;

insert_entry:
	entry->objcg = objcg;
	if (objcg) {
		obj_cgroup_charge_zswap(objcg, entry->length);
		/* Account before objcg ref is moved to tree */
		count_objcg_event(objcg, ZSWPOUT);
	}

	/* map */
	spin_lock(&tree->lock);
	do {
		ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
		if (ret == -EEXIST) {
			zswap_duplicate_entry++;
			/* remove from rbtree */
			zswap_rb_erase(&tree->rbroot, dupentry);
			zswap_entry_put(tree, dupentry);
		}
	} while (ret == -EEXIST);
	spin_unlock(&tree->lock);

	/* update stats */
	atomic_inc(&zswap_stored_pages);
	zswap_update_total_size();
	count_vm_event(ZSWPOUT);

	return 0;

put_dstmem:
	mutex_unlock(acomp_ctx->mutex);
	zswap_pool_put(entry->pool);
freepage:
	zswap_entry_cache_free(entry);
reject:
	if (objcg)
		obj_cgroup_put(objcg);
	return ret;

shrink:
	pool = zswap_pool_last_get();
	if (pool)
		queue_work(shrink_wq, &pool->shrink_work);
	ret = -ENOMEM;
	goto reject;
}

/*
 * returns 0 if the page was successfully decompressed
 * return -1 on entry not found or error
*/
static int zswap_frontswap_load(unsigned type, pgoff_t offset,
				struct page *page)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry;
	struct scatterlist input, output;
	struct crypto_acomp_ctx *acomp_ctx;
	u8 *src, *dst, *tmp;
	unsigned int dlen;
	int ret;

	/* find */
	spin_lock(&tree->lock);
	entry = zswap_entry_find_get(&tree->rbroot, offset);
	if (!entry) {
		/* entry was written back */
		spin_unlock(&tree->lock);
		return -1;
	}
	spin_unlock(&tree->lock);

	if (!entry->length) {
		dst = kmap_atomic(page);
		zswap_fill_page(dst, entry->value);
		kunmap_atomic(dst);
		ret = 0;
		goto stats;
	}

	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
		tmp = kmalloc(entry->length, GFP_KERNEL);
		if (!tmp) {
			ret = -ENOMEM;
			goto freeentry;
		}
	}

	/* decompress */
	dlen = PAGE_SIZE;
	src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
	if (zpool_evictable(entry->pool->zpool))
		src += sizeof(struct zswap_header);

	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
		memcpy(tmp, src, entry->length);
		src = tmp;
		zpool_unmap_handle(entry->pool->zpool, entry->handle);
	}

	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
	mutex_lock(acomp_ctx->mutex);
	sg_init_one(&input, src, entry->length);
	sg_init_table(&output, 1);
	sg_set_page(&output, page, PAGE_SIZE, 0);
	acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
	ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
	mutex_unlock(acomp_ctx->mutex);

	if (zpool_can_sleep_mapped(entry->pool->zpool))
		zpool_unmap_handle(entry->pool->zpool, entry->handle);
	else
		kfree(tmp);

	BUG_ON(ret);
stats:
	count_vm_event(ZSWPIN);
	if (entry->objcg)
		count_objcg_event(entry->objcg, ZSWPIN);
freeentry:
	spin_lock(&tree->lock);
	zswap_entry_put(tree, entry);
	spin_unlock(&tree->lock);

	return ret;
}

/* frees an entry in zswap */
static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry;

	/* find */
	spin_lock(&tree->lock);
	entry = zswap_rb_search(&tree->rbroot, offset);
	if (!entry) {
		/* entry was written back */
		spin_unlock(&tree->lock);
		return;
	}

	/* remove from rbtree */
	zswap_rb_erase(&tree->rbroot, entry);

	/* drop the initial reference from entry creation */
	zswap_entry_put(tree, entry);

	spin_unlock(&tree->lock);
}

/* frees all zswap entries for the given swap type */
static void zswap_frontswap_invalidate_area(unsigned type)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry, *n;

	if (!tree)
		return;

	/* walk the tree and free everything */
	spin_lock(&tree->lock);
	rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
		zswap_free_entry(entry);
	tree->rbroot = RB_ROOT;
	spin_unlock(&tree->lock);
	kfree(tree);
	zswap_trees[type] = NULL;
}

static void zswap_frontswap_init(unsigned type)
{
	struct zswap_tree *tree;

	tree = kzalloc(sizeof(*tree), GFP_KERNEL);
	if (!tree) {
		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
		return;
	}

	tree->rbroot = RB_ROOT;
	spin_lock_init(&tree->lock);
	zswap_trees[type] = tree;
}

static const struct frontswap_ops zswap_frontswap_ops = {
	.store = zswap_frontswap_store,
	.load = zswap_frontswap_load,
	.invalidate_page = zswap_frontswap_invalidate_page,
	.invalidate_area = zswap_frontswap_invalidate_area,
	.init = zswap_frontswap_init
};

/*********************************
* debugfs functions
**********************************/
#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>

static struct dentry *zswap_debugfs_root;

static int zswap_debugfs_init(void)
{
	if (!debugfs_initialized())
		return -ENODEV;

	zswap_debugfs_root = debugfs_create_dir("zswap", NULL);

	debugfs_create_u64("pool_limit_hit", 0444,
			   zswap_debugfs_root, &zswap_pool_limit_hit);
	debugfs_create_u64("reject_reclaim_fail", 0444,
			   zswap_debugfs_root, &zswap_reject_reclaim_fail);
	debugfs_create_u64("reject_alloc_fail", 0444,
			   zswap_debugfs_root, &zswap_reject_alloc_fail);
	debugfs_create_u64("reject_kmemcache_fail", 0444,
			   zswap_debugfs_root, &zswap_reject_kmemcache_fail);
	debugfs_create_u64("reject_compress_poor", 0444,
			   zswap_debugfs_root, &zswap_reject_compress_poor);
	debugfs_create_u64("written_back_pages", 0444,
			   zswap_debugfs_root, &zswap_written_back_pages);
	debugfs_create_u64("duplicate_entry", 0444,
			   zswap_debugfs_root, &zswap_duplicate_entry);
	debugfs_create_u64("pool_total_size", 0444,
			   zswap_debugfs_root, &zswap_pool_total_size);
	debugfs_create_atomic_t("stored_pages", 0444,
				zswap_debugfs_root, &zswap_stored_pages);
	debugfs_create_atomic_t("same_filled_pages", 0444,
				zswap_debugfs_root, &zswap_same_filled_pages);

	return 0;
}
#else
static int zswap_debugfs_init(void)
{
	return 0;
}
#endif

/*********************************
* module init and exit
**********************************/
static int zswap_setup(void)
{
	struct zswap_pool *pool;
	int ret;

	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
	if (!zswap_entry_cache) {
		pr_err("entry cache creation failed\n");
		goto cache_fail;
	}

	ret = cpuhp_setup_state(CPUHP_MM_ZSWP_MEM_PREPARE, "mm/zswap:prepare",
				zswap_dstmem_prepare, zswap_dstmem_dead);
	if (ret) {
		pr_err("dstmem alloc failed\n");
		goto dstmem_fail;
	}

	ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
				      "mm/zswap_pool:prepare",
				      zswap_cpu_comp_prepare,
				      zswap_cpu_comp_dead);
	if (ret)
		goto hp_fail;

	pool = __zswap_pool_create_fallback();
	if (pool) {
		pr_info("loaded using pool %s/%s\n", pool->tfm_name,
			zpool_get_type(pool->zpool));
		list_add(&pool->list, &zswap_pools);
		zswap_has_pool = true;
	} else {
		pr_err("pool creation failed\n");
		zswap_enabled = false;
	}

	shrink_wq = create_workqueue("zswap-shrink");
	if (!shrink_wq)
		goto fallback_fail;

	ret = frontswap_register_ops(&zswap_frontswap_ops);
	if (ret)
		goto destroy_wq;
	if (zswap_debugfs_init())
		pr_warn("debugfs initialization failed\n");
	zswap_init_state = ZSWAP_INIT_SUCCEED;
	return 0;

destroy_wq:
	destroy_workqueue(shrink_wq);
fallback_fail:
	if (pool)
		zswap_pool_destroy(pool);
hp_fail:
	cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
dstmem_fail:
	kmem_cache_destroy(zswap_entry_cache);
cache_fail:
	/* if built-in, we aren't unloaded on failure; don't allow use */
	zswap_init_state = ZSWAP_INIT_FAILED;
	zswap_enabled = false;
	return -ENOMEM;
}

static int __init zswap_init(void)
{
	if (!zswap_enabled)
		return 0;
	return zswap_setup();
}
/* must be late so crypto has time to come up */
late_initcall(zswap_init);

MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
MODULE_DESCRIPTION("Compressed cache for swap pages");