Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: df4ebdb2b10a373723330dc0124957cd2cb1c021 (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
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/mmu_notifier.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/mm_inline.h>
#include <linux/kthread.h>
#include <linux/khugepaged.h>
#include <linux/freezer.h>
#include <linux/mman.h>
#include <linux/hashtable.h>
#include <linux/userfaultfd_k.h>
#include <linux/page_idle.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>

#include <asm/tlb.h>
#include <asm/pgalloc.h>
#include "internal.h"

enum scan_result {
	SCAN_FAIL,
	SCAN_SUCCEED,
	SCAN_PMD_NULL,
	SCAN_EXCEED_NONE_PTE,
	SCAN_PTE_NON_PRESENT,
	SCAN_PAGE_RO,
	SCAN_LACK_REFERENCED_PAGE,
	SCAN_PAGE_NULL,
	SCAN_SCAN_ABORT,
	SCAN_PAGE_COUNT,
	SCAN_PAGE_LRU,
	SCAN_PAGE_LOCK,
	SCAN_PAGE_ANON,
	SCAN_PAGE_COMPOUND,
	SCAN_ANY_PROCESS,
	SCAN_VMA_NULL,
	SCAN_VMA_CHECK,
	SCAN_ADDRESS_RANGE,
	SCAN_SWAP_CACHE_PAGE,
	SCAN_DEL_PAGE_LRU,
	SCAN_ALLOC_HUGE_PAGE_FAIL,
	SCAN_CGROUP_CHARGE_FAIL,
	SCAN_EXCEED_SWAP_PTE,
	SCAN_TRUNCATED,
};

#define CREATE_TRACE_POINTS
#include <trace/events/huge_memory.h>

/* default scan 8*512 pte (or vmas) every 30 second */
static unsigned int khugepaged_pages_to_scan __read_mostly;
static unsigned int khugepaged_pages_collapsed;
static unsigned int khugepaged_full_scans;
static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
/* during fragmentation poll the hugepage allocator once every minute */
static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
static unsigned long khugepaged_sleep_expire;
static DEFINE_SPINLOCK(khugepaged_mm_lock);
static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
/*
 * default collapse hugepages if there is at least one pte mapped like
 * it would have happened if the vma was large enough during page
 * fault.
 */
static unsigned int khugepaged_max_ptes_none __read_mostly;
static unsigned int khugepaged_max_ptes_swap __read_mostly;

#define MM_SLOTS_HASH_BITS 10
static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);

static struct kmem_cache *mm_slot_cache __read_mostly;

/**
 * struct mm_slot - hash lookup from mm to mm_slot
 * @hash: hash collision list
 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
 * @mm: the mm that this information is valid for
 */
struct mm_slot {
	struct hlist_node hash;
	struct list_head mm_node;
	struct mm_struct *mm;
};

/**
 * struct khugepaged_scan - cursor for scanning
 * @mm_head: the head of the mm list to scan
 * @mm_slot: the current mm_slot we are scanning
 * @address: the next address inside that to be scanned
 *
 * There is only the one khugepaged_scan instance of this cursor structure.
 */
struct khugepaged_scan {
	struct list_head mm_head;
	struct mm_slot *mm_slot;
	unsigned long address;
};

static struct khugepaged_scan khugepaged_scan = {
	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
};

#ifdef CONFIG_SYSFS
static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
					 struct kobj_attribute *attr,
					 char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
}

static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
					  struct kobj_attribute *attr,
					  const char *buf, size_t count)
{
	unsigned long msecs;
	int err;

	err = kstrtoul(buf, 10, &msecs);
	if (err || msecs > UINT_MAX)
		return -EINVAL;

	khugepaged_scan_sleep_millisecs = msecs;
	khugepaged_sleep_expire = 0;
	wake_up_interruptible(&khugepaged_wait);

	return count;
}
static struct kobj_attribute scan_sleep_millisecs_attr =
	__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
	       scan_sleep_millisecs_store);

static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
					  struct kobj_attribute *attr,
					  char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
}

static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
					   struct kobj_attribute *attr,
					   const char *buf, size_t count)
{
	unsigned long msecs;
	int err;

	err = kstrtoul(buf, 10, &msecs);
	if (err || msecs > UINT_MAX)
		return -EINVAL;

	khugepaged_alloc_sleep_millisecs = msecs;
	khugepaged_sleep_expire = 0;
	wake_up_interruptible(&khugepaged_wait);

	return count;
}
static struct kobj_attribute alloc_sleep_millisecs_attr =
	__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
	       alloc_sleep_millisecs_store);

static ssize_t pages_to_scan_show(struct kobject *kobj,
				  struct kobj_attribute *attr,
				  char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
}
static ssize_t pages_to_scan_store(struct kobject *kobj,
				   struct kobj_attribute *attr,
				   const char *buf, size_t count)
{
	int err;
	unsigned long pages;

	err = kstrtoul(buf, 10, &pages);
	if (err || !pages || pages > UINT_MAX)
		return -EINVAL;

	khugepaged_pages_to_scan = pages;

	return count;
}
static struct kobj_attribute pages_to_scan_attr =
	__ATTR(pages_to_scan, 0644, pages_to_scan_show,
	       pages_to_scan_store);

static ssize_t pages_collapsed_show(struct kobject *kobj,
				    struct kobj_attribute *attr,
				    char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
}
static struct kobj_attribute pages_collapsed_attr =
	__ATTR_RO(pages_collapsed);

static ssize_t full_scans_show(struct kobject *kobj,
			       struct kobj_attribute *attr,
			       char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_full_scans);
}
static struct kobj_attribute full_scans_attr =
	__ATTR_RO(full_scans);

static ssize_t khugepaged_defrag_show(struct kobject *kobj,
				      struct kobj_attribute *attr, char *buf)
{
	return single_hugepage_flag_show(kobj, attr, buf,
				TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
}
static ssize_t khugepaged_defrag_store(struct kobject *kobj,
				       struct kobj_attribute *attr,
				       const char *buf, size_t count)
{
	return single_hugepage_flag_store(kobj, attr, buf, count,
				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
}
static struct kobj_attribute khugepaged_defrag_attr =
	__ATTR(defrag, 0644, khugepaged_defrag_show,
	       khugepaged_defrag_store);

/*
 * max_ptes_none controls if khugepaged should collapse hugepages over
 * any unmapped ptes in turn potentially increasing the memory
 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
 * reduce the available free memory in the system as it
 * runs. Increasing max_ptes_none will instead potentially reduce the
 * free memory in the system during the khugepaged scan.
 */
static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
					     struct kobj_attribute *attr,
					     char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
}
static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
					      struct kobj_attribute *attr,
					      const char *buf, size_t count)
{
	int err;
	unsigned long max_ptes_none;

	err = kstrtoul(buf, 10, &max_ptes_none);
	if (err || max_ptes_none > HPAGE_PMD_NR-1)
		return -EINVAL;

	khugepaged_max_ptes_none = max_ptes_none;

	return count;
}
static struct kobj_attribute khugepaged_max_ptes_none_attr =
	__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
	       khugepaged_max_ptes_none_store);

static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
					     struct kobj_attribute *attr,
					     char *buf)
{
	return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
}

static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
					      struct kobj_attribute *attr,
					      const char *buf, size_t count)
{
	int err;
	unsigned long max_ptes_swap;

	err  = kstrtoul(buf, 10, &max_ptes_swap);
	if (err || max_ptes_swap > HPAGE_PMD_NR-1)
		return -EINVAL;

	khugepaged_max_ptes_swap = max_ptes_swap;

	return count;
}

static struct kobj_attribute khugepaged_max_ptes_swap_attr =
	__ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
	       khugepaged_max_ptes_swap_store);

static struct attribute *khugepaged_attr[] = {
	&khugepaged_defrag_attr.attr,
	&khugepaged_max_ptes_none_attr.attr,
	&pages_to_scan_attr.attr,
	&pages_collapsed_attr.attr,
	&full_scans_attr.attr,
	&scan_sleep_millisecs_attr.attr,
	&alloc_sleep_millisecs_attr.attr,
	&khugepaged_max_ptes_swap_attr.attr,
	NULL,
};

struct attribute_group khugepaged_attr_group = {
	.attrs = khugepaged_attr,
	.name = "khugepaged",
};
#endif /* CONFIG_SYSFS */

#define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)

int hugepage_madvise(struct vm_area_struct *vma,
		     unsigned long *vm_flags, int advice)
{
	switch (advice) {
	case MADV_HUGEPAGE:
#ifdef CONFIG_S390
		/*
		 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
		 * can't handle this properly after s390_enable_sie, so we simply
		 * ignore the madvise to prevent qemu from causing a SIGSEGV.
		 */
		if (mm_has_pgste(vma->vm_mm))
			return 0;
#endif
		*vm_flags &= ~VM_NOHUGEPAGE;
		*vm_flags |= VM_HUGEPAGE;
		/*
		 * If the vma become good for khugepaged to scan,
		 * register it here without waiting a page fault that
		 * may not happen any time soon.
		 */
		if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
				khugepaged_enter_vma_merge(vma, *vm_flags))
			return -ENOMEM;
		break;
	case MADV_NOHUGEPAGE:
		*vm_flags &= ~VM_HUGEPAGE;
		*vm_flags |= VM_NOHUGEPAGE;
		/*
		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
		 * this vma even if we leave the mm registered in khugepaged if
		 * it got registered before VM_NOHUGEPAGE was set.
		 */
		break;
	}

	return 0;
}

int __init khugepaged_init(void)
{
	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
					  sizeof(struct mm_slot),
					  __alignof__(struct mm_slot), 0, NULL);
	if (!mm_slot_cache)
		return -ENOMEM;

	khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
	khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
	khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;

	return 0;
}

void __init khugepaged_destroy(void)
{
	kmem_cache_destroy(mm_slot_cache);
}

static inline struct mm_slot *alloc_mm_slot(void)
{
	if (!mm_slot_cache)	/* initialization failed */
		return NULL;
	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
}

static inline void free_mm_slot(struct mm_slot *mm_slot)
{
	kmem_cache_free(mm_slot_cache, mm_slot);
}

static struct mm_slot *get_mm_slot(struct mm_struct *mm)
{
	struct mm_slot *mm_slot;

	hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
		if (mm == mm_slot->mm)
			return mm_slot;

	return NULL;
}

static void insert_to_mm_slots_hash(struct mm_struct *mm,
				    struct mm_slot *mm_slot)
{
	mm_slot->mm = mm;
	hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
}

static inline int khugepaged_test_exit(struct mm_struct *mm)
{
	return atomic_read(&mm->mm_users) == 0;
}

int __khugepaged_enter(struct mm_struct *mm)
{
	struct mm_slot *mm_slot;
	int wakeup;

	mm_slot = alloc_mm_slot();
	if (!mm_slot)
		return -ENOMEM;

	/* __khugepaged_exit() must not run from under us */
	VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
		free_mm_slot(mm_slot);
		return 0;
	}

	spin_lock(&khugepaged_mm_lock);
	insert_to_mm_slots_hash(mm, mm_slot);
	/*
	 * Insert just behind the scanning cursor, to let the area settle
	 * down a little.
	 */
	wakeup = list_empty(&khugepaged_scan.mm_head);
	list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
	spin_unlock(&khugepaged_mm_lock);

	mmgrab(mm);
	if (wakeup)
		wake_up_interruptible(&khugepaged_wait);

	return 0;
}

int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
			       unsigned long vm_flags)
{
	unsigned long hstart, hend;
	if (!vma->anon_vma)
		/*
		 * Not yet faulted in so we will register later in the
		 * page fault if needed.
		 */
		return 0;
	if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
		/* khugepaged not yet working on file or special mappings */
		return 0;
	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
	hend = vma->vm_end & HPAGE_PMD_MASK;
	if (hstart < hend)
		return khugepaged_enter(vma, vm_flags);
	return 0;
}

void __khugepaged_exit(struct mm_struct *mm)
{
	struct mm_slot *mm_slot;
	int free = 0;

	spin_lock(&khugepaged_mm_lock);
	mm_slot = get_mm_slot(mm);
	if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
		hash_del(&mm_slot->hash);
		list_del(&mm_slot->mm_node);
		free = 1;
	}
	spin_unlock(&khugepaged_mm_lock);

	if (free) {
		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
		free_mm_slot(mm_slot);
		mmdrop(mm);
	} else if (mm_slot) {
		/*
		 * This is required to serialize against
		 * khugepaged_test_exit() (which is guaranteed to run
		 * under mmap sem read mode). Stop here (after we
		 * return all pagetables will be destroyed) until
		 * khugepaged has finished working on the pagetables
		 * under the mmap_sem.
		 */
		down_write(&mm->mmap_sem);
		up_write(&mm->mmap_sem);
	}
}

static void release_pte_page(struct page *page)
{
	dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
	unlock_page(page);
	putback_lru_page(page);
}

static void release_pte_pages(pte_t *pte, pte_t *_pte)
{
	while (--_pte >= pte) {
		pte_t pteval = *_pte;
		if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
			release_pte_page(pte_page(pteval));
	}
}

static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
					unsigned long address,
					pte_t *pte)
{
	struct page *page = NULL;
	pte_t *_pte;
	int none_or_zero = 0, result = 0, referenced = 0;
	bool writable = false;

	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
	     _pte++, address += PAGE_SIZE) {
		pte_t pteval = *_pte;
		if (pte_none(pteval) || (pte_present(pteval) &&
				is_zero_pfn(pte_pfn(pteval)))) {
			if (!userfaultfd_armed(vma) &&
			    ++none_or_zero <= khugepaged_max_ptes_none) {
				continue;
			} else {
				result = SCAN_EXCEED_NONE_PTE;
				goto out;
			}
		}
		if (!pte_present(pteval)) {
			result = SCAN_PTE_NON_PRESENT;
			goto out;
		}
		page = vm_normal_page(vma, address, pteval);
		if (unlikely(!page)) {
			result = SCAN_PAGE_NULL;
			goto out;
		}

		VM_BUG_ON_PAGE(PageCompound(page), page);
		VM_BUG_ON_PAGE(!PageAnon(page), page);

		/*
		 * We can do it before isolate_lru_page because the
		 * page can't be freed from under us. NOTE: PG_lock
		 * is needed to serialize against split_huge_page
		 * when invoked from the VM.
		 */
		if (!trylock_page(page)) {
			result = SCAN_PAGE_LOCK;
			goto out;
		}

		/*
		 * cannot use mapcount: can't collapse if there's a gup pin.
		 * The page must only be referenced by the scanned process
		 * and page swap cache.
		 */
		if (page_count(page) != 1 + PageSwapCache(page)) {
			unlock_page(page);
			result = SCAN_PAGE_COUNT;
			goto out;
		}
		if (pte_write(pteval)) {
			writable = true;
		} else {
			if (PageSwapCache(page) &&
			    !reuse_swap_page(page, NULL)) {
				unlock_page(page);
				result = SCAN_SWAP_CACHE_PAGE;
				goto out;
			}
			/*
			 * Page is not in the swap cache. It can be collapsed
			 * into a THP.
			 */
		}

		/*
		 * Isolate the page to avoid collapsing an hugepage
		 * currently in use by the VM.
		 */
		if (isolate_lru_page(page)) {
			unlock_page(page);
			result = SCAN_DEL_PAGE_LRU;
			goto out;
		}
		inc_node_page_state(page,
				NR_ISOLATED_ANON + page_is_file_cache(page));
		VM_BUG_ON_PAGE(!PageLocked(page), page);
		VM_BUG_ON_PAGE(PageLRU(page), page);

		/* There should be enough young pte to collapse the page */
		if (pte_young(pteval) ||
		    page_is_young(page) || PageReferenced(page) ||
		    mmu_notifier_test_young(vma->vm_mm, address))
			referenced++;
	}
	if (likely(writable)) {
		if (likely(referenced)) {
			result = SCAN_SUCCEED;
			trace_mm_collapse_huge_page_isolate(page, none_or_zero,
							    referenced, writable, result);
			return 1;
		}
	} else {
		result = SCAN_PAGE_RO;
	}

out:
	release_pte_pages(pte, _pte);
	trace_mm_collapse_huge_page_isolate(page, none_or_zero,
					    referenced, writable, result);
	return 0;
}

static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
				      struct vm_area_struct *vma,
				      unsigned long address,
				      spinlock_t *ptl)
{
	pte_t *_pte;
	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
				_pte++, page++, address += PAGE_SIZE) {
		pte_t pteval = *_pte;
		struct page *src_page;

		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
			clear_user_highpage(page, address);
			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
			if (is_zero_pfn(pte_pfn(pteval))) {
				/*
				 * ptl mostly unnecessary.
				 */
				spin_lock(ptl);
				/*
				 * paravirt calls inside pte_clear here are
				 * superfluous.
				 */
				pte_clear(vma->vm_mm, address, _pte);
				spin_unlock(ptl);
			}
		} else {
			src_page = pte_page(pteval);
			copy_user_highpage(page, src_page, address, vma);
			VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
			release_pte_page(src_page);
			/*
			 * ptl mostly unnecessary, but preempt has to
			 * be disabled to update the per-cpu stats
			 * inside page_remove_rmap().
			 */
			spin_lock(ptl);
			/*
			 * paravirt calls inside pte_clear here are
			 * superfluous.
			 */
			pte_clear(vma->vm_mm, address, _pte);
			page_remove_rmap(src_page, false);
			spin_unlock(ptl);
			free_page_and_swap_cache(src_page);
		}
	}
}

static void khugepaged_alloc_sleep(void)
{
	DEFINE_WAIT(wait);

	add_wait_queue(&khugepaged_wait, &wait);
	freezable_schedule_timeout_interruptible(
		msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
	remove_wait_queue(&khugepaged_wait, &wait);
}

static int khugepaged_node_load[MAX_NUMNODES];

static bool khugepaged_scan_abort(int nid)
{
	int i;

	/*
	 * If node_reclaim_mode is disabled, then no extra effort is made to
	 * allocate memory locally.
	 */
	if (!node_reclaim_mode)
		return false;

	/* If there is a count for this node already, it must be acceptable */
	if (khugepaged_node_load[nid])
		return false;

	for (i = 0; i < MAX_NUMNODES; i++) {
		if (!khugepaged_node_load[i])
			continue;
		if (node_distance(nid, i) > RECLAIM_DISTANCE)
			return true;
	}
	return false;
}

/* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
{
	return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
}

#ifdef CONFIG_NUMA
static int khugepaged_find_target_node(void)
{
	static int last_khugepaged_target_node = NUMA_NO_NODE;
	int nid, target_node = 0, max_value = 0;

	/* find first node with max normal pages hit */
	for (nid = 0; nid < MAX_NUMNODES; nid++)
		if (khugepaged_node_load[nid] > max_value) {
			max_value = khugepaged_node_load[nid];
			target_node = nid;
		}

	/* do some balance if several nodes have the same hit record */
	if (target_node <= last_khugepaged_target_node)
		for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
				nid++)
			if (max_value == khugepaged_node_load[nid]) {
				target_node = nid;
				break;
			}

	last_khugepaged_target_node = target_node;
	return target_node;
}

static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
{
	if (IS_ERR(*hpage)) {
		if (!*wait)
			return false;

		*wait = false;
		*hpage = NULL;
		khugepaged_alloc_sleep();
	} else if (*hpage) {
		put_page(*hpage);
		*hpage = NULL;
	}

	return true;
}

static struct page *
khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
{
	VM_BUG_ON_PAGE(*hpage, *hpage);

	*hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
	if (unlikely(!*hpage)) {
		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
		*hpage = ERR_PTR(-ENOMEM);
		return NULL;
	}

	prep_transhuge_page(*hpage);
	count_vm_event(THP_COLLAPSE_ALLOC);
	return *hpage;
}
#else
static int khugepaged_find_target_node(void)
{
	return 0;
}

static inline struct page *alloc_khugepaged_hugepage(void)
{
	struct page *page;

	page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
			   HPAGE_PMD_ORDER);
	if (page)
		prep_transhuge_page(page);
	return page;
}

static struct page *khugepaged_alloc_hugepage(bool *wait)
{
	struct page *hpage;

	do {
		hpage = alloc_khugepaged_hugepage();
		if (!hpage) {
			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
			if (!*wait)
				return NULL;

			*wait = false;
			khugepaged_alloc_sleep();
		} else
			count_vm_event(THP_COLLAPSE_ALLOC);
	} while (unlikely(!hpage) && likely(khugepaged_enabled()));

	return hpage;
}

static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
{
	if (!*hpage)
		*hpage = khugepaged_alloc_hugepage(wait);

	if (unlikely(!*hpage))
		return false;

	return true;
}

static struct page *
khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
{
	VM_BUG_ON(!*hpage);

	return  *hpage;
}
#endif

static bool hugepage_vma_check(struct vm_area_struct *vma)
{
	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
	    (vma->vm_flags & VM_NOHUGEPAGE))
		return false;
	if (shmem_file(vma->vm_file)) {
		if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
			return false;
		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
				HPAGE_PMD_NR);
	}
	if (!vma->anon_vma || vma->vm_ops)
		return false;
	if (is_vma_temporary_stack(vma))
		return false;
	return !(vma->vm_flags & VM_NO_KHUGEPAGED);
}

/*
 * If mmap_sem temporarily dropped, revalidate vma
 * before taking mmap_sem.
 * Return 0 if succeeds, otherwise return none-zero
 * value (scan code).
 */

static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
		struct vm_area_struct **vmap)
{
	struct vm_area_struct *vma;
	unsigned long hstart, hend;

	if (unlikely(khugepaged_test_exit(mm)))
		return SCAN_ANY_PROCESS;

	*vmap = vma = find_vma(mm, address);
	if (!vma)
		return SCAN_VMA_NULL;

	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
	hend = vma->vm_end & HPAGE_PMD_MASK;
	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
		return SCAN_ADDRESS_RANGE;
	if (!hugepage_vma_check(vma))
		return SCAN_VMA_CHECK;
	return 0;
}

/*
 * Bring missing pages in from swap, to complete THP collapse.
 * Only done if khugepaged_scan_pmd believes it is worthwhile.
 *
 * Called and returns without pte mapped or spinlocks held,
 * but with mmap_sem held to protect against vma changes.
 */

static bool __collapse_huge_page_swapin(struct mm_struct *mm,
					struct vm_area_struct *vma,
					unsigned long address, pmd_t *pmd,
					int referenced)
{
	int swapped_in = 0, ret = 0;
	struct vm_fault vmf = {
		.vma = vma,
		.address = address,
		.flags = FAULT_FLAG_ALLOW_RETRY,
		.pmd = pmd,
		.pgoff = linear_page_index(vma, address),
	};

	/* we only decide to swapin, if there is enough young ptes */
	if (referenced < HPAGE_PMD_NR/2) {
		trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
		return false;
	}
	vmf.pte = pte_offset_map(pmd, address);
	for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
			vmf.pte++, vmf.address += PAGE_SIZE) {
		vmf.orig_pte = *vmf.pte;
		if (!is_swap_pte(vmf.orig_pte))
			continue;
		swapped_in++;
		ret = do_swap_page(&vmf);

		/* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
		if (ret & VM_FAULT_RETRY) {
			down_read(&mm->mmap_sem);
			if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
				/* vma is no longer available, don't continue to swapin */
				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
				return false;
			}
			/* check if the pmd is still valid */
			if (mm_find_pmd(mm, address) != pmd) {
				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
				return false;
			}
		}
		if (ret & VM_FAULT_ERROR) {
			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
			return false;
		}
		/* pte is unmapped now, we need to map it */
		vmf.pte = pte_offset_map(pmd, vmf.address);
	}
	vmf.pte--;
	pte_unmap(vmf.pte);
	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
	return true;
}

static void collapse_huge_page(struct mm_struct *mm,
				   unsigned long address,
				   struct page **hpage,
				   int node, int referenced)
{
	pmd_t *pmd, _pmd;
	pte_t *pte;
	pgtable_t pgtable;
	struct page *new_page;
	spinlock_t *pmd_ptl, *pte_ptl;
	int isolated = 0, result = 0;
	struct mem_cgroup *memcg;
	struct vm_area_struct *vma;
	unsigned long mmun_start;	/* For mmu_notifiers */
	unsigned long mmun_end;		/* For mmu_notifiers */
	gfp_t gfp;

	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

	/* Only allocate from the target node */
	gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;

	/*
	 * Before allocating the hugepage, release the mmap_sem read lock.
	 * The allocation can take potentially a long time if it involves
	 * sync compaction, and we do not need to hold the mmap_sem during
	 * that. We will recheck the vma after taking it again in write mode.
	 */
	up_read(&mm->mmap_sem);
	new_page = khugepaged_alloc_page(hpage, gfp, node);
	if (!new_page) {
		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
		goto out_nolock;
	}

	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
		result = SCAN_CGROUP_CHARGE_FAIL;
		goto out_nolock;
	}

	down_read(&mm->mmap_sem);
	result = hugepage_vma_revalidate(mm, address, &vma);
	if (result) {
		mem_cgroup_cancel_charge(new_page, memcg, true);
		up_read(&mm->mmap_sem);
		goto out_nolock;
	}

	pmd = mm_find_pmd(mm, address);
	if (!pmd) {
		result = SCAN_PMD_NULL;
		mem_cgroup_cancel_charge(new_page, memcg, true);
		up_read(&mm->mmap_sem);
		goto out_nolock;
	}

	/*
	 * __collapse_huge_page_swapin always returns with mmap_sem locked.
	 * If it fails, we release mmap_sem and jump out_nolock.
	 * Continuing to collapse causes inconsistency.
	 */
	if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
		mem_cgroup_cancel_charge(new_page, memcg, true);
		up_read(&mm->mmap_sem);
		goto out_nolock;
	}

	up_read(&mm->mmap_sem);
	/*
	 * Prevent all access to pagetables with the exception of
	 * gup_fast later handled by the ptep_clear_flush and the VM
	 * handled by the anon_vma lock + PG_lock.
	 */
	down_write(&mm->mmap_sem);
	result = hugepage_vma_revalidate(mm, address, &vma);
	if (result)
		goto out;
	/* check if the pmd is still valid */
	if (mm_find_pmd(mm, address) != pmd)
		goto out;

	anon_vma_lock_write(vma->anon_vma);

	pte = pte_offset_map(pmd, address);
	pte_ptl = pte_lockptr(mm, pmd);

	mmun_start = address;
	mmun_end   = address + HPAGE_PMD_SIZE;
	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
	pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
	/*
	 * After this gup_fast can't run anymore. This also removes
	 * any huge TLB entry from the CPU so we won't allow
	 * huge and small TLB entries for the same virtual address
	 * to avoid the risk of CPU bugs in that area.
	 */
	_pmd = pmdp_collapse_flush(vma, address, pmd);
	spin_unlock(pmd_ptl);
	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);

	spin_lock(pte_ptl);
	isolated = __collapse_huge_page_isolate(vma, address, pte);
	spin_unlock(pte_ptl);

	if (unlikely(!isolated)) {
		pte_unmap(pte);
		spin_lock(pmd_ptl);
		BUG_ON(!pmd_none(*pmd));
		/*
		 * We can only use set_pmd_at when establishing
		 * hugepmds and never for establishing regular pmds that
		 * points to regular pagetables. Use pmd_populate for that
		 */
		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
		spin_unlock(pmd_ptl);
		anon_vma_unlock_write(vma->anon_vma);
		result = SCAN_FAIL;
		goto out;
	}

	/*
	 * All pages are isolated and locked so anon_vma rmap
	 * can't run anymore.
	 */
	anon_vma_unlock_write(vma->anon_vma);

	__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
	pte_unmap(pte);
	__SetPageUptodate(new_page);
	pgtable = pmd_pgtable(_pmd);

	_pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);

	/*
	 * spin_lock() below is not the equivalent of smp_wmb(), so
	 * this is needed to avoid the copy_huge_page writes to become
	 * visible after the set_pmd_at() write.
	 */
	smp_wmb();

	spin_lock(pmd_ptl);
	BUG_ON(!pmd_none(*pmd));
	page_add_new_anon_rmap(new_page, vma, address, true);
	mem_cgroup_commit_charge(new_page, memcg, false, true);
	lru_cache_add_active_or_unevictable(new_page, vma);
	pgtable_trans_huge_deposit(mm, pmd, pgtable);
	set_pmd_at(mm, address, pmd, _pmd);
	update_mmu_cache_pmd(vma, address, pmd);
	spin_unlock(pmd_ptl);

	*hpage = NULL;

	khugepaged_pages_collapsed++;
	result = SCAN_SUCCEED;
out_up_write:
	up_write(&mm->mmap_sem);
out_nolock:
	trace_mm_collapse_huge_page(mm, isolated, result);
	return;
out:
	mem_cgroup_cancel_charge(new_page, memcg, true);
	goto out_up_write;
}

static int khugepaged_scan_pmd(struct mm_struct *mm,
			       struct vm_area_struct *vma,
			       unsigned long address,
			       struct page **hpage)
{
	pmd_t *pmd;
	pte_t *pte, *_pte;
	int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
	struct page *page = NULL;
	unsigned long _address;
	spinlock_t *ptl;
	int node = NUMA_NO_NODE, unmapped = 0;
	bool writable = false;

	VM_BUG_ON(address & ~HPAGE_PMD_MASK);

	pmd = mm_find_pmd(mm, address);
	if (!pmd) {
		result = SCAN_PMD_NULL;
		goto out;
	}

	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
	     _pte++, _address += PAGE_SIZE) {
		pte_t pteval = *_pte;
		if (is_swap_pte(pteval)) {
			if (++unmapped <= khugepaged_max_ptes_swap) {
				continue;
			} else {
				result = SCAN_EXCEED_SWAP_PTE;
				goto out_unmap;
			}
		}
		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
			if (!userfaultfd_armed(vma) &&
			    ++none_or_zero <= khugepaged_max_ptes_none) {
				continue;
			} else {
				result = SCAN_EXCEED_NONE_PTE;
				goto out_unmap;
			}
		}
		if (!pte_present(pteval)) {
			result = SCAN_PTE_NON_PRESENT;
			goto out_unmap;
		}
		if (pte_write(pteval))
			writable = true;

		page = vm_normal_page(vma, _address, pteval);
		if (unlikely(!page)) {
			result = SCAN_PAGE_NULL;
			goto out_unmap;
		}

		/* TODO: teach khugepaged to collapse THP mapped with pte */
		if (PageCompound(page)) {
			result = SCAN_PAGE_COMPOUND;
			goto out_unmap;
		}

		/*
		 * Record which node the original page is from and save this
		 * information to khugepaged_node_load[].
		 * Khupaged will allocate hugepage from the node has the max
		 * hit record.
		 */
		node = page_to_nid(page);
		if (khugepaged_scan_abort(node)) {
			result = SCAN_SCAN_ABORT;
			goto out_unmap;
		}
		khugepaged_node_load[node]++;
		if (!PageLRU(page)) {
			result = SCAN_PAGE_LRU;
			goto out_unmap;
		}
		if (PageLocked(page)) {
			result = SCAN_PAGE_LOCK;
			goto out_unmap;
		}
		if (!PageAnon(page)) {
			result = SCAN_PAGE_ANON;
			goto out_unmap;
		}

		/*
		 * cannot use mapcount: can't collapse if there's a gup pin.
		 * The page must only be referenced by the scanned process
		 * and page swap cache.
		 */
		if (page_count(page) != 1 + PageSwapCache(page)) {
			result = SCAN_PAGE_COUNT;
			goto out_unmap;
		}
		if (pte_young(pteval) ||
		    page_is_young(page) || PageReferenced(page) ||
		    mmu_notifier_test_young(vma->vm_mm, address))
			referenced++;
	}
	if (writable) {
		if (referenced) {
			result = SCAN_SUCCEED;
			ret = 1;
		} else {
			result = SCAN_LACK_REFERENCED_PAGE;
		}
	} else {
		result = SCAN_PAGE_RO;
	}
out_unmap:
	pte_unmap_unlock(pte, ptl);
	if (ret) {
		node = khugepaged_find_target_node();
		/* collapse_huge_page will return with the mmap_sem released */
		collapse_huge_page(mm, address, hpage, node, referenced);
	}
out:
	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
				     none_or_zero, result, unmapped);
	return ret;
}

static void collect_mm_slot(struct mm_slot *mm_slot)
{
	struct mm_struct *mm = mm_slot->mm;

	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));

	if (khugepaged_test_exit(mm)) {
		/* free mm_slot */
		hash_del(&mm_slot->hash);
		list_del(&mm_slot->mm_node);

		/*
		 * Not strictly needed because the mm exited already.
		 *
		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
		 */

		/* khugepaged_mm_lock actually not necessary for the below */
		free_mm_slot(mm_slot);
		mmdrop(mm);
	}
}

#if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
{
	struct vm_area_struct *vma;
	unsigned long addr;
	pmd_t *pmd, _pmd;

	i_mmap_lock_write(mapping);
	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
		/* probably overkill */
		if (vma->anon_vma)
			continue;
		addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
		if (addr & ~HPAGE_PMD_MASK)
			continue;
		if (vma->vm_end < addr + HPAGE_PMD_SIZE)
			continue;
		pmd = mm_find_pmd(vma->vm_mm, addr);
		if (!pmd)
			continue;
		/*
		 * We need exclusive mmap_sem to retract page table.
		 * If trylock fails we would end up with pte-mapped THP after
		 * re-fault. Not ideal, but it's more important to not disturb
		 * the system too much.
		 */
		if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
			spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
			/* assume page table is clear */
			_pmd = pmdp_collapse_flush(vma, addr, pmd);
			spin_unlock(ptl);
			up_write(&vma->vm_mm->mmap_sem);
			atomic_long_dec(&vma->vm_mm->nr_ptes);
			pte_free(vma->vm_mm, pmd_pgtable(_pmd));
		}
	}
	i_mmap_unlock_write(mapping);
}

/**
 * collapse_shmem - collapse small tmpfs/shmem pages into huge one.
 *
 * Basic scheme is simple, details are more complex:
 *  - allocate and freeze a new huge page;
 *  - scan over radix tree replacing old pages the new one
 *    + swap in pages if necessary;
 *    + fill in gaps;
 *    + keep old pages around in case if rollback is required;
 *  - if replacing succeed:
 *    + copy data over;
 *    + free old pages;
 *    + unfreeze huge page;
 *  - if replacing failed;
 *    + put all pages back and unfreeze them;
 *    + restore gaps in the radix-tree;
 *    + free huge page;
 */
static void collapse_shmem(struct mm_struct *mm,
		struct address_space *mapping, pgoff_t start,
		struct page **hpage, int node)
{
	gfp_t gfp;
	struct page *page, *new_page, *tmp;
	struct mem_cgroup *memcg;
	pgoff_t index, end = start + HPAGE_PMD_NR;
	LIST_HEAD(pagelist);
	struct radix_tree_iter iter;
	void **slot;
	int nr_none = 0, result = SCAN_SUCCEED;

	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));

	/* Only allocate from the target node */
	gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;

	new_page = khugepaged_alloc_page(hpage, gfp, node);
	if (!new_page) {
		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
		goto out;
	}

	if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
		result = SCAN_CGROUP_CHARGE_FAIL;
		goto out;
	}

	new_page->index = start;
	new_page->mapping = mapping;
	__SetPageSwapBacked(new_page);
	__SetPageLocked(new_page);
	BUG_ON(!page_ref_freeze(new_page, 1));


	/*
	 * At this point the new_page is 'frozen' (page_count() is zero), locked
	 * and not up-to-date. It's safe to insert it into radix tree, because
	 * nobody would be able to map it or use it in other way until we
	 * unfreeze it.
	 */

	index = start;
	spin_lock_irq(&mapping->tree_lock);
	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
		int n = min(iter.index, end) - index;

		/*
		 * Handle holes in the radix tree: charge it from shmem and
		 * insert relevant subpage of new_page into the radix-tree.
		 */
		if (n && !shmem_charge(mapping->host, n)) {
			result = SCAN_FAIL;
			break;
		}
		nr_none += n;
		for (; index < min(iter.index, end); index++) {
			radix_tree_insert(&mapping->page_tree, index,
					new_page + (index % HPAGE_PMD_NR));
		}

		/* We are done. */
		if (index >= end)
			break;

		page = radix_tree_deref_slot_protected(slot,
				&mapping->tree_lock);
		if (radix_tree_exceptional_entry(page) || !PageUptodate(page)) {
			spin_unlock_irq(&mapping->tree_lock);
			/* swap in or instantiate fallocated page */
			if (shmem_getpage(mapping->host, index, &page,
						SGP_NOHUGE)) {
				result = SCAN_FAIL;
				goto tree_unlocked;
			}
			spin_lock_irq(&mapping->tree_lock);
		} else if (trylock_page(page)) {
			get_page(page);
		} else {
			result = SCAN_PAGE_LOCK;
			break;
		}

		/*
		 * The page must be locked, so we can drop the tree_lock
		 * without racing with truncate.
		 */
		VM_BUG_ON_PAGE(!PageLocked(page), page);
		VM_BUG_ON_PAGE(!PageUptodate(page), page);
		VM_BUG_ON_PAGE(PageTransCompound(page), page);

		if (page_mapping(page) != mapping) {
			result = SCAN_TRUNCATED;
			goto out_unlock;
		}
		spin_unlock_irq(&mapping->tree_lock);

		if (isolate_lru_page(page)) {
			result = SCAN_DEL_PAGE_LRU;
			goto out_isolate_failed;
		}

		if (page_mapped(page))
			unmap_mapping_range(mapping, index << PAGE_SHIFT,
					PAGE_SIZE, 0);

		spin_lock_irq(&mapping->tree_lock);

		slot = radix_tree_lookup_slot(&mapping->page_tree, index);
		VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
					&mapping->tree_lock), page);
		VM_BUG_ON_PAGE(page_mapped(page), page);

		/*
		 * The page is expected to have page_count() == 3:
		 *  - we hold a pin on it;
		 *  - one reference from radix tree;
		 *  - one from isolate_lru_page;
		 */
		if (!page_ref_freeze(page, 3)) {
			result = SCAN_PAGE_COUNT;
			goto out_lru;
		}

		/*
		 * Add the page to the list to be able to undo the collapse if
		 * something go wrong.
		 */
		list_add_tail(&page->lru, &pagelist);

		/* Finally, replace with the new page. */
		radix_tree_replace_slot(&mapping->page_tree, slot,
				new_page + (index % HPAGE_PMD_NR));

		slot = radix_tree_iter_resume(slot, &iter);
		index++;
		continue;
out_lru:
		spin_unlock_irq(&mapping->tree_lock);
		putback_lru_page(page);
out_isolate_failed:
		unlock_page(page);
		put_page(page);
		goto tree_unlocked;
out_unlock:
		unlock_page(page);
		put_page(page);
		break;
	}

	/*
	 * Handle hole in radix tree at the end of the range.
	 * This code only triggers if there's nothing in radix tree
	 * beyond 'end'.
	 */
	if (result == SCAN_SUCCEED && index < end) {
		int n = end - index;

		if (!shmem_charge(mapping->host, n)) {
			result = SCAN_FAIL;
			goto tree_locked;
		}

		for (; index < end; index++) {
			radix_tree_insert(&mapping->page_tree, index,
					new_page + (index % HPAGE_PMD_NR));
		}
		nr_none += n;
	}

tree_locked:
	spin_unlock_irq(&mapping->tree_lock);
tree_unlocked:

	if (result == SCAN_SUCCEED) {
		unsigned long flags;
		struct zone *zone = page_zone(new_page);

		/*
		 * Replacing old pages with new one has succeed, now we need to
		 * copy the content and free old pages.
		 */
		list_for_each_entry_safe(page, tmp, &pagelist, lru) {
			copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
					page);
			list_del(&page->lru);
			unlock_page(page);
			page_ref_unfreeze(page, 1);
			page->mapping = NULL;
			ClearPageActive(page);
			ClearPageUnevictable(page);
			put_page(page);
		}

		local_irq_save(flags);
		__inc_node_page_state(new_page, NR_SHMEM_THPS);
		if (nr_none) {
			__mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
			__mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
		}
		local_irq_restore(flags);

		/*
		 * Remove pte page tables, so we can re-faulti
		 * the page as huge.
		 */
		retract_page_tables(mapping, start);

		/* Everything is ready, let's unfreeze the new_page */
		set_page_dirty(new_page);
		SetPageUptodate(new_page);
		page_ref_unfreeze(new_page, HPAGE_PMD_NR);
		mem_cgroup_commit_charge(new_page, memcg, false, true);
		lru_cache_add_anon(new_page);
		unlock_page(new_page);

		*hpage = NULL;
	} else {
		/* Something went wrong: rollback changes to the radix-tree */
		shmem_uncharge(mapping->host, nr_none);
		spin_lock_irq(&mapping->tree_lock);
		radix_tree_for_each_slot(slot, &mapping->page_tree, &iter,
				start) {
			if (iter.index >= end)
				break;
			page = list_first_entry_or_null(&pagelist,
					struct page, lru);
			if (!page || iter.index < page->index) {
				if (!nr_none)
					break;
				nr_none--;
				/* Put holes back where they were */
				radix_tree_delete(&mapping->page_tree,
						  iter.index);
				continue;
			}

			VM_BUG_ON_PAGE(page->index != iter.index, page);

			/* Unfreeze the page. */
			list_del(&page->lru);
			page_ref_unfreeze(page, 2);
			radix_tree_replace_slot(&mapping->page_tree,
						slot, page);
			slot = radix_tree_iter_resume(slot, &iter);
			spin_unlock_irq(&mapping->tree_lock);
			putback_lru_page(page);
			unlock_page(page);
			spin_lock_irq(&mapping->tree_lock);
		}
		VM_BUG_ON(nr_none);
		spin_unlock_irq(&mapping->tree_lock);

		/* Unfreeze new_page, caller would take care about freeing it */
		page_ref_unfreeze(new_page, 1);
		mem_cgroup_cancel_charge(new_page, memcg, true);
		unlock_page(new_page);
		new_page->mapping = NULL;
	}
out:
	VM_BUG_ON(!list_empty(&pagelist));
	/* TODO: tracepoints */
}

static void khugepaged_scan_shmem(struct mm_struct *mm,
		struct address_space *mapping,
		pgoff_t start, struct page **hpage)
{
	struct page *page = NULL;
	struct radix_tree_iter iter;
	void **slot;
	int present, swap;
	int node = NUMA_NO_NODE;
	int result = SCAN_SUCCEED;

	present = 0;
	swap = 0;
	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
	rcu_read_lock();
	radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
		if (iter.index >= start + HPAGE_PMD_NR)
			break;

		page = radix_tree_deref_slot(slot);
		if (radix_tree_deref_retry(page)) {
			slot = radix_tree_iter_retry(&iter);
			continue;
		}

		if (radix_tree_exception(page)) {
			if (++swap > khugepaged_max_ptes_swap) {
				result = SCAN_EXCEED_SWAP_PTE;
				break;
			}
			continue;
		}

		if (PageTransCompound(page)) {
			result = SCAN_PAGE_COMPOUND;
			break;
		}

		node = page_to_nid(page);
		if (khugepaged_scan_abort(node)) {
			result = SCAN_SCAN_ABORT;
			break;
		}
		khugepaged_node_load[node]++;

		if (!PageLRU(page)) {
			result = SCAN_PAGE_LRU;
			break;
		}

		if (page_count(page) != 1 + page_mapcount(page)) {
			result = SCAN_PAGE_COUNT;
			break;
		}

		/*
		 * We probably should check if the page is referenced here, but
		 * nobody would transfer pte_young() to PageReferenced() for us.
		 * And rmap walk here is just too costly...
		 */

		present++;

		if (need_resched()) {
			slot = radix_tree_iter_resume(slot, &iter);
			cond_resched_rcu();
		}
	}
	rcu_read_unlock();

	if (result == SCAN_SUCCEED) {
		if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
			result = SCAN_EXCEED_NONE_PTE;
		} else {
			node = khugepaged_find_target_node();
			collapse_shmem(mm, mapping, start, hpage, node);
		}
	}

	/* TODO: tracepoints */
}
#else
static void khugepaged_scan_shmem(struct mm_struct *mm,
		struct address_space *mapping,
		pgoff_t start, struct page **hpage)
{
	BUILD_BUG();
}
#endif

static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
					    struct page **hpage)
	__releases(&khugepaged_mm_lock)
	__acquires(&khugepaged_mm_lock)
{
	struct mm_slot *mm_slot;
	struct mm_struct *mm;
	struct vm_area_struct *vma;
	int progress = 0;

	VM_BUG_ON(!pages);
	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));

	if (khugepaged_scan.mm_slot)
		mm_slot = khugepaged_scan.mm_slot;
	else {
		mm_slot = list_entry(khugepaged_scan.mm_head.next,
				     struct mm_slot, mm_node);
		khugepaged_scan.address = 0;
		khugepaged_scan.mm_slot = mm_slot;
	}
	spin_unlock(&khugepaged_mm_lock);

	mm = mm_slot->mm;
	down_read(&mm->mmap_sem);
	if (unlikely(khugepaged_test_exit(mm)))
		vma = NULL;
	else
		vma = find_vma(mm, khugepaged_scan.address);

	progress++;
	for (; vma; vma = vma->vm_next) {
		unsigned long hstart, hend;

		cond_resched();
		if (unlikely(khugepaged_test_exit(mm))) {
			progress++;
			break;
		}
		if (!hugepage_vma_check(vma)) {
skip:
			progress++;
			continue;
		}
		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
		hend = vma->vm_end & HPAGE_PMD_MASK;
		if (hstart >= hend)
			goto skip;
		if (khugepaged_scan.address > hend)
			goto skip;
		if (khugepaged_scan.address < hstart)
			khugepaged_scan.address = hstart;
		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);

		while (khugepaged_scan.address < hend) {
			int ret;
			cond_resched();
			if (unlikely(khugepaged_test_exit(mm)))
				goto breakouterloop;

			VM_BUG_ON(khugepaged_scan.address < hstart ||
				  khugepaged_scan.address + HPAGE_PMD_SIZE >
				  hend);
			if (shmem_file(vma->vm_file)) {
				struct file *file;
				pgoff_t pgoff = linear_page_index(vma,
						khugepaged_scan.address);
				if (!shmem_huge_enabled(vma))
					goto skip;
				file = get_file(vma->vm_file);
				up_read(&mm->mmap_sem);
				ret = 1;
				khugepaged_scan_shmem(mm, file->f_mapping,
						pgoff, hpage);
				fput(file);
			} else {
				ret = khugepaged_scan_pmd(mm, vma,
						khugepaged_scan.address,
						hpage);
			}
			/* move to next address */
			khugepaged_scan.address += HPAGE_PMD_SIZE;
			progress += HPAGE_PMD_NR;
			if (ret)
				/* we released mmap_sem so break loop */
				goto breakouterloop_mmap_sem;
			if (progress >= pages)
				goto breakouterloop;
		}
	}
breakouterloop:
	up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
breakouterloop_mmap_sem:

	spin_lock(&khugepaged_mm_lock);
	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
	/*
	 * Release the current mm_slot if this mm is about to die, or
	 * if we scanned all vmas of this mm.
	 */
	if (khugepaged_test_exit(mm) || !vma) {
		/*
		 * Make sure that if mm_users is reaching zero while
		 * khugepaged runs here, khugepaged_exit will find
		 * mm_slot not pointing to the exiting mm.
		 */
		if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
			khugepaged_scan.mm_slot = list_entry(
				mm_slot->mm_node.next,
				struct mm_slot, mm_node);
			khugepaged_scan.address = 0;
		} else {
			khugepaged_scan.mm_slot = NULL;
			khugepaged_full_scans++;
		}

		collect_mm_slot(mm_slot);
	}

	return progress;
}

static int khugepaged_has_work(void)
{
	return !list_empty(&khugepaged_scan.mm_head) &&
		khugepaged_enabled();
}

static int khugepaged_wait_event(void)
{
	return !list_empty(&khugepaged_scan.mm_head) ||
		kthread_should_stop();
}

static void khugepaged_do_scan(void)
{
	struct page *hpage = NULL;
	unsigned int progress = 0, pass_through_head = 0;
	unsigned int pages = khugepaged_pages_to_scan;
	bool wait = true;

	barrier(); /* write khugepaged_pages_to_scan to local stack */

	while (progress < pages) {
		if (!khugepaged_prealloc_page(&hpage, &wait))
			break;

		cond_resched();

		if (unlikely(kthread_should_stop() || try_to_freeze()))
			break;

		spin_lock(&khugepaged_mm_lock);
		if (!khugepaged_scan.mm_slot)
			pass_through_head++;
		if (khugepaged_has_work() &&
		    pass_through_head < 2)
			progress += khugepaged_scan_mm_slot(pages - progress,
							    &hpage);
		else
			progress = pages;
		spin_unlock(&khugepaged_mm_lock);
	}

	if (!IS_ERR_OR_NULL(hpage))
		put_page(hpage);
}

static bool khugepaged_should_wakeup(void)
{
	return kthread_should_stop() ||
	       time_after_eq(jiffies, khugepaged_sleep_expire);
}

static void khugepaged_wait_work(void)
{
	if (khugepaged_has_work()) {
		const unsigned long scan_sleep_jiffies =
			msecs_to_jiffies(khugepaged_scan_sleep_millisecs);

		if (!scan_sleep_jiffies)
			return;

		khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
		wait_event_freezable_timeout(khugepaged_wait,
					     khugepaged_should_wakeup(),
					     scan_sleep_jiffies);
		return;
	}

	if (khugepaged_enabled())
		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
}

static int khugepaged(void *none)
{
	struct mm_slot *mm_slot;

	set_freezable();
	set_user_nice(current, MAX_NICE);

	while (!kthread_should_stop()) {
		khugepaged_do_scan();
		khugepaged_wait_work();
	}

	spin_lock(&khugepaged_mm_lock);
	mm_slot = khugepaged_scan.mm_slot;
	khugepaged_scan.mm_slot = NULL;
	if (mm_slot)
		collect_mm_slot(mm_slot);
	spin_unlock(&khugepaged_mm_lock);
	return 0;
}

static void set_recommended_min_free_kbytes(void)
{
	struct zone *zone;
	int nr_zones = 0;
	unsigned long recommended_min;

	for_each_populated_zone(zone)
		nr_zones++;

	/* Ensure 2 pageblocks are free to assist fragmentation avoidance */
	recommended_min = pageblock_nr_pages * nr_zones * 2;

	/*
	 * Make sure that on average at least two pageblocks are almost free
	 * of another type, one for a migratetype to fall back to and a
	 * second to avoid subsequent fallbacks of other types There are 3
	 * MIGRATE_TYPES we care about.
	 */
	recommended_min += pageblock_nr_pages * nr_zones *
			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;

	/* don't ever allow to reserve more than 5% of the lowmem */
	recommended_min = min(recommended_min,
			      (unsigned long) nr_free_buffer_pages() / 20);
	recommended_min <<= (PAGE_SHIFT-10);

	if (recommended_min > min_free_kbytes) {
		if (user_min_free_kbytes >= 0)
			pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
				min_free_kbytes, recommended_min);

		min_free_kbytes = recommended_min;
	}
	setup_per_zone_wmarks();
}

int start_stop_khugepaged(void)
{
	static struct task_struct *khugepaged_thread __read_mostly;
	static DEFINE_MUTEX(khugepaged_mutex);
	int err = 0;

	mutex_lock(&khugepaged_mutex);
	if (khugepaged_enabled()) {
		if (!khugepaged_thread)
			khugepaged_thread = kthread_run(khugepaged, NULL,
							"khugepaged");
		if (IS_ERR(khugepaged_thread)) {
			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
			err = PTR_ERR(khugepaged_thread);
			khugepaged_thread = NULL;
			goto fail;
		}

		if (!list_empty(&khugepaged_scan.mm_head))
			wake_up_interruptible(&khugepaged_wait);

		set_recommended_min_free_kbytes();
	} else if (khugepaged_thread) {
		kthread_stop(khugepaged_thread);
		khugepaged_thread = NULL;
	}
fail:
	mutex_unlock(&khugepaged_mutex);
	return err;
}