summaryrefslogtreecommitdiff
path: root/mm/zswap.c
blob: 9dec853647c8e4c6fc1d0a4b0de0849ea3102a47 (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
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * zswap.c - zswap driver file
 *
 * zswap is a cache 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/rbtree.h>
#include <linux/swap.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <linux/mempolicy.h>
#include <linux/mempool.h>
#include <linux/zpool.h>
#include <crypto/acompress.h>
#include <linux/zswap.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 <linux/list_lru.h>

#include "swap.h"
#include "internal.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;
/* Store failed due to compression algorithm failure */
static u64 zswap_reject_compress_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;

/* 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);

/* Number of zpools in zswap_pool (empirically determined for scalability) */
#define ZSWAP_NR_ZPOOLS 32

/* Enable/disable memory pressure-based shrinker. */
static bool zswap_shrinker_enabled = IS_ENABLED(
		CONFIG_ZSWAP_SHRINKER_DEFAULT_ON);
module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);

bool is_zswap_enabled(void)
{
	return zswap_enabled;
}

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

struct crypto_acomp_ctx {
	struct crypto_acomp *acomp;
	struct acomp_req *req;
	struct crypto_wait wait;
	u8 *buffer;
	struct mutex mutex;
	bool is_sleepable;
};

/*
 * The lock ordering is zswap_tree.lock -> zswap_pool.lru_lock.
 * The only case where lru_lock is not acquired while holding tree.lock is
 * when a zswap_entry is taken off the lru for writeback, in that case it
 * needs to be verified that it's still valid in the tree.
 */
struct zswap_pool {
	struct zpool *zpools[ZSWAP_NR_ZPOOLS];
	struct crypto_acomp_ctx __percpu *acomp_ctx;
	struct percpu_ref ref;
	struct list_head list;
	struct work_struct release_work;
	struct hlist_node node;
	char tfm_name[CRYPTO_MAX_ALG_NAME];
};

/* Global LRU lists shared by all zswap pools. */
static struct list_lru zswap_list_lru;
/* counter of pages stored in all zswap pools. */
static atomic_t zswap_nr_stored = ATOMIC_INIT(0);

/* The lock protects zswap_next_shrink updates. */
static DEFINE_SPINLOCK(zswap_shrink_lock);
static struct mem_cgroup *zswap_next_shrink;
static struct work_struct zswap_shrink_work;
static struct shrinker *zswap_shrinker;

/*
 * 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
 * swpentry - associated swap entry, the offset indexes into the red-black tree
 * length - the length in bytes of the compressed page data.  Needed during
 *          decompression. For a same value filled page length is 0, and both
 *          pool and lru are invalid and must be ignored.
 * 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
 * objcg - the obj_cgroup that the compressed memory is charged to
 * lru - handle to the pool's lru used to evict pages.
 */
struct zswap_entry {
	struct rb_node rbnode;
	swp_entry_t swpentry;
	unsigned int length;
	struct zswap_pool *pool;
	union {
		unsigned long handle;
		unsigned long value;
	};
	struct obj_cgroup *objcg;
	struct list_head lru;
};

struct zswap_tree {
	struct rb_root rbroot;
	spinlock_t lock;
};

static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
static unsigned int nr_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
**********************************/

static inline struct zswap_tree *swap_zswap_tree(swp_entry_t swp)
{
	return &zswap_trees[swp_type(swp)][swp_offset(swp)
		>> SWAP_ADDRESS_SPACE_SHIFT];
}

#define zswap_pool_debug(msg, p)				\
	pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,		\
		 zpool_get_type((p)->zpools[0]))

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 u64 get_zswap_pool_size(struct zswap_pool *pool)
{
	u64 pool_size = 0;
	int i;

	for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
		pool_size += zpool_get_total_size(pool->zpools[i]);

	return pool_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 += get_zswap_pool_size(pool);

	rcu_read_unlock();

	zswap_pool_total_size = total;
}

/*********************************
* pool functions
**********************************/
static void __zswap_pool_empty(struct percpu_ref *ref);

static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
{
	int i;
	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;

	for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) {
		/* unique name for each pool specifically required by zsmalloc */
		snprintf(name, 38, "zswap%x",
			 atomic_inc_return(&zswap_pools_count));

		pool->zpools[i] = zpool_create_pool(type, name, gfp);
		if (!pool->zpools[i]) {
			pr_err("%s zpool not available\n", type);
			goto error;
		}
	}
	pr_debug("using %s zpool\n", zpool_get_type(pool->zpools[0]));

	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;

	/* being the current pool takes 1 ref; this func expects the
	 * caller to always add the new pool as the current pool
	 */
	ret = percpu_ref_init(&pool->ref, __zswap_pool_empty,
			      PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
	if (ret)
		goto ref_fail;
	INIT_LIST_HEAD(&pool->list);

	zswap_pool_debug("created", pool);

	return pool;

ref_fail:
	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
error:
	if (pool->acomp_ctx)
		free_percpu(pool->acomp_ctx);
	while (i--)
		zpool_destroy_pool(pool->zpools[i]);
	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)
{
	int i;

	zswap_pool_debug("destroying", pool);

	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
	free_percpu(pool->acomp_ctx);

	for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
		zpool_destroy_pool(pool->zpools[i]);
	kfree(pool);
}

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 ref... */
	WARN_ON(!percpu_ref_is_zero(&pool->ref));
	percpu_ref_exit(&pool->ref);

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

static struct zswap_pool *zswap_pool_current(void);

static void __zswap_pool_empty(struct percpu_ref *ref)
{
	struct zswap_pool *pool;

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

	spin_lock_bh(&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_bh(&zswap_pools_lock);
}

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

	return percpu_ref_tryget(&pool->ref);
}

static void zswap_pool_put(struct zswap_pool *pool)
{
	percpu_ref_put(&pool->ref);
}

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;
}

/* 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;
		/* all zpools share the same type */
		if (strcmp(zpool_get_type(pool->zpools[0]), type))
			continue;
		/* if we can't get it, it's about to be destroyed */
		if (!zswap_pool_get(pool))
			continue;
		return pool;
	}

	return NULL;
}

/*********************************
* 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_bh(&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_bh(&zswap_pools_lock);

	if (!pool)
		pool = zswap_pool_create(type, compressor);
	else {
		/*
		 * Restore the initial ref dropped by percpu_ref_kill()
		 * when the pool was decommissioned and switch it again
		 * to percpu mode.
		 */
		percpu_ref_resurrect(&pool->ref);

		/* Drop the ref from zswap_pool_find_get(). */
		zswap_pool_put(pool);
	}

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

	spin_lock_bh(&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_bh(&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)
		percpu_ref_kill(&put_pool->ref);

	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;
}

/*********************************
* lru functions
**********************************/

/* should be called under RCU */
#ifdef CONFIG_MEMCG
static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
{
	return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
}
#else
static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
{
	return NULL;
}
#endif

static inline int entry_to_nid(struct zswap_entry *entry)
{
	return page_to_nid(virt_to_page(entry));
}

static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
{
	atomic_long_t *nr_zswap_protected;
	unsigned long lru_size, old, new;
	int nid = entry_to_nid(entry);
	struct mem_cgroup *memcg;
	struct lruvec *lruvec;

	/*
	 * Note that it is safe to use rcu_read_lock() here, even in the face of
	 * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection
	 * used in list_lru lookup, only two scenarios are possible:
	 *
	 * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The
	 *    new entry will be reparented to memcg's parent's list_lru.
	 * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The
	 *    new entry will be added directly to memcg's parent's list_lru.
	 *
	 * Similar reasoning holds for list_lru_del().
	 */
	rcu_read_lock();
	memcg = mem_cgroup_from_entry(entry);
	/* will always succeed */
	list_lru_add(list_lru, &entry->lru, nid, memcg);

	/* Update the protection area */
	lru_size = list_lru_count_one(list_lru, nid, memcg);
	lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
	nr_zswap_protected = &lruvec->zswap_lruvec_state.nr_zswap_protected;
	old = atomic_long_inc_return(nr_zswap_protected);
	/*
	 * Decay to avoid overflow and adapt to changing workloads.
	 * This is based on LRU reclaim cost decaying heuristics.
	 */
	do {
		new = old > lru_size / 4 ? old / 2 : old;
	} while (!atomic_long_try_cmpxchg(nr_zswap_protected, &old, new));
	rcu_read_unlock();
}

static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
{
	int nid = entry_to_nid(entry);
	struct mem_cgroup *memcg;

	rcu_read_lock();
	memcg = mem_cgroup_from_entry(entry);
	/* will always succeed */
	list_lru_del(list_lru, &entry->lru, nid, memcg);
	rcu_read_unlock();
}

void zswap_lruvec_state_init(struct lruvec *lruvec)
{
	atomic_long_set(&lruvec->zswap_lruvec_state.nr_zswap_protected, 0);
}

void zswap_folio_swapin(struct folio *folio)
{
	struct lruvec *lruvec;

	if (folio) {
		lruvec = folio_lruvec(folio);
		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_zswap_protected);
	}
}

void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
{
	/* lock out zswap shrinker walking memcg tree */
	spin_lock(&zswap_shrink_lock);
	if (zswap_next_shrink == memcg)
		zswap_next_shrink = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
	spin_unlock(&zswap_shrink_lock);
}

/*********************************
* 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;
	pgoff_t entry_offset;

	while (node) {
		entry = rb_entry(node, struct zswap_entry, rbnode);
		entry_offset = swp_offset(entry->swpentry);
		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;
	pgoff_t myentry_offset, entry_offset = swp_offset(entry->swpentry);

	while (*link) {
		parent = *link;
		myentry = rb_entry(parent, struct zswap_entry, rbnode);
		myentry_offset = swp_offset(myentry->swpentry);
		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)
{
	rb_erase(&entry->rbnode, root);
	RB_CLEAR_NODE(&entry->rbnode);
}

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

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

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

static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
{
	int i = 0;

	if (ZSWAP_NR_ZPOOLS > 1)
		i = hash_ptr(entry, ilog2(ZSWAP_NR_ZPOOLS));

	return entry->pool->zpools[i];
}

/*
 * 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_entry_free(struct zswap_entry *entry)
{
	if (!entry->length)
		atomic_dec(&zswap_same_filled_pages);
	else {
		zswap_lru_del(&zswap_list_lru, entry);
		zpool_free(zswap_find_zpool(entry), entry->handle);
		atomic_dec(&zswap_nr_stored);
		zswap_pool_put(entry->pool);
	}
	if (entry->objcg) {
		obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
		obj_cgroup_put(entry->objcg);
	}
	zswap_entry_cache_free(entry);
	atomic_dec(&zswap_stored_pages);
	zswap_update_total_size();
}

/*
 * The caller hold the tree lock and search the entry from the tree,
 * so it must be on the tree, remove it from the tree and free it.
 */
static void zswap_invalidate_entry(struct zswap_tree *tree,
				   struct zswap_entry *entry)
{
	zswap_rb_erase(&tree->rbroot, entry);
	zswap_entry_free(entry);
}

/*********************************
* compressed storage functions
**********************************/
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;
	int ret;

	mutex_init(&acomp_ctx->mutex);

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

	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));
		ret = PTR_ERR(acomp);
		goto acomp_fail;
	}
	acomp_ctx->acomp = acomp;
	acomp_ctx->is_sleepable = acomp_is_async(acomp);

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

	return 0;

req_fail:
	crypto_free_acomp(acomp_ctx->acomp);
acomp_fail:
	kfree(acomp_ctx->buffer);
	return ret;
}

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);
		kfree(acomp_ctx->buffer);
	}

	return 0;
}

static bool zswap_compress(struct folio *folio, struct zswap_entry *entry)
{
	struct crypto_acomp_ctx *acomp_ctx;
	struct scatterlist input, output;
	int comp_ret = 0, alloc_ret = 0;
	unsigned int dlen = PAGE_SIZE;
	unsigned long handle;
	struct zpool *zpool;
	char *buf;
	gfp_t gfp;
	u8 *dst;

	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);

	mutex_lock(&acomp_ctx->mutex);

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

	/*
	 * We need PAGE_SIZE * 2 here since there maybe over-compression case,
	 * and hardware-accelerators may won't check the dst buffer size, so
	 * giving the dst buffer with enough length to avoid buffer overflow.
	 */
	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, zswap 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 zwap.
	 * but in different threads running on different cpu, we have different
	 * acomp instance, so multiple threads can do (de)compression in parallel.
	 */
	comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
	dlen = acomp_ctx->req->dlen;
	if (comp_ret)
		goto unlock;

	zpool = zswap_find_zpool(entry);
	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
	if (zpool_malloc_support_movable(zpool))
		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
	alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle);
	if (alloc_ret)
		goto unlock;

	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
	memcpy(buf, dst, dlen);
	zpool_unmap_handle(zpool, handle);

	entry->handle = handle;
	entry->length = dlen;

unlock:
	if (comp_ret == -ENOSPC || alloc_ret == -ENOSPC)
		zswap_reject_compress_poor++;
	else if (comp_ret)
		zswap_reject_compress_fail++;
	else if (alloc_ret)
		zswap_reject_alloc_fail++;

	mutex_unlock(&acomp_ctx->mutex);
	return comp_ret == 0 && alloc_ret == 0;
}

static void zswap_decompress(struct zswap_entry *entry, struct page *page)
{
	struct zpool *zpool = zswap_find_zpool(entry);
	struct scatterlist input, output;
	struct crypto_acomp_ctx *acomp_ctx;
	u8 *src;

	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
	mutex_lock(&acomp_ctx->mutex);

	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
	if (acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) {
		memcpy(acomp_ctx->buffer, src, entry->length);
		src = acomp_ctx->buffer;
		zpool_unmap_handle(zpool, entry->handle);
	}

	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, PAGE_SIZE);
	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
	mutex_unlock(&acomp_ctx->mutex);

	if (!acomp_ctx->is_sleepable || zpool_can_sleep_mapped(zpool))
		zpool_unmap_handle(zpool, entry->handle);
}

/*********************************
* writeback code
**********************************/
/*
 * Attempts to free an entry by adding a folio to the swap cache,
 * decompressing the entry data into the folio, and issuing a
 * bio write to write the folio back to the swap device.
 *
 * This can be thought of as a "resumed writeback" of the folio
 * to the swap device.  We are basically resuming the same swap
 * writeback path that was intercepted with the zswap_store()
 * in the first place.  After the folio has been decompressed into
 * the swap cache, the compressed version stored by zswap can be
 * freed.
 */
static int zswap_writeback_entry(struct zswap_entry *entry,
				 swp_entry_t swpentry)
{
	struct zswap_tree *tree;
	struct folio *folio;
	struct mempolicy *mpol;
	bool folio_was_allocated;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_NONE,
	};

	/* try to allocate swap cache folio */
	mpol = get_task_policy(current);
	folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
				NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
	if (!folio)
		return -ENOMEM;

	/*
	 * Found an existing folio, we raced with swapin or concurrent
	 * shrinker. We generally writeback cold folios from zswap, and
	 * swapin means the folio just became hot, so skip this folio.
	 * For unlikely concurrent shrinker case, it will be unlinked
	 * and freed when invalidated by the concurrent shrinker anyway.
	 */
	if (!folio_was_allocated) {
		folio_put(folio);
		return -EEXIST;
	}

	/*
	 * folio is locked, and the swapcache is now secured against
	 * concurrent swapping to and from the slot, and concurrent
	 * swapoff so we can safely dereference the zswap tree here.
	 * Verify that the swap entry hasn't been invalidated and recycled
	 * behind our backs, to avoid overwriting a new swap folio with
	 * old compressed data. Only when this is successful can the entry
	 * be dereferenced.
	 */
	tree = swap_zswap_tree(swpentry);
	spin_lock(&tree->lock);
	if (zswap_rb_search(&tree->rbroot, swp_offset(swpentry)) != entry) {
		spin_unlock(&tree->lock);
		delete_from_swap_cache(folio);
		folio_unlock(folio);
		folio_put(folio);
		return -ENOMEM;
	}

	/* Safe to deref entry after the entry is verified above. */
	zswap_rb_erase(&tree->rbroot, entry);
	spin_unlock(&tree->lock);

	zswap_decompress(entry, &folio->page);

	count_vm_event(ZSWPWB);
	if (entry->objcg)
		count_objcg_event(entry->objcg, ZSWPWB);

	zswap_entry_free(entry);

	/* folio is up to date */
	folio_mark_uptodate(folio);

	/* move it to the tail of the inactive list after end_writeback */
	folio_set_reclaim(folio);

	/* start writeback */
	__swap_writepage(folio, &wbc);
	folio_put(folio);

	return 0;
}

/*********************************
* shrinker functions
**********************************/
static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
				       spinlock_t *lock, void *arg)
{
	struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
	bool *encountered_page_in_swapcache = (bool *)arg;
	swp_entry_t swpentry;
	enum lru_status ret = LRU_REMOVED_RETRY;
	int writeback_result;

	/*
	 * As soon as we drop the LRU lock, the entry can be freed by
	 * a concurrent invalidation. This means the following:
	 *
	 * 1. We extract the swp_entry_t to the stack, allowing
	 *    zswap_writeback_entry() to pin the swap entry and
	 *    then validate the zwap entry against that swap entry's
	 *    tree using pointer value comparison. Only when that
	 *    is successful can the entry be dereferenced.
	 *
	 * 2. Usually, objects are taken off the LRU for reclaim. In
	 *    this case this isn't possible, because if reclaim fails
	 *    for whatever reason, we have no means of knowing if the
	 *    entry is alive to put it back on the LRU.
	 *
	 *    So rotate it before dropping the lock. If the entry is
	 *    written back or invalidated, the free path will unlink
	 *    it. For failures, rotation is the right thing as well.
	 *
	 *    Temporary failures, where the same entry should be tried
	 *    again immediately, almost never happen for this shrinker.
	 *    We don't do any trylocking; -ENOMEM comes closest,
	 *    but that's extremely rare and doesn't happen spuriously
	 *    either. Don't bother distinguishing this case.
	 */
	list_move_tail(item, &l->list);

	/*
	 * Once the lru lock is dropped, the entry might get freed. The
	 * swpentry is copied to the stack, and entry isn't deref'd again
	 * until the entry is verified to still be alive in the tree.
	 */
	swpentry = entry->swpentry;

	/*
	 * It's safe to drop the lock here because we return either
	 * LRU_REMOVED_RETRY or LRU_RETRY.
	 */
	spin_unlock(lock);

	writeback_result = zswap_writeback_entry(entry, swpentry);

	if (writeback_result) {
		zswap_reject_reclaim_fail++;
		ret = LRU_RETRY;

		/*
		 * Encountering a page already in swap cache is a sign that we are shrinking
		 * into the warmer region. We should terminate shrinking (if we're in the dynamic
		 * shrinker context).
		 */
		if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
			ret = LRU_STOP;
			*encountered_page_in_swapcache = true;
		}
	} else {
		zswap_written_back_pages++;
	}

	spin_lock(lock);
	return ret;
}

static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
		struct shrink_control *sc)
{
	struct lruvec *lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
	unsigned long shrink_ret, nr_protected, lru_size;
	bool encountered_page_in_swapcache = false;

	if (!zswap_shrinker_enabled ||
			!mem_cgroup_zswap_writeback_enabled(sc->memcg)) {
		sc->nr_scanned = 0;
		return SHRINK_STOP;
	}

	nr_protected =
		atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
	lru_size = list_lru_shrink_count(&zswap_list_lru, sc);

	/*
	 * Abort if we are shrinking into the protected region.
	 *
	 * This short-circuiting is necessary because if we have too many multiple
	 * concurrent reclaimers getting the freeable zswap object counts at the
	 * same time (before any of them made reasonable progress), the total
	 * number of reclaimed objects might be more than the number of unprotected
	 * objects (i.e the reclaimers will reclaim into the protected area of the
	 * zswap LRU).
	 */
	if (nr_protected >= lru_size - sc->nr_to_scan) {
		sc->nr_scanned = 0;
		return SHRINK_STOP;
	}

	shrink_ret = list_lru_shrink_walk(&zswap_list_lru, sc, &shrink_memcg_cb,
		&encountered_page_in_swapcache);

	if (encountered_page_in_swapcache)
		return SHRINK_STOP;

	return shrink_ret ? shrink_ret : SHRINK_STOP;
}

static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
		struct shrink_control *sc)
{
	struct mem_cgroup *memcg = sc->memcg;
	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid));
	unsigned long nr_backing, nr_stored, nr_freeable, nr_protected;

	if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg))
		return 0;

#ifdef CONFIG_MEMCG_KMEM
	mem_cgroup_flush_stats(memcg);
	nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
	nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
#else
	/* use pool stats instead of memcg stats */
	nr_backing = zswap_pool_total_size >> PAGE_SHIFT;
	nr_stored = atomic_read(&zswap_nr_stored);
#endif

	if (!nr_stored)
		return 0;

	nr_protected =
		atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected);
	nr_freeable = list_lru_shrink_count(&zswap_list_lru, sc);
	/*
	 * Subtract the lru size by an estimate of the number of pages
	 * that should be protected.
	 */
	nr_freeable = nr_freeable > nr_protected ? nr_freeable - nr_protected : 0;

	/*
	 * Scale the number of freeable pages by the memory saving factor.
	 * This ensures that the better zswap compresses memory, the fewer
	 * pages we will evict to swap (as it will otherwise incur IO for
	 * relatively small memory saving).
	 */
	return mult_frac(nr_freeable, nr_backing, nr_stored);
}

static struct shrinker *zswap_alloc_shrinker(void)
{
	struct shrinker *shrinker;

	shrinker =
		shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap");
	if (!shrinker)
		return NULL;

	shrinker->scan_objects = zswap_shrinker_scan;
	shrinker->count_objects = zswap_shrinker_count;
	shrinker->batch = 0;
	shrinker->seeks = DEFAULT_SEEKS;
	return shrinker;
}

static int shrink_memcg(struct mem_cgroup *memcg)
{
	int nid, shrunk = 0;

	if (!mem_cgroup_zswap_writeback_enabled(memcg))
		return -EINVAL;

	/*
	 * Skip zombies because their LRUs are reparented and we would be
	 * reclaiming from the parent instead of the dead memcg.
	 */
	if (memcg && !mem_cgroup_online(memcg))
		return -ENOENT;

	for_each_node_state(nid, N_NORMAL_MEMORY) {
		unsigned long nr_to_walk = 1;

		shrunk += list_lru_walk_one(&zswap_list_lru, nid, memcg,
					    &shrink_memcg_cb, NULL, &nr_to_walk);
	}
	return shrunk ? 0 : -EAGAIN;
}

static void shrink_worker(struct work_struct *w)
{
	struct mem_cgroup *memcg;
	int ret, failures = 0;

	/* global reclaim will select cgroup in a round-robin fashion. */
	do {
		spin_lock(&zswap_shrink_lock);
		zswap_next_shrink = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
		memcg = zswap_next_shrink;

		/*
		 * We need to retry if we have gone through a full round trip, or if we
		 * got an offline memcg (or else we risk undoing the effect of the
		 * zswap memcg offlining cleanup callback). This is not catastrophic
		 * per se, but it will keep the now offlined memcg hostage for a while.
		 *
		 * Note that if we got an online memcg, we will keep the extra
		 * reference in case the original reference obtained by mem_cgroup_iter
		 * is dropped by the zswap memcg offlining callback, ensuring that the
		 * memcg is not killed when we are reclaiming.
		 */
		if (!memcg) {
			spin_unlock(&zswap_shrink_lock);
			if (++failures == MAX_RECLAIM_RETRIES)
				break;

			goto resched;
		}

		if (!mem_cgroup_tryget_online(memcg)) {
			/* drop the reference from mem_cgroup_iter() */
			mem_cgroup_iter_break(NULL, memcg);
			zswap_next_shrink = NULL;
			spin_unlock(&zswap_shrink_lock);

			if (++failures == MAX_RECLAIM_RETRIES)
				break;

			goto resched;
		}
		spin_unlock(&zswap_shrink_lock);

		ret = shrink_memcg(memcg);
		/* drop the extra reference */
		mem_cgroup_put(memcg);

		if (ret == -EINVAL)
			break;
		if (ret && ++failures == MAX_RECLAIM_RETRIES)
			break;

resched:
		cond_resched();
	} while (!zswap_can_accept());
}

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));
}

bool zswap_store(struct folio *folio)
{
	swp_entry_t swp = folio->swap;
	pgoff_t offset = swp_offset(swp);
	struct zswap_tree *tree = swap_zswap_tree(swp);
	struct zswap_entry *entry, *dupentry;
	struct obj_cgroup *objcg = NULL;
	struct mem_cgroup *memcg = NULL;

	VM_WARN_ON_ONCE(!folio_test_locked(folio));
	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));

	/* Large folios aren't supported */
	if (folio_test_large(folio))
		return false;

	if (!zswap_enabled)
		goto check_old;

	objcg = get_obj_cgroup_from_folio(folio);
	if (objcg && !obj_cgroup_may_zswap(objcg)) {
		memcg = get_mem_cgroup_from_objcg(objcg);
		if (shrink_memcg(memcg)) {
			mem_cgroup_put(memcg);
			goto reject;
		}
		mem_cgroup_put(memcg);
	}

	/* 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())
			goto shrink;
		else
			zswap_pool_reached_full = false;
	}

	/* allocate entry */
	entry = zswap_entry_cache_alloc(GFP_KERNEL, folio_nid(folio));
	if (!entry) {
		zswap_reject_kmemcache_fail++;
		goto reject;
	}

	if (zswap_same_filled_pages_enabled) {
		unsigned long value;
		u8 *src;

		src = kmap_local_folio(folio, 0);
		if (zswap_is_page_same_filled(src, &value)) {
			kunmap_local(src);
			entry->length = 0;
			entry->value = value;
			atomic_inc(&zswap_same_filled_pages);
			goto insert_entry;
		}
		kunmap_local(src);
	}

	if (!zswap_non_same_filled_pages_enabled)
		goto freepage;

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

	if (objcg) {
		memcg = get_mem_cgroup_from_objcg(objcg);
		if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) {
			mem_cgroup_put(memcg);
			goto put_pool;
		}
		mem_cgroup_put(memcg);
	}

	if (!zswap_compress(folio, entry))
		goto put_pool;

insert_entry:
	entry->swpentry = swp;
	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);
	/*
	 * The folio may have been dirtied again, invalidate the
	 * possibly stale entry before inserting the new entry.
	 */
	if (zswap_rb_insert(&tree->rbroot, entry, &dupentry) == -EEXIST) {
		zswap_invalidate_entry(tree, dupentry);
		WARN_ON(zswap_rb_insert(&tree->rbroot, entry, &dupentry));
	}
	if (entry->length) {
		INIT_LIST_HEAD(&entry->lru);
		zswap_lru_add(&zswap_list_lru, entry);
		atomic_inc(&zswap_nr_stored);
	}
	spin_unlock(&tree->lock);

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

	return true;

put_pool:
	zswap_pool_put(entry->pool);
freepage:
	zswap_entry_cache_free(entry);
reject:
	if (objcg)
		obj_cgroup_put(objcg);
check_old:
	/*
	 * If the zswap store fails or zswap is disabled, we must invalidate the
	 * possibly stale entry which was previously stored at this offset.
	 * Otherwise, writeback could overwrite the new data in the swapfile.
	 */
	spin_lock(&tree->lock);
	entry = zswap_rb_search(&tree->rbroot, offset);
	if (entry)
		zswap_invalidate_entry(tree, entry);
	spin_unlock(&tree->lock);
	return false;

shrink:
	queue_work(shrink_wq, &zswap_shrink_work);
	goto reject;
}

bool zswap_load(struct folio *folio)
{
	swp_entry_t swp = folio->swap;
	pgoff_t offset = swp_offset(swp);
	struct page *page = &folio->page;
	struct zswap_tree *tree = swap_zswap_tree(swp);
	struct zswap_entry *entry;
	u8 *dst;

	VM_WARN_ON_ONCE(!folio_test_locked(folio));

	spin_lock(&tree->lock);
	entry = zswap_rb_search(&tree->rbroot, offset);
	if (!entry) {
		spin_unlock(&tree->lock);
		return false;
	}
	zswap_rb_erase(&tree->rbroot, entry);
	spin_unlock(&tree->lock);

	if (entry->length)
		zswap_decompress(entry, page);
	else {
		dst = kmap_local_page(page);
		zswap_fill_page(dst, entry->value);
		kunmap_local(dst);
	}

	count_vm_event(ZSWPIN);
	if (entry->objcg)
		count_objcg_event(entry->objcg, ZSWPIN);

	zswap_entry_free(entry);

	folio_mark_dirty(folio);

	return true;
}

void zswap_invalidate(swp_entry_t swp)
{
	pgoff_t offset = swp_offset(swp);
	struct zswap_tree *tree = swap_zswap_tree(swp);
	struct zswap_entry *entry;

	spin_lock(&tree->lock);
	entry = zswap_rb_search(&tree->rbroot, offset);
	if (entry)
		zswap_invalidate_entry(tree, entry);
	spin_unlock(&tree->lock);
}

int zswap_swapon(int type, unsigned long nr_pages)
{
	struct zswap_tree *trees, *tree;
	unsigned int nr, i;

	nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
	trees = kvcalloc(nr, sizeof(*tree), GFP_KERNEL);
	if (!trees) {
		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
		return -ENOMEM;
	}

	for (i = 0; i < nr; i++) {
		tree = trees + i;
		tree->rbroot = RB_ROOT;
		spin_lock_init(&tree->lock);
	}

	nr_zswap_trees[type] = nr;
	zswap_trees[type] = trees;
	return 0;
}

void zswap_swapoff(int type)
{
	struct zswap_tree *trees = zswap_trees[type];
	unsigned int i;

	if (!trees)
		return;

	/* try_to_unuse() invalidated all the entries already */
	for (i = 0; i < nr_zswap_trees[type]; i++)
		WARN_ON_ONCE(!RB_EMPTY_ROOT(&trees[i].rbroot));

	kvfree(trees);
	nr_zswap_trees[type] = 0;
	zswap_trees[type] = NULL;
}

/*********************************
* 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_fail", 0444,
			   zswap_debugfs_root, &zswap_reject_compress_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("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_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
				      "mm/zswap_pool:prepare",
				      zswap_cpu_comp_prepare,
				      zswap_cpu_comp_dead);
	if (ret)
		goto hp_fail;

	shrink_wq = alloc_workqueue("zswap-shrink",
			WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
	if (!shrink_wq)
		goto shrink_wq_fail;

	zswap_shrinker = zswap_alloc_shrinker();
	if (!zswap_shrinker)
		goto shrinker_fail;
	if (list_lru_init_memcg(&zswap_list_lru, zswap_shrinker))
		goto lru_fail;
	shrinker_register(zswap_shrinker);

	INIT_WORK(&zswap_shrink_work, shrink_worker);

	pool = __zswap_pool_create_fallback();
	if (pool) {
		pr_info("loaded using pool %s/%s\n", pool->tfm_name,
			zpool_get_type(pool->zpools[0]));
		list_add(&pool->list, &zswap_pools);
		zswap_has_pool = true;
	} else {
		pr_err("pool creation failed\n");
		zswap_enabled = false;
	}

	if (zswap_debugfs_init())
		pr_warn("debugfs initialization failed\n");
	zswap_init_state = ZSWAP_INIT_SUCCEED;
	return 0;

lru_fail:
	shrinker_free(zswap_shrinker);
shrinker_fail:
	destroy_workqueue(shrink_wq);
shrink_wq_fail:
	cpuhp_remove_multi_state(CPUHP_MM_ZSWP_POOL_PREPARE);
hp_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");