summaryrefslogtreecommitdiff
path: root/mm/swapfile.c
blob: 0789a762ce2f49add4f8823c38ba366d88bda9e1 (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
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/swapfile.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 */

#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/shmem_fs.h>
#include <linux/blkdev.h>
#include <linux/random.h>
#include <linux/writeback.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/init.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/security.h>
#include <linux/backing-dev.h>
#include <linux/mutex.h>
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/memcontrol.h>
#include <linux/poll.h>
#include <linux/oom.h>
#include <linux/frontswap.h>
#include <linux/swapfile.h>
#include <linux/export.h>
#include <linux/swap_slots.h>
#include <linux/sort.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <linux/swapops.h>
#include <linux/swap_cgroup.h>

static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
				 unsigned char);
static void free_swap_count_continuations(struct swap_info_struct *);
static sector_t map_swap_entry(swp_entry_t, struct block_device**);

DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
atomic_long_t nr_swap_pages;
/*
 * Some modules use swappable objects and may try to swap them out under
 * memory pressure (via the shrinker). Before doing so, they may wish to
 * check to see if any swap space is available.
 */
EXPORT_SYMBOL_GPL(nr_swap_pages);
/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
long total_swap_pages;
static int least_priority = -1;

static const char Bad_file[] = "Bad swap file entry ";
static const char Unused_file[] = "Unused swap file entry ";
static const char Bad_offset[] = "Bad swap offset entry ";
static const char Unused_offset[] = "Unused swap offset entry ";

/*
 * all active swap_info_structs
 * protected with swap_lock, and ordered by priority.
 */
PLIST_HEAD(swap_active_head);

/*
 * all available (active, not full) swap_info_structs
 * protected with swap_avail_lock, ordered by priority.
 * This is used by get_swap_page() instead of swap_active_head
 * because swap_active_head includes all swap_info_structs,
 * but get_swap_page() doesn't need to look at full ones.
 * This uses its own lock instead of swap_lock because when a
 * swap_info_struct changes between not-full/full, it needs to
 * add/remove itself to/from this list, but the swap_info_struct->lock
 * is held and the locking order requires swap_lock to be taken
 * before any swap_info_struct->lock.
 */
static struct plist_head *swap_avail_heads;
static DEFINE_SPINLOCK(swap_avail_lock);

struct swap_info_struct *swap_info[MAX_SWAPFILES];

static DEFINE_MUTEX(swapon_mutex);

static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
/* Activity counter to indicate that a swapon or swapoff has occurred */
static atomic_t proc_poll_event = ATOMIC_INIT(0);

atomic_t nr_rotate_swap = ATOMIC_INIT(0);

static struct swap_info_struct *swap_type_to_swap_info(int type)
{
	if (type >= READ_ONCE(nr_swapfiles))
		return NULL;

	smp_rmb();	/* Pairs with smp_wmb in alloc_swap_info. */
	return READ_ONCE(swap_info[type]);
}

static inline unsigned char swap_count(unsigned char ent)
{
	return ent & ~SWAP_HAS_CACHE;	/* may include COUNT_CONTINUED flag */
}

/* Reclaim the swap entry anyway if possible */
#define TTRS_ANYWAY		0x1
/*
 * Reclaim the swap entry if there are no more mappings of the
 * corresponding page
 */
#define TTRS_UNMAPPED		0x2
/* Reclaim the swap entry if swap is getting full*/
#define TTRS_FULL		0x4

/* returns 1 if swap entry is freed */
static int __try_to_reclaim_swap(struct swap_info_struct *si,
				 unsigned long offset, unsigned long flags)
{
	swp_entry_t entry = swp_entry(si->type, offset);
	struct page *page;
	int ret = 0;

	page = find_get_page(swap_address_space(entry), offset);
	if (!page)
		return 0;
	/*
	 * When this function is called from scan_swap_map_slots() and it's
	 * called by vmscan.c at reclaiming pages. So, we hold a lock on a page,
	 * here. We have to use trylock for avoiding deadlock. This is a special
	 * case and you should use try_to_free_swap() with explicit lock_page()
	 * in usual operations.
	 */
	if (trylock_page(page)) {
		if ((flags & TTRS_ANYWAY) ||
		    ((flags & TTRS_UNMAPPED) && !page_mapped(page)) ||
		    ((flags & TTRS_FULL) && mem_cgroup_swap_full(page)))
			ret = try_to_free_swap(page);
		unlock_page(page);
	}
	put_page(page);
	return ret;
}

static inline struct swap_extent *first_se(struct swap_info_struct *sis)
{
	struct rb_node *rb = rb_first(&sis->swap_extent_root);
	return rb_entry(rb, struct swap_extent, rb_node);
}

static inline struct swap_extent *next_se(struct swap_extent *se)
{
	struct rb_node *rb = rb_next(&se->rb_node);
	return rb ? rb_entry(rb, struct swap_extent, rb_node) : NULL;
}

/*
 * swapon tell device that all the old swap contents can be discarded,
 * to allow the swap device to optimize its wear-levelling.
 */
static int discard_swap(struct swap_info_struct *si)
{
	struct swap_extent *se;
	sector_t start_block;
	sector_t nr_blocks;
	int err = 0;

	/* Do not discard the swap header page! */
	se = first_se(si);
	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
	if (nr_blocks) {
		err = blkdev_issue_discard(si->bdev, start_block,
				nr_blocks, GFP_KERNEL, 0);
		if (err)
			return err;
		cond_resched();
	}

	for (se = next_se(se); se; se = next_se(se)) {
		start_block = se->start_block << (PAGE_SHIFT - 9);
		nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);

		err = blkdev_issue_discard(si->bdev, start_block,
				nr_blocks, GFP_KERNEL, 0);
		if (err)
			break;

		cond_resched();
	}
	return err;		/* That will often be -EOPNOTSUPP */
}

static struct swap_extent *
offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset)
{
	struct swap_extent *se;
	struct rb_node *rb;

	rb = sis->swap_extent_root.rb_node;
	while (rb) {
		se = rb_entry(rb, struct swap_extent, rb_node);
		if (offset < se->start_page)
			rb = rb->rb_left;
		else if (offset >= se->start_page + se->nr_pages)
			rb = rb->rb_right;
		else
			return se;
	}
	/* It *must* be present */
	BUG();
}

/*
 * swap allocation tell device that a cluster of swap can now be discarded,
 * to allow the swap device to optimize its wear-levelling.
 */
static void discard_swap_cluster(struct swap_info_struct *si,
				 pgoff_t start_page, pgoff_t nr_pages)
{
	struct swap_extent *se = offset_to_swap_extent(si, start_page);

	while (nr_pages) {
		pgoff_t offset = start_page - se->start_page;
		sector_t start_block = se->start_block + offset;
		sector_t nr_blocks = se->nr_pages - offset;

		if (nr_blocks > nr_pages)
			nr_blocks = nr_pages;
		start_page += nr_blocks;
		nr_pages -= nr_blocks;

		start_block <<= PAGE_SHIFT - 9;
		nr_blocks <<= PAGE_SHIFT - 9;
		if (blkdev_issue_discard(si->bdev, start_block,
					nr_blocks, GFP_NOIO, 0))
			break;

		se = next_se(se);
	}
}

#ifdef CONFIG_THP_SWAP
#define SWAPFILE_CLUSTER	HPAGE_PMD_NR

#define swap_entry_size(size)	(size)
#else
#define SWAPFILE_CLUSTER	256

/*
 * Define swap_entry_size() as constant to let compiler to optimize
 * out some code if !CONFIG_THP_SWAP
 */
#define swap_entry_size(size)	1
#endif
#define LATENCY_LIMIT		256

static inline void cluster_set_flag(struct swap_cluster_info *info,
	unsigned int flag)
{
	info->flags = flag;
}

static inline unsigned int cluster_count(struct swap_cluster_info *info)
{
	return info->data;
}

static inline void cluster_set_count(struct swap_cluster_info *info,
				     unsigned int c)
{
	info->data = c;
}

static inline void cluster_set_count_flag(struct swap_cluster_info *info,
					 unsigned int c, unsigned int f)
{
	info->flags = f;
	info->data = c;
}

static inline unsigned int cluster_next(struct swap_cluster_info *info)
{
	return info->data;
}

static inline void cluster_set_next(struct swap_cluster_info *info,
				    unsigned int n)
{
	info->data = n;
}

static inline void cluster_set_next_flag(struct swap_cluster_info *info,
					 unsigned int n, unsigned int f)
{
	info->flags = f;
	info->data = n;
}

static inline bool cluster_is_free(struct swap_cluster_info *info)
{
	return info->flags & CLUSTER_FLAG_FREE;
}

static inline bool cluster_is_null(struct swap_cluster_info *info)
{
	return info->flags & CLUSTER_FLAG_NEXT_NULL;
}

static inline void cluster_set_null(struct swap_cluster_info *info)
{
	info->flags = CLUSTER_FLAG_NEXT_NULL;
	info->data = 0;
}

static inline bool cluster_is_huge(struct swap_cluster_info *info)
{
	if (IS_ENABLED(CONFIG_THP_SWAP))
		return info->flags & CLUSTER_FLAG_HUGE;
	return false;
}

static inline void cluster_clear_huge(struct swap_cluster_info *info)
{
	info->flags &= ~CLUSTER_FLAG_HUGE;
}

static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
						     unsigned long offset)
{
	struct swap_cluster_info *ci;

	ci = si->cluster_info;
	if (ci) {
		ci += offset / SWAPFILE_CLUSTER;
		spin_lock(&ci->lock);
	}
	return ci;
}

static inline void unlock_cluster(struct swap_cluster_info *ci)
{
	if (ci)
		spin_unlock(&ci->lock);
}

/*
 * Determine the locking method in use for this device.  Return
 * swap_cluster_info if SSD-style cluster-based locking is in place.
 */
static inline struct swap_cluster_info *lock_cluster_or_swap_info(
		struct swap_info_struct *si, unsigned long offset)
{
	struct swap_cluster_info *ci;

	/* Try to use fine-grained SSD-style locking if available: */
	ci = lock_cluster(si, offset);
	/* Otherwise, fall back to traditional, coarse locking: */
	if (!ci)
		spin_lock(&si->lock);

	return ci;
}

static inline void unlock_cluster_or_swap_info(struct swap_info_struct *si,
					       struct swap_cluster_info *ci)
{
	if (ci)
		unlock_cluster(ci);
	else
		spin_unlock(&si->lock);
}

static inline bool cluster_list_empty(struct swap_cluster_list *list)
{
	return cluster_is_null(&list->head);
}

static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
{
	return cluster_next(&list->head);
}

static void cluster_list_init(struct swap_cluster_list *list)
{
	cluster_set_null(&list->head);
	cluster_set_null(&list->tail);
}

static void cluster_list_add_tail(struct swap_cluster_list *list,
				  struct swap_cluster_info *ci,
				  unsigned int idx)
{
	if (cluster_list_empty(list)) {
		cluster_set_next_flag(&list->head, idx, 0);
		cluster_set_next_flag(&list->tail, idx, 0);
	} else {
		struct swap_cluster_info *ci_tail;
		unsigned int tail = cluster_next(&list->tail);

		/*
		 * Nested cluster lock, but both cluster locks are
		 * only acquired when we held swap_info_struct->lock
		 */
		ci_tail = ci + tail;
		spin_lock_nested(&ci_tail->lock, SINGLE_DEPTH_NESTING);
		cluster_set_next(ci_tail, idx);
		spin_unlock(&ci_tail->lock);
		cluster_set_next_flag(&list->tail, idx, 0);
	}
}

static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
					   struct swap_cluster_info *ci)
{
	unsigned int idx;

	idx = cluster_next(&list->head);
	if (cluster_next(&list->tail) == idx) {
		cluster_set_null(&list->head);
		cluster_set_null(&list->tail);
	} else
		cluster_set_next_flag(&list->head,
				      cluster_next(&ci[idx]), 0);

	return idx;
}

/* Add a cluster to discard list and schedule it to do discard */
static void swap_cluster_schedule_discard(struct swap_info_struct *si,
		unsigned int idx)
{
	/*
	 * If scan_swap_map() can't find a free cluster, it will check
	 * si->swap_map directly. To make sure the discarding cluster isn't
	 * taken by scan_swap_map(), mark the swap entries bad (occupied). It
	 * will be cleared after discard
	 */
	memset(si->swap_map + idx * SWAPFILE_CLUSTER,
			SWAP_MAP_BAD, SWAPFILE_CLUSTER);

	cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);

	schedule_work(&si->discard_work);
}

static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
{
	struct swap_cluster_info *ci = si->cluster_info;

	cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
	cluster_list_add_tail(&si->free_clusters, ci, idx);
}

/*
 * Doing discard actually. After a cluster discard is finished, the cluster
 * will be added to free cluster list. caller should hold si->lock.
*/
static void swap_do_scheduled_discard(struct swap_info_struct *si)
{
	struct swap_cluster_info *info, *ci;
	unsigned int idx;

	info = si->cluster_info;

	while (!cluster_list_empty(&si->discard_clusters)) {
		idx = cluster_list_del_first(&si->discard_clusters, info);
		spin_unlock(&si->lock);

		discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
				SWAPFILE_CLUSTER);

		spin_lock(&si->lock);
		ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
		__free_cluster(si, idx);
		memset(si->swap_map + idx * SWAPFILE_CLUSTER,
				0, SWAPFILE_CLUSTER);
		unlock_cluster(ci);
	}
}

static void swap_discard_work(struct work_struct *work)
{
	struct swap_info_struct *si;

	si = container_of(work, struct swap_info_struct, discard_work);

	spin_lock(&si->lock);
	swap_do_scheduled_discard(si);
	spin_unlock(&si->lock);
}

static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
{
	struct swap_cluster_info *ci = si->cluster_info;

	VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
	cluster_list_del_first(&si->free_clusters, ci);
	cluster_set_count_flag(ci + idx, 0, 0);
}

static void free_cluster(struct swap_info_struct *si, unsigned long idx)
{
	struct swap_cluster_info *ci = si->cluster_info + idx;

	VM_BUG_ON(cluster_count(ci) != 0);
	/*
	 * If the swap is discardable, prepare discard the cluster
	 * instead of free it immediately. The cluster will be freed
	 * after discard.
	 */
	if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
	    (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
		swap_cluster_schedule_discard(si, idx);
		return;
	}

	__free_cluster(si, idx);
}

/*
 * The cluster corresponding to page_nr will be used. The cluster will be
 * removed from free cluster list and its usage counter will be increased.
 */
static void inc_cluster_info_page(struct swap_info_struct *p,
	struct swap_cluster_info *cluster_info, unsigned long page_nr)
{
	unsigned long idx = page_nr / SWAPFILE_CLUSTER;

	if (!cluster_info)
		return;
	if (cluster_is_free(&cluster_info[idx]))
		alloc_cluster(p, idx);

	VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
	cluster_set_count(&cluster_info[idx],
		cluster_count(&cluster_info[idx]) + 1);
}

/*
 * The cluster corresponding to page_nr decreases one usage. If the usage
 * counter becomes 0, which means no page in the cluster is in using, we can
 * optionally discard the cluster and add it to free cluster list.
 */
static void dec_cluster_info_page(struct swap_info_struct *p,
	struct swap_cluster_info *cluster_info, unsigned long page_nr)
{
	unsigned long idx = page_nr / SWAPFILE_CLUSTER;

	if (!cluster_info)
		return;

	VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
	cluster_set_count(&cluster_info[idx],
		cluster_count(&cluster_info[idx]) - 1);

	if (cluster_count(&cluster_info[idx]) == 0)
		free_cluster(p, idx);
}

/*
 * It's possible scan_swap_map() uses a free cluster in the middle of free
 * cluster list. Avoiding such abuse to avoid list corruption.
 */
static bool
scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
	unsigned long offset)
{
	struct percpu_cluster *percpu_cluster;
	bool conflict;

	offset /= SWAPFILE_CLUSTER;
	conflict = !cluster_list_empty(&si->free_clusters) &&
		offset != cluster_list_first(&si->free_clusters) &&
		cluster_is_free(&si->cluster_info[offset]);

	if (!conflict)
		return false;

	percpu_cluster = this_cpu_ptr(si->percpu_cluster);
	cluster_set_null(&percpu_cluster->index);
	return true;
}

/*
 * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
 * might involve allocating a new cluster for current CPU too.
 */
static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
	unsigned long *offset, unsigned long *scan_base)
{
	struct percpu_cluster *cluster;
	struct swap_cluster_info *ci;
	bool found_free;
	unsigned long tmp, max;

new_cluster:
	cluster = this_cpu_ptr(si->percpu_cluster);
	if (cluster_is_null(&cluster->index)) {
		if (!cluster_list_empty(&si->free_clusters)) {
			cluster->index = si->free_clusters.head;
			cluster->next = cluster_next(&cluster->index) *
					SWAPFILE_CLUSTER;
		} else if (!cluster_list_empty(&si->discard_clusters)) {
			/*
			 * we don't have free cluster but have some clusters in
			 * discarding, do discard now and reclaim them
			 */
			swap_do_scheduled_discard(si);
			*scan_base = *offset = si->cluster_next;
			goto new_cluster;
		} else
			return false;
	}

	found_free = false;

	/*
	 * Other CPUs can use our cluster if they can't find a free cluster,
	 * check if there is still free entry in the cluster
	 */
	tmp = cluster->next;
	max = min_t(unsigned long, si->max,
		    (cluster_next(&cluster->index) + 1) * SWAPFILE_CLUSTER);
	if (tmp >= max) {
		cluster_set_null(&cluster->index);
		goto new_cluster;
	}
	ci = lock_cluster(si, tmp);
	while (tmp < max) {
		if (!si->swap_map[tmp]) {
			found_free = true;
			break;
		}
		tmp++;
	}
	unlock_cluster(ci);
	if (!found_free) {
		cluster_set_null(&cluster->index);
		goto new_cluster;
	}
	cluster->next = tmp + 1;
	*offset = tmp;
	*scan_base = tmp;
	return found_free;
}

static void __del_from_avail_list(struct swap_info_struct *p)
{
	int nid;

	for_each_node(nid)
		plist_del(&p->avail_lists[nid], &swap_avail_heads[nid]);
}

static void del_from_avail_list(struct swap_info_struct *p)
{
	spin_lock(&swap_avail_lock);
	__del_from_avail_list(p);
	spin_unlock(&swap_avail_lock);
}

static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
			     unsigned int nr_entries)
{
	unsigned int end = offset + nr_entries - 1;

	if (offset == si->lowest_bit)
		si->lowest_bit += nr_entries;
	if (end == si->highest_bit)
		si->highest_bit -= nr_entries;
	si->inuse_pages += nr_entries;
	if (si->inuse_pages == si->pages) {
		si->lowest_bit = si->max;
		si->highest_bit = 0;
		del_from_avail_list(si);
	}
}

static void add_to_avail_list(struct swap_info_struct *p)
{
	int nid;

	spin_lock(&swap_avail_lock);
	for_each_node(nid) {
		WARN_ON(!plist_node_empty(&p->avail_lists[nid]));
		plist_add(&p->avail_lists[nid], &swap_avail_heads[nid]);
	}
	spin_unlock(&swap_avail_lock);
}

static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
			    unsigned int nr_entries)
{
	unsigned long end = offset + nr_entries - 1;
	void (*swap_slot_free_notify)(struct block_device *, unsigned long);

	if (offset < si->lowest_bit)
		si->lowest_bit = offset;
	if (end > si->highest_bit) {
		bool was_full = !si->highest_bit;

		si->highest_bit = end;
		if (was_full && (si->flags & SWP_WRITEOK))
			add_to_avail_list(si);
	}
	atomic_long_add(nr_entries, &nr_swap_pages);
	si->inuse_pages -= nr_entries;
	if (si->flags & SWP_BLKDEV)
		swap_slot_free_notify =
			si->bdev->bd_disk->fops->swap_slot_free_notify;
	else
		swap_slot_free_notify = NULL;
	while (offset <= end) {
		frontswap_invalidate_page(si->type, offset);
		if (swap_slot_free_notify)
			swap_slot_free_notify(si->bdev, offset);
		offset++;
	}
}

static int scan_swap_map_slots(struct swap_info_struct *si,
			       unsigned char usage, int nr,
			       swp_entry_t slots[])
{
	struct swap_cluster_info *ci;
	unsigned long offset;
	unsigned long scan_base;
	unsigned long last_in_cluster = 0;
	int latency_ration = LATENCY_LIMIT;
	int n_ret = 0;

	if (nr > SWAP_BATCH)
		nr = SWAP_BATCH;

	/*
	 * We try to cluster swap pages by allocating them sequentially
	 * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
	 * way, however, we resort to first-free allocation, starting
	 * a new cluster.  This prevents us from scattering swap pages
	 * all over the entire swap partition, so that we reduce
	 * overall disk seek times between swap pages.  -- sct
	 * But we do now try to find an empty cluster.  -Andrea
	 * And we let swap pages go all over an SSD partition.  Hugh
	 */

	si->flags += SWP_SCANNING;
	scan_base = offset = si->cluster_next;

	/* SSD algorithm */
	if (si->cluster_info) {
		if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base))
			goto checks;
		else
			goto scan;
	}

	if (unlikely(!si->cluster_nr--)) {
		if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
			si->cluster_nr = SWAPFILE_CLUSTER - 1;
			goto checks;
		}

		spin_unlock(&si->lock);

		/*
		 * If seek is expensive, start searching for new cluster from
		 * start of partition, to minimize the span of allocated swap.
		 * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
		 * case, just handled by scan_swap_map_try_ssd_cluster() above.
		 */
		scan_base = offset = si->lowest_bit;
		last_in_cluster = offset + SWAPFILE_CLUSTER - 1;

		/* Locate the first empty (unaligned) cluster */
		for (; last_in_cluster <= si->highest_bit; offset++) {
			if (si->swap_map[offset])
				last_in_cluster = offset + SWAPFILE_CLUSTER;
			else if (offset == last_in_cluster) {
				spin_lock(&si->lock);
				offset -= SWAPFILE_CLUSTER - 1;
				si->cluster_next = offset;
				si->cluster_nr = SWAPFILE_CLUSTER - 1;
				goto checks;
			}
			if (unlikely(--latency_ration < 0)) {
				cond_resched();
				latency_ration = LATENCY_LIMIT;
			}
		}

		offset = scan_base;
		spin_lock(&si->lock);
		si->cluster_nr = SWAPFILE_CLUSTER - 1;
	}

checks:
	if (si->cluster_info) {
		while (scan_swap_map_ssd_cluster_conflict(si, offset)) {
		/* take a break if we already got some slots */
			if (n_ret)
				goto done;
			if (!scan_swap_map_try_ssd_cluster(si, &offset,
							&scan_base))
				goto scan;
		}
	}
	if (!(si->flags & SWP_WRITEOK))
		goto no_page;
	if (!si->highest_bit)
		goto no_page;
	if (offset > si->highest_bit)
		scan_base = offset = si->lowest_bit;

	ci = lock_cluster(si, offset);
	/* reuse swap entry of cache-only swap if not busy. */
	if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
		int swap_was_freed;
		unlock_cluster(ci);
		spin_unlock(&si->lock);
		swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
		spin_lock(&si->lock);
		/* entry was freed successfully, try to use this again */
		if (swap_was_freed)
			goto checks;
		goto scan; /* check next one */
	}

	if (si->swap_map[offset]) {
		unlock_cluster(ci);
		if (!n_ret)
			goto scan;
		else
			goto done;
	}
	si->swap_map[offset] = usage;
	inc_cluster_info_page(si, si->cluster_info, offset);
	unlock_cluster(ci);

	swap_range_alloc(si, offset, 1);
	si->cluster_next = offset + 1;
	slots[n_ret++] = swp_entry(si->type, offset);

	/* got enough slots or reach max slots? */
	if ((n_ret == nr) || (offset >= si->highest_bit))
		goto done;

	/* search for next available slot */

	/* time to take a break? */
	if (unlikely(--latency_ration < 0)) {
		if (n_ret)
			goto done;
		spin_unlock(&si->lock);
		cond_resched();
		spin_lock(&si->lock);
		latency_ration = LATENCY_LIMIT;
	}

	/* try to get more slots in cluster */
	if (si->cluster_info) {
		if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base))
			goto checks;
		else
			goto done;
	}
	/* non-ssd case */
	++offset;

	/* non-ssd case, still more slots in cluster? */
	if (si->cluster_nr && !si->swap_map[offset]) {
		--si->cluster_nr;
		goto checks;
	}

done:
	si->flags -= SWP_SCANNING;
	return n_ret;

scan:
	spin_unlock(&si->lock);
	while (++offset <= si->highest_bit) {
		if (!si->swap_map[offset]) {
			spin_lock(&si->lock);
			goto checks;
		}
		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
			spin_lock(&si->lock);
			goto checks;
		}
		if (unlikely(--latency_ration < 0)) {
			cond_resched();
			latency_ration = LATENCY_LIMIT;
		}
	}
	offset = si->lowest_bit;
	while (offset < scan_base) {
		if (!si->swap_map[offset]) {
			spin_lock(&si->lock);
			goto checks;
		}
		if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
			spin_lock(&si->lock);
			goto checks;
		}
		if (unlikely(--latency_ration < 0)) {
			cond_resched();
			latency_ration = LATENCY_LIMIT;
		}
		offset++;
	}
	spin_lock(&si->lock);

no_page:
	si->flags -= SWP_SCANNING;
	return n_ret;
}

static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
{
	unsigned long idx;
	struct swap_cluster_info *ci;
	unsigned long offset, i;
	unsigned char *map;

	/*
	 * Should not even be attempting cluster allocations when huge
	 * page swap is disabled.  Warn and fail the allocation.
	 */
	if (!IS_ENABLED(CONFIG_THP_SWAP)) {
		VM_WARN_ON_ONCE(1);
		return 0;
	}

	if (cluster_list_empty(&si->free_clusters))
		return 0;

	idx = cluster_list_first(&si->free_clusters);
	offset = idx * SWAPFILE_CLUSTER;
	ci = lock_cluster(si, offset);
	alloc_cluster(si, idx);
	cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE);

	map = si->swap_map + offset;
	for (i = 0; i < SWAPFILE_CLUSTER; i++)
		map[i] = SWAP_HAS_CACHE;
	unlock_cluster(ci);
	swap_range_alloc(si, offset, SWAPFILE_CLUSTER);
	*slot = swp_entry(si->type, offset);

	return 1;
}

static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
{
	unsigned long offset = idx * SWAPFILE_CLUSTER;
	struct swap_cluster_info *ci;

	ci = lock_cluster(si, offset);
	memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER);
	cluster_set_count_flag(ci, 0, 0);
	free_cluster(si, idx);
	unlock_cluster(ci);
	swap_range_free(si, offset, SWAPFILE_CLUSTER);
}

static unsigned long scan_swap_map(struct swap_info_struct *si,
				   unsigned char usage)
{
	swp_entry_t entry;
	int n_ret;

	n_ret = scan_swap_map_slots(si, usage, 1, &entry);

	if (n_ret)
		return swp_offset(entry);
	else
		return 0;

}

int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
{
	unsigned long size = swap_entry_size(entry_size);
	struct swap_info_struct *si, *next;
	long avail_pgs;
	int n_ret = 0;
	int node;

	/* Only single cluster request supported */
	WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER);

	avail_pgs = atomic_long_read(&nr_swap_pages) / size;
	if (avail_pgs <= 0)
		goto noswap;

	if (n_goal > SWAP_BATCH)
		n_goal = SWAP_BATCH;

	if (n_goal > avail_pgs)
		n_goal = avail_pgs;

	atomic_long_sub(n_goal * size, &nr_swap_pages);

	spin_lock(&swap_avail_lock);

start_over:
	node = numa_node_id();
	plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
		/* requeue si to after same-priority siblings */
		plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
		spin_unlock(&swap_avail_lock);
		spin_lock(&si->lock);
		if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
			spin_lock(&swap_avail_lock);
			if (plist_node_empty(&si->avail_lists[node])) {
				spin_unlock(&si->lock);
				goto nextsi;
			}
			WARN(!si->highest_bit,
			     "swap_info %d in list but !highest_bit\n",
			     si->type);
			WARN(!(si->flags & SWP_WRITEOK),
			     "swap_info %d in list but !SWP_WRITEOK\n",
			     si->type);
			__del_from_avail_list(si);
			spin_unlock(&si->lock);
			goto nextsi;
		}
		if (size == SWAPFILE_CLUSTER) {
			if (!(si->flags & SWP_FS))
				n_ret = swap_alloc_cluster(si, swp_entries);
		} else
			n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
						    n_goal, swp_entries);
		spin_unlock(&si->lock);
		if (n_ret || size == SWAPFILE_CLUSTER)
			goto check_out;
		pr_debug("scan_swap_map of si %d failed to find offset\n",
			si->type);

		spin_lock(&swap_avail_lock);
nextsi:
		/*
		 * if we got here, it's likely that si was almost full before,
		 * and since scan_swap_map() can drop the si->lock, multiple
		 * callers probably all tried to get a page from the same si
		 * and it filled up before we could get one; or, the si filled
		 * up between us dropping swap_avail_lock and taking si->lock.
		 * Since we dropped the swap_avail_lock, the swap_avail_head
		 * list may have been modified; so if next is still in the
		 * swap_avail_head list then try it, otherwise start over
		 * if we have not gotten any slots.
		 */
		if (plist_node_empty(&next->avail_lists[node]))
			goto start_over;
	}

	spin_unlock(&swap_avail_lock);

check_out:
	if (n_ret < n_goal)
		atomic_long_add((long)(n_goal - n_ret) * size,
				&nr_swap_pages);
noswap:
	return n_ret;
}

/* The only caller of this function is now suspend routine */
swp_entry_t get_swap_page_of_type(int type)
{
	struct swap_info_struct *si = swap_type_to_swap_info(type);
	pgoff_t offset;

	if (!si)
		goto fail;

	spin_lock(&si->lock);
	if (si->flags & SWP_WRITEOK) {
		atomic_long_dec(&nr_swap_pages);
		/* This is called for allocating swap entry, not cache */
		offset = scan_swap_map(si, 1);
		if (offset) {
			spin_unlock(&si->lock);
			return swp_entry(type, offset);
		}
		atomic_long_inc(&nr_swap_pages);
	}
	spin_unlock(&si->lock);
fail:
	return (swp_entry_t) {0};
}

static struct swap_info_struct *__swap_info_get(swp_entry_t entry)
{
	struct swap_info_struct *p;
	unsigned long offset;

	if (!entry.val)
		goto out;
	p = swp_swap_info(entry);
	if (!p)
		goto bad_nofile;
	if (!(p->flags & SWP_USED))
		goto bad_device;
	offset = swp_offset(entry);
	if (offset >= p->max)
		goto bad_offset;
	return p;

bad_offset:
	pr_err("swap_info_get: %s%08lx\n", Bad_offset, entry.val);
	goto out;
bad_device:
	pr_err("swap_info_get: %s%08lx\n", Unused_file, entry.val);
	goto out;
bad_nofile:
	pr_err("swap_info_get: %s%08lx\n", Bad_file, entry.val);
out:
	return NULL;
}

static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
{
	struct swap_info_struct *p;

	p = __swap_info_get(entry);
	if (!p)
		goto out;
	if (!p->swap_map[swp_offset(entry)])
		goto bad_free;
	return p;

bad_free:
	pr_err("swap_info_get: %s%08lx\n", Unused_offset, entry.val);
	goto out;
out:
	return NULL;
}

static struct swap_info_struct *swap_info_get(swp_entry_t entry)
{
	struct swap_info_struct *p;

	p = _swap_info_get(entry);
	if (p)
		spin_lock(&p->lock);
	return p;
}

static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
					struct swap_info_struct *q)
{
	struct swap_info_struct *p;

	p = _swap_info_get(entry);

	if (p != q) {
		if (q != NULL)
			spin_unlock(&q->lock);
		if (p != NULL)
			spin_lock(&p->lock);
	}
	return p;
}

static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
					      unsigned long offset,
					      unsigned char usage)
{
	unsigned char count;
	unsigned char has_cache;

	count = p->swap_map[offset];

	has_cache = count & SWAP_HAS_CACHE;
	count &= ~SWAP_HAS_CACHE;

	if (usage == SWAP_HAS_CACHE) {
		VM_BUG_ON(!has_cache);
		has_cache = 0;
	} else if (count == SWAP_MAP_SHMEM) {
		/*
		 * Or we could insist on shmem.c using a special
		 * swap_shmem_free() and free_shmem_swap_and_cache()...
		 */
		count = 0;
	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
		if (count == COUNT_CONTINUED) {
			if (swap_count_continued(p, offset, count))
				count = SWAP_MAP_MAX | COUNT_CONTINUED;
			else
				count = SWAP_MAP_MAX;
		} else
			count--;
	}

	usage = count | has_cache;
	p->swap_map[offset] = usage ? : SWAP_HAS_CACHE;

	return usage;
}

/*
 * Check whether swap entry is valid in the swap device.  If so,
 * return pointer to swap_info_struct, and keep the swap entry valid
 * via preventing the swap device from being swapoff, until
 * put_swap_device() is called.  Otherwise return NULL.
 *
 * The entirety of the RCU read critical section must come before the
 * return from or after the call to synchronize_rcu() in
 * enable_swap_info() or swapoff().  So if "si->flags & SWP_VALID" is
 * true, the si->map, si->cluster_info, etc. must be valid in the
 * critical section.
 *
 * Notice that swapoff or swapoff+swapon can still happen before the
 * rcu_read_lock() in get_swap_device() or after the rcu_read_unlock()
 * in put_swap_device() if there isn't any other way to prevent
 * swapoff, such as page lock, page table lock, etc.  The caller must
 * be prepared for that.  For example, the following situation is
 * possible.
 *
 *   CPU1				CPU2
 *   do_swap_page()
 *     ...				swapoff+swapon
 *     __read_swap_cache_async()
 *       swapcache_prepare()
 *         __swap_duplicate()
 *           // check swap_map
 *     // verify PTE not changed
 *
 * In __swap_duplicate(), the swap_map need to be checked before
 * changing partly because the specified swap entry may be for another
 * swap device which has been swapoff.  And in do_swap_page(), after
 * the page is read from the swap device, the PTE is verified not
 * changed with the page table locked to check whether the swap device
 * has been swapoff or swapoff+swapon.
 */
struct swap_info_struct *get_swap_device(swp_entry_t entry)
{
	struct swap_info_struct *si;
	unsigned long offset;

	if (!entry.val)
		goto out;
	si = swp_swap_info(entry);
	if (!si)
		goto bad_nofile;

	rcu_read_lock();
	if (!(si->flags & SWP_VALID))
		goto unlock_out;
	offset = swp_offset(entry);
	if (offset >= si->max)
		goto unlock_out;

	return si;
bad_nofile:
	pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
out:
	return NULL;
unlock_out:
	rcu_read_unlock();
	return NULL;
}

static unsigned char __swap_entry_free(struct swap_info_struct *p,
				       swp_entry_t entry, unsigned char usage)
{
	struct swap_cluster_info *ci;
	unsigned long offset = swp_offset(entry);

	ci = lock_cluster_or_swap_info(p, offset);
	usage = __swap_entry_free_locked(p, offset, usage);
	unlock_cluster_or_swap_info(p, ci);
	if (!usage)
		free_swap_slot(entry);

	return usage;
}

static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
{
	struct swap_cluster_info *ci;
	unsigned long offset = swp_offset(entry);
	unsigned char count;

	ci = lock_cluster(p, offset);
	count = p->swap_map[offset];
	VM_BUG_ON(count != SWAP_HAS_CACHE);
	p->swap_map[offset] = 0;
	dec_cluster_info_page(p, p->cluster_info, offset);
	unlock_cluster(ci);

	mem_cgroup_uncharge_swap(entry, 1);
	swap_range_free(p, offset, 1);
}

/*
 * Caller has made sure that the swap device corresponding to entry
 * is still around or has not been recycled.
 */
void swap_free(swp_entry_t entry)
{
	struct swap_info_struct *p;

	p = _swap_info_get(entry);
	if (p)
		__swap_entry_free(p, entry, 1);
}

/*
 * Called after dropping swapcache to decrease refcnt to swap entries.
 */
void put_swap_page(struct page *page, swp_entry_t entry)
{
	unsigned long offset = swp_offset(entry);
	unsigned long idx = offset / SWAPFILE_CLUSTER;
	struct swap_cluster_info *ci;
	struct swap_info_struct *si;
	unsigned char *map;
	unsigned int i, free_entries = 0;
	unsigned char val;
	int size = swap_entry_size(hpage_nr_pages(page));

	si = _swap_info_get(entry);
	if (!si)
		return;

	ci = lock_cluster_or_swap_info(si, offset);
	if (size == SWAPFILE_CLUSTER) {
		VM_BUG_ON(!cluster_is_huge(ci));
		map = si->swap_map + offset;
		for (i = 0; i < SWAPFILE_CLUSTER; i++) {
			val = map[i];
			VM_BUG_ON(!(val & SWAP_HAS_CACHE));
			if (val == SWAP_HAS_CACHE)
				free_entries++;
		}
		cluster_clear_huge(ci);
		if (free_entries == SWAPFILE_CLUSTER) {
			unlock_cluster_or_swap_info(si, ci);
			spin_lock(&si->lock);
			mem_cgroup_uncharge_swap(entry, SWAPFILE_CLUSTER);
			swap_free_cluster(si, idx);
			spin_unlock(&si->lock);
			return;
		}
	}
	for (i = 0; i < size; i++, entry.val++) {
		if (!__swap_entry_free_locked(si, offset + i, SWAP_HAS_CACHE)) {
			unlock_cluster_or_swap_info(si, ci);
			free_swap_slot(entry);
			if (i == size - 1)
				return;
			lock_cluster_or_swap_info(si, offset);
		}
	}
	unlock_cluster_or_swap_info(si, ci);
}

#ifdef CONFIG_THP_SWAP
int split_swap_cluster(swp_entry_t entry)
{
	struct swap_info_struct *si;
	struct swap_cluster_info *ci;
	unsigned long offset = swp_offset(entry);

	si = _swap_info_get(entry);
	if (!si)
		return -EBUSY;
	ci = lock_cluster(si, offset);
	cluster_clear_huge(ci);
	unlock_cluster(ci);
	return 0;
}
#endif

static int swp_entry_cmp(const void *ent1, const void *ent2)
{
	const swp_entry_t *e1 = ent1, *e2 = ent2;

	return (int)swp_type(*e1) - (int)swp_type(*e2);
}

void swapcache_free_entries(swp_entry_t *entries, int n)
{
	struct swap_info_struct *p, *prev;
	int i;

	if (n <= 0)
		return;

	prev = NULL;
	p = NULL;

	/*
	 * Sort swap entries by swap device, so each lock is only taken once.
	 * nr_swapfiles isn't absolutely correct, but the overhead of sort() is
	 * so low that it isn't necessary to optimize further.
	 */
	if (nr_swapfiles > 1)
		sort(entries, n, sizeof(entries[0]), swp_entry_cmp, NULL);
	for (i = 0; i < n; ++i) {
		p = swap_info_get_cont(entries[i], prev);
		if (p)
			swap_entry_free(p, entries[i]);
		prev = p;
	}
	if (p)
		spin_unlock(&p->lock);
}

/*
 * How many references to page are currently swapped out?
 * This does not give an exact answer when swap count is continued,
 * but does include the high COUNT_CONTINUED flag to allow for that.
 */
int page_swapcount(struct page *page)
{
	int count = 0;
	struct swap_info_struct *p;
	struct swap_cluster_info *ci;
	swp_entry_t entry;
	unsigned long offset;

	entry.val = page_private(page);
	p = _swap_info_get(entry);
	if (p) {
		offset = swp_offset(entry);
		ci = lock_cluster_or_swap_info(p, offset);
		count = swap_count(p->swap_map[offset]);
		unlock_cluster_or_swap_info(p, ci);
	}
	return count;
}

int __swap_count(swp_entry_t entry)
{
	struct swap_info_struct *si;
	pgoff_t offset = swp_offset(entry);
	int count = 0;

	si = get_swap_device(entry);
	if (si) {
		count = swap_count(si->swap_map[offset]);
		put_swap_device(si);
	}
	return count;
}

static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
{
	int count = 0;
	pgoff_t offset = swp_offset(entry);
	struct swap_cluster_info *ci;

	ci = lock_cluster_or_swap_info(si, offset);
	count = swap_count(si->swap_map[offset]);
	unlock_cluster_or_swap_info(si, ci);
	return count;
}

/*
 * How many references to @entry are currently swapped out?
 * This does not give an exact answer when swap count is continued,
 * but does include the high COUNT_CONTINUED flag to allow for that.
 */
int __swp_swapcount(swp_entry_t entry)
{
	int count = 0;
	struct swap_info_struct *si;

	si = get_swap_device(entry);
	if (si) {
		count = swap_swapcount(si, entry);
		put_swap_device(si);
	}
	return count;
}

/*
 * How many references to @entry are currently swapped out?
 * This considers COUNT_CONTINUED so it returns exact answer.
 */
int swp_swapcount(swp_entry_t entry)
{
	int count, tmp_count, n;
	struct swap_info_struct *p;
	struct swap_cluster_info *ci;
	struct page *page;
	pgoff_t offset;
	unsigned char *map;

	p = _swap_info_get(entry);
	if (!p)
		return 0;

	offset = swp_offset(entry);

	ci = lock_cluster_or_swap_info(p, offset);

	count = swap_count(p->swap_map[offset]);
	if (!(count & COUNT_CONTINUED))
		goto out;

	count &= ~COUNT_CONTINUED;
	n = SWAP_MAP_MAX + 1;

	page = vmalloc_to_page(p->swap_map + offset);
	offset &= ~PAGE_MASK;
	VM_BUG_ON(page_private(page) != SWP_CONTINUED);

	do {
		page = list_next_entry(page, lru);
		map = kmap_atomic(page);
		tmp_count = map[offset];
		kunmap_atomic(map);

		count += (tmp_count & ~COUNT_CONTINUED) * n;
		n *= (SWAP_CONT_MAX + 1);
	} while (tmp_count & COUNT_CONTINUED);
out:
	unlock_cluster_or_swap_info(p, ci);
	return count;
}

static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
					 swp_entry_t entry)
{
	struct swap_cluster_info *ci;
	unsigned char *map = si->swap_map;
	unsigned long roffset = swp_offset(entry);
	unsigned long offset = round_down(roffset, SWAPFILE_CLUSTER);
	int i;
	bool ret = false;

	ci = lock_cluster_or_swap_info(si, offset);
	if (!ci || !cluster_is_huge(ci)) {
		if (swap_count(map[roffset]))
			ret = true;
		goto unlock_out;
	}
	for (i = 0; i < SWAPFILE_CLUSTER; i++) {
		if (swap_count(map[offset + i])) {
			ret = true;
			break;
		}
	}
unlock_out:
	unlock_cluster_or_swap_info(si, ci);
	return ret;
}

static bool page_swapped(struct page *page)
{
	swp_entry_t entry;
	struct swap_info_struct *si;

	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page)))
		return page_swapcount(page) != 0;

	page = compound_head(page);
	entry.val = page_private(page);
	si = _swap_info_get(entry);
	if (si)
		return swap_page_trans_huge_swapped(si, entry);
	return false;
}

static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
					 int *total_swapcount)
{
	int i, map_swapcount, _total_mapcount, _total_swapcount;
	unsigned long offset = 0;
	struct swap_info_struct *si;
	struct swap_cluster_info *ci = NULL;
	unsigned char *map = NULL;
	int mapcount, swapcount = 0;

	/* hugetlbfs shouldn't call it */
	VM_BUG_ON_PAGE(PageHuge(page), page);

	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
		mapcount = page_trans_huge_mapcount(page, total_mapcount);
		if (PageSwapCache(page))
			swapcount = page_swapcount(page);
		if (total_swapcount)
			*total_swapcount = swapcount;
		return mapcount + swapcount;
	}

	page = compound_head(page);

	_total_mapcount = _total_swapcount = map_swapcount = 0;
	if (PageSwapCache(page)) {
		swp_entry_t entry;

		entry.val = page_private(page);
		si = _swap_info_get(entry);
		if (si) {
			map = si->swap_map;
			offset = swp_offset(entry);
		}
	}
	if (map)
		ci = lock_cluster(si, offset);
	for (i = 0; i < HPAGE_PMD_NR; i++) {
		mapcount = atomic_read(&page[i]._mapcount) + 1;
		_total_mapcount += mapcount;
		if (map) {
			swapcount = swap_count(map[offset + i]);
			_total_swapcount += swapcount;
		}
		map_swapcount = max(map_swapcount, mapcount + swapcount);
	}
	unlock_cluster(ci);
	if (PageDoubleMap(page)) {
		map_swapcount -= 1;
		_total_mapcount -= HPAGE_PMD_NR;
	}
	mapcount = compound_mapcount(page);
	map_swapcount += mapcount;
	_total_mapcount += mapcount;
	if (total_mapcount)
		*total_mapcount = _total_mapcount;
	if (total_swapcount)
		*total_swapcount = _total_swapcount;

	return map_swapcount;
}

/*
 * We can write to an anon page without COW if there are no other references
 * to it.  And as a side-effect, free up its swap: because the old content
 * on disk will never be read, and seeking back there to write new content
 * later would only waste time away from clustering.
 *
 * NOTE: total_map_swapcount should not be relied upon by the caller if
 * reuse_swap_page() returns false, but it may be always overwritten
 * (see the other implementation for CONFIG_SWAP=n).
 */
bool reuse_swap_page(struct page *page, int *total_map_swapcount)
{
	int count, total_mapcount, total_swapcount;

	VM_BUG_ON_PAGE(!PageLocked(page), page);
	if (unlikely(PageKsm(page)))
		return false;
	count = page_trans_huge_map_swapcount(page, &total_mapcount,
					      &total_swapcount);
	if (total_map_swapcount)
		*total_map_swapcount = total_mapcount + total_swapcount;
	if (count == 1 && PageSwapCache(page) &&
	    (likely(!PageTransCompound(page)) ||
	     /* The remaining swap count will be freed soon */
	     total_swapcount == page_swapcount(page))) {
		if (!PageWriteback(page)) {
			page = compound_head(page);
			delete_from_swap_cache(page);
			SetPageDirty(page);
		} else {
			swp_entry_t entry;
			struct swap_info_struct *p;

			entry.val = page_private(page);
			p = swap_info_get(entry);
			if (p->flags & SWP_STABLE_WRITES) {
				spin_unlock(&p->lock);
				return false;
			}
			spin_unlock(&p->lock);
		}
	}

	return count <= 1;
}

/*
 * If swap is getting full, or if there are no more mappings of this page,
 * then try_to_free_swap is called to free its swap space.
 */
int try_to_free_swap(struct page *page)
{
	VM_BUG_ON_PAGE(!PageLocked(page), page);

	if (!PageSwapCache(page))
		return 0;
	if (PageWriteback(page))
		return 0;
	if (page_swapped(page))
		return 0;

	/*
	 * Once hibernation has begun to create its image of memory,
	 * there's a danger that one of the calls to try_to_free_swap()
	 * - most probably a call from __try_to_reclaim_swap() while
	 * hibernation is allocating its own swap pages for the image,
	 * but conceivably even a call from memory reclaim - will free
	 * the swap from a page which has already been recorded in the
	 * image as a clean swapcache page, and then reuse its swap for
	 * another page of the image.  On waking from hibernation, the
	 * original page might be freed under memory pressure, then
	 * later read back in from swap, now with the wrong data.
	 *
	 * Hibernation suspends storage while it is writing the image
	 * to disk so check that here.
	 */
	if (pm_suspended_storage())
		return 0;

	page = compound_head(page);
	delete_from_swap_cache(page);
	SetPageDirty(page);
	return 1;
}

/*
 * Free the swap entry like above, but also try to
 * free the page cache entry if it is the last user.
 */
int free_swap_and_cache(swp_entry_t entry)
{
	struct swap_info_struct *p;
	unsigned char count;

	if (non_swap_entry(entry))
		return 1;

	p = _swap_info_get(entry);
	if (p) {
		count = __swap_entry_free(p, entry, 1);
		if (count == SWAP_HAS_CACHE &&
		    !swap_page_trans_huge_swapped(p, entry))
			__try_to_reclaim_swap(p, swp_offset(entry),
					      TTRS_UNMAPPED | TTRS_FULL);
	}
	return p != NULL;
}

#ifdef CONFIG_HIBERNATION
/*
 * Find the swap type that corresponds to given device (if any).
 *
 * @offset - number of the PAGE_SIZE-sized block of the device, starting
 * from 0, in which the swap header is expected to be located.
 *
 * This is needed for the suspend to disk (aka swsusp).
 */
int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
{
	struct block_device *bdev = NULL;
	int type;

	if (device)
		bdev = bdget(device);

	spin_lock(&swap_lock);
	for (type = 0; type < nr_swapfiles; type++) {
		struct swap_info_struct *sis = swap_info[type];

		if (!(sis->flags & SWP_WRITEOK))
			continue;

		if (!bdev) {
			if (bdev_p)
				*bdev_p = bdgrab(sis->bdev);

			spin_unlock(&swap_lock);
			return type;
		}
		if (bdev == sis->bdev) {
			struct swap_extent *se = first_se(sis);

			if (se->start_block == offset) {
				if (bdev_p)
					*bdev_p = bdgrab(sis->bdev);

				spin_unlock(&swap_lock);
				bdput(bdev);
				return type;
			}
		}
	}
	spin_unlock(&swap_lock);
	if (bdev)
		bdput(bdev);

	return -ENODEV;
}

/*
 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
 * corresponding to given index in swap_info (swap type).
 */
sector_t swapdev_block(int type, pgoff_t offset)
{
	struct block_device *bdev;
	struct swap_info_struct *si = swap_type_to_swap_info(type);

	if (!si || !(si->flags & SWP_WRITEOK))
		return 0;
	return map_swap_entry(swp_entry(type, offset), &bdev);
}

/*
 * Return either the total number of swap pages of given type, or the number
 * of free pages of that type (depending on @free)
 *
 * This is needed for software suspend
 */
unsigned int count_swap_pages(int type, int free)
{
	unsigned int n = 0;

	spin_lock(&swap_lock);
	if ((unsigned int)type < nr_swapfiles) {
		struct swap_info_struct *sis = swap_info[type];

		spin_lock(&sis->lock);
		if (sis->flags & SWP_WRITEOK) {
			n = sis->pages;
			if (free)
				n -= sis->inuse_pages;
		}
		spin_unlock(&sis->lock);
	}
	spin_unlock(&swap_lock);
	return n;
}
#endif /* CONFIG_HIBERNATION */

static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
{
	return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
}

/*
 * No need to decide whether this PTE shares the swap entry with others,
 * just let do_wp_page work it out if a write is requested later - to
 * force COW, vm_page_prot omits write permission from any private vma.
 */
static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
		unsigned long addr, swp_entry_t entry, struct page *page)
{
	struct page *swapcache;
	struct mem_cgroup *memcg;
	spinlock_t *ptl;
	pte_t *pte;
	int ret = 1;

	swapcache = page;
	page = ksm_might_need_to_copy(page, vma, addr);
	if (unlikely(!page))
		return -ENOMEM;

	if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
				&memcg, false)) {
		ret = -ENOMEM;
		goto out_nolock;
	}

	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
	if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
		mem_cgroup_cancel_charge(page, memcg, false);
		ret = 0;
		goto out;
	}

	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
	get_page(page);
	set_pte_at(vma->vm_mm, addr, pte,
		   pte_mkold(mk_pte(page, vma->vm_page_prot)));
	if (page == swapcache) {
		page_add_anon_rmap(page, vma, addr, false);
		mem_cgroup_commit_charge(page, memcg, true, false);
	} else { /* ksm created a completely new copy */
		page_add_new_anon_rmap(page, vma, addr, false);
		mem_cgroup_commit_charge(page, memcg, false, false);
		lru_cache_add_active_or_unevictable(page, vma);
	}
	swap_free(entry);
	/*
	 * Move the page to the active list so it is not
	 * immediately swapped out again after swapon.
	 */
	activate_page(page);
out:
	pte_unmap_unlock(pte, ptl);
out_nolock:
	if (page != swapcache) {
		unlock_page(page);
		put_page(page);
	}
	return ret;
}

static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
			unsigned long addr, unsigned long end,
			unsigned int type, bool frontswap,
			unsigned long *fs_pages_to_unuse)
{
	struct page *page;
	swp_entry_t entry;
	pte_t *pte;
	struct swap_info_struct *si;
	unsigned long offset;
	int ret = 0;
	volatile unsigned char *swap_map;

	si = swap_info[type];
	pte = pte_offset_map(pmd, addr);
	do {
		struct vm_fault vmf;

		if (!is_swap_pte(*pte))
			continue;

		entry = pte_to_swp_entry(*pte);
		if (swp_type(entry) != type)
			continue;

		offset = swp_offset(entry);
		if (frontswap && !frontswap_test(si, offset))
			continue;

		pte_unmap(pte);
		swap_map = &si->swap_map[offset];
		vmf.vma = vma;
		vmf.address = addr;
		vmf.pmd = pmd;
		page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE, &vmf);
		if (!page) {
			if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)
				goto try_next;
			return -ENOMEM;
		}

		lock_page(page);
		wait_on_page_writeback(page);
		ret = unuse_pte(vma, pmd, addr, entry, page);
		if (ret < 0) {
			unlock_page(page);
			put_page(page);
			goto out;
		}

		try_to_free_swap(page);
		unlock_page(page);
		put_page(page);

		if (*fs_pages_to_unuse && !--(*fs_pages_to_unuse)) {
			ret = FRONTSWAP_PAGES_UNUSED;
			goto out;
		}
try_next:
		pte = pte_offset_map(pmd, addr);
	} while (pte++, addr += PAGE_SIZE, addr != end);
	pte_unmap(pte - 1);

	ret = 0;
out:
	return ret;
}

static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
				unsigned long addr, unsigned long end,
				unsigned int type, bool frontswap,
				unsigned long *fs_pages_to_unuse)
{
	pmd_t *pmd;
	unsigned long next;
	int ret;

	pmd = pmd_offset(pud, addr);
	do {
		cond_resched();
		next = pmd_addr_end(addr, end);
		if (pmd_none_or_trans_huge_or_clear_bad(pmd))
			continue;
		ret = unuse_pte_range(vma, pmd, addr, next, type,
				      frontswap, fs_pages_to_unuse);
		if (ret)
			return ret;
	} while (pmd++, addr = next, addr != end);
	return 0;
}

static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
				unsigned long addr, unsigned long end,
				unsigned int type, bool frontswap,
				unsigned long *fs_pages_to_unuse)
{
	pud_t *pud;
	unsigned long next;
	int ret;

	pud = pud_offset(p4d, addr);
	do {
		next = pud_addr_end(addr, end);
		if (pud_none_or_clear_bad(pud))
			continue;
		ret = unuse_pmd_range(vma, pud, addr, next, type,
				      frontswap, fs_pages_to_unuse);
		if (ret)
			return ret;
	} while (pud++, addr = next, addr != end);
	return 0;
}

static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd,
				unsigned long addr, unsigned long end,
				unsigned int type, bool frontswap,
				unsigned long *fs_pages_to_unuse)
{
	p4d_t *p4d;
	unsigned long next;
	int ret;

	p4d = p4d_offset(pgd, addr);
	do {
		next = p4d_addr_end(addr, end);
		if (p4d_none_or_clear_bad(p4d))
			continue;
		ret = unuse_pud_range(vma, p4d, addr, next, type,
				      frontswap, fs_pages_to_unuse);
		if (ret)
			return ret;
	} while (p4d++, addr = next, addr != end);
	return 0;
}

static int unuse_vma(struct vm_area_struct *vma, unsigned int type,
		     bool frontswap, unsigned long *fs_pages_to_unuse)
{
	pgd_t *pgd;
	unsigned long addr, end, next;
	int ret;

	addr = vma->vm_start;
	end = vma->vm_end;

	pgd = pgd_offset(vma->vm_mm, addr);
	do {
		next = pgd_addr_end(addr, end);
		if (pgd_none_or_clear_bad(pgd))
			continue;
		ret = unuse_p4d_range(vma, pgd, addr, next, type,
				      frontswap, fs_pages_to_unuse);
		if (ret)
			return ret;
	} while (pgd++, addr = next, addr != end);
	return 0;
}

static int unuse_mm(struct mm_struct *mm, unsigned int type,
		    bool frontswap, unsigned long *fs_pages_to_unuse)
{
	struct vm_area_struct *vma;
	int ret = 0;

	down_read(&mm->mmap_sem);
	for (vma = mm->mmap; vma; vma = vma->vm_next) {
		if (vma->anon_vma) {
			ret = unuse_vma(vma, type, frontswap,
					fs_pages_to_unuse);
			if (ret)
				break;
		}
		cond_resched();
	}
	up_read(&mm->mmap_sem);
	return ret;
}

/*
 * Scan swap_map (or frontswap_map if frontswap parameter is true)
 * from current position to next entry still in use. Return 0
 * if there are no inuse entries after prev till end of the map.
 */
static unsigned int find_next_to_unuse(struct swap_info_struct *si,
					unsigned int prev, bool frontswap)
{
	unsigned int i;
	unsigned char count;

	/*
	 * No need for swap_lock here: we're just looking
	 * for whether an entry is in use, not modifying it; false
	 * hits are okay, and sys_swapoff() has already prevented new
	 * allocations from this area (while holding swap_lock).
	 */
	for (i = prev + 1; i < si->max; i++) {
		count = READ_ONCE(si->swap_map[i]);
		if (count && swap_count(count) != SWAP_MAP_BAD)
			if (!frontswap || frontswap_test(si, i))
				break;
		if ((i % LATENCY_LIMIT) == 0)
			cond_resched();
	}

	if (i == si->max)
		i = 0;

	return i;
}

/*
 * If the boolean frontswap is true, only unuse pages_to_unuse pages;
 * pages_to_unuse==0 means all pages; ignored if frontswap is false
 */
int try_to_unuse(unsigned int type, bool frontswap,
		 unsigned long pages_to_unuse)
{
	struct mm_struct *prev_mm;
	struct mm_struct *mm;
	struct list_head *p;
	int retval = 0;
	struct swap_info_struct *si = swap_info[type];
	struct page *page;
	swp_entry_t entry;
	unsigned int i;

	if (!si->inuse_pages)
		return 0;

	if (!frontswap)
		pages_to_unuse = 0;

retry:
	retval = shmem_unuse(type, frontswap, &pages_to_unuse);
	if (retval)
		goto out;

	prev_mm = &init_mm;
	mmget(prev_mm);

	spin_lock(&mmlist_lock);
	p = &init_mm.mmlist;
	while (si->inuse_pages &&
	       !signal_pending(current) &&
	       (p = p->next) != &init_mm.mmlist) {

		mm = list_entry(p, struct mm_struct, mmlist);
		if (!mmget_not_zero(mm))
			continue;
		spin_unlock(&mmlist_lock);
		mmput(prev_mm);
		prev_mm = mm;
		retval = unuse_mm(mm, type, frontswap, &pages_to_unuse);

		if (retval) {
			mmput(prev_mm);
			goto out;
		}

		/*
		 * Make sure that we aren't completely killing
		 * interactive performance.
		 */
		cond_resched();
		spin_lock(&mmlist_lock);
	}
	spin_unlock(&mmlist_lock);

	mmput(prev_mm);

	i = 0;
	while (si->inuse_pages &&
	       !signal_pending(current) &&
	       (i = find_next_to_unuse(si, i, frontswap)) != 0) {

		entry = swp_entry(type, i);
		page = find_get_page(swap_address_space(entry), i);
		if (!page)
			continue;

		/*
		 * It is conceivable that a racing task removed this page from
		 * swap cache just before we acquired the page lock. The page
		 * might even be back in swap cache on another swap area. But
		 * that is okay, try_to_free_swap() only removes stale pages.
		 */
		lock_page(page);
		wait_on_page_writeback(page);
		try_to_free_swap(page);
		unlock_page(page);
		put_page(page);

		/*
		 * For frontswap, we just need to unuse pages_to_unuse, if
		 * it was specified. Need not check frontswap again here as
		 * we already zeroed out pages_to_unuse if not frontswap.
		 */
		if (pages_to_unuse && --pages_to_unuse == 0)
			goto out;
	}

	/*
	 * Lets check again to see if there are still swap entries in the map.
	 * If yes, we would need to do retry the unuse logic again.
	 * Under global memory pressure, swap entries can be reinserted back
	 * into process space after the mmlist loop above passes over them.
	 *
	 * Limit the number of retries? No: when mmget_not_zero() above fails,
	 * that mm is likely to be freeing swap from exit_mmap(), which proceeds
	 * at its own independent pace; and even shmem_writepage() could have
	 * been preempted after get_swap_page(), temporarily hiding that swap.
	 * It's easy and robust (though cpu-intensive) just to keep retrying.
	 */
	if (si->inuse_pages) {
		if (!signal_pending(current))
			goto retry;
		retval = -EINTR;
	}
out:
	return (retval == FRONTSWAP_PAGES_UNUSED) ? 0 : retval;
}

/*
 * After a successful try_to_unuse, if no swap is now in use, we know
 * we can empty the mmlist.  swap_lock must be held on entry and exit.
 * Note that mmlist_lock nests inside swap_lock, and an mm must be
 * added to the mmlist just after page_duplicate - before would be racy.
 */
static void drain_mmlist(void)
{
	struct list_head *p, *next;
	unsigned int type;

	for (type = 0; type < nr_swapfiles; type++)
		if (swap_info[type]->inuse_pages)
			return;
	spin_lock(&mmlist_lock);
	list_for_each_safe(p, next, &init_mm.mmlist)
		list_del_init(p);
	spin_unlock(&mmlist_lock);
}

/*
 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
 * corresponds to page offset for the specified swap entry.
 * Note that the type of this function is sector_t, but it returns page offset
 * into the bdev, not sector offset.
 */
static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
{
	struct swap_info_struct *sis;
	struct swap_extent *se;
	pgoff_t offset;

	sis = swp_swap_info(entry);
	*bdev = sis->bdev;

	offset = swp_offset(entry);
	se = offset_to_swap_extent(sis, offset);
	return se->start_block + (offset - se->start_page);
}

/*
 * Returns the page offset into bdev for the specified page's swap entry.
 */
sector_t map_swap_page(struct page *page, struct block_device **bdev)
{
	swp_entry_t entry;
	entry.val = page_private(page);
	return map_swap_entry(entry, bdev);
}

/*
 * Free all of a swapdev's extent information
 */
static void destroy_swap_extents(struct swap_info_struct *sis)
{
	while (!RB_EMPTY_ROOT(&sis->swap_extent_root)) {
		struct rb_node *rb = sis->swap_extent_root.rb_node;
		struct swap_extent *se = rb_entry(rb, struct swap_extent, rb_node);

		rb_erase(rb, &sis->swap_extent_root);
		kfree(se);
	}

	if (sis->flags & SWP_ACTIVATED) {
		struct file *swap_file = sis->swap_file;
		struct address_space *mapping = swap_file->f_mapping;

		sis->flags &= ~SWP_ACTIVATED;
		if (mapping->a_ops->swap_deactivate)
			mapping->a_ops->swap_deactivate(swap_file);
	}
}

/*
 * Add a block range (and the corresponding page range) into this swapdev's
 * extent tree.
 *
 * This function rather assumes that it is called in ascending page order.
 */
int
add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
		unsigned long nr_pages, sector_t start_block)
{
	struct rb_node **link = &sis->swap_extent_root.rb_node, *parent = NULL;
	struct swap_extent *se;
	struct swap_extent *new_se;

	/*
	 * place the new node at the right most since the
	 * function is called in ascending page order.
	 */
	while (*link) {
		parent = *link;
		link = &parent->rb_right;
	}

	if (parent) {
		se = rb_entry(parent, struct swap_extent, rb_node);
		BUG_ON(se->start_page + se->nr_pages != start_page);
		if (se->start_block + se->nr_pages == start_block) {
			/* Merge it */
			se->nr_pages += nr_pages;
			return 0;
		}
	}

	/* No merge, insert a new extent. */
	new_se = kmalloc(sizeof(*se), GFP_KERNEL);
	if (new_se == NULL)
		return -ENOMEM;
	new_se->start_page = start_page;
	new_se->nr_pages = nr_pages;
	new_se->start_block = start_block;

	rb_link_node(&new_se->rb_node, parent, link);
	rb_insert_color(&new_se->rb_node, &sis->swap_extent_root);
	return 1;
}
EXPORT_SYMBOL_GPL(add_swap_extent);

/*
 * A `swap extent' is a simple thing which maps a contiguous range of pages
 * onto a contiguous range of disk blocks.  An ordered list of swap extents
 * is built at swapon time and is then used at swap_writepage/swap_readpage
 * time for locating where on disk a page belongs.
 *
 * If the swapfile is an S_ISBLK block device, a single extent is installed.
 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
 * swap files identically.
 *
 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
 * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
 * swapfiles are handled *identically* after swapon time.
 *
 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
 * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
 * requirements, they are simply tossed out - we will never use those blocks
 * for swapping.
 *
 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
 * which will scribble on the fs.
 *
 * The amount of disk space which a single swap extent represents varies.
 * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
 * extents in the list.  To avoid much list walking, we cache the previous
 * search location in `curr_swap_extent', and start new searches from there.
 * This is extremely effective.  The average number of iterations in
 * map_swap_page() has been measured at about 0.3 per page.  - akpm.
 */
static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
{
	struct file *swap_file = sis->swap_file;
	struct address_space *mapping = swap_file->f_mapping;
	struct inode *inode = mapping->host;
	int ret;

	if (S_ISBLK(inode->i_mode)) {
		ret = add_swap_extent(sis, 0, sis->max, 0);
		*span = sis->pages;
		return ret;
	}

	if (mapping->a_ops->swap_activate) {
		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
		if (ret >= 0)
			sis->flags |= SWP_ACTIVATED;
		if (!ret) {
			sis->flags |= SWP_FS;
			ret = add_swap_extent(sis, 0, sis->max, 0);
			*span = sis->pages;
		}
		return ret;
	}

	return generic_swapfile_activate(sis, swap_file, span);
}

static int swap_node(struct swap_info_struct *p)
{
	struct block_device *bdev;

	if (p->bdev)
		bdev = p->bdev;
	else
		bdev = p->swap_file->f_inode->i_sb->s_bdev;

	return bdev ? bdev->bd_disk->node_id : NUMA_NO_NODE;
}

static void setup_swap_info(struct swap_info_struct *p, int prio,
			    unsigned char *swap_map,
			    struct swap_cluster_info *cluster_info)
{
	int i;

	if (prio >= 0)
		p->prio = prio;
	else
		p->prio = --least_priority;
	/*
	 * the plist prio is negated because plist ordering is
	 * low-to-high, while swap ordering is high-to-low
	 */
	p->list.prio = -p->prio;
	for_each_node(i) {
		if (p->prio >= 0)
			p->avail_lists[i].prio = -p->prio;
		else {
			if (swap_node(p) == i)
				p->avail_lists[i].prio = 1;
			else
				p->avail_lists[i].prio = -p->prio;
		}
	}
	p->swap_map = swap_map;
	p->cluster_info = cluster_info;
}

static void _enable_swap_info(struct swap_info_struct *p)
{
	p->flags |= SWP_WRITEOK | SWP_VALID;
	atomic_long_add(p->pages, &nr_swap_pages);
	total_swap_pages += p->pages;

	assert_spin_locked(&swap_lock);
	/*
	 * both lists are plists, and thus priority ordered.
	 * swap_active_head needs to be priority ordered for swapoff(),
	 * which on removal of any swap_info_struct with an auto-assigned
	 * (i.e. negative) priority increments the auto-assigned priority
	 * of any lower-priority swap_info_structs.
	 * swap_avail_head needs to be priority ordered for get_swap_page(),
	 * which allocates swap pages from the highest available priority
	 * swap_info_struct.
	 */
	plist_add(&p->list, &swap_active_head);
	add_to_avail_list(p);
}

static void enable_swap_info(struct swap_info_struct *p, int prio,
				unsigned char *swap_map,
				struct swap_cluster_info *cluster_info,
				unsigned long *frontswap_map)
{
	frontswap_init(p->type, frontswap_map);
	spin_lock(&swap_lock);
	spin_lock(&p->lock);
	setup_swap_info(p, prio, swap_map, cluster_info);
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);
	/*
	 * Guarantee swap_map, cluster_info, etc. fields are valid
	 * between get/put_swap_device() if SWP_VALID bit is set
	 */
	synchronize_rcu();
	spin_lock(&swap_lock);
	spin_lock(&p->lock);
	_enable_swap_info(p);
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);
}

static void reinsert_swap_info(struct swap_info_struct *p)
{
	spin_lock(&swap_lock);
	spin_lock(&p->lock);
	setup_swap_info(p, p->prio, p->swap_map, p->cluster_info);
	_enable_swap_info(p);
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);
}

bool has_usable_swap(void)
{
	bool ret = true;

	spin_lock(&swap_lock);
	if (plist_head_empty(&swap_active_head))
		ret = false;
	spin_unlock(&swap_lock);
	return ret;
}

SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
{
	struct swap_info_struct *p = NULL;
	unsigned char *swap_map;
	struct swap_cluster_info *cluster_info;
	unsigned long *frontswap_map;
	struct file *swap_file, *victim;
	struct address_space *mapping;
	struct inode *inode;
	struct filename *pathname;
	int err, found = 0;
	unsigned int old_block_size;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	BUG_ON(!current->mm);

	pathname = getname(specialfile);
	if (IS_ERR(pathname))
		return PTR_ERR(pathname);

	victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
	err = PTR_ERR(victim);
	if (IS_ERR(victim))
		goto out;

	mapping = victim->f_mapping;
	spin_lock(&swap_lock);
	plist_for_each_entry(p, &swap_active_head, list) {
		if (p->flags & SWP_WRITEOK) {
			if (p->swap_file->f_mapping == mapping) {
				found = 1;
				break;
			}
		}
	}
	if (!found) {
		err = -EINVAL;
		spin_unlock(&swap_lock);
		goto out_dput;
	}
	if (!security_vm_enough_memory_mm(current->mm, p->pages))
		vm_unacct_memory(p->pages);
	else {
		err = -ENOMEM;
		spin_unlock(&swap_lock);
		goto out_dput;
	}
	del_from_avail_list(p);
	spin_lock(&p->lock);
	if (p->prio < 0) {
		struct swap_info_struct *si = p;
		int nid;

		plist_for_each_entry_continue(si, &swap_active_head, list) {
			si->prio++;
			si->list.prio--;
			for_each_node(nid) {
				if (si->avail_lists[nid].prio != 1)
					si->avail_lists[nid].prio--;
			}
		}
		least_priority++;
	}
	plist_del(&p->list, &swap_active_head);
	atomic_long_sub(p->pages, &nr_swap_pages);
	total_swap_pages -= p->pages;
	p->flags &= ~SWP_WRITEOK;
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);

	disable_swap_slots_cache_lock();

	set_current_oom_origin();
	err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
	clear_current_oom_origin();

	if (err) {
		/* re-insert swap space back into swap_list */
		reinsert_swap_info(p);
		reenable_swap_slots_cache_unlock();
		goto out_dput;
	}

	reenable_swap_slots_cache_unlock();

	spin_lock(&swap_lock);
	spin_lock(&p->lock);
	p->flags &= ~SWP_VALID;		/* mark swap device as invalid */
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);
	/*
	 * wait for swap operations protected by get/put_swap_device()
	 * to complete
	 */
	synchronize_rcu();

	flush_work(&p->discard_work);

	destroy_swap_extents(p);
	if (p->flags & SWP_CONTINUED)
		free_swap_count_continuations(p);

	if (!p->bdev || !blk_queue_nonrot(bdev_get_queue(p->bdev)))
		atomic_dec(&nr_rotate_swap);

	mutex_lock(&swapon_mutex);
	spin_lock(&swap_lock);
	spin_lock(&p->lock);
	drain_mmlist();

	/* wait for anyone still in scan_swap_map */
	p->highest_bit = 0;		/* cuts scans short */
	while (p->flags >= SWP_SCANNING) {
		spin_unlock(&p->lock);
		spin_unlock(&swap_lock);
		schedule_timeout_uninterruptible(1);
		spin_lock(&swap_lock);
		spin_lock(&p->lock);
	}

	swap_file = p->swap_file;
	old_block_size = p->old_block_size;
	p->swap_file = NULL;
	p->max = 0;
	swap_map = p->swap_map;
	p->swap_map = NULL;
	cluster_info = p->cluster_info;
	p->cluster_info = NULL;
	frontswap_map = frontswap_map_get(p);
	spin_unlock(&p->lock);
	spin_unlock(&swap_lock);
	frontswap_invalidate_area(p->type);
	frontswap_map_set(p, NULL);
	mutex_unlock(&swapon_mutex);
	free_percpu(p->percpu_cluster);
	p->percpu_cluster = NULL;
	vfree(swap_map);
	kvfree(cluster_info);
	kvfree(frontswap_map);
	/* Destroy swap account information */
	swap_cgroup_swapoff(p->type);
	exit_swap_address_space(p->type);

	inode = mapping->host;
	if (S_ISBLK(inode->i_mode)) {
		struct block_device *bdev = I_BDEV(inode);
		set_blocksize(bdev, old_block_size);
		blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
	} else {
		inode_lock(inode);
		inode->i_flags &= ~S_SWAPFILE;
		inode_unlock(inode);
	}
	filp_close(swap_file, NULL);

	/*
	 * Clear the SWP_USED flag after all resources are freed so that swapon
	 * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
	 * not hold p->lock after we cleared its SWP_WRITEOK.
	 */
	spin_lock(&swap_lock);
	p->flags = 0;
	spin_unlock(&swap_lock);

	err = 0;
	atomic_inc(&proc_poll_event);
	wake_up_interruptible(&proc_poll_wait);

out_dput:
	filp_close(victim, NULL);
out:
	putname(pathname);
	return err;
}

#ifdef CONFIG_PROC_FS
static __poll_t swaps_poll(struct file *file, poll_table *wait)
{
	struct seq_file *seq = file->private_data;

	poll_wait(file, &proc_poll_wait, wait);

	if (seq->poll_event != atomic_read(&proc_poll_event)) {
		seq->poll_event = atomic_read(&proc_poll_event);
		return EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;
	}

	return EPOLLIN | EPOLLRDNORM;
}

/* iterator */
static void *swap_start(struct seq_file *swap, loff_t *pos)
{
	struct swap_info_struct *si;
	int type;
	loff_t l = *pos;

	mutex_lock(&swapon_mutex);

	if (!l)
		return SEQ_START_TOKEN;

	for (type = 0; (si = swap_type_to_swap_info(type)); type++) {
		if (!(si->flags & SWP_USED) || !si->swap_map)
			continue;
		if (!--l)
			return si;
	}

	return NULL;
}

static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
{
	struct swap_info_struct *si = v;
	int type;

	if (v == SEQ_START_TOKEN)
		type = 0;
	else
		type = si->type + 1;

	for (; (si = swap_type_to_swap_info(type)); type++) {
		if (!(si->flags & SWP_USED) || !si->swap_map)
			continue;
		++*pos;
		return si;
	}

	return NULL;
}

static void swap_stop(struct seq_file *swap, void *v)
{
	mutex_unlock(&swapon_mutex);
}

static int swap_show(struct seq_file *swap, void *v)
{
	struct swap_info_struct *si = v;
	struct file *file;
	int len;

	if (si == SEQ_START_TOKEN) {
		seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
		return 0;
	}

	file = si->swap_file;
	len = seq_file_path(swap, file, " \t\n\\");
	seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
			len < 40 ? 40 - len : 1, " ",
			S_ISBLK(file_inode(file)->i_mode) ?
				"partition" : "file\t",
			si->pages << (PAGE_SHIFT - 10),
			si->inuse_pages << (PAGE_SHIFT - 10),
			si->prio);
	return 0;
}

static const struct seq_operations swaps_op = {
	.start =	swap_start,
	.next =		swap_next,
	.stop =		swap_stop,
	.show =		swap_show
};

static int swaps_open(struct inode *inode, struct file *file)
{
	struct seq_file *seq;
	int ret;

	ret = seq_open(file, &swaps_op);
	if (ret)
		return ret;

	seq = file->private_data;
	seq->poll_event = atomic_read(&proc_poll_event);
	return 0;
}

static const struct file_operations proc_swaps_operations = {
	.open		= swaps_open,
	.read		= seq_read,
	.llseek		= seq_lseek,
	.release	= seq_release,
	.poll		= swaps_poll,
};

static int __init procswaps_init(void)
{
	proc_create("swaps", 0, NULL, &proc_swaps_operations);
	return 0;
}
__initcall(procswaps_init);
#endif /* CONFIG_PROC_FS */

#ifdef MAX_SWAPFILES_CHECK
static int __init max_swapfiles_check(void)
{
	MAX_SWAPFILES_CHECK();
	return 0;
}
late_initcall(max_swapfiles_check);
#endif

static struct swap_info_struct *alloc_swap_info(void)
{
	struct swap_info_struct *p;
	unsigned int type;
	int i;

	p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
	if (!p)
		return ERR_PTR(-ENOMEM);

	spin_lock(&swap_lock);
	for (type = 0; type < nr_swapfiles; type++) {
		if (!(swap_info[type]->flags & SWP_USED))
			break;
	}
	if (type >= MAX_SWAPFILES) {
		spin_unlock(&swap_lock);
		kvfree(p);
		return ERR_PTR(-EPERM);
	}
	if (type >= nr_swapfiles) {
		p->type = type;
		WRITE_ONCE(swap_info[type], p);
		/*
		 * Write swap_info[type] before nr_swapfiles, in case a
		 * racing procfs swap_start() or swap_next() is reading them.
		 * (We never shrink nr_swapfiles, we never free this entry.)
		 */
		smp_wmb();
		WRITE_ONCE(nr_swapfiles, nr_swapfiles + 1);
	} else {
		kvfree(p);
		p = swap_info[type];
		/*
		 * Do not memset this entry: a racing procfs swap_next()
		 * would be relying on p->type to remain valid.
		 */
	}
	p->swap_extent_root = RB_ROOT;
	plist_node_init(&p->list, 0);
	for_each_node(i)
		plist_node_init(&p->avail_lists[i], 0);
	p->flags = SWP_USED;
	spin_unlock(&swap_lock);
	spin_lock_init(&p->lock);
	spin_lock_init(&p->cont_lock);

	return p;
}

static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
{
	int error;

	if (S_ISBLK(inode->i_mode)) {
		p->bdev = bdgrab(I_BDEV(inode));
		error = blkdev_get(p->bdev,
				   FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
		if (error < 0) {
			p->bdev = NULL;
			return error;
		}
		p->old_block_size = block_size(p->bdev);
		error = set_blocksize(p->bdev, PAGE_SIZE);
		if (error < 0)
			return error;
		p->flags |= SWP_BLKDEV;
	} else if (S_ISREG(inode->i_mode)) {
		p->bdev = inode->i_sb->s_bdev;
		inode_lock(inode);
		if (IS_SWAPFILE(inode))
			return -EBUSY;
	} else
		return -EINVAL;

	return 0;
}


/*
 * Find out how many pages are allowed for a single swap device. There
 * are two limiting factors:
 * 1) the number of bits for the swap offset in the swp_entry_t type, and
 * 2) the number of bits in the swap pte, as defined by the different
 * architectures.
 *
 * In order to find the largest possible bit mask, a swap entry with
 * swap type 0 and swap offset ~0UL is created, encoded to a swap pte,
 * decoded to a swp_entry_t again, and finally the swap offset is
 * extracted.
 *
 * This will mask all the bits from the initial ~0UL mask that can't
 * be encoded in either the swp_entry_t or the architecture definition
 * of a swap pte.
 */
unsigned long generic_max_swapfile_size(void)
{
	return swp_offset(pte_to_swp_entry(
			swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
}

/* Can be overridden by an architecture for additional checks. */
__weak unsigned long max_swapfile_size(void)
{
	return generic_max_swapfile_size();
}

static unsigned long read_swap_header(struct swap_info_struct *p,
					union swap_header *swap_header,
					struct inode *inode)
{
	int i;
	unsigned long maxpages;
	unsigned long swapfilepages;
	unsigned long last_page;

	if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
		pr_err("Unable to find swap-space signature\n");
		return 0;
	}

	/* swap partition endianess hack... */
	if (swab32(swap_header->info.version) == 1) {
		swab32s(&swap_header->info.version);
		swab32s(&swap_header->info.last_page);
		swab32s(&swap_header->info.nr_badpages);
		if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
			return 0;
		for (i = 0; i < swap_header->info.nr_badpages; i++)
			swab32s(&swap_header->info.badpages[i]);
	}
	/* Check the swap header's sub-version */
	if (swap_header->info.version != 1) {
		pr_warn("Unable to handle swap header version %d\n",
			swap_header->info.version);
		return 0;
	}

	p->lowest_bit  = 1;
	p->cluster_next = 1;
	p->cluster_nr = 0;

	maxpages = max_swapfile_size();
	last_page = swap_header->info.last_page;
	if (!last_page) {
		pr_warn("Empty swap-file\n");
		return 0;
	}
	if (last_page > maxpages) {
		pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
			maxpages << (PAGE_SHIFT - 10),
			last_page << (PAGE_SHIFT - 10));
	}
	if (maxpages > last_page) {
		maxpages = last_page + 1;
		/* p->max is an unsigned int: don't overflow it */
		if ((unsigned int)maxpages == 0)
			maxpages = UINT_MAX;
	}
	p->highest_bit = maxpages - 1;

	if (!maxpages)
		return 0;
	swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
	if (swapfilepages && maxpages > swapfilepages) {
		pr_warn("Swap area shorter than signature indicates\n");
		return 0;
	}
	if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
		return 0;
	if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
		return 0;

	return maxpages;
}

#define SWAP_CLUSTER_INFO_COLS						\
	DIV_ROUND_UP(L1_CACHE_BYTES, sizeof(struct swap_cluster_info))
#define SWAP_CLUSTER_SPACE_COLS						\
	DIV_ROUND_UP(SWAP_ADDRESS_SPACE_PAGES, SWAPFILE_CLUSTER)
#define SWAP_CLUSTER_COLS						\
	max_t(unsigned int, SWAP_CLUSTER_INFO_COLS, SWAP_CLUSTER_SPACE_COLS)

static int setup_swap_map_and_extents(struct swap_info_struct *p,
					union swap_header *swap_header,
					unsigned char *swap_map,
					struct swap_cluster_info *cluster_info,
					unsigned long maxpages,
					sector_t *span)
{
	unsigned int j, k;
	unsigned int nr_good_pages;
	int nr_extents;
	unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
	unsigned long col = p->cluster_next / SWAPFILE_CLUSTER % SWAP_CLUSTER_COLS;
	unsigned long i, idx;

	nr_good_pages = maxpages - 1;	/* omit header page */

	cluster_list_init(&p->free_clusters);
	cluster_list_init(&p->discard_clusters);

	for (i = 0; i < swap_header->info.nr_badpages; i++) {
		unsigned int page_nr = swap_header->info.badpages[i];
		if (page_nr == 0 || page_nr > swap_header->info.last_page)
			return -EINVAL;
		if (page_nr < maxpages) {
			swap_map[page_nr] = SWAP_MAP_BAD;
			nr_good_pages--;
			/*
			 * Haven't marked the cluster free yet, no list
			 * operation involved
			 */
			inc_cluster_info_page(p, cluster_info, page_nr);
		}
	}

	/* Haven't marked the cluster free yet, no list operation involved */
	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
		inc_cluster_info_page(p, cluster_info, i);

	if (nr_good_pages) {
		swap_map[0] = SWAP_MAP_BAD;
		/*
		 * Not mark the cluster free yet, no list
		 * operation involved
		 */
		inc_cluster_info_page(p, cluster_info, 0);
		p->max = maxpages;
		p->pages = nr_good_pages;
		nr_extents = setup_swap_extents(p, span);
		if (nr_extents < 0)
			return nr_extents;
		nr_good_pages = p->pages;
	}
	if (!nr_good_pages) {
		pr_warn("Empty swap-file\n");
		return -EINVAL;
	}

	if (!cluster_info)
		return nr_extents;


	/*
	 * Reduce false cache line sharing between cluster_info and
	 * sharing same address space.
	 */
	for (k = 0; k < SWAP_CLUSTER_COLS; k++) {
		j = (k + col) % SWAP_CLUSTER_COLS;
		for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) {
			idx = i * SWAP_CLUSTER_COLS + j;
			if (idx >= nr_clusters)
				continue;
			if (cluster_count(&cluster_info[idx]))
				continue;
			cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
			cluster_list_add_tail(&p->free_clusters, cluster_info,
					      idx);
		}
	}
	return nr_extents;
}

/*
 * Helper to sys_swapon determining if a given swap
 * backing device queue supports DISCARD operations.
 */
static bool swap_discardable(struct swap_info_struct *si)
{
	struct request_queue *q = bdev_get_queue(si->bdev);

	if (!q || !blk_queue_discard(q))
		return false;

	return true;
}

SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
{
	struct swap_info_struct *p;
	struct filename *name;
	struct file *swap_file = NULL;
	struct address_space *mapping;
	int prio;
	int error;
	union swap_header *swap_header;
	int nr_extents;
	sector_t span;
	unsigned long maxpages;
	unsigned char *swap_map = NULL;
	struct swap_cluster_info *cluster_info = NULL;
	unsigned long *frontswap_map = NULL;
	struct page *page = NULL;
	struct inode *inode = NULL;
	bool inced_nr_rotate_swap = false;

	if (swap_flags & ~SWAP_FLAGS_VALID)
		return -EINVAL;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if (!swap_avail_heads)
		return -ENOMEM;

	p = alloc_swap_info();
	if (IS_ERR(p))
		return PTR_ERR(p);

	INIT_WORK(&p->discard_work, swap_discard_work);

	name = getname(specialfile);
	if (IS_ERR(name)) {
		error = PTR_ERR(name);
		name = NULL;
		goto bad_swap;
	}
	swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
	if (IS_ERR(swap_file)) {
		error = PTR_ERR(swap_file);
		swap_file = NULL;
		goto bad_swap;
	}

	p->swap_file = swap_file;
	mapping = swap_file->f_mapping;
	inode = mapping->host;

	/* If S_ISREG(inode->i_mode) will do inode_lock(inode); */
	error = claim_swapfile(p, inode);
	if (unlikely(error))
		goto bad_swap;

	/*
	 * Read the swap header.
	 */
	if (!mapping->a_ops->readpage) {
		error = -EINVAL;
		goto bad_swap;
	}
	page = read_mapping_page(mapping, 0, swap_file);
	if (IS_ERR(page)) {
		error = PTR_ERR(page);
		goto bad_swap;
	}
	swap_header = kmap(page);

	maxpages = read_swap_header(p, swap_header, inode);
	if (unlikely(!maxpages)) {
		error = -EINVAL;
		goto bad_swap;
	}

	/* OK, set up the swap map and apply the bad block list */
	swap_map = vzalloc(maxpages);
	if (!swap_map) {
		error = -ENOMEM;
		goto bad_swap;
	}

	if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
		p->flags |= SWP_STABLE_WRITES;

	if (bdi_cap_synchronous_io(inode_to_bdi(inode)))
		p->flags |= SWP_SYNCHRONOUS_IO;

	if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
		int cpu;
		unsigned long ci, nr_cluster;

		p->flags |= SWP_SOLIDSTATE;
		/*
		 * select a random position to start with to help wear leveling
		 * SSD
		 */
		p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
		nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);

		cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
					GFP_KERNEL);
		if (!cluster_info) {
			error = -ENOMEM;
			goto bad_swap;
		}

		for (ci = 0; ci < nr_cluster; ci++)
			spin_lock_init(&((cluster_info + ci)->lock));

		p->percpu_cluster = alloc_percpu(struct percpu_cluster);
		if (!p->percpu_cluster) {
			error = -ENOMEM;
			goto bad_swap;
		}
		for_each_possible_cpu(cpu) {
			struct percpu_cluster *cluster;
			cluster = per_cpu_ptr(p->percpu_cluster, cpu);
			cluster_set_null(&cluster->index);
		}
	} else {
		atomic_inc(&nr_rotate_swap);
		inced_nr_rotate_swap = true;
	}

	error = swap_cgroup_swapon(p->type, maxpages);
	if (error)
		goto bad_swap;

	nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
		cluster_info, maxpages, &span);
	if (unlikely(nr_extents < 0)) {
		error = nr_extents;
		goto bad_swap;
	}
	/* frontswap enabled? set up bit-per-page map for frontswap */
	if (IS_ENABLED(CONFIG_FRONTSWAP))
		frontswap_map = kvcalloc(BITS_TO_LONGS(maxpages),
					 sizeof(long),
					 GFP_KERNEL);

	if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
		/*
		 * When discard is enabled for swap with no particular
		 * policy flagged, we set all swap discard flags here in
		 * order to sustain backward compatibility with older
		 * swapon(8) releases.
		 */
		p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
			     SWP_PAGE_DISCARD);

		/*
		 * By flagging sys_swapon, a sysadmin can tell us to
		 * either do single-time area discards only, or to just
		 * perform discards for released swap page-clusters.
		 * Now it's time to adjust the p->flags accordingly.
		 */
		if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
			p->flags &= ~SWP_PAGE_DISCARD;
		else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
			p->flags &= ~SWP_AREA_DISCARD;

		/* issue a swapon-time discard if it's still required */
		if (p->flags & SWP_AREA_DISCARD) {
			int err = discard_swap(p);
			if (unlikely(err))
				pr_err("swapon: discard_swap(%p): %d\n",
					p, err);
		}
	}

	error = init_swap_address_space(p->type, maxpages);
	if (error)
		goto bad_swap;

	mutex_lock(&swapon_mutex);
	prio = -1;
	if (swap_flags & SWAP_FLAG_PREFER)
		prio =
		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
	enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);

	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
		p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
		(p->flags & SWP_DISCARDABLE) ? "D" : "",
		(p->flags & SWP_AREA_DISCARD) ? "s" : "",
		(p->flags & SWP_PAGE_DISCARD) ? "c" : "",
		(frontswap_map) ? "FS" : "");

	mutex_unlock(&swapon_mutex);
	atomic_inc(&proc_poll_event);
	wake_up_interruptible(&proc_poll_wait);

	if (S_ISREG(inode->i_mode))
		inode->i_flags |= S_SWAPFILE;
	error = 0;
	goto out;
bad_swap:
	free_percpu(p->percpu_cluster);
	p->percpu_cluster = NULL;
	if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
		set_blocksize(p->bdev, p->old_block_size);
		blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
	}
	destroy_swap_extents(p);
	swap_cgroup_swapoff(p->type);
	spin_lock(&swap_lock);
	p->swap_file = NULL;
	p->flags = 0;
	spin_unlock(&swap_lock);
	vfree(swap_map);
	kvfree(cluster_info);
	kvfree(frontswap_map);
	if (inced_nr_rotate_swap)
		atomic_dec(&nr_rotate_swap);
	if (swap_file) {
		if (inode && S_ISREG(inode->i_mode)) {
			inode_unlock(inode);
			inode = NULL;
		}
		filp_close(swap_file, NULL);
	}
out:
	if (page && !IS_ERR(page)) {
		kunmap(page);
		put_page(page);
	}
	if (name)
		putname(name);
	if (inode && S_ISREG(inode->i_mode))
		inode_unlock(inode);
	if (!error)
		enable_swap_slots_cache();
	return error;
}

void si_swapinfo(struct sysinfo *val)
{
	unsigned int type;
	unsigned long nr_to_be_unused = 0;

	spin_lock(&swap_lock);
	for (type = 0; type < nr_swapfiles; type++) {
		struct swap_info_struct *si = swap_info[type];

		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
			nr_to_be_unused += si->inuse_pages;
	}
	val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
	val->totalswap = total_swap_pages + nr_to_be_unused;
	spin_unlock(&swap_lock);
}

/*
 * Verify that a swap entry is valid and increment its swap map count.
 *
 * Returns error code in following case.
 * - success -> 0
 * - swp_entry is invalid -> EINVAL
 * - swp_entry is migration entry -> EINVAL
 * - swap-cache reference is requested but there is already one. -> EEXIST
 * - swap-cache reference is requested but the entry is not used. -> ENOENT
 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
 */
static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
{
	struct swap_info_struct *p;
	struct swap_cluster_info *ci;
	unsigned long offset;
	unsigned char count;
	unsigned char has_cache;
	int err = -EINVAL;

	p = get_swap_device(entry);
	if (!p)
		goto out;

	offset = swp_offset(entry);
	ci = lock_cluster_or_swap_info(p, offset);

	count = p->swap_map[offset];

	/*
	 * swapin_readahead() doesn't check if a swap entry is valid, so the
	 * swap entry could be SWAP_MAP_BAD. Check here with lock held.
	 */
	if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
		err = -ENOENT;
		goto unlock_out;
	}

	has_cache = count & SWAP_HAS_CACHE;
	count &= ~SWAP_HAS_CACHE;
	err = 0;

	if (usage == SWAP_HAS_CACHE) {

		/* set SWAP_HAS_CACHE if there is no cache and entry is used */
		if (!has_cache && count)
			has_cache = SWAP_HAS_CACHE;
		else if (has_cache)		/* someone else added cache */
			err = -EEXIST;
		else				/* no users remaining */
			err = -ENOENT;

	} else if (count || has_cache) {

		if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
			count += usage;
		else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
			err = -EINVAL;
		else if (swap_count_continued(p, offset, count))
			count = COUNT_CONTINUED;
		else
			err = -ENOMEM;
	} else
		err = -ENOENT;			/* unused swap entry */

	p->swap_map[offset] = count | has_cache;

unlock_out:
	unlock_cluster_or_swap_info(p, ci);
out:
	if (p)
		put_swap_device(p);
	return err;
}

/*
 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
 * (in which case its reference count is never incremented).
 */
void swap_shmem_alloc(swp_entry_t entry)
{
	__swap_duplicate(entry, SWAP_MAP_SHMEM);
}

/*
 * Increase reference count of swap entry by 1.
 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
 * but could not be atomically allocated.  Returns 0, just as if it succeeded,
 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
 * might occur if a page table entry has got corrupted.
 */
int swap_duplicate(swp_entry_t entry)
{
	int err = 0;

	while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
		err = add_swap_count_continuation(entry, GFP_ATOMIC);
	return err;
}

/*
 * @entry: swap entry for which we allocate swap cache.
 *
 * Called when allocating swap cache for existing swap entry,
 * This can return error codes. Returns 0 at success.
 * -EBUSY means there is a swap cache.
 * Note: return code is different from swap_duplicate().
 */
int swapcache_prepare(swp_entry_t entry)
{
	return __swap_duplicate(entry, SWAP_HAS_CACHE);
}

struct swap_info_struct *swp_swap_info(swp_entry_t entry)
{
	return swap_type_to_swap_info(swp_type(entry));
}

struct swap_info_struct *page_swap_info(struct page *page)
{
	swp_entry_t entry = { .val = page_private(page) };
	return swp_swap_info(entry);
}

/*
 * out-of-line __page_file_ methods to avoid include hell.
 */
struct address_space *__page_file_mapping(struct page *page)
{
	return page_swap_info(page)->swap_file->f_mapping;
}
EXPORT_SYMBOL_GPL(__page_file_mapping);

pgoff_t __page_file_index(struct page *page)
{
	swp_entry_t swap = { .val = page_private(page) };
	return swp_offset(swap);
}
EXPORT_SYMBOL_GPL(__page_file_index);

/*
 * add_swap_count_continuation - called when a swap count is duplicated
 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
 * page of the original vmalloc'ed swap_map, to hold the continuation count
 * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
 *
 * These continuation pages are seldom referenced: the common paths all work
 * on the original swap_map, only referring to a continuation page when the
 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
 *
 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
 * can be called after dropping locks.
 */
int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
{
	struct swap_info_struct *si;
	struct swap_cluster_info *ci;
	struct page *head;
	struct page *page;
	struct page *list_page;
	pgoff_t offset;
	unsigned char count;
	int ret = 0;

	/*
	 * When debugging, it's easier to use __GFP_ZERO here; but it's better
	 * for latency not to zero a page while GFP_ATOMIC and holding locks.
	 */
	page = alloc_page(gfp_mask | __GFP_HIGHMEM);

	si = get_swap_device(entry);
	if (!si) {
		/*
		 * An acceptable race has occurred since the failing
		 * __swap_duplicate(): the swap device may be swapoff
		 */
		goto outer;
	}
	spin_lock(&si->lock);

	offset = swp_offset(entry);

	ci = lock_cluster(si, offset);

	count = si->swap_map[offset] & ~SWAP_HAS_CACHE;

	if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
		/*
		 * The higher the swap count, the more likely it is that tasks
		 * will race to add swap count continuation: we need to avoid
		 * over-provisioning.
		 */
		goto out;
	}

	if (!page) {
		ret = -ENOMEM;
		goto out;
	}

	/*
	 * We are fortunate that although vmalloc_to_page uses pte_offset_map,
	 * no architecture is using highmem pages for kernel page tables: so it
	 * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
	 */
	head = vmalloc_to_page(si->swap_map + offset);
	offset &= ~PAGE_MASK;

	spin_lock(&si->cont_lock);
	/*
	 * Page allocation does not initialize the page's lru field,
	 * but it does always reset its private field.
	 */
	if (!page_private(head)) {
		BUG_ON(count & COUNT_CONTINUED);
		INIT_LIST_HEAD(&head->lru);
		set_page_private(head, SWP_CONTINUED);
		si->flags |= SWP_CONTINUED;
	}

	list_for_each_entry(list_page, &head->lru, lru) {
		unsigned char *map;

		/*
		 * If the previous map said no continuation, but we've found
		 * a continuation page, free our allocation and use this one.
		 */
		if (!(count & COUNT_CONTINUED))
			goto out_unlock_cont;

		map = kmap_atomic(list_page) + offset;
		count = *map;
		kunmap_atomic(map);

		/*
		 * If this continuation count now has some space in it,
		 * free our allocation and use this one.
		 */
		if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
			goto out_unlock_cont;
	}

	list_add_tail(&page->lru, &head->lru);
	page = NULL;			/* now it's attached, don't free it */
out_unlock_cont:
	spin_unlock(&si->cont_lock);
out:
	unlock_cluster(ci);
	spin_unlock(&si->lock);
	put_swap_device(si);
outer:
	if (page)
		__free_page(page);
	return ret;
}

/*
 * swap_count_continued - when the original swap_map count is incremented
 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
 * into, carry if so, or else fail until a new continuation page is allocated;
 * when the original swap_map count is decremented from 0 with continuation,
 * borrow from the continuation and report whether it still holds more.
 * Called while __swap_duplicate() or swap_entry_free() holds swap or cluster
 * lock.
 */
static bool swap_count_continued(struct swap_info_struct *si,
				 pgoff_t offset, unsigned char count)
{
	struct page *head;
	struct page *page;
	unsigned char *map;
	bool ret;

	head = vmalloc_to_page(si->swap_map + offset);
	if (page_private(head) != SWP_CONTINUED) {
		BUG_ON(count & COUNT_CONTINUED);
		return false;		/* need to add count continuation */
	}

	spin_lock(&si->cont_lock);
	offset &= ~PAGE_MASK;
	page = list_entry(head->lru.next, struct page, lru);
	map = kmap_atomic(page) + offset;

	if (count == SWAP_MAP_MAX)	/* initial increment from swap_map */
		goto init_map;		/* jump over SWAP_CONT_MAX checks */

	if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
		/*
		 * Think of how you add 1 to 999
		 */
		while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
			kunmap_atomic(map);
			page = list_entry(page->lru.next, struct page, lru);
			BUG_ON(page == head);
			map = kmap_atomic(page) + offset;
		}
		if (*map == SWAP_CONT_MAX) {
			kunmap_atomic(map);
			page = list_entry(page->lru.next, struct page, lru);
			if (page == head) {
				ret = false;	/* add count continuation */
				goto out;
			}
			map = kmap_atomic(page) + offset;
init_map:		*map = 0;		/* we didn't zero the page */
		}
		*map += 1;
		kunmap_atomic(map);
		page = list_entry(page->lru.prev, struct page, lru);
		while (page != head) {
			map = kmap_atomic(page) + offset;
			*map = COUNT_CONTINUED;
			kunmap_atomic(map);
			page = list_entry(page->lru.prev, struct page, lru);
		}
		ret = true;			/* incremented */

	} else {				/* decrementing */
		/*
		 * Think of how you subtract 1 from 1000
		 */
		BUG_ON(count != COUNT_CONTINUED);
		while (*map == COUNT_CONTINUED) {
			kunmap_atomic(map);
			page = list_entry(page->lru.next, struct page, lru);
			BUG_ON(page == head);
			map = kmap_atomic(page) + offset;
		}
		BUG_ON(*map == 0);
		*map -= 1;
		if (*map == 0)
			count = 0;
		kunmap_atomic(map);
		page = list_entry(page->lru.prev, struct page, lru);
		while (page != head) {
			map = kmap_atomic(page) + offset;
			*map = SWAP_CONT_MAX | count;
			count = COUNT_CONTINUED;
			kunmap_atomic(map);
			page = list_entry(page->lru.prev, struct page, lru);
		}
		ret = count == COUNT_CONTINUED;
	}
out:
	spin_unlock(&si->cont_lock);
	return ret;
}

/*
 * free_swap_count_continuations - swapoff free all the continuation pages
 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
 */
static void free_swap_count_continuations(struct swap_info_struct *si)
{
	pgoff_t offset;

	for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
		struct page *head;
		head = vmalloc_to_page(si->swap_map + offset);
		if (page_private(head)) {
			struct page *page, *next;

			list_for_each_entry_safe(page, next, &head->lru, lru) {
				list_del(&page->lru);
				__free_page(page);
			}
		}
	}
}

#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
void mem_cgroup_throttle_swaprate(struct mem_cgroup *memcg, int node,
				  gfp_t gfp_mask)
{
	struct swap_info_struct *si, *next;
	if (!(gfp_mask & __GFP_IO) || !memcg)
		return;

	if (!blk_cgroup_congested())
		return;

	/*
	 * We've already scheduled a throttle, avoid taking the global swap
	 * lock.
	 */
	if (current->throttle_queue)
		return;

	spin_lock(&swap_avail_lock);
	plist_for_each_entry_safe(si, next, &swap_avail_heads[node],
				  avail_lists[node]) {
		if (si->bdev) {
			blkcg_schedule_throttle(bdev_get_queue(si->bdev),
						true);
			break;
		}
	}
	spin_unlock(&swap_avail_lock);
}
#endif

static int __init swapfile_init(void)
{
	int nid;

	swap_avail_heads = kmalloc_array(nr_node_ids, sizeof(struct plist_head),
					 GFP_KERNEL);
	if (!swap_avail_heads) {
		pr_emerg("Not enough memory for swap heads, swap is disabled\n");
		return -ENOMEM;
	}

	for_each_node(nid)
		plist_head_init(&swap_avail_heads[nid]);

	return 0;
}
subsys_initcall(swapfile_init);