summaryrefslogtreecommitdiff
path: root/mm/zsmalloc.c
blob: a8ff24a296931b660c36a51ca6ec30702bb5dce3 (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
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
/*
 * zsmalloc memory allocator
 *
 * Copyright (C) 2011  Nitin Gupta
 * Copyright (C) 2012, 2013 Minchan Kim
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the license that better fits your requirements.
 *
 * Released under the terms of 3-clause BSD License
 * Released under the terms of GNU General Public License Version 2.0
 */

/*
 * Following is how we use various fields and flags of underlying
 * struct page(s) to form a zspage.
 *
 * Usage of struct page fields:
 *	page->first_page: points to the first component (0-order) page
 *	page->index (union with page->freelist): offset of the first object
 *		starting in this page. For the first page, this is
 *		always 0, so we use this field (aka freelist) to point
 *		to the first free object in zspage.
 *	page->lru: links together all component pages (except the first page)
 *		of a zspage
 *
 *	For _first_ page only:
 *
 *	page->private (union with page->first_page): refers to the
 *		component page after the first page
 *		If the page is first_page for huge object, it stores handle.
 *		Look at size_class->huge.
 *	page->freelist: points to the first free object in zspage.
 *		Free objects are linked together using in-place
 *		metadata.
 *	page->objects: maximum number of objects we can store in this
 *		zspage (class->zspage_order * PAGE_SIZE / class->size)
 *	page->lru: links together first pages of various zspages.
 *		Basically forming list of zspages in a fullness group.
 *	page->mapping: class index and fullness group of the zspage
 *	page->inuse: the number of objects that are used in this zspage
 *
 * Usage of struct page flags:
 *	PG_private: identifies the first component page
 *	PG_private2: identifies the last component page
 *
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>
#include <linux/cpumask.h>
#include <linux/cpu.h>
#include <linux/vmalloc.h>
#include <linux/preempt.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/zsmalloc.h>
#include <linux/zpool.h>

/*
 * This must be power of 2 and greater than of equal to sizeof(link_free).
 * These two conditions ensure that any 'struct link_free' itself doesn't
 * span more than 1 page which avoids complex case of mapping 2 pages simply
 * to restore link_free pointer values.
 */
#define ZS_ALIGN		8

/*
 * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
 * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N.
 */
#define ZS_MAX_ZSPAGE_ORDER 2
#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)

#define ZS_HANDLE_SIZE (sizeof(unsigned long))

/*
 * Object location (<PFN>, <obj_idx>) is encoded as
 * as single (unsigned long) handle value.
 *
 * Note that object index <obj_idx> is relative to system
 * page <PFN> it is stored in, so for each sub-page belonging
 * to a zspage, obj_idx starts with 0.
 *
 * This is made more complicated by various memory models and PAE.
 */

#ifndef MAX_PHYSMEM_BITS
#ifdef CONFIG_HIGHMEM64G
#define MAX_PHYSMEM_BITS 36
#else /* !CONFIG_HIGHMEM64G */
/*
 * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
 * be PAGE_SHIFT
 */
#define MAX_PHYSMEM_BITS BITS_PER_LONG
#endif
#endif
#define _PFN_BITS		(MAX_PHYSMEM_BITS - PAGE_SHIFT)

/*
 * Memory for allocating for handle keeps object position by
 * encoding <page, obj_idx> and the encoded value has a room
 * in least bit(ie, look at obj_to_location).
 * We use the bit to synchronize between object access by
 * user and migration.
 */
#define HANDLE_PIN_BIT	0

/*
 * Head in allocated object should have OBJ_ALLOCATED_TAG
 * to identify the object was allocated or not.
 * It's okay to add the status bit in the least bit because
 * header keeps handle which is 4byte-aligned address so we
 * have room for two bit at least.
 */
#define OBJ_ALLOCATED_TAG 1
#define OBJ_TAG_BITS 1
#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
#define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)

#define MAX(a, b) ((a) >= (b) ? (a) : (b))
/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
#define ZS_MIN_ALLOC_SIZE \
	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
/* each chunk includes extra space to keep handle */
#define ZS_MAX_ALLOC_SIZE	PAGE_SIZE

/*
 * On systems with 4K page size, this gives 255 size classes! There is a
 * trader-off here:
 *  - Large number of size classes is potentially wasteful as free page are
 *    spread across these classes
 *  - Small number of size classes causes large internal fragmentation
 *  - Probably its better to use specific size classes (empirically
 *    determined). NOTE: all those class sizes must be set as multiple of
 *    ZS_ALIGN to make sure link_free itself never has to span 2 pages.
 *
 *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
 *  (reason above)
 */
#define ZS_SIZE_CLASS_DELTA	(PAGE_SIZE >> 8)

/*
 * We do not maintain any list for completely empty or full pages
 */
enum fullness_group {
	ZS_ALMOST_FULL,
	ZS_ALMOST_EMPTY,
	_ZS_NR_FULLNESS_GROUPS,

	ZS_EMPTY,
	ZS_FULL
};

enum zs_stat_type {
	OBJ_ALLOCATED,
	OBJ_USED,
	CLASS_ALMOST_FULL,
	CLASS_ALMOST_EMPTY,
	NR_ZS_STAT_TYPE,
};

struct zs_size_stat {
	unsigned long objs[NR_ZS_STAT_TYPE];
};

#ifdef CONFIG_ZSMALLOC_STAT
static struct dentry *zs_stat_root;
#endif

/*
 * number of size_classes
 */
static int zs_size_classes;

/*
 * We assign a page to ZS_ALMOST_EMPTY fullness group when:
 *	n <= N / f, where
 * n = number of allocated objects
 * N = total number of objects zspage can store
 * f = fullness_threshold_frac
 *
 * Similarly, we assign zspage to:
 *	ZS_ALMOST_FULL	when n > N / f
 *	ZS_EMPTY	when n == 0
 *	ZS_FULL		when n == N
 *
 * (see: fix_fullness_group())
 */
static const int fullness_threshold_frac = 4;

struct size_class {
	spinlock_t lock;
	struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
	/*
	 * Size of objects stored in this class. Must be multiple
	 * of ZS_ALIGN.
	 */
	int size;
	unsigned int index;

	/* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
	int pages_per_zspage;
	struct zs_size_stat stats;

	/* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
	bool huge;
};

/*
 * Placed within free objects to form a singly linked list.
 * For every zspage, first_page->freelist gives head of this list.
 *
 * This must be power of 2 and less than or equal to ZS_ALIGN
 */
struct link_free {
	union {
		/*
		 * Position of next free chunk (encodes <PFN, obj_idx>)
		 * It's valid for non-allocated object
		 */
		void *next;
		/*
		 * Handle of allocated object.
		 */
		unsigned long handle;
	};
};

struct zs_pool {
	const char *name;

	struct size_class **size_class;
	struct kmem_cache *handle_cachep;

	gfp_t flags;	/* allocation flags used when growing pool */
	atomic_long_t pages_allocated;

	struct zs_pool_stats stats;

	/* Compact classes */
	struct shrinker shrinker;
	/*
	 * To signify that register_shrinker() was successful
	 * and unregister_shrinker() will not Oops.
	 */
	bool shrinker_enabled;
#ifdef CONFIG_ZSMALLOC_STAT
	struct dentry *stat_dentry;
#endif
};

/*
 * A zspage's class index and fullness group
 * are encoded in its (first)page->mapping
 */
#define CLASS_IDX_BITS	28
#define FULLNESS_BITS	4
#define CLASS_IDX_MASK	((1 << CLASS_IDX_BITS) - 1)
#define FULLNESS_MASK	((1 << FULLNESS_BITS) - 1)

struct mapping_area {
#ifdef CONFIG_PGTABLE_MAPPING
	struct vm_struct *vm; /* vm area for mapping object that span pages */
#else
	char *vm_buf; /* copy buffer for objects that span pages */
#endif
	char *vm_addr; /* address of kmap_atomic()'ed pages */
	enum zs_mapmode vm_mm; /* mapping mode */
	bool huge;
};

static int create_handle_cache(struct zs_pool *pool)
{
	pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
					0, 0, NULL);
	return pool->handle_cachep ? 0 : 1;
}

static void destroy_handle_cache(struct zs_pool *pool)
{
	kmem_cache_destroy(pool->handle_cachep);
}

static unsigned long alloc_handle(struct zs_pool *pool)
{
	return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
		pool->flags & ~__GFP_HIGHMEM);
}

static void free_handle(struct zs_pool *pool, unsigned long handle)
{
	kmem_cache_free(pool->handle_cachep, (void *)handle);
}

static void record_obj(unsigned long handle, unsigned long obj)
{
	*(unsigned long *)handle = obj;
}

/* zpool driver */

#ifdef CONFIG_ZPOOL

static void *zs_zpool_create(const char *name, gfp_t gfp,
			     const struct zpool_ops *zpool_ops,
			     struct zpool *zpool)
{
	return zs_create_pool(name, gfp);
}

static void zs_zpool_destroy(void *pool)
{
	zs_destroy_pool(pool);
}

static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
			unsigned long *handle)
{
	*handle = zs_malloc(pool, size);
	return *handle ? 0 : -1;
}
static void zs_zpool_free(void *pool, unsigned long handle)
{
	zs_free(pool, handle);
}

static int zs_zpool_shrink(void *pool, unsigned int pages,
			unsigned int *reclaimed)
{
	return -EINVAL;
}

static void *zs_zpool_map(void *pool, unsigned long handle,
			enum zpool_mapmode mm)
{
	enum zs_mapmode zs_mm;

	switch (mm) {
	case ZPOOL_MM_RO:
		zs_mm = ZS_MM_RO;
		break;
	case ZPOOL_MM_WO:
		zs_mm = ZS_MM_WO;
		break;
	case ZPOOL_MM_RW: /* fallthru */
	default:
		zs_mm = ZS_MM_RW;
		break;
	}

	return zs_map_object(pool, handle, zs_mm);
}
static void zs_zpool_unmap(void *pool, unsigned long handle)
{
	zs_unmap_object(pool, handle);
}

static u64 zs_zpool_total_size(void *pool)
{
	return zs_get_total_pages(pool) << PAGE_SHIFT;
}

static struct zpool_driver zs_zpool_driver = {
	.type =		"zsmalloc",
	.owner =	THIS_MODULE,
	.create =	zs_zpool_create,
	.destroy =	zs_zpool_destroy,
	.malloc =	zs_zpool_malloc,
	.free =		zs_zpool_free,
	.shrink =	zs_zpool_shrink,
	.map =		zs_zpool_map,
	.unmap =	zs_zpool_unmap,
	.total_size =	zs_zpool_total_size,
};

MODULE_ALIAS("zpool-zsmalloc");
#endif /* CONFIG_ZPOOL */

static unsigned int get_maxobj_per_zspage(int size, int pages_per_zspage)
{
	return pages_per_zspage * PAGE_SIZE / size;
}

/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
static DEFINE_PER_CPU(struct mapping_area, zs_map_area);

static int is_first_page(struct page *page)
{
	return PagePrivate(page);
}

static int is_last_page(struct page *page)
{
	return PagePrivate2(page);
}

static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
				enum fullness_group *fullness)
{
	unsigned long m;
	BUG_ON(!is_first_page(page));

	m = (unsigned long)page->mapping;
	*fullness = m & FULLNESS_MASK;
	*class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
}

static void set_zspage_mapping(struct page *page, unsigned int class_idx,
				enum fullness_group fullness)
{
	unsigned long m;
	BUG_ON(!is_first_page(page));

	m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) |
			(fullness & FULLNESS_MASK);
	page->mapping = (struct address_space *)m;
}

/*
 * zsmalloc divides the pool into various size classes where each
 * class maintains a list of zspages where each zspage is divided
 * into equal sized chunks. Each allocation falls into one of these
 * classes depending on its size. This function returns index of the
 * size class which has chunk size big enough to hold the give size.
 */
static int get_size_class_index(int size)
{
	int idx = 0;

	if (likely(size > ZS_MIN_ALLOC_SIZE))
		idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
				ZS_SIZE_CLASS_DELTA);

	return min(zs_size_classes - 1, idx);
}

static inline void zs_stat_inc(struct size_class *class,
				enum zs_stat_type type, unsigned long cnt)
{
	class->stats.objs[type] += cnt;
}

static inline void zs_stat_dec(struct size_class *class,
				enum zs_stat_type type, unsigned long cnt)
{
	class->stats.objs[type] -= cnt;
}

static inline unsigned long zs_stat_get(struct size_class *class,
				enum zs_stat_type type)
{
	return class->stats.objs[type];
}

#ifdef CONFIG_ZSMALLOC_STAT

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

	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
	if (!zs_stat_root)
		return -ENOMEM;

	return 0;
}

static void __exit zs_stat_exit(void)
{
	debugfs_remove_recursive(zs_stat_root);
}

static int zs_stats_size_show(struct seq_file *s, void *v)
{
	int i;
	struct zs_pool *pool = s->private;
	struct size_class *class;
	int objs_per_zspage;
	unsigned long class_almost_full, class_almost_empty;
	unsigned long obj_allocated, obj_used, pages_used;
	unsigned long total_class_almost_full = 0, total_class_almost_empty = 0;
	unsigned long total_objs = 0, total_used_objs = 0, total_pages = 0;

	seq_printf(s, " %5s %5s %11s %12s %13s %10s %10s %16s\n",
			"class", "size", "almost_full", "almost_empty",
			"obj_allocated", "obj_used", "pages_used",
			"pages_per_zspage");

	for (i = 0; i < zs_size_classes; i++) {
		class = pool->size_class[i];

		if (class->index != i)
			continue;

		spin_lock(&class->lock);
		class_almost_full = zs_stat_get(class, CLASS_ALMOST_FULL);
		class_almost_empty = zs_stat_get(class, CLASS_ALMOST_EMPTY);
		obj_allocated = zs_stat_get(class, OBJ_ALLOCATED);
		obj_used = zs_stat_get(class, OBJ_USED);
		spin_unlock(&class->lock);

		objs_per_zspage = get_maxobj_per_zspage(class->size,
				class->pages_per_zspage);
		pages_used = obj_allocated / objs_per_zspage *
				class->pages_per_zspage;

		seq_printf(s, " %5u %5u %11lu %12lu %13lu %10lu %10lu %16d\n",
			i, class->size, class_almost_full, class_almost_empty,
			obj_allocated, obj_used, pages_used,
			class->pages_per_zspage);

		total_class_almost_full += class_almost_full;
		total_class_almost_empty += class_almost_empty;
		total_objs += obj_allocated;
		total_used_objs += obj_used;
		total_pages += pages_used;
	}

	seq_puts(s, "\n");
	seq_printf(s, " %5s %5s %11lu %12lu %13lu %10lu %10lu\n",
			"Total", "", total_class_almost_full,
			total_class_almost_empty, total_objs,
			total_used_objs, total_pages);

	return 0;
}

static int zs_stats_size_open(struct inode *inode, struct file *file)
{
	return single_open(file, zs_stats_size_show, inode->i_private);
}

static const struct file_operations zs_stat_size_ops = {
	.open           = zs_stats_size_open,
	.read           = seq_read,
	.llseek         = seq_lseek,
	.release        = single_release,
};

static int zs_pool_stat_create(const char *name, struct zs_pool *pool)
{
	struct dentry *entry;

	if (!zs_stat_root)
		return -ENODEV;

	entry = debugfs_create_dir(name, zs_stat_root);
	if (!entry) {
		pr_warn("debugfs dir <%s> creation failed\n", name);
		return -ENOMEM;
	}
	pool->stat_dentry = entry;

	entry = debugfs_create_file("classes", S_IFREG | S_IRUGO,
			pool->stat_dentry, pool, &zs_stat_size_ops);
	if (!entry) {
		pr_warn("%s: debugfs file entry <%s> creation failed\n",
				name, "classes");
		return -ENOMEM;
	}

	return 0;
}

static void zs_pool_stat_destroy(struct zs_pool *pool)
{
	debugfs_remove_recursive(pool->stat_dentry);
}

#else /* CONFIG_ZSMALLOC_STAT */
static int __init zs_stat_init(void)
{
	return 0;
}

static void __exit zs_stat_exit(void)
{
}

static inline int zs_pool_stat_create(const char *name, struct zs_pool *pool)
{
	return 0;
}

static inline void zs_pool_stat_destroy(struct zs_pool *pool)
{
}
#endif


/*
 * For each size class, zspages are divided into different groups
 * depending on how "full" they are. This was done so that we could
 * easily find empty or nearly empty zspages when we try to shrink
 * the pool (not yet implemented). This function returns fullness
 * status of the given page.
 */
static enum fullness_group get_fullness_group(struct page *page)
{
	int inuse, max_objects;
	enum fullness_group fg;
	BUG_ON(!is_first_page(page));

	inuse = page->inuse;
	max_objects = page->objects;

	if (inuse == 0)
		fg = ZS_EMPTY;
	else if (inuse == max_objects)
		fg = ZS_FULL;
	else if (inuse <= 3 * max_objects / fullness_threshold_frac)
		fg = ZS_ALMOST_EMPTY;
	else
		fg = ZS_ALMOST_FULL;

	return fg;
}

/*
 * Each size class maintains various freelists and zspages are assigned
 * to one of these freelists based on the number of live objects they
 * have. This functions inserts the given zspage into the freelist
 * identified by <class, fullness_group>.
 */
static void insert_zspage(struct page *page, struct size_class *class,
				enum fullness_group fullness)
{
	struct page **head;

	BUG_ON(!is_first_page(page));

	if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

	zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
			CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);

	head = &class->fullness_list[fullness];
	if (!*head) {
		*head = page;
		return;
	}

	/*
	 * We want to see more ZS_FULL pages and less almost
	 * empty/full. Put pages with higher ->inuse first.
	 */
	list_add_tail(&page->lru, &(*head)->lru);
	if (page->inuse >= (*head)->inuse)
		*head = page;
}

/*
 * This function removes the given zspage from the freelist identified
 * by <class, fullness_group>.
 */
static void remove_zspage(struct page *page, struct size_class *class,
				enum fullness_group fullness)
{
	struct page **head;

	BUG_ON(!is_first_page(page));

	if (fullness >= _ZS_NR_FULLNESS_GROUPS)
		return;

	head = &class->fullness_list[fullness];
	BUG_ON(!*head);
	if (list_empty(&(*head)->lru))
		*head = NULL;
	else if (*head == page)
		*head = (struct page *)list_entry((*head)->lru.next,
					struct page, lru);

	list_del_init(&page->lru);
	zs_stat_dec(class, fullness == ZS_ALMOST_EMPTY ?
			CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
}

/*
 * Each size class maintains zspages in different fullness groups depending
 * on the number of live objects they contain. When allocating or freeing
 * objects, the fullness status of the page can change, say, from ALMOST_FULL
 * to ALMOST_EMPTY when freeing an object. This function checks if such
 * a status change has occurred for the given page and accordingly moves the
 * page from the freelist of the old fullness group to that of the new
 * fullness group.
 */
static enum fullness_group fix_fullness_group(struct size_class *class,
						struct page *page)
{
	int class_idx;
	enum fullness_group currfg, newfg;

	BUG_ON(!is_first_page(page));

	get_zspage_mapping(page, &class_idx, &currfg);
	newfg = get_fullness_group(page);
	if (newfg == currfg)
		goto out;

	remove_zspage(page, class, currfg);
	insert_zspage(page, class, newfg);
	set_zspage_mapping(page, class_idx, newfg);

out:
	return newfg;
}

/*
 * We have to decide on how many pages to link together
 * to form a zspage for each size class. This is important
 * to reduce wastage due to unusable space left at end of
 * each zspage which is given as:
 *     wastage = Zp % class_size
 *     usage = Zp - wastage
 * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
 *
 * For example, for size class of 3/8 * PAGE_SIZE, we should
 * link together 3 PAGE_SIZE sized pages to form a zspage
 * since then we can perfectly fit in 8 such objects.
 */
static int get_pages_per_zspage(int class_size)
{
	int i, max_usedpc = 0;
	/* zspage order which gives maximum used size per KB */
	int max_usedpc_order = 1;

	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
		int zspage_size;
		int waste, usedpc;

		zspage_size = i * PAGE_SIZE;
		waste = zspage_size % class_size;
		usedpc = (zspage_size - waste) * 100 / zspage_size;

		if (usedpc > max_usedpc) {
			max_usedpc = usedpc;
			max_usedpc_order = i;
		}
	}

	return max_usedpc_order;
}

/*
 * A single 'zspage' is composed of many system pages which are
 * linked together using fields in struct page. This function finds
 * the first/head page, given any component page of a zspage.
 */
static struct page *get_first_page(struct page *page)
{
	if (is_first_page(page))
		return page;
	else
		return page->first_page;
}

static struct page *get_next_page(struct page *page)
{
	struct page *next;

	if (is_last_page(page))
		next = NULL;
	else if (is_first_page(page))
		next = (struct page *)page_private(page);
	else
		next = list_entry(page->lru.next, struct page, lru);

	return next;
}

/*
 * Encode <page, obj_idx> as a single handle value.
 * We use the least bit of handle for tagging.
 */
static void *location_to_obj(struct page *page, unsigned long obj_idx)
{
	unsigned long obj;

	if (!page) {
		BUG_ON(obj_idx);
		return NULL;
	}

	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
	obj |= ((obj_idx) & OBJ_INDEX_MASK);
	obj <<= OBJ_TAG_BITS;

	return (void *)obj;
}

/*
 * Decode <page, obj_idx> pair from the given object handle. We adjust the
 * decoded obj_idx back to its original value since it was adjusted in
 * location_to_obj().
 */
static void obj_to_location(unsigned long obj, struct page **page,
				unsigned long *obj_idx)
{
	obj >>= OBJ_TAG_BITS;
	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
	*obj_idx = (obj & OBJ_INDEX_MASK);
}

static unsigned long handle_to_obj(unsigned long handle)
{
	return *(unsigned long *)handle;
}

static unsigned long obj_to_head(struct size_class *class, struct page *page,
			void *obj)
{
	if (class->huge) {
		VM_BUG_ON(!is_first_page(page));
		return page_private(page);
	} else
		return *(unsigned long *)obj;
}

static unsigned long obj_idx_to_offset(struct page *page,
				unsigned long obj_idx, int class_size)
{
	unsigned long off = 0;

	if (!is_first_page(page))
		off = page->index;

	return off + obj_idx * class_size;
}

static inline int trypin_tag(unsigned long handle)
{
	unsigned long *ptr = (unsigned long *)handle;

	return !test_and_set_bit_lock(HANDLE_PIN_BIT, ptr);
}

static void pin_tag(unsigned long handle)
{
	while (!trypin_tag(handle));
}

static void unpin_tag(unsigned long handle)
{
	unsigned long *ptr = (unsigned long *)handle;

	clear_bit_unlock(HANDLE_PIN_BIT, ptr);
}

static void reset_page(struct page *page)
{
	clear_bit(PG_private, &page->flags);
	clear_bit(PG_private_2, &page->flags);
	set_page_private(page, 0);
	page->mapping = NULL;
	page->freelist = NULL;
	page_mapcount_reset(page);
}

static void free_zspage(struct page *first_page)
{
	struct page *nextp, *tmp, *head_extra;

	BUG_ON(!is_first_page(first_page));
	BUG_ON(first_page->inuse);

	head_extra = (struct page *)page_private(first_page);

	reset_page(first_page);
	__free_page(first_page);

	/* zspage with only 1 system page */
	if (!head_extra)
		return;

	list_for_each_entry_safe(nextp, tmp, &head_extra->lru, lru) {
		list_del(&nextp->lru);
		reset_page(nextp);
		__free_page(nextp);
	}
	reset_page(head_extra);
	__free_page(head_extra);
}

/* Initialize a newly allocated zspage */
static void init_zspage(struct page *first_page, struct size_class *class)
{
	unsigned long off = 0;
	struct page *page = first_page;

	BUG_ON(!is_first_page(first_page));
	while (page) {
		struct page *next_page;
		struct link_free *link;
		unsigned int i = 1;
		void *vaddr;

		/*
		 * page->index stores offset of first object starting
		 * in the page. For the first page, this is always 0,
		 * so we use first_page->index (aka ->freelist) to store
		 * head of corresponding zspage's freelist.
		 */
		if (page != first_page)
			page->index = off;

		vaddr = kmap_atomic(page);
		link = (struct link_free *)vaddr + off / sizeof(*link);

		while ((off += class->size) < PAGE_SIZE) {
			link->next = location_to_obj(page, i++);
			link += class->size / sizeof(*link);
		}

		/*
		 * We now come to the last (full or partial) object on this
		 * page, which must point to the first object on the next
		 * page (if present)
		 */
		next_page = get_next_page(page);
		link->next = location_to_obj(next_page, 0);
		kunmap_atomic(vaddr);
		page = next_page;
		off %= PAGE_SIZE;
	}
}

/*
 * Allocate a zspage for the given size class
 */
static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
{
	int i, error;
	struct page *first_page = NULL, *uninitialized_var(prev_page);

	/*
	 * Allocate individual pages and link them together as:
	 * 1. first page->private = first sub-page
	 * 2. all sub-pages are linked together using page->lru
	 * 3. each sub-page is linked to the first page using page->first_page
	 *
	 * For each size class, First/Head pages are linked together using
	 * page->lru. Also, we set PG_private to identify the first page
	 * (i.e. no other sub-page has this flag set) and PG_private_2 to
	 * identify the last page.
	 */
	error = -ENOMEM;
	for (i = 0; i < class->pages_per_zspage; i++) {
		struct page *page;

		page = alloc_page(flags);
		if (!page)
			goto cleanup;

		INIT_LIST_HEAD(&page->lru);
		if (i == 0) {	/* first page */
			SetPagePrivate(page);
			set_page_private(page, 0);
			first_page = page;
			first_page->inuse = 0;
		}
		if (i == 1)
			set_page_private(first_page, (unsigned long)page);
		if (i >= 1)
			page->first_page = first_page;
		if (i >= 2)
			list_add(&page->lru, &prev_page->lru);
		if (i == class->pages_per_zspage - 1)	/* last page */
			SetPagePrivate2(page);
		prev_page = page;
	}

	init_zspage(first_page, class);

	first_page->freelist = location_to_obj(first_page, 0);
	/* Maximum number of objects we can store in this zspage */
	first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;

	error = 0; /* Success */

cleanup:
	if (unlikely(error) && first_page) {
		free_zspage(first_page);
		first_page = NULL;
	}

	return first_page;
}

static struct page *find_get_zspage(struct size_class *class)
{
	int i;
	struct page *page;

	for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
		page = class->fullness_list[i];
		if (page)
			break;
	}

	return page;
}

#ifdef CONFIG_PGTABLE_MAPPING
static inline int __zs_cpu_up(struct mapping_area *area)
{
	/*
	 * Make sure we don't leak memory if a cpu UP notification
	 * and zs_init() race and both call zs_cpu_up() on the same cpu
	 */
	if (area->vm)
		return 0;
	area->vm = alloc_vm_area(PAGE_SIZE * 2, NULL);
	if (!area->vm)
		return -ENOMEM;
	return 0;
}

static inline void __zs_cpu_down(struct mapping_area *area)
{
	if (area->vm)
		free_vm_area(area->vm);
	area->vm = NULL;
}

static inline void *__zs_map_object(struct mapping_area *area,
				struct page *pages[2], int off, int size)
{
	BUG_ON(map_vm_area(area->vm, PAGE_KERNEL, pages));
	area->vm_addr = area->vm->addr;
	return area->vm_addr + off;
}

static inline void __zs_unmap_object(struct mapping_area *area,
				struct page *pages[2], int off, int size)
{
	unsigned long addr = (unsigned long)area->vm_addr;

	unmap_kernel_range(addr, PAGE_SIZE * 2);
}

#else /* CONFIG_PGTABLE_MAPPING */

static inline int __zs_cpu_up(struct mapping_area *area)
{
	/*
	 * Make sure we don't leak memory if a cpu UP notification
	 * and zs_init() race and both call zs_cpu_up() on the same cpu
	 */
	if (area->vm_buf)
		return 0;
	area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE, GFP_KERNEL);
	if (!area->vm_buf)
		return -ENOMEM;
	return 0;
}

static inline void __zs_cpu_down(struct mapping_area *area)
{
	kfree(area->vm_buf);
	area->vm_buf = NULL;
}

static void *__zs_map_object(struct mapping_area *area,
			struct page *pages[2], int off, int size)
{
	int sizes[2];
	void *addr;
	char *buf = area->vm_buf;

	/* disable page faults to match kmap_atomic() return conditions */
	pagefault_disable();

	/* no read fastpath */
	if (area->vm_mm == ZS_MM_WO)
		goto out;

	sizes[0] = PAGE_SIZE - off;
	sizes[1] = size - sizes[0];

	/* copy object to per-cpu buffer */
	addr = kmap_atomic(pages[0]);
	memcpy(buf, addr + off, sizes[0]);
	kunmap_atomic(addr);
	addr = kmap_atomic(pages[1]);
	memcpy(buf + sizes[0], addr, sizes[1]);
	kunmap_atomic(addr);
out:
	return area->vm_buf;
}

static void __zs_unmap_object(struct mapping_area *area,
			struct page *pages[2], int off, int size)
{
	int sizes[2];
	void *addr;
	char *buf;

	/* no write fastpath */
	if (area->vm_mm == ZS_MM_RO)
		goto out;

	buf = area->vm_buf;
	if (!area->huge) {
		buf = buf + ZS_HANDLE_SIZE;
		size -= ZS_HANDLE_SIZE;
		off += ZS_HANDLE_SIZE;
	}

	sizes[0] = PAGE_SIZE - off;
	sizes[1] = size - sizes[0];

	/* copy per-cpu buffer to object */
	addr = kmap_atomic(pages[0]);
	memcpy(addr + off, buf, sizes[0]);
	kunmap_atomic(addr);
	addr = kmap_atomic(pages[1]);
	memcpy(addr, buf + sizes[0], sizes[1]);
	kunmap_atomic(addr);

out:
	/* enable page faults to match kunmap_atomic() return conditions */
	pagefault_enable();
}

#endif /* CONFIG_PGTABLE_MAPPING */

static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
				void *pcpu)
{
	int ret, cpu = (long)pcpu;
	struct mapping_area *area;

	switch (action) {
	case CPU_UP_PREPARE:
		area = &per_cpu(zs_map_area, cpu);
		ret = __zs_cpu_up(area);
		if (ret)
			return notifier_from_errno(ret);
		break;
	case CPU_DEAD:
	case CPU_UP_CANCELED:
		area = &per_cpu(zs_map_area, cpu);
		__zs_cpu_down(area);
		break;
	}

	return NOTIFY_OK;
}

static struct notifier_block zs_cpu_nb = {
	.notifier_call = zs_cpu_notifier
};

static int zs_register_cpu_notifier(void)
{
	int cpu, uninitialized_var(ret);

	cpu_notifier_register_begin();

	__register_cpu_notifier(&zs_cpu_nb);
	for_each_online_cpu(cpu) {
		ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
		if (notifier_to_errno(ret))
			break;
	}

	cpu_notifier_register_done();
	return notifier_to_errno(ret);
}

static void zs_unregister_cpu_notifier(void)
{
	int cpu;

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
	__unregister_cpu_notifier(&zs_cpu_nb);

	cpu_notifier_register_done();
}

static void init_zs_size_classes(void)
{
	int nr;

	nr = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1;
	if ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA)
		nr += 1;

	zs_size_classes = nr;
}

static bool can_merge(struct size_class *prev, int size, int pages_per_zspage)
{
	if (prev->pages_per_zspage != pages_per_zspage)
		return false;

	if (get_maxobj_per_zspage(prev->size, prev->pages_per_zspage)
		!= get_maxobj_per_zspage(size, pages_per_zspage))
		return false;

	return true;
}

static bool zspage_full(struct page *page)
{
	BUG_ON(!is_first_page(page));

	return page->inuse == page->objects;
}

unsigned long zs_get_total_pages(struct zs_pool *pool)
{
	return atomic_long_read(&pool->pages_allocated);
}
EXPORT_SYMBOL_GPL(zs_get_total_pages);

/**
 * zs_map_object - get address of allocated object from handle.
 * @pool: pool from which the object was allocated
 * @handle: handle returned from zs_malloc
 *
 * Before using an object allocated from zs_malloc, it must be mapped using
 * this function. When done with the object, it must be unmapped using
 * zs_unmap_object.
 *
 * Only one object can be mapped per cpu at a time. There is no protection
 * against nested mappings.
 *
 * This function returns with preemption and page faults disabled.
 */
void *zs_map_object(struct zs_pool *pool, unsigned long handle,
			enum zs_mapmode mm)
{
	struct page *page;
	unsigned long obj, obj_idx, off;

	unsigned int class_idx;
	enum fullness_group fg;
	struct size_class *class;
	struct mapping_area *area;
	struct page *pages[2];
	void *ret;

	BUG_ON(!handle);

	/*
	 * Because we use per-cpu mapping areas shared among the
	 * pools/users, we can't allow mapping in interrupt context
	 * because it can corrupt another users mappings.
	 */
	BUG_ON(in_interrupt());

	/* From now on, migration cannot move the object */
	pin_tag(handle);

	obj = handle_to_obj(handle);
	obj_to_location(obj, &page, &obj_idx);
	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
	class = pool->size_class[class_idx];
	off = obj_idx_to_offset(page, obj_idx, class->size);

	area = &get_cpu_var(zs_map_area);
	area->vm_mm = mm;
	if (off + class->size <= PAGE_SIZE) {
		/* this object is contained entirely within a page */
		area->vm_addr = kmap_atomic(page);
		ret = area->vm_addr + off;
		goto out;
	}

	/* this object spans two pages */
	pages[0] = page;
	pages[1] = get_next_page(page);
	BUG_ON(!pages[1]);

	ret = __zs_map_object(area, pages, off, class->size);
out:
	if (!class->huge)
		ret += ZS_HANDLE_SIZE;

	return ret;
}
EXPORT_SYMBOL_GPL(zs_map_object);

void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
	struct page *page;
	unsigned long obj, obj_idx, off;

	unsigned int class_idx;
	enum fullness_group fg;
	struct size_class *class;
	struct mapping_area *area;

	BUG_ON(!handle);

	obj = handle_to_obj(handle);
	obj_to_location(obj, &page, &obj_idx);
	get_zspage_mapping(get_first_page(page), &class_idx, &fg);
	class = pool->size_class[class_idx];
	off = obj_idx_to_offset(page, obj_idx, class->size);

	area = this_cpu_ptr(&zs_map_area);
	if (off + class->size <= PAGE_SIZE)
		kunmap_atomic(area->vm_addr);
	else {
		struct page *pages[2];

		pages[0] = page;
		pages[1] = get_next_page(page);
		BUG_ON(!pages[1]);

		__zs_unmap_object(area, pages, off, class->size);
	}
	put_cpu_var(zs_map_area);
	unpin_tag(handle);
}
EXPORT_SYMBOL_GPL(zs_unmap_object);

static unsigned long obj_malloc(struct page *first_page,
		struct size_class *class, unsigned long handle)
{
	unsigned long obj;
	struct link_free *link;

	struct page *m_page;
	unsigned long m_objidx, m_offset;
	void *vaddr;

	handle |= OBJ_ALLOCATED_TAG;
	obj = (unsigned long)first_page->freelist;
	obj_to_location(obj, &m_page, &m_objidx);
	m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);

	vaddr = kmap_atomic(m_page);
	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
	first_page->freelist = link->next;
	if (!class->huge)
		/* record handle in the header of allocated chunk */
		link->handle = handle;
	else
		/* record handle in first_page->private */
		set_page_private(first_page, handle);
	kunmap_atomic(vaddr);
	first_page->inuse++;
	zs_stat_inc(class, OBJ_USED, 1);

	return obj;
}


/**
 * zs_malloc - Allocate block of given size from pool.
 * @pool: pool to allocate from
 * @size: size of block to allocate
 *
 * On success, handle to the allocated object is returned,
 * otherwise 0.
 * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
 */
unsigned long zs_malloc(struct zs_pool *pool, size_t size)
{
	unsigned long handle, obj;
	struct size_class *class;
	struct page *first_page;

	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
		return 0;

	handle = alloc_handle(pool);
	if (!handle)
		return 0;

	/* extra space in chunk to keep the handle */
	size += ZS_HANDLE_SIZE;
	class = pool->size_class[get_size_class_index(size)];

	spin_lock(&class->lock);
	first_page = find_get_zspage(class);

	if (!first_page) {
		spin_unlock(&class->lock);
		first_page = alloc_zspage(class, pool->flags);
		if (unlikely(!first_page)) {
			free_handle(pool, handle);
			return 0;
		}

		set_zspage_mapping(first_page, class->index, ZS_EMPTY);
		atomic_long_add(class->pages_per_zspage,
					&pool->pages_allocated);

		spin_lock(&class->lock);
		zs_stat_inc(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
				class->size, class->pages_per_zspage));
	}

	obj = obj_malloc(first_page, class, handle);
	/* Now move the zspage to another fullness group, if required */
	fix_fullness_group(class, first_page);
	record_obj(handle, obj);
	spin_unlock(&class->lock);

	return handle;
}
EXPORT_SYMBOL_GPL(zs_malloc);

static void obj_free(struct zs_pool *pool, struct size_class *class,
			unsigned long obj)
{
	struct link_free *link;
	struct page *first_page, *f_page;
	unsigned long f_objidx, f_offset;
	void *vaddr;

	BUG_ON(!obj);

	obj &= ~OBJ_ALLOCATED_TAG;
	obj_to_location(obj, &f_page, &f_objidx);
	first_page = get_first_page(f_page);

	f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);

	vaddr = kmap_atomic(f_page);

	/* Insert this object in containing zspage's freelist */
	link = (struct link_free *)(vaddr + f_offset);
	link->next = first_page->freelist;
	if (class->huge)
		set_page_private(first_page, 0);
	kunmap_atomic(vaddr);
	first_page->freelist = (void *)obj;
	first_page->inuse--;
	zs_stat_dec(class, OBJ_USED, 1);
}

void zs_free(struct zs_pool *pool, unsigned long handle)
{
	struct page *first_page, *f_page;
	unsigned long obj, f_objidx;
	int class_idx;
	struct size_class *class;
	enum fullness_group fullness;

	if (unlikely(!handle))
		return;

	pin_tag(handle);
	obj = handle_to_obj(handle);
	obj_to_location(obj, &f_page, &f_objidx);
	first_page = get_first_page(f_page);

	get_zspage_mapping(first_page, &class_idx, &fullness);
	class = pool->size_class[class_idx];

	spin_lock(&class->lock);
	obj_free(pool, class, obj);
	fullness = fix_fullness_group(class, first_page);
	if (fullness == ZS_EMPTY) {
		zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
				class->size, class->pages_per_zspage));
		atomic_long_sub(class->pages_per_zspage,
				&pool->pages_allocated);
		free_zspage(first_page);
	}
	spin_unlock(&class->lock);
	unpin_tag(handle);

	free_handle(pool, handle);
}
EXPORT_SYMBOL_GPL(zs_free);

static void zs_object_copy(unsigned long dst, unsigned long src,
				struct size_class *class)
{
	struct page *s_page, *d_page;
	unsigned long s_objidx, d_objidx;
	unsigned long s_off, d_off;
	void *s_addr, *d_addr;
	int s_size, d_size, size;
	int written = 0;

	s_size = d_size = class->size;

	obj_to_location(src, &s_page, &s_objidx);
	obj_to_location(dst, &d_page, &d_objidx);

	s_off = obj_idx_to_offset(s_page, s_objidx, class->size);
	d_off = obj_idx_to_offset(d_page, d_objidx, class->size);

	if (s_off + class->size > PAGE_SIZE)
		s_size = PAGE_SIZE - s_off;

	if (d_off + class->size > PAGE_SIZE)
		d_size = PAGE_SIZE - d_off;

	s_addr = kmap_atomic(s_page);
	d_addr = kmap_atomic(d_page);

	while (1) {
		size = min(s_size, d_size);
		memcpy(d_addr + d_off, s_addr + s_off, size);
		written += size;

		if (written == class->size)
			break;

		s_off += size;
		s_size -= size;
		d_off += size;
		d_size -= size;

		if (s_off >= PAGE_SIZE) {
			kunmap_atomic(d_addr);
			kunmap_atomic(s_addr);
			s_page = get_next_page(s_page);
			BUG_ON(!s_page);
			s_addr = kmap_atomic(s_page);
			d_addr = kmap_atomic(d_page);
			s_size = class->size - written;
			s_off = 0;
		}

		if (d_off >= PAGE_SIZE) {
			kunmap_atomic(d_addr);
			d_page = get_next_page(d_page);
			BUG_ON(!d_page);
			d_addr = kmap_atomic(d_page);
			d_size = class->size - written;
			d_off = 0;
		}
	}

	kunmap_atomic(d_addr);
	kunmap_atomic(s_addr);
}

/*
 * Find alloced object in zspage from index object and
 * return handle.
 */
static unsigned long find_alloced_obj(struct page *page, int index,
					struct size_class *class)
{
	unsigned long head;
	int offset = 0;
	unsigned long handle = 0;
	void *addr = kmap_atomic(page);

	if (!is_first_page(page))
		offset = page->index;
	offset += class->size * index;

	while (offset < PAGE_SIZE) {
		head = obj_to_head(class, page, addr + offset);
		if (head & OBJ_ALLOCATED_TAG) {
			handle = head & ~OBJ_ALLOCATED_TAG;
			if (trypin_tag(handle))
				break;
			handle = 0;
		}

		offset += class->size;
		index++;
	}

	kunmap_atomic(addr);
	return handle;
}

struct zs_compact_control {
	/* Source page for migration which could be a subpage of zspage. */
	struct page *s_page;
	/* Destination page for migration which should be a first page
	 * of zspage. */
	struct page *d_page;
	 /* Starting object index within @s_page which used for live object
	  * in the subpage. */
	int index;
};

static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
				struct zs_compact_control *cc)
{
	unsigned long used_obj, free_obj;
	unsigned long handle;
	struct page *s_page = cc->s_page;
	struct page *d_page = cc->d_page;
	unsigned long index = cc->index;
	int ret = 0;

	while (1) {
		handle = find_alloced_obj(s_page, index, class);
		if (!handle) {
			s_page = get_next_page(s_page);
			if (!s_page)
				break;
			index = 0;
			continue;
		}

		/* Stop if there is no more space */
		if (zspage_full(d_page)) {
			unpin_tag(handle);
			ret = -ENOMEM;
			break;
		}

		used_obj = handle_to_obj(handle);
		free_obj = obj_malloc(d_page, class, handle);
		zs_object_copy(free_obj, used_obj, class);
		index++;
		record_obj(handle, free_obj);
		unpin_tag(handle);
		obj_free(pool, class, used_obj);
	}

	/* Remember last position in this iteration */
	cc->s_page = s_page;
	cc->index = index;

	return ret;
}

static struct page *isolate_target_page(struct size_class *class)
{
	int i;
	struct page *page;

	for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
		page = class->fullness_list[i];
		if (page) {
			remove_zspage(page, class, i);
			break;
		}
	}

	return page;
}

/*
 * putback_zspage - add @first_page into right class's fullness list
 * @pool: target pool
 * @class: destination class
 * @first_page: target page
 *
 * Return @fist_page's fullness_group
 */
static enum fullness_group putback_zspage(struct zs_pool *pool,
			struct size_class *class,
			struct page *first_page)
{
	enum fullness_group fullness;

	BUG_ON(!is_first_page(first_page));

	fullness = get_fullness_group(first_page);
	insert_zspage(first_page, class, fullness);
	set_zspage_mapping(first_page, class->index, fullness);

	if (fullness == ZS_EMPTY) {
		zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
			class->size, class->pages_per_zspage));
		atomic_long_sub(class->pages_per_zspage,
				&pool->pages_allocated);

		free_zspage(first_page);
	}

	return fullness;
}

static struct page *isolate_source_page(struct size_class *class)
{
	int i;
	struct page *page = NULL;

	for (i = ZS_ALMOST_EMPTY; i >= ZS_ALMOST_FULL; i--) {
		page = class->fullness_list[i];
		if (!page)
			continue;

		remove_zspage(page, class, i);
		break;
	}

	return page;
}

/*
 *
 * Based on the number of unused allocated objects calculate
 * and return the number of pages that we can free.
 */
static unsigned long zs_can_compact(struct size_class *class)
{
	unsigned long obj_wasted;

	obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) -
		zs_stat_get(class, OBJ_USED);

	obj_wasted /= get_maxobj_per_zspage(class->size,
			class->pages_per_zspage);

	return obj_wasted * class->pages_per_zspage;
}

static void __zs_compact(struct zs_pool *pool, struct size_class *class)
{
	struct zs_compact_control cc;
	struct page *src_page;
	struct page *dst_page = NULL;

	spin_lock(&class->lock);
	while ((src_page = isolate_source_page(class))) {

		BUG_ON(!is_first_page(src_page));

		if (!zs_can_compact(class))
			break;

		cc.index = 0;
		cc.s_page = src_page;

		while ((dst_page = isolate_target_page(class))) {
			cc.d_page = dst_page;
			/*
			 * If there is no more space in dst_page, resched
			 * and see if anyone had allocated another zspage.
			 */
			if (!migrate_zspage(pool, class, &cc))
				break;

			putback_zspage(pool, class, dst_page);
		}

		/* Stop if we couldn't find slot */
		if (dst_page == NULL)
			break;

		putback_zspage(pool, class, dst_page);
		if (putback_zspage(pool, class, src_page) == ZS_EMPTY)
			pool->stats.pages_compacted += class->pages_per_zspage;
		spin_unlock(&class->lock);
		cond_resched();
		spin_lock(&class->lock);
	}

	if (src_page)
		putback_zspage(pool, class, src_page);

	spin_unlock(&class->lock);
}

unsigned long zs_compact(struct zs_pool *pool)
{
	int i;
	struct size_class *class;

	for (i = zs_size_classes - 1; i >= 0; i--) {
		class = pool->size_class[i];
		if (!class)
			continue;
		if (class->index != i)
			continue;
		__zs_compact(pool, class);
	}

	return pool->stats.pages_compacted;
}
EXPORT_SYMBOL_GPL(zs_compact);

void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats)
{
	memcpy(stats, &pool->stats, sizeof(struct zs_pool_stats));
}
EXPORT_SYMBOL_GPL(zs_pool_stats);

static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
		struct shrink_control *sc)
{
	unsigned long pages_freed;
	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
			shrinker);

	pages_freed = pool->stats.pages_compacted;
	/*
	 * Compact classes and calculate compaction delta.
	 * Can run concurrently with a manually triggered
	 * (by user) compaction.
	 */
	pages_freed = zs_compact(pool) - pages_freed;

	return pages_freed ? pages_freed : SHRINK_STOP;
}

static unsigned long zs_shrinker_count(struct shrinker *shrinker,
		struct shrink_control *sc)
{
	int i;
	struct size_class *class;
	unsigned long pages_to_free = 0;
	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
			shrinker);

	for (i = zs_size_classes - 1; i >= 0; i--) {
		class = pool->size_class[i];
		if (!class)
			continue;
		if (class->index != i)
			continue;

		pages_to_free += zs_can_compact(class);
	}

	return pages_to_free;
}

static void zs_unregister_shrinker(struct zs_pool *pool)
{
	if (pool->shrinker_enabled) {
		unregister_shrinker(&pool->shrinker);
		pool->shrinker_enabled = false;
	}
}

static int zs_register_shrinker(struct zs_pool *pool)
{
	pool->shrinker.scan_objects = zs_shrinker_scan;
	pool->shrinker.count_objects = zs_shrinker_count;
	pool->shrinker.batch = 0;
	pool->shrinker.seeks = DEFAULT_SEEKS;

	return register_shrinker(&pool->shrinker);
}

/**
 * zs_create_pool - Creates an allocation pool to work from.
 * @flags: allocation flags used to allocate pool metadata
 *
 * This function must be called before anything when using
 * the zsmalloc allocator.
 *
 * On success, a pointer to the newly created pool is returned,
 * otherwise NULL.
 */
struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
{
	int i;
	struct zs_pool *pool;
	struct size_class *prev_class = NULL;

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

	pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
			GFP_KERNEL);
	if (!pool->size_class) {
		kfree(pool);
		return NULL;
	}

	pool->name = kstrdup(name, GFP_KERNEL);
	if (!pool->name)
		goto err;

	if (create_handle_cache(pool))
		goto err;

	/*
	 * Iterate reversly, because, size of size_class that we want to use
	 * for merging should be larger or equal to current size.
	 */
	for (i = zs_size_classes - 1; i >= 0; i--) {
		int size;
		int pages_per_zspage;
		struct size_class *class;

		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
		if (size > ZS_MAX_ALLOC_SIZE)
			size = ZS_MAX_ALLOC_SIZE;
		pages_per_zspage = get_pages_per_zspage(size);

		/*
		 * size_class is used for normal zsmalloc operation such
		 * as alloc/free for that size. Although it is natural that we
		 * have one size_class for each size, there is a chance that we
		 * can get more memory utilization if we use one size_class for
		 * many different sizes whose size_class have same
		 * characteristics. So, we makes size_class point to
		 * previous size_class if possible.
		 */
		if (prev_class) {
			if (can_merge(prev_class, size, pages_per_zspage)) {
				pool->size_class[i] = prev_class;
				continue;
			}
		}

		class = kzalloc(sizeof(struct size_class), GFP_KERNEL);
		if (!class)
			goto err;

		class->size = size;
		class->index = i;
		class->pages_per_zspage = pages_per_zspage;
		if (pages_per_zspage == 1 &&
			get_maxobj_per_zspage(size, pages_per_zspage) == 1)
			class->huge = true;
		spin_lock_init(&class->lock);
		pool->size_class[i] = class;

		prev_class = class;
	}

	pool->flags = flags;

	if (zs_pool_stat_create(name, pool))
		goto err;

	/*
	 * Not critical, we still can use the pool
	 * and user can trigger compaction manually.
	 */
	if (zs_register_shrinker(pool) == 0)
		pool->shrinker_enabled = true;
	return pool;

err:
	zs_destroy_pool(pool);
	return NULL;
}
EXPORT_SYMBOL_GPL(zs_create_pool);

void zs_destroy_pool(struct zs_pool *pool)
{
	int i;

	zs_unregister_shrinker(pool);
	zs_pool_stat_destroy(pool);

	for (i = 0; i < zs_size_classes; i++) {
		int fg;
		struct size_class *class = pool->size_class[i];

		if (!class)
			continue;

		if (class->index != i)
			continue;

		for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
			if (class->fullness_list[fg]) {
				pr_info("Freeing non-empty class with size %db, fullness group %d\n",
					class->size, fg);
			}
		}
		kfree(class);
	}

	destroy_handle_cache(pool);
	kfree(pool->size_class);
	kfree(pool->name);
	kfree(pool);
}
EXPORT_SYMBOL_GPL(zs_destroy_pool);

static int __init zs_init(void)
{
	int ret = zs_register_cpu_notifier();

	if (ret)
		goto notifier_fail;

	init_zs_size_classes();

#ifdef CONFIG_ZPOOL
	zpool_register_driver(&zs_zpool_driver);
#endif

	ret = zs_stat_init();
	if (ret) {
		pr_err("zs stat initialization failed\n");
		goto stat_fail;
	}
	return 0;

stat_fail:
#ifdef CONFIG_ZPOOL
	zpool_unregister_driver(&zs_zpool_driver);
#endif
notifier_fail:
	zs_unregister_cpu_notifier();

	return ret;
}

static void __exit zs_exit(void)
{
#ifdef CONFIG_ZPOOL
	zpool_unregister_driver(&zs_zpool_driver);
#endif
	zs_unregister_cpu_notifier();

	zs_stat_exit();
}

module_init(zs_init);
module_exit(zs_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");