free electrons

Embedded Linux Experts

   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
/*
 * fs/fs-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 *
 * Contains all the functions related to writing back and waiting
 * upon dirty inodes against superblocks, and writing back dirty
 * pages against inodes.  ie: data writeback.  Writeout of the
 * inode itself is not handled here.
 *
 * 10Apr2002	Andrew Morton
 *		Split out of fs/inode.c
 *		Additions for address_space-based writeback
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/kthread.h>
#include <linux/writeback.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/tracepoint.h>
#include <linux/device.h>
#include <linux/memcontrol.h>
#include "internal.h"

/*
 * 4MB minimal write chunk size
 */
#define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))

struct wb_completion {
	atomic_t		cnt;
};

/*
 * Passed into wb_writeback(), essentially a subset of writeback_control
 */
struct wb_writeback_work {
	long nr_pages;
	struct super_block *sb;
	unsigned long *older_than_this;
	enum writeback_sync_modes sync_mode;
	unsigned int tagged_writepages:1;
	unsigned int for_kupdate:1;
	unsigned int range_cyclic:1;
	unsigned int for_background:1;
	unsigned int for_sync:1;	/* sync(2) WB_SYNC_ALL writeback */
	unsigned int auto_free:1;	/* free on completion */
	enum wb_reason reason;		/* why was writeback initiated? */

	struct list_head list;		/* pending work list */
	struct wb_completion *done;	/* set if the caller waits */
};

/*
 * If one wants to wait for one or more wb_writeback_works, each work's
 * ->done should be set to a wb_completion defined using the following
 * macro.  Once all work items are issued with wb_queue_work(), the caller
 * can wait for the completion of all using wb_wait_for_completion().  Work
 * items which are waited upon aren't freed automatically on completion.
 */
#define DEFINE_WB_COMPLETION_ONSTACK(cmpl)				\
	struct wb_completion cmpl = {					\
		.cnt		= ATOMIC_INIT(1),			\
	}


/*
 * If an inode is constantly having its pages dirtied, but then the
 * updates stop dirtytime_expire_interval seconds in the past, it's
 * possible for the worst case time between when an inode has its
 * timestamps updated and when they finally get written out to be two
 * dirtytime_expire_intervals.  We set the default to 12 hours (in
 * seconds), which means most of the time inodes will have their
 * timestamps written to disk after 12 hours, but in the worst case a
 * few inodes might not their timestamps updated for 24 hours.
 */
unsigned int dirtytime_expire_interval = 12 * 60 * 60;

static inline struct inode *wb_inode(struct list_head *head)
{
	return list_entry(head, struct inode, i_io_list);
}

/*
 * Include the creation of the trace points after defining the
 * wb_writeback_work structure and inline functions so that the definition
 * remains local to this file.
 */
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.h>

EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);

static bool wb_io_lists_populated(struct bdi_writeback *wb)
{
	if (wb_has_dirty_io(wb)) {
		return false;
	} else {
		set_bit(WB_has_dirty_io, &wb->state);
		WARN_ON_ONCE(!wb->avg_write_bandwidth);
		atomic_long_add(wb->avg_write_bandwidth,
				&wb->bdi->tot_write_bandwidth);
		return true;
	}
}

static void wb_io_lists_depopulated(struct bdi_writeback *wb)
{
	if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
	    list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
		clear_bit(WB_has_dirty_io, &wb->state);
		WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
					&wb->bdi->tot_write_bandwidth) < 0);
	}
}

/**
 * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
 * @inode: inode to be moved
 * @wb: target bdi_writeback
 * @head: one of @wb->b_{dirty|io|more_io}
 *
 * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
 * Returns %true if @inode is the first occupant of the !dirty_time IO
 * lists; otherwise, %false.
 */
static bool inode_io_list_move_locked(struct inode *inode,
				      struct bdi_writeback *wb,
				      struct list_head *head)
{
	assert_spin_locked(&wb->list_lock);

	list_move(&inode->i_io_list, head);

	/* dirty_time doesn't count as dirty_io until expiration */
	if (head != &wb->b_dirty_time)
		return wb_io_lists_populated(wb);

	wb_io_lists_depopulated(wb);
	return false;
}

/**
 * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
 * @inode: inode to be removed
 * @wb: bdi_writeback @inode is being removed from
 *
 * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
 * clear %WB_has_dirty_io if all are empty afterwards.
 */
static void inode_io_list_del_locked(struct inode *inode,
				     struct bdi_writeback *wb)
{
	assert_spin_locked(&wb->list_lock);

	list_del_init(&inode->i_io_list);
	wb_io_lists_depopulated(wb);
}

static void wb_wakeup(struct bdi_writeback *wb)
{
	spin_lock_bh(&wb->work_lock);
	if (test_bit(WB_registered, &wb->state))
		mod_delayed_work(bdi_wq, &wb->dwork, 0);
	spin_unlock_bh(&wb->work_lock);
}

static void finish_writeback_work(struct bdi_writeback *wb,
				  struct wb_writeback_work *work)
{
	struct wb_completion *done = work->done;

	if (work->auto_free)
		kfree(work);
	if (done && atomic_dec_and_test(&done->cnt))
		wake_up_all(&wb->bdi->wb_waitq);
}

static void wb_queue_work(struct bdi_writeback *wb,
			  struct wb_writeback_work *work)
{
	trace_writeback_queue(wb, work);

	if (work->done)
		atomic_inc(&work->done->cnt);

	spin_lock_bh(&wb->work_lock);

	if (test_bit(WB_registered, &wb->state)) {
		list_add_tail(&work->list, &wb->work_list);
		mod_delayed_work(bdi_wq, &wb->dwork, 0);
	} else
		finish_writeback_work(wb, work);

	spin_unlock_bh(&wb->work_lock);
}

/**
 * wb_wait_for_completion - wait for completion of bdi_writeback_works
 * @bdi: bdi work items were issued to
 * @done: target wb_completion
 *
 * Wait for one or more work items issued to @bdi with their ->done field
 * set to @done, which should have been defined with
 * DEFINE_WB_COMPLETION_ONSTACK().  This function returns after all such
 * work items are completed.  Work items which are waited upon aren't freed
 * automatically on completion.
 */
static void wb_wait_for_completion(struct backing_dev_info *bdi,
				   struct wb_completion *done)
{
	atomic_dec(&done->cnt);		/* put down the initial count */
	wait_event(bdi->wb_waitq, !atomic_read(&done->cnt));
}

#ifdef CONFIG_CGROUP_WRITEBACK

/* parameters for foreign inode detection, see wb_detach_inode() */
#define WB_FRN_TIME_SHIFT	13	/* 1s = 2^13, upto 8 secs w/ 16bit */
#define WB_FRN_TIME_AVG_SHIFT	3	/* avg = avg * 7/8 + new * 1/8 */
#define WB_FRN_TIME_CUT_DIV	2	/* ignore rounds < avg / 2 */
#define WB_FRN_TIME_PERIOD	(2 * (1 << WB_FRN_TIME_SHIFT))	/* 2s */

#define WB_FRN_HIST_SLOTS	16	/* inode->i_wb_frn_history is 16bit */
#define WB_FRN_HIST_UNIT	(WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
					/* each slot's duration is 2s / 16 */
#define WB_FRN_HIST_THR_SLOTS	(WB_FRN_HIST_SLOTS / 2)
					/* if foreign slots >= 8, switch */
#define WB_FRN_HIST_MAX_SLOTS	(WB_FRN_HIST_THR_SLOTS / 2 + 1)
					/* one round can affect upto 5 slots */

static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
static struct workqueue_struct *isw_wq;

void __inode_attach_wb(struct inode *inode, struct page *page)
{
	struct backing_dev_info *bdi = inode_to_bdi(inode);
	struct bdi_writeback *wb = NULL;

	if (inode_cgwb_enabled(inode)) {
		struct cgroup_subsys_state *memcg_css;

		if (page) {
			memcg_css = mem_cgroup_css_from_page(page);
			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
		} else {
			/* must pin memcg_css, see wb_get_create() */
			memcg_css = task_get_css(current, memory_cgrp_id);
			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
			css_put(memcg_css);
		}
	}

	if (!wb)
		wb = &bdi->wb;

	/*
	 * There may be multiple instances of this function racing to
	 * update the same inode.  Use cmpxchg() to tell the winner.
	 */
	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
		wb_put(wb);
}

/**
 * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
 * @inode: inode of interest with i_lock held
 *
 * Returns @inode's wb with its list_lock held.  @inode->i_lock must be
 * held on entry and is released on return.  The returned wb is guaranteed
 * to stay @inode's associated wb until its list_lock is released.
 */
static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode *inode)
	__releases(&inode->i_lock)
	__acquires(&wb->list_lock)
{
	while (true) {
		struct bdi_writeback *wb = inode_to_wb(inode);

		/*
		 * inode_to_wb() association is protected by both
		 * @inode->i_lock and @wb->list_lock but list_lock nests
		 * outside i_lock.  Drop i_lock and verify that the
		 * association hasn't changed after acquiring list_lock.
		 */
		wb_get(wb);
		spin_unlock(&inode->i_lock);
		spin_lock(&wb->list_lock);

		/* i_wb may have changed inbetween, can't use inode_to_wb() */
		if (likely(wb == inode->i_wb)) {
			wb_put(wb);	/* @inode already has ref */
			return wb;
		}

		spin_unlock(&wb->list_lock);
		wb_put(wb);
		cpu_relax();
		spin_lock(&inode->i_lock);
	}
}

/**
 * inode_to_wb_and_lock_list - determine an inode's wb and lock it
 * @inode: inode of interest
 *
 * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
 * on entry.
 */
static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
	__acquires(&wb->list_lock)
{
	spin_lock(&inode->i_lock);
	return locked_inode_to_wb_and_lock_list(inode);
}

struct inode_switch_wbs_context {
	struct inode		*inode;
	struct bdi_writeback	*new_wb;

	struct rcu_head		rcu_head;
	struct work_struct	work;
};

static void inode_switch_wbs_work_fn(struct work_struct *work)
{
	struct inode_switch_wbs_context *isw =
		container_of(work, struct inode_switch_wbs_context, work);
	struct inode *inode = isw->inode;
	struct address_space *mapping = inode->i_mapping;
	struct bdi_writeback *old_wb = inode->i_wb;
	struct bdi_writeback *new_wb = isw->new_wb;
	struct radix_tree_iter iter;
	bool switched = false;
	void **slot;

	/*
	 * By the time control reaches here, RCU grace period has passed
	 * since I_WB_SWITCH assertion and all wb stat update transactions
	 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
	 * synchronizing against mapping->tree_lock.
	 *
	 * Grabbing old_wb->list_lock, inode->i_lock and mapping->tree_lock
	 * gives us exclusion against all wb related operations on @inode
	 * including IO list manipulations and stat updates.
	 */
	if (old_wb < new_wb) {
		spin_lock(&old_wb->list_lock);
		spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
	} else {
		spin_lock(&new_wb->list_lock);
		spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
	}
	spin_lock(&inode->i_lock);
	spin_lock_irq(&mapping->tree_lock);

	/*
	 * Once I_FREEING is visible under i_lock, the eviction path owns
	 * the inode and we shouldn't modify ->i_io_list.
	 */
	if (unlikely(inode->i_state & I_FREEING))
		goto skip_switch;

	/*
	 * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
	 * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
	 * pages actually under underwriteback.
	 */
	radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
				   PAGECACHE_TAG_DIRTY) {
		struct page *page = radix_tree_deref_slot_protected(slot,
							&mapping->tree_lock);
		if (likely(page) && PageDirty(page)) {
			__dec_wb_stat(old_wb, WB_RECLAIMABLE);
			__inc_wb_stat(new_wb, WB_RECLAIMABLE);
		}
	}

	radix_tree_for_each_tagged(slot, &mapping->page_tree, &iter, 0,
				   PAGECACHE_TAG_WRITEBACK) {
		struct page *page = radix_tree_deref_slot_protected(slot,
							&mapping->tree_lock);
		if (likely(page)) {
			WARN_ON_ONCE(!PageWriteback(page));
			__dec_wb_stat(old_wb, WB_WRITEBACK);
			__inc_wb_stat(new_wb, WB_WRITEBACK);
		}
	}

	wb_get(new_wb);

	/*
	 * Transfer to @new_wb's IO list if necessary.  The specific list
	 * @inode was on is ignored and the inode is put on ->b_dirty which
	 * is always correct including from ->b_dirty_time.  The transfer
	 * preserves @inode->dirtied_when ordering.
	 */
	if (!list_empty(&inode->i_io_list)) {
		struct inode *pos;

		inode_io_list_del_locked(inode, old_wb);
		inode->i_wb = new_wb;
		list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
			if (time_after_eq(inode->dirtied_when,
					  pos->dirtied_when))
				break;
		inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
	} else {
		inode->i_wb = new_wb;
	}

	/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
	inode->i_wb_frn_winner = 0;
	inode->i_wb_frn_avg_time = 0;
	inode->i_wb_frn_history = 0;
	switched = true;
skip_switch:
	/*
	 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
	 * ensures that the new wb is visible if they see !I_WB_SWITCH.
	 */
	smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);

	spin_unlock_irq(&mapping->tree_lock);
	spin_unlock(&inode->i_lock);
	spin_unlock(&new_wb->list_lock);
	spin_unlock(&old_wb->list_lock);

	if (switched) {
		wb_wakeup(new_wb);
		wb_put(old_wb);
	}
	wb_put(new_wb);

	iput(inode);
	kfree(isw);

	atomic_dec(&isw_nr_in_flight);
}

static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
{
	struct inode_switch_wbs_context *isw = container_of(rcu_head,
				struct inode_switch_wbs_context, rcu_head);

	/* needs to grab bh-unsafe locks, bounce to work item */
	INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
	queue_work(isw_wq, &isw->work);
}

/**
 * inode_switch_wbs - change the wb association of an inode
 * @inode: target inode
 * @new_wb_id: ID of the new wb
 *
 * Switch @inode's wb association to the wb identified by @new_wb_id.  The
 * switching is performed asynchronously and may fail silently.
 */
static void inode_switch_wbs(struct inode *inode, int new_wb_id)
{
	struct backing_dev_info *bdi = inode_to_bdi(inode);
	struct cgroup_subsys_state *memcg_css;
	struct inode_switch_wbs_context *isw;

	/* noop if seems to be already in progress */
	if (inode->i_state & I_WB_SWITCH)
		return;

	isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
	if (!isw)
		return;

	/* find and pin the new wb */
	rcu_read_lock();
	memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
	if (memcg_css)
		isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
	rcu_read_unlock();
	if (!isw->new_wb)
		goto out_free;

	/* while holding I_WB_SWITCH, no one else can update the association */
	spin_lock(&inode->i_lock);
	if (!(inode->i_sb->s_flags & MS_ACTIVE) ||
	    inode->i_state & (I_WB_SWITCH | I_FREEING) ||
	    inode_to_wb(inode) == isw->new_wb) {
		spin_unlock(&inode->i_lock);
		goto out_free;
	}
	inode->i_state |= I_WB_SWITCH;
	__iget(inode);
	spin_unlock(&inode->i_lock);

	isw->inode = inode;

	atomic_inc(&isw_nr_in_flight);

	/*
	 * In addition to synchronizing among switchers, I_WB_SWITCH tells
	 * the RCU protected stat update paths to grab the mapping's
	 * tree_lock so that stat transfer can synchronize against them.
	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
	 */
	call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
	return;

out_free:
	if (isw->new_wb)
		wb_put(isw->new_wb);
	kfree(isw);
}

/**
 * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
 * @wbc: writeback_control of interest
 * @inode: target inode
 *
 * @inode is locked and about to be written back under the control of @wbc.
 * Record @inode's writeback context into @wbc and unlock the i_lock.  On
 * writeback completion, wbc_detach_inode() should be called.  This is used
 * to track the cgroup writeback context.
 */
void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
				 struct inode *inode)
{
	if (!inode_cgwb_enabled(inode)) {
		spin_unlock(&inode->i_lock);
		return;
	}

	wbc->wb = inode_to_wb(inode);
	wbc->inode = inode;

	wbc->wb_id = wbc->wb->memcg_css->id;
	wbc->wb_lcand_id = inode->i_wb_frn_winner;
	wbc->wb_tcand_id = 0;
	wbc->wb_bytes = 0;
	wbc->wb_lcand_bytes = 0;
	wbc->wb_tcand_bytes = 0;

	wb_get(wbc->wb);
	spin_unlock(&inode->i_lock);

	/*
	 * A dying wb indicates that the memcg-blkcg mapping has changed
	 * and a new wb is already serving the memcg.  Switch immediately.
	 */
	if (unlikely(wb_dying(wbc->wb)))
		inode_switch_wbs(inode, wbc->wb_id);
}

/**
 * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
 * @wbc: writeback_control of the just finished writeback
 *
 * To be called after a writeback attempt of an inode finishes and undoes
 * wbc_attach_and_unlock_inode().  Can be called under any context.
 *
 * As concurrent write sharing of an inode is expected to be very rare and
 * memcg only tracks page ownership on first-use basis severely confining
 * the usefulness of such sharing, cgroup writeback tracks ownership
 * per-inode.  While the support for concurrent write sharing of an inode
 * is deemed unnecessary, an inode being written to by different cgroups at
 * different points in time is a lot more common, and, more importantly,
 * charging only by first-use can too readily lead to grossly incorrect
 * behaviors (single foreign page can lead to gigabytes of writeback to be
 * incorrectly attributed).
 *
 * To resolve this issue, cgroup writeback detects the majority dirtier of
 * an inode and transfers the ownership to it.  To avoid unnnecessary
 * oscillation, the detection mechanism keeps track of history and gives
 * out the switch verdict only if the foreign usage pattern is stable over
 * a certain amount of time and/or writeback attempts.
 *
 * On each writeback attempt, @wbc tries to detect the majority writer
 * using Boyer-Moore majority vote algorithm.  In addition to the byte
 * count from the majority voting, it also counts the bytes written for the
 * current wb and the last round's winner wb (max of last round's current
 * wb, the winner from two rounds ago, and the last round's majority
 * candidate).  Keeping track of the historical winner helps the algorithm
 * to semi-reliably detect the most active writer even when it's not the
 * absolute majority.
 *
 * Once the winner of the round is determined, whether the winner is
 * foreign or not and how much IO time the round consumed is recorded in
 * inode->i_wb_frn_history.  If the amount of recorded foreign IO time is
 * over a certain threshold, the switch verdict is given.
 */
void wbc_detach_inode(struct writeback_control *wbc)
{
	struct bdi_writeback *wb = wbc->wb;
	struct inode *inode = wbc->inode;
	unsigned long avg_time, max_bytes, max_time;
	u16 history;
	int max_id;

	if (!wb)
		return;

	history = inode->i_wb_frn_history;
	avg_time = inode->i_wb_frn_avg_time;

	/* pick the winner of this round */
	if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
	    wbc->wb_bytes >= wbc->wb_tcand_bytes) {
		max_id = wbc->wb_id;
		max_bytes = wbc->wb_bytes;
	} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
		max_id = wbc->wb_lcand_id;
		max_bytes = wbc->wb_lcand_bytes;
	} else {
		max_id = wbc->wb_tcand_id;
		max_bytes = wbc->wb_tcand_bytes;
	}

	/*
	 * Calculate the amount of IO time the winner consumed and fold it
	 * into the running average kept per inode.  If the consumed IO
	 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
	 * deciding whether to switch or not.  This is to prevent one-off
	 * small dirtiers from skewing the verdict.
	 */
	max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
				wb->avg_write_bandwidth);
	if (avg_time)
		avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
			    (avg_time >> WB_FRN_TIME_AVG_SHIFT);
	else
		avg_time = max_time;	/* immediate catch up on first run */

	if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
		int slots;

		/*
		 * The switch verdict is reached if foreign wb's consume
		 * more than a certain proportion of IO time in a
		 * WB_FRN_TIME_PERIOD.  This is loosely tracked by 16 slot
		 * history mask where each bit represents one sixteenth of
		 * the period.  Determine the number of slots to shift into
		 * history from @max_time.
		 */
		slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
			    (unsigned long)WB_FRN_HIST_MAX_SLOTS);
		history <<= slots;
		if (wbc->wb_id != max_id)
			history |= (1U << slots) - 1;

		/*
		 * Switch if the current wb isn't the consistent winner.
		 * If there are multiple closely competing dirtiers, the
		 * inode may switch across them repeatedly over time, which
		 * is okay.  The main goal is avoiding keeping an inode on
		 * the wrong wb for an extended period of time.
		 */
		if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
			inode_switch_wbs(inode, max_id);
	}

	/*
	 * Multiple instances of this function may race to update the
	 * following fields but we don't mind occassional inaccuracies.
	 */
	inode->i_wb_frn_winner = max_id;
	inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
	inode->i_wb_frn_history = history;

	wb_put(wbc->wb);
	wbc->wb = NULL;
}

/**
 * wbc_account_io - account IO issued during writeback
 * @wbc: writeback_control of the writeback in progress
 * @page: page being written out
 * @bytes: number of bytes being written out
 *
 * @bytes from @page are about to written out during the writeback
 * controlled by @wbc.  Keep the book for foreign inode detection.  See
 * wbc_detach_inode().
 */
void wbc_account_io(struct writeback_control *wbc, struct page *page,
		    size_t bytes)
{
	int id;

	/*
	 * pageout() path doesn't attach @wbc to the inode being written
	 * out.  This is intentional as we don't want the function to block
	 * behind a slow cgroup.  Ultimately, we want pageout() to kick off
	 * regular writeback instead of writing things out itself.
	 */
	if (!wbc->wb)
		return;

	id = mem_cgroup_css_from_page(page)->id;

	if (id == wbc->wb_id) {
		wbc->wb_bytes += bytes;
		return;
	}

	if (id == wbc->wb_lcand_id)
		wbc->wb_lcand_bytes += bytes;

	/* Boyer-Moore majority vote algorithm */
	if (!wbc->wb_tcand_bytes)
		wbc->wb_tcand_id = id;
	if (id == wbc->wb_tcand_id)
		wbc->wb_tcand_bytes += bytes;
	else
		wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
}
EXPORT_SYMBOL_GPL(wbc_account_io);

/**
 * inode_congested - test whether an inode is congested
 * @inode: inode to test for congestion (may be NULL)
 * @cong_bits: mask of WB_[a]sync_congested bits to test
 *
 * Tests whether @inode is congested.  @cong_bits is the mask of congestion
 * bits to test and the return value is the mask of set bits.
 *
 * If cgroup writeback is enabled for @inode, the congestion state is
 * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
 * associated with @inode is congested; otherwise, the root wb's congestion
 * state is used.
 *
 * @inode is allowed to be NULL as this function is often called on
 * mapping->host which is NULL for the swapper space.
 */
int inode_congested(struct inode *inode, int cong_bits)
{
	/*
	 * Once set, ->i_wb never becomes NULL while the inode is alive.
	 * Start transaction iff ->i_wb is visible.
	 */
	if (inode && inode_to_wb_is_valid(inode)) {
		struct bdi_writeback *wb;
		bool locked, congested;

		wb = unlocked_inode_to_wb_begin(inode, &locked);
		congested = wb_congested(wb, cong_bits);
		unlocked_inode_to_wb_end(inode, locked);
		return congested;
	}

	return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
}
EXPORT_SYMBOL_GPL(inode_congested);

/**
 * wb_split_bdi_pages - split nr_pages to write according to bandwidth
 * @wb: target bdi_writeback to split @nr_pages to
 * @nr_pages: number of pages to write for the whole bdi
 *
 * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
 * relation to the total write bandwidth of all wb's w/ dirty inodes on
 * @wb->bdi.
 */
static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
	unsigned long this_bw = wb->avg_write_bandwidth;
	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);

	if (nr_pages == LONG_MAX)
		return LONG_MAX;

	/*
	 * This may be called on clean wb's and proportional distribution
	 * may not make sense, just use the original @nr_pages in those
	 * cases.  In general, we wanna err on the side of writing more.
	 */
	if (!tot_bw || this_bw >= tot_bw)
		return nr_pages;
	else
		return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
}

/**
 * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
 * @bdi: target backing_dev_info
 * @base_work: wb_writeback_work to issue
 * @skip_if_busy: skip wb's which already have writeback in progress
 *
 * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
 * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
 * distributed to the busy wbs according to each wb's proportion in the
 * total active write bandwidth of @bdi.
 */
static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
				  struct wb_writeback_work *base_work,
				  bool skip_if_busy)
{
	struct bdi_writeback *last_wb = NULL;
	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
					      struct bdi_writeback, bdi_node);

	might_sleep();
restart:
	rcu_read_lock();
	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
		DEFINE_WB_COMPLETION_ONSTACK(fallback_work_done);
		struct wb_writeback_work fallback_work;
		struct wb_writeback_work *work;
		long nr_pages;

		if (last_wb) {
			wb_put(last_wb);
			last_wb = NULL;
		}

		/* SYNC_ALL writes out I_DIRTY_TIME too */
		if (!wb_has_dirty_io(wb) &&
		    (base_work->sync_mode == WB_SYNC_NONE ||
		     list_empty(&wb->b_dirty_time)))
			continue;
		if (skip_if_busy && writeback_in_progress(wb))
			continue;

		nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);

		work = kmalloc(sizeof(*work), GFP_ATOMIC);
		if (work) {
			*work = *base_work;
			work->nr_pages = nr_pages;
			work->auto_free = 1;
			wb_queue_work(wb, work);
			continue;
		}

		/* alloc failed, execute synchronously using on-stack fallback */
		work = &fallback_work;
		*work = *base_work;
		work->nr_pages = nr_pages;
		work->auto_free = 0;
		work->done = &fallback_work_done;

		wb_queue_work(wb, work);

		/*
		 * Pin @wb so that it stays on @bdi->wb_list.  This allows
		 * continuing iteration from @wb after dropping and
		 * regrabbing rcu read lock.
		 */
		wb_get(wb);
		last_wb = wb;

		rcu_read_unlock();
		wb_wait_for_completion(bdi, &fallback_work_done);
		goto restart;
	}
	rcu_read_unlock();

	if (last_wb)
		wb_put(last_wb);
}

/**
 * cgroup_writeback_umount - flush inode wb switches for umount
 *
 * This function is called when a super_block is about to be destroyed and
 * flushes in-flight inode wb switches.  An inode wb switch goes through
 * RCU and then workqueue, so the two need to be flushed in order to ensure
 * that all previously scheduled switches are finished.  As wb switches are
 * rare occurrences and synchronize_rcu() can take a while, perform
 * flushing iff wb switches are in flight.
 */
void cgroup_writeback_umount(void)
{
	if (atomic_read(&isw_nr_in_flight)) {
		synchronize_rcu();
		flush_workqueue(isw_wq);
	}
}

static int __init cgroup_writeback_init(void)
{
	isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
	if (!isw_wq)
		return -ENOMEM;
	return 0;
}
fs_initcall(cgroup_writeback_init);

#else	/* CONFIG_CGROUP_WRITEBACK */

static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode *inode)
	__releases(&inode->i_lock)
	__acquires(&wb->list_lock)
{
	struct bdi_writeback *wb = inode_to_wb(inode);

	spin_unlock(&inode->i_lock);
	spin_lock(&wb->list_lock);
	return wb;
}

static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
	__acquires(&wb->list_lock)
{
	struct bdi_writeback *wb = inode_to_wb(inode);

	spin_lock(&wb->list_lock);
	return wb;
}

static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
{
	return nr_pages;
}

static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
				  struct wb_writeback_work *base_work,
				  bool skip_if_busy)
{
	might_sleep();

	if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
		base_work->auto_free = 0;
		wb_queue_work(&bdi->wb, base_work);
	}
}

#endif	/* CONFIG_CGROUP_WRITEBACK */

void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
			bool range_cyclic, enum wb_reason reason)
{
	struct wb_writeback_work *work;

	if (!wb_has_dirty_io(wb))
		return;

	/*
	 * This is WB_SYNC_NONE writeback, so if allocation fails just
	 * wakeup the thread for old dirty data writeback
	 */
	work = kzalloc(sizeof(*work),
		       GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
	if (!work) {
		trace_writeback_nowork(wb);
		wb_wakeup(wb);
		return;
	}

	work->sync_mode	= WB_SYNC_NONE;
	work->nr_pages	= nr_pages;
	work->range_cyclic = range_cyclic;
	work->reason	= reason;
	work->auto_free	= 1;

	wb_queue_work(wb, work);
}

/**
 * wb_start_background_writeback - start background writeback
 * @wb: bdi_writback to write from
 *
 * Description:
 *   This makes sure WB_SYNC_NONE background writeback happens. When
 *   this function returns, it is only guaranteed that for given wb
 *   some IO is happening if we are over background dirty threshold.
 *   Caller need not hold sb s_umount semaphore.
 */
void wb_start_background_writeback(struct bdi_writeback *wb)
{
	/*
	 * We just wake up the flusher thread. It will perform background
	 * writeback as soon as there is no other work to do.
	 */
	trace_writeback_wake_background(wb);
	wb_wakeup(wb);
}

/*
 * Remove the inode from the writeback list it is on.
 */
void inode_io_list_del(struct inode *inode)
{
	struct bdi_writeback *wb;

	wb = inode_to_wb_and_lock_list(inode);
	inode_io_list_del_locked(inode, wb);
	spin_unlock(&wb->list_lock);
}

/*
 * mark an inode as under writeback on the sb
 */
void sb_mark_inode_writeback(struct inode *inode)
{
	struct super_block *sb = inode->i_sb;
	unsigned long flags;

	if (list_empty(&inode->i_wb_list)) {
		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
		if (list_empty(&inode->i_wb_list)) {
			list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
			trace_sb_mark_inode_writeback(inode);
		}
		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
	}
}

/*
 * clear an inode as under writeback on the sb
 */
void sb_clear_inode_writeback(struct inode *inode)
{
	struct super_block *sb = inode->i_sb;
	unsigned long flags;

	if (!list_empty(&inode->i_wb_list)) {
		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
		if (!list_empty(&inode->i_wb_list)) {
			list_del_init(&inode->i_wb_list);
			trace_sb_clear_inode_writeback(inode);
		}
		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
	}
}

/*
 * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
 * furthest end of its superblock's dirty-inode list.
 *
 * Before stamping the inode's ->dirtied_when, we check to see whether it is
 * already the most-recently-dirtied inode on the b_dirty list.  If that is
 * the case then the inode must have been redirtied while it was being written
 * out and we don't reset its dirtied_when.
 */
static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
{
	if (!list_empty(&wb->b_dirty)) {
		struct inode *tail;

		tail = wb_inode(wb->b_dirty.next);
		if (time_before(inode->dirtied_when, tail->dirtied_when))
			inode->dirtied_when = jiffies;
	}
	inode_io_list_move_locked(inode, wb, &wb->b_dirty);
}

/*
 * requeue inode for re-scanning after bdi->b_io list is exhausted.
 */
static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
{
	inode_io_list_move_locked(inode, wb, &wb->b_more_io);
}

static void inode_sync_complete(struct inode *inode)
{
	inode->i_state &= ~I_SYNC;
	/* If inode is clean an unused, put it into LRU now... */
	inode_add_lru(inode);
	/* Waiters must see I_SYNC cleared before being woken up */
	smp_mb();
	wake_up_bit(&inode->i_state, __I_SYNC);
}

static bool inode_dirtied_after(struct inode *inode, unsigned long t)
{
	bool ret = time_after(inode->dirtied_when, t);
#ifndef CONFIG_64BIT
	/*
	 * For inodes being constantly redirtied, dirtied_when can get stuck.
	 * It _appears_ to be in the future, but is actually in distant past.
	 * This test is necessary to prevent such wrapped-around relative times
	 * from permanently stopping the whole bdi writeback.
	 */
	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
#endif
	return ret;
}

#define EXPIRE_DIRTY_ATIME 0x0001

/*
 * Move expired (dirtied before work->older_than_this) dirty inodes from
 * @delaying_queue to @dispatch_queue.
 */
static int move_expired_inodes(struct list_head *delaying_queue,
			       struct list_head *dispatch_queue,
			       int flags,
			       struct wb_writeback_work *work)
{
	unsigned long *older_than_this = NULL;
	unsigned long expire_time;
	LIST_HEAD(tmp);
	struct list_head *pos, *node;
	struct super_block *sb = NULL;
	struct inode *inode;
	int do_sb_sort = 0;
	int moved = 0;

	if ((flags & EXPIRE_DIRTY_ATIME) == 0)
		older_than_this = work->older_than_this;
	else if (!work->for_sync) {
		expire_time = jiffies - (dirtytime_expire_interval * HZ);
		older_than_this = &expire_time;
	}
	while (!list_empty(delaying_queue)) {
		inode = wb_inode(delaying_queue->prev);
		if (older_than_this &&
		    inode_dirtied_after(inode, *older_than_this))
			break;
		list_move(&inode->i_io_list, &tmp);
		moved++;
		if (flags & EXPIRE_DIRTY_ATIME)
			set_bit(__I_DIRTY_TIME_EXPIRED, &inode->i_state);
		if (sb_is_blkdev_sb(inode->i_sb))
			continue;
		if (sb && sb != inode->i_sb)
			do_sb_sort = 1;
		sb = inode->i_sb;
	}

	/* just one sb in list, splice to dispatch_queue and we're done */
	if (!do_sb_sort) {
		list_splice(&tmp, dispatch_queue);
		goto out;
	}

	/* Move inodes from one superblock together */
	while (!list_empty(&tmp)) {
		sb = wb_inode(tmp.prev)->i_sb;
		list_for_each_prev_safe(pos, node, &tmp) {
			inode = wb_inode(pos);
			if (inode->i_sb == sb)
				list_move(&inode->i_io_list, dispatch_queue);
		}
	}
out:
	return moved;
}

/*
 * Queue all expired dirty inodes for io, eldest first.
 * Before
 *         newly dirtied     b_dirty    b_io    b_more_io
 *         =============>    gf         edc     BA
 * After
 *         newly dirtied     b_dirty    b_io    b_more_io
 *         =============>    g          fBAedc
 *                                           |
 *                                           +--> dequeue for IO
 */
static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work)
{
	int moved;

	assert_spin_locked(&wb->list_lock);
	list_splice_init(&wb->b_more_io, &wb->b_io);
	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, 0, work);
	moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
				     EXPIRE_DIRTY_ATIME, work);
	if (moved)
		wb_io_lists_populated(wb);
	trace_writeback_queue_io(wb, work, moved);
}

static int write_inode(struct inode *inode, struct writeback_control *wbc)
{
	int ret;

	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
		trace_writeback_write_inode_start(inode, wbc);
		ret = inode->i_sb->s_op->write_inode(inode, wbc);
		trace_writeback_write_inode(inode, wbc);
		return ret;
	}
	return 0;
}

/*
 * Wait for writeback on an inode to complete. Called with i_lock held.
 * Caller must make sure inode cannot go away when we drop i_lock.
 */
static void __inode_wait_for_writeback(struct inode *inode)
	__releases(inode->i_lock)
	__acquires(inode->i_lock)
{
	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
	wait_queue_head_t *wqh;

	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
	while (inode->i_state & I_SYNC) {
		spin_unlock(&inode->i_lock);
		__wait_on_bit(wqh, &wq, bit_wait,
			      TASK_UNINTERRUPTIBLE);
		spin_lock(&inode->i_lock);
	}
}

/*
 * Wait for writeback on an inode to complete. Caller must have inode pinned.
 */
void inode_wait_for_writeback(struct inode *inode)
{
	spin_lock(&inode->i_lock);
	__inode_wait_for_writeback(inode);
	spin_unlock(&inode->i_lock);
}

/*
 * Sleep until I_SYNC is cleared. This function must be called with i_lock
 * held and drops it. It is aimed for callers not holding any inode reference
 * so once i_lock is dropped, inode can go away.
 */
static void inode_sleep_on_writeback(struct inode *inode)
	__releases(inode->i_lock)
{
	DEFINE_WAIT(wait);
	wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
	int sleep;

	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
	sleep = inode->i_state & I_SYNC;
	spin_unlock(&inode->i_lock);
	if (sleep)
		schedule();
	finish_wait(wqh, &wait);
}

/*
 * Find proper writeback list for the inode depending on its current state and
 * possibly also change of its state while we were doing writeback.  Here we
 * handle things such as livelock prevention or fairness of writeback among
 * inodes. This function can be called only by flusher thread - noone else
 * processes all inodes in writeback lists and requeueing inodes behind flusher
 * thread's back can have unexpected consequences.
 */
static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
			  struct writeback_control *wbc)
{
	if (inode->i_state & I_FREEING)
		return;

	/*
	 * Sync livelock prevention. Each inode is tagged and synced in one
	 * shot. If still dirty, it will be redirty_tail()'ed below.  Update
	 * the dirty time to prevent enqueue and sync it again.
	 */
	if ((inode->i_state & I_DIRTY) &&
	    (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
		inode->dirtied_when = jiffies;

	if (wbc->pages_skipped) {
		/*
		 * writeback is not making progress due to locked
		 * buffers. Skip this inode for now.
		 */
		redirty_tail(inode, wb);
		return;
	}

	if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
		/*
		 * We didn't write back all the pages.  nfs_writepages()
		 * sometimes bales out without doing anything.
		 */
		if (wbc->nr_to_write <= 0) {
			/* Slice used up. Queue for next turn. */
			requeue_io(inode, wb);
		} else {
			/*
			 * Writeback blocked by something other than
			 * congestion. Delay the inode for some time to
			 * avoid spinning on the CPU (100% iowait)
			 * retrying writeback of the dirty page/inode
			 * that cannot be performed immediately.
			 */
			redirty_tail(inode, wb);
		}
	} else if (inode->i_state & I_DIRTY) {
		/*
		 * Filesystems can dirty the inode during writeback operations,
		 * such as delayed allocation during submission or metadata
		 * updates after data IO completion.
		 */
		redirty_tail(inode, wb);
	} else if (inode->i_state & I_DIRTY_TIME) {
		inode->dirtied_when = jiffies;
		inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
	} else {
		/* The inode is clean. Remove from writeback lists. */
		inode_io_list_del_locked(inode, wb);
	}
}

/*
 * Write out an inode and its dirty pages. Do not update the writeback list
 * linkage. That is left to the caller. The caller is also responsible for
 * setting I_SYNC flag and calling inode_sync_complete() to clear it.
 */
static int
__writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
{
	struct address_space *mapping = inode->i_mapping;
	long nr_to_write = wbc->nr_to_write;
	unsigned dirty;
	int ret;

	WARN_ON(!(inode->i_state & I_SYNC));

	trace_writeback_single_inode_start(inode, wbc, nr_to_write);

	ret = do_writepages(mapping, wbc);

	/*
	 * Make sure to wait on the data before writing out the metadata.
	 * This is important for filesystems that modify metadata on data
	 * I/O completion. We don't do it for sync(2) writeback because it has a
	 * separate, external IO completion path and ->sync_fs for guaranteeing
	 * inode metadata is written back correctly.
	 */
	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
		int err = filemap_fdatawait(mapping);
		if (ret == 0)
			ret = err;
	}

	/*
	 * Some filesystems may redirty the inode during the writeback
	 * due to delalloc, clear dirty metadata flags right before
	 * write_inode()
	 */
	spin_lock(&inode->i_lock);

	dirty = inode->i_state & I_DIRTY;
	if (inode->i_state & I_DIRTY_TIME) {
		if ((dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) ||
		    wbc->sync_mode == WB_SYNC_ALL ||
		    unlikely(inode->i_state & I_DIRTY_TIME_EXPIRED) ||
		    unlikely(time_after(jiffies,
					(inode->dirtied_time_when +
					 dirtytime_expire_interval * HZ)))) {
			dirty |= I_DIRTY_TIME | I_DIRTY_TIME_EXPIRED;
			trace_writeback_lazytime(inode);
		}
	} else
		inode->i_state &= ~I_DIRTY_TIME_EXPIRED;
	inode->i_state &= ~dirty;

	/*
	 * Paired with smp_mb() in __mark_inode_dirty().  This allows
	 * __mark_inode_dirty() to test i_state without grabbing i_lock -
	 * either they see the I_DIRTY bits cleared or we see the dirtied
	 * inode.
	 *
	 * I_DIRTY_PAGES is always cleared together above even if @mapping
	 * still has dirty pages.  The flag is reinstated after smp_mb() if
	 * necessary.  This guarantees that either __mark_inode_dirty()
	 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
	 */
	smp_mb();

	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
		inode->i_state |= I_DIRTY_PAGES;

	spin_unlock(&inode->i_lock);

	if (dirty & I_DIRTY_TIME)
		mark_inode_dirty_sync(inode);
	/* Don't write the inode if only I_DIRTY_PAGES was set */
	if (dirty & ~I_DIRTY_PAGES) {
		int err = write_inode(inode, wbc);
		if (ret == 0)
			ret = err;
	}
	trace_writeback_single_inode(inode, wbc, nr_to_write);
	return ret;
}

/*
 * Write out an inode's dirty pages. Either the caller has an active reference
 * on the inode or the inode has I_WILL_FREE set.
 *
 * This function is designed to be called for writing back one inode which
 * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
 * and does more profound writeback list handling in writeback_sb_inodes().
 */
static int writeback_single_inode(struct inode *inode,
				  struct writeback_control *wbc)
{
	struct bdi_writeback *wb;
	int ret = 0;

	spin_lock(&inode->i_lock);
	if (!atomic_read(&inode->i_count))
		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
	else
		WARN_ON(inode->i_state & I_WILL_FREE);

	if (inode->i_state & I_SYNC) {
		if (wbc->sync_mode != WB_SYNC_ALL)
			goto out;
		/*
		 * It's a data-integrity sync. We must wait. Since callers hold
		 * inode reference or inode has I_WILL_FREE set, it cannot go
		 * away under us.
		 */
		__inode_wait_for_writeback(inode);
	}
	WARN_ON(inode->i_state & I_SYNC);
	/*
	 * Skip inode if it is clean and we have no outstanding writeback in
	 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
	 * function since flusher thread may be doing for example sync in
	 * parallel and if we move the inode, it could get skipped. So here we
	 * make sure inode is on some writeback list and leave it there unless
	 * we have completely cleaned the inode.
	 */
	if (!(inode->i_state & I_DIRTY_ALL) &&
	    (wbc->sync_mode != WB_SYNC_ALL ||
	     !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
		goto out;
	inode->i_state |= I_SYNC;
	wbc_attach_and_unlock_inode(wbc, inode);

	ret = __writeback_single_inode(inode, wbc);

	wbc_detach_inode(wbc);

	wb = inode_to_wb_and_lock_list(inode);
	spin_lock(&inode->i_lock);
	/*
	 * If inode is clean, remove it from writeback lists. Otherwise don't
	 * touch it. See comment above for explanation.
	 */
	if (!(inode->i_state & I_DIRTY_ALL))
		inode_io_list_del_locked(inode, wb);
	spin_unlock(&wb->list_lock);
	inode_sync_complete(inode);
out:
	spin_unlock(&inode->i_lock);
	return ret;
}

static long writeback_chunk_size(struct bdi_writeback *wb,
				 struct wb_writeback_work *work)
{
	long pages;

	/*
	 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
	 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
	 * here avoids calling into writeback_inodes_wb() more than once.
	 *
	 * The intended call sequence for WB_SYNC_ALL writeback is:
	 *
	 *      wb_writeback()
	 *          writeback_sb_inodes()       <== called only once
	 *              write_cache_pages()     <== called once for each inode
	 *                   (quickly) tag currently dirty pages
	 *                   (maybe slowly) sync all tagged pages
	 */
	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
		pages = LONG_MAX;
	else {
		pages = min(wb->avg_write_bandwidth / 2,
			    global_wb_domain.dirty_limit / DIRTY_SCOPE);
		pages = min(pages, work->nr_pages);
		pages = round_down(pages + MIN_WRITEBACK_PAGES,
				   MIN_WRITEBACK_PAGES);
	}

	return pages;
}

/*
 * Write a portion of b_io inodes which belong to @sb.
 *
 * Return the number of pages and/or inodes written.
 *
 * NOTE! This is called with wb->list_lock held, and will
 * unlock and relock that for each inode it ends up doing
 * IO for.
 */
static long writeback_sb_inodes(struct super_block *sb,
				struct bdi_writeback *wb,
				struct wb_writeback_work *work)
{
	struct writeback_control wbc = {
		.sync_mode		= work->sync_mode,
		.tagged_writepages	= work->tagged_writepages,
		.for_kupdate		= work->for_kupdate,
		.for_background		= work->for_background,
		.for_sync		= work->for_sync,
		.range_cyclic		= work->range_cyclic,
		.range_start		= 0,
		.range_end		= LLONG_MAX,
	};
	unsigned long start_time = jiffies;
	long write_chunk;
	long wrote = 0;  /* count both pages and inodes */

	while (!list_empty(&wb->b_io)) {
		struct inode *inode = wb_inode(wb->b_io.prev);
		struct bdi_writeback *tmp_wb;

		if (inode->i_sb != sb) {
			if (work->sb) {
				/*
				 * We only want to write back data for this
				 * superblock, move all inodes not belonging
				 * to it back onto the dirty list.
				 */
				redirty_tail(inode, wb);
				continue;
			}

			/*
			 * The inode belongs to a different superblock.
			 * Bounce back to the caller to unpin this and
			 * pin the next superblock.
			 */
			break;
		}

		/*
		 * Don't bother with new inodes or inodes being freed, first
		 * kind does not need periodic writeout yet, and for the latter
		 * kind writeout is handled by the freer.
		 */
		spin_lock(&inode->i_lock);
		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
			spin_unlock(&inode->i_lock);
			redirty_tail(inode, wb);
			continue;
		}
		if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
			/*
			 * If this inode is locked for writeback and we are not
			 * doing writeback-for-data-integrity, move it to
			 * b_more_io so that writeback can proceed with the
			 * other inodes on s_io.
			 *
			 * We'll have another go at writing back this inode
			 * when we completed a full scan of b_io.
			 */
			spin_unlock(&inode->i_lock);
			requeue_io(inode, wb);
			trace_writeback_sb_inodes_requeue(inode);
			continue;
		}
		spin_unlock(&wb->list_lock);

		/*
		 * We already requeued the inode if it had I_SYNC set and we
		 * are doing WB_SYNC_NONE writeback. So this catches only the
		 * WB_SYNC_ALL case.
		 */
		if (inode->i_state & I_SYNC) {
			/* Wait for I_SYNC. This function drops i_lock... */
			inode_sleep_on_writeback(inode);
			/* Inode may be gone, start again */
			spin_lock(&wb->list_lock);
			continue;
		}
		inode->i_state |= I_SYNC;
		wbc_attach_and_unlock_inode(&wbc, inode);

		write_chunk = writeback_chunk_size(wb, work);
		wbc.nr_to_write = write_chunk;
		wbc.pages_skipped = 0;

		/*
		 * We use I_SYNC to pin the inode in memory. While it is set
		 * evict_inode() will wait so the inode cannot be freed.
		 */
		__writeback_single_inode(inode, &wbc);

		wbc_detach_inode(&wbc);
		work->nr_pages -= write_chunk - wbc.nr_to_write;
		wrote += write_chunk - wbc.nr_to_write;

		if (need_resched()) {
			/*
			 * We're trying to balance between building up a nice
			 * long list of IOs to improve our merge rate, and
			 * getting those IOs out quickly for anyone throttling
			 * in balance_dirty_pages().  cond_resched() doesn't
			 * unplug, so get our IOs out the door before we
			 * give up the CPU.
			 */
			blk_flush_plug(current);
			cond_resched();
		}

		/*
		 * Requeue @inode if still dirty.  Be careful as @inode may
		 * have been switched to another wb in the meantime.
		 */
		tmp_wb = inode_to_wb_and_lock_list(inode);
		spin_lock(&inode->i_lock);
		if (!(inode->i_state & I_DIRTY_ALL))
			wrote++;
		requeue_inode(inode, tmp_wb, &wbc);
		inode_sync_complete(inode);
		spin_unlock(&inode->i_lock);

		if (unlikely(tmp_wb != wb)) {
			spin_unlock(&tmp_wb->list_lock);
			spin_lock(&wb->list_lock);
		}

		/*
		 * bail out to wb_writeback() often enough to check
		 * background threshold and other termination conditions.
		 */
		if (wrote) {
			if (time_is_before_jiffies(start_time + HZ / 10UL))
				break;
			if (work->nr_pages <= 0)
				break;
		}
	}
	return wrote;
}

static long __writeback_inodes_wb(struct bdi_writeback *wb,
				  struct wb_writeback_work *work)
{
	unsigned long start_time = jiffies;
	long wrote = 0;

	while (!list_empty(&wb->b_io)) {
		struct inode *inode = wb_inode(wb->b_io.prev);
		struct super_block *sb = inode->i_sb;

		if (!trylock_super(sb)) {
			/*
			 * trylock_super() may fail consistently due to
			 * s_umount being grabbed by someone else. Don't use
			 * requeue_io() to avoid busy retrying the inode/sb.
			 */
			redirty_tail(inode, wb);
			continue;
		}
		wrote += writeback_sb_inodes(sb, wb, work);
		up_read(&sb->s_umount);

		/* refer to the same tests at the end of writeback_sb_inodes */
		if (wrote) {
			if (time_is_before_jiffies(start_time + HZ / 10UL))
				break;
			if (work->nr_pages <= 0)
				break;
		}
	}
	/* Leave any unwritten inodes on b_io */
	return wrote;
}

static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
				enum wb_reason reason)
{
	struct wb_writeback_work work = {
		.nr_pages	= nr_pages,
		.sync_mode	= WB_SYNC_NONE,
		.range_cyclic	= 1,
		.reason		= reason,
	};
	struct blk_plug plug;

	blk_start_plug(&plug);
	spin_lock(&wb->list_lock);
	if (list_empty(&wb->b_io))
		queue_io(wb, &work);
	__writeback_inodes_wb(wb, &work);
	spin_unlock(&wb->list_lock);
	blk_finish_plug(&plug);

	return nr_pages - work.nr_pages;
}

/*
 * Explicit flushing or periodic writeback of "old" data.
 *
 * Define "old": the first time one of an inode's pages is dirtied, we mark the
 * dirtying-time in the inode's address_space.  So this periodic writeback code
 * just walks the superblock inode list, writing back any inodes which are
 * older than a specific point in time.
 *
 * Try to run once per dirty_writeback_interval.  But if a writeback event
 * takes longer than a dirty_writeback_interval interval, then leave a
 * one-second gap.
 *
 * older_than_this takes precedence over nr_to_write.  So we'll only write back
 * all dirty pages if they are all attached to "old" mappings.
 */
static long wb_writeback(struct bdi_writeback *wb,
			 struct wb_writeback_work *work)
{
	unsigned long wb_start = jiffies;
	long nr_pages = work->nr_pages;
	unsigned long oldest_jif;
	struct inode *inode;
	long progress;
	struct blk_plug plug;

	oldest_jif = jiffies;
	work->older_than_this = &oldest_jif;

	blk_start_plug(&plug);
	spin_lock(&wb->list_lock);
	for (;;) {
		/*
		 * Stop writeback when nr_pages has been consumed
		 */
		if (work->nr_pages <= 0)
			break;

		/*
		 * Background writeout and kupdate-style writeback may
		 * run forever. Stop them if there is other work to do
		 * so that e.g. sync can proceed. They'll be restarted
		 * after the other works are all done.
		 */
		if ((work->for_background || work->for_kupdate) &&
		    !list_empty(&wb->work_list))
			break;

		/*
		 * For background writeout, stop when we are below the
		 * background dirty threshold
		 */
		if (work->for_background && !wb_over_bg_thresh(wb))
			break;

		/*
		 * Kupdate and background works are special and we want to
		 * include all inodes that need writing. Livelock avoidance is
		 * handled by these works yielding to any other work so we are
		 * safe.
		 */
		if (work->for_kupdate) {
			oldest_jif = jiffies -
				msecs_to_jiffies(dirty_expire_interval * 10);
		} else if (work->for_background)
			oldest_jif = jiffies;

		trace_writeback_start(wb, work);
		if (list_empty(&wb->b_io))
			queue_io(wb, work);
		if (work->sb)
			progress = writeback_sb_inodes(work->sb, wb, work);
		else
			progress = __writeback_inodes_wb(wb, work);
		trace_writeback_written(wb, work);

		wb_update_bandwidth(wb, wb_start);

		/*
		 * Did we write something? Try for more
		 *
		 * Dirty inodes are moved to b_io for writeback in batches.
		 * The completion of the current batch does not necessarily
		 * mean the overall work is done. So we keep looping as long
		 * as made some progress on cleaning pages or inodes.
		 */
		if (progress)
			continue;
		/*
		 * No more inodes for IO, bail
		 */
		if (list_empty(&wb->b_more_io))
			break;
		/*
		 * Nothing written. Wait for some inode to
		 * become available for writeback. Otherwise
		 * we'll just busyloop.
		 */
		trace_writeback_wait(wb, work);
		inode = wb_inode(wb->b_more_io.prev);
		spin_lock(&inode->i_lock);
		spin_unlock(&wb->list_lock);
		/* This function drops i_lock... */
		inode_sleep_on_writeback(inode);
		spin_lock(&wb->list_lock);
	}
	spin_unlock(&wb->list_lock);
	blk_finish_plug(&plug);

	return nr_pages - work->nr_pages;
}

/*
 * Return the next wb_writeback_work struct that hasn't been processed yet.
 */
static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
{
	struct wb_writeback_work *work = NULL;

	spin_lock_bh(&wb->work_lock);
	if (!list_empty(&wb->work_list)) {
		work = list_entry(wb->work_list.next,
				  struct wb_writeback_work, list);
		list_del_init(&work->list);
	}
	spin_unlock_bh(&wb->work_lock);
	return work;
}

/*
 * Add in the number of potentially dirty inodes, because each inode
 * write can dirty pagecache in the underlying blockdev.
 */
static unsigned long get_nr_dirty_pages(void)
{
	return global_node_page_state(NR_FILE_DIRTY) +
		global_node_page_state(NR_UNSTABLE_NFS) +
		get_nr_dirty_inodes();
}

static long wb_check_background_flush(struct bdi_writeback *wb)
{
	if (wb_over_bg_thresh(wb)) {

		struct wb_writeback_work work = {
			.nr_pages	= LONG_MAX,
			.sync_mode	= WB_SYNC_NONE,
			.for_background	= 1,
			.range_cyclic	= 1,
			.reason		= WB_REASON_BACKGROUND,
		};

		return wb_writeback(wb, &work);
	}

	return 0;
}

static long wb_check_old_data_flush(struct bdi_writeback *wb)
{
	unsigned long expired;
	long nr_pages;

	/*
	 * When set to zero, disable periodic writeback
	 */
	if (!dirty_writeback_interval)
		return 0;

	expired = wb->last_old_flush +
			msecs_to_jiffies(dirty_writeback_interval * 10);
	if (time_before(jiffies, expired))
		return 0;

	wb->last_old_flush = jiffies;
	nr_pages = get_nr_dirty_pages();

	if (nr_pages) {
		struct wb_writeback_work work = {
			.nr_pages	= nr_pages,
			.sync_mode	= WB_SYNC_NONE,
			.for_kupdate	= 1,
			.range_cyclic	= 1,
			.reason		= WB_REASON_PERIODIC,
		};

		return wb_writeback(wb, &work);
	}

	return 0;
}

/*
 * Retrieve work items and do the writeback they describe
 */
static long wb_do_writeback(struct bdi_writeback *wb)
{
	struct wb_writeback_work *work;
	long wrote = 0;

	set_bit(WB_writeback_running, &wb->state);
	while ((work = get_next_work_item(wb)) != NULL) {
		trace_writeback_exec(wb, work);
		wrote += wb_writeback(wb, work);
		finish_writeback_work(wb, work);
	}

	/*
	 * Check for periodic writeback, kupdated() style
	 */
	wrote += wb_check_old_data_flush(wb);
	wrote += wb_check_background_flush(wb);
	clear_bit(WB_writeback_running, &wb->state);

	return wrote;
}

/*
 * Handle writeback of dirty data for the device backed by this bdi. Also
 * reschedules periodically and does kupdated style flushing.
 */
void wb_workfn(struct work_struct *work)
{
	struct bdi_writeback *wb = container_of(to_delayed_work(work),
						struct bdi_writeback, dwork);
	long pages_written;

	set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
	current->flags |= PF_SWAPWRITE;

	if (likely(!current_is_workqueue_rescuer() ||
		   !test_bit(WB_registered, &wb->state))) {
		/*
		 * The normal path.  Keep writing back @wb until its
		 * work_list is empty.  Note that this path is also taken
		 * if @wb is shutting down even when we're running off the
		 * rescuer as work_list needs to be drained.
		 */
		do {
			pages_written = wb_do_writeback(wb);
			trace_writeback_pages_written(pages_written);
		} while (!list_empty(&wb->work_list));
	} else {
		/*
		 * bdi_wq can't get enough workers and we're running off
		 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
		 * enough for efficient IO.
		 */
		pages_written = writeback_inodes_wb(wb, 1024,
						    WB_REASON_FORKER_THREAD);
		trace_writeback_pages_written(pages_written);
	}

	if (!list_empty(&wb->work_list))
		mod_delayed_work(bdi_wq, &wb->dwork, 0);
	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
		wb_wakeup_delayed(wb);

	current->flags &= ~PF_SWAPWRITE;
}

/*
 * Start writeback of `nr_pages' pages.  If `nr_pages' is zero, write back
 * the whole world.
 */
void wakeup_flusher_threads(long nr_pages, enum wb_reason reason)
{
	struct backing_dev_info *bdi;

	/*
	 * If we are expecting writeback progress we must submit plugged IO.
	 */
	if (blk_needs_flush_plug(current))
		blk_schedule_flush_plug(current);

	if (!nr_pages)
		nr_pages = get_nr_dirty_pages();

	rcu_read_lock();
	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
		struct bdi_writeback *wb;

		if (!bdi_has_dirty_io(bdi))
			continue;

		list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
			wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
					   false, reason);
	}
	rcu_read_unlock();
}

/*
 * Wake up bdi's periodically to make sure dirtytime inodes gets
 * written back periodically.  We deliberately do *not* check the
 * b_dirtytime list in wb_has_dirty_io(), since this would cause the
 * kernel to be constantly waking up once there are any dirtytime
 * inodes on the system.  So instead we define a separate delayed work
 * function which gets called much more rarely.  (By default, only
 * once every 12 hours.)
 *
 * If there is any other write activity going on in the file system,
 * this function won't be necessary.  But if the only thing that has
 * happened on the file system is a dirtytime inode caused by an atime
 * update, we need this infrastructure below to make sure that inode
 * eventually gets pushed out to disk.
 */
static void wakeup_dirtytime_writeback(struct work_struct *w);
static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);

static void wakeup_dirtytime_writeback(struct work_struct *w)
{
	struct backing_dev_info *bdi;

	rcu_read_lock();
	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
		struct bdi_writeback *wb;

		list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
			if (!list_empty(&wb->b_dirty_time))
				wb_wakeup(wb);
	}
	rcu_read_unlock();
	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
}

static int __init start_dirtytime_writeback(void)
{
	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
	return 0;
}
__initcall(start_dirtytime_writeback);

int dirtytime_interval_handler(struct ctl_table *table, int write,
			       void __user *buffer, size_t *lenp, loff_t *ppos)
{
	int ret;

	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
	if (ret == 0 && write)
		mod_delayed_work(system_wq, &dirtytime_work, 0);
	return ret;
}

static noinline void block_dump___mark_inode_dirty(struct inode *inode)
{
	if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
		struct dentry *dentry;
		const char *name = "?";

		dentry = d_find_alias(inode);
		if (dentry) {
			spin_lock(&dentry->d_lock);
			name = (const char *) dentry->d_name.name;
		}
		printk(KERN_DEBUG
		       "%s(%d): dirtied inode %lu (%s) on %s\n",
		       current->comm, task_pid_nr(current), inode->i_ino,
		       name, inode->i_sb->s_id);
		if (dentry) {
			spin_unlock(&dentry->d_lock);
			dput(dentry);
		}
	}
}

/**
 *	__mark_inode_dirty -	internal function
 *	@inode: inode to mark
 *	@flags: what kind of dirty (i.e. I_DIRTY_SYNC)
 *	Mark an inode as dirty. Callers should use mark_inode_dirty or
 *  	mark_inode_dirty_sync.
 *
 * Put the inode on the super block's dirty list.
 *
 * CAREFUL! We mark it dirty unconditionally, but move it onto the
 * dirty list only if it is hashed or if it refers to a blockdev.
 * If it was not hashed, it will never be added to the dirty list
 * even if it is later hashed, as it will have been marked dirty already.
 *
 * In short, make sure you hash any inodes _before_ you start marking
 * them dirty.
 *
 * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
 * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
 * the kernel-internal blockdev inode represents the dirtying time of the
 * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
 * page->mapping->host, so the page-dirtying time is recorded in the internal
 * blockdev inode.
 */
void __mark_inode_dirty(struct inode *inode, int flags)
{
#define I_DIRTY_INODE (I_DIRTY_SYNC | I_DIRTY_DATASYNC)
	struct super_block *sb = inode->i_sb;
	int dirtytime;

	trace_writeback_mark_inode_dirty(inode, flags);

	/*
	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
	 * dirty the inode itself
	 */
	if (flags & (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_TIME)) {
		trace_writeback_dirty_inode_start(inode, flags);

		if (sb->s_op->dirty_inode)
			sb->s_op->dirty_inode(inode, flags);

		trace_writeback_dirty_inode(inode, flags);
	}
	if (flags & I_DIRTY_INODE)
		flags &= ~I_DIRTY_TIME;
	dirtytime = flags & I_DIRTY_TIME;

	/*
	 * Paired with smp_mb() in __writeback_single_inode() for the
	 * following lockless i_state test.  See there for details.
	 */
	smp_mb();

	if (((inode->i_state & flags) == flags) ||
	    (dirtytime && (inode->i_state & I_DIRTY_INODE)))
		return;

	if (unlikely(block_dump))
		block_dump___mark_inode_dirty(inode);

	spin_lock(&inode->i_lock);
	if (dirtytime && (inode->i_state & I_DIRTY_INODE))
		goto out_unlock_inode;
	if ((inode->i_state & flags) != flags) {
		const int was_dirty = inode->i_state & I_DIRTY;

		inode_attach_wb(inode, NULL);

		if (flags & I_DIRTY_INODE)
			inode->i_state &= ~I_DIRTY_TIME;
		inode->i_state |= flags;

		/*
		 * If the inode is being synced, just update its dirty state.
		 * The unlocker will place the inode on the appropriate
		 * superblock list, based upon its state.
		 */
		if (inode->i_state & I_SYNC)
			goto out_unlock_inode;

		/*
		 * Only add valid (hashed) inodes to the superblock's
		 * dirty list.  Add blockdev inodes as well.
		 */
		if (!S_ISBLK(inode->i_mode)) {
			if (inode_unhashed(inode))
				goto out_unlock_inode;
		}
		if (inode->i_state & I_FREEING)
			goto out_unlock_inode;

		/*
		 * If the inode was already on b_dirty/b_io/b_more_io, don't
		 * reposition it (that would break b_dirty time-ordering).
		 */
		if (!was_dirty) {
			struct bdi_writeback *wb;
			struct list_head *dirty_list;
			bool wakeup_bdi = false;

			wb = locked_inode_to_wb_and_lock_list(inode);

			WARN(bdi_cap_writeback_dirty(wb->bdi) &&
			     !test_bit(WB_registered, &wb->state),
			     "bdi-%s not registered\n", wb->bdi->name);

			inode->dirtied_when = jiffies;
			if (dirtytime)
				inode->dirtied_time_when = jiffies;

			if (inode->i_state & (I_DIRTY_INODE | I_DIRTY_PAGES))
				dirty_list = &wb->b_dirty;
			else
				dirty_list = &wb->b_dirty_time;

			wakeup_bdi = inode_io_list_move_locked(inode, wb,
							       dirty_list);

			spin_unlock(&wb->list_lock);
			trace_writeback_dirty_inode_enqueue(inode);

			/*
			 * If this is the first dirty inode for this bdi,
			 * we have to wake-up the corresponding bdi thread
			 * to make sure background write-back happens
			 * later.
			 */
			if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
				wb_wakeup_delayed(wb);
			return;
		}
	}
out_unlock_inode:
	spin_unlock(&inode->i_lock);

#undef I_DIRTY_INODE
}
EXPORT_SYMBOL(__mark_inode_dirty);

/*
 * The @s_sync_lock is used to serialise concurrent sync operations
 * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
 * Concurrent callers will block on the s_sync_lock rather than doing contending
 * walks. The queueing maintains sync(2) required behaviour as all the IO that
 * has been issued up to the time this function is enter is guaranteed to be
 * completed by the time we have gained the lock and waited for all IO that is
 * in progress regardless of the order callers are granted the lock.
 */
static void wait_sb_inodes(struct super_block *sb)
{
	LIST_HEAD(sync_list);

	/*
	 * We need to be protected against the filesystem going from
	 * r/o to r/w or vice versa.
	 */
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	mutex_lock(&sb->s_sync_lock);

	/*
	 * Splice the writeback list onto a temporary list to avoid waiting on
	 * inodes that have started writeback after this point.
	 *
	 * Use rcu_read_lock() to keep the inodes around until we have a
	 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
	 * the local list because inodes can be dropped from either by writeback
	 * completion.
	 */
	rcu_read_lock();
	spin_lock_irq(&sb->s_inode_wblist_lock);
	list_splice_init(&sb->s_inodes_wb, &sync_list);

	/*
	 * Data integrity sync. Must wait for all pages under writeback, because
	 * there may have been pages dirtied before our sync call, but which had
	 * writeout started before we write it out.  In which case, the inode
	 * may not be on the dirty list, but we still have to wait for that
	 * writeout.
	 */
	while (!list_empty(&sync_list)) {
		struct inode *inode = list_first_entry(&sync_list, struct inode,
						       i_wb_list);
		struct address_space *mapping = inode->i_mapping;

		/*
		 * Move each inode back to the wb list before we drop the lock
		 * to preserve consistency between i_wb_list and the mapping
		 * writeback tag. Writeback completion is responsible to remove
		 * the inode from either list once the writeback tag is cleared.
		 */
		list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);

		/*
		 * The mapping can appear untagged while still on-list since we
		 * do not have the mapping lock. Skip it here, wb completion
		 * will remove it.
		 */
		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
			continue;

		spin_unlock_irq(&sb->s_inode_wblist_lock);

		spin_lock(&inode->i_lock);
		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
			spin_unlock(&inode->i_lock);

			spin_lock_irq(&sb->s_inode_wblist_lock);
			continue;
		}
		__iget(inode);
		spin_unlock(&inode->i_lock);
		rcu_read_unlock();

		/*
		 * We keep the error status of individual mapping so that
		 * applications can catch the writeback error using fsync(2).
		 * See filemap_fdatawait_keep_errors() for details.
		 */
		filemap_fdatawait_keep_errors(mapping);

		cond_resched();

		iput(inode);

		rcu_read_lock();
		spin_lock_irq(&sb->s_inode_wblist_lock);
	}
	spin_unlock_irq(&sb->s_inode_wblist_lock);
	rcu_read_unlock();
	mutex_unlock(&sb->s_sync_lock);
}

static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
				     enum wb_reason reason, bool skip_if_busy)
{
	DEFINE_WB_COMPLETION_ONSTACK(done);
	struct wb_writeback_work work = {
		.sb			= sb,
		.sync_mode		= WB_SYNC_NONE,
		.tagged_writepages	= 1,
		.done			= &done,
		.nr_pages		= nr,
		.reason			= reason,
	};
	struct backing_dev_info *bdi = sb->s_bdi;

	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
		return;
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
	wb_wait_for_completion(bdi, &done);
}

/**
 * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block
 * @sb: the superblock
 * @nr: the number of pages to write
 * @reason: reason why some writeback work initiated
 *
 * Start writeback on some inodes on this super_block. No guarantees are made
 * on how many (if any) will be written, and this function does not wait
 * for IO completion of submitted IO.
 */
void writeback_inodes_sb_nr(struct super_block *sb,
			    unsigned long nr,
			    enum wb_reason reason)
{
	__writeback_inodes_sb_nr(sb, nr, reason, false);
}
EXPORT_SYMBOL(writeback_inodes_sb_nr);

/**
 * writeback_inodes_sb	-	writeback dirty inodes from given super_block
 * @sb: the superblock
 * @reason: reason why some writeback work was initiated
 *
 * Start writeback on some inodes on this super_block. No guarantees are made
 * on how many (if any) will be written, and this function does not wait
 * for IO completion of submitted IO.
 */
void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(writeback_inodes_sb);

/**
 * try_to_writeback_inodes_sb_nr - try to start writeback if none underway
 * @sb: the superblock
 * @nr: the number of pages to write
 * @reason: the reason of writeback
 *
 * Invoke writeback_inodes_sb_nr if no writeback is currently underway.
 * Returns 1 if writeback was started, 0 if not.
 */
bool try_to_writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
				   enum wb_reason reason)
{
	if (!down_read_trylock(&sb->s_umount))
		return false;

	__writeback_inodes_sb_nr(sb, nr, reason, true);
	up_read(&sb->s_umount);
	return true;
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb_nr);

/**
 * try_to_writeback_inodes_sb - try to start writeback if none underway
 * @sb: the superblock
 * @reason: reason why some writeback work was initiated
 *
 * Implement by try_to_writeback_inodes_sb_nr()
 * Returns 1 if writeback was started, 0 if not.
 */
bool try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
{
	return try_to_writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
}
EXPORT_SYMBOL(try_to_writeback_inodes_sb);

/**
 * sync_inodes_sb	-	sync sb inode pages
 * @sb: the superblock
 *
 * This function writes and waits on any dirty inode belonging to this
 * super_block.
 */
void sync_inodes_sb(struct super_block *sb)
{
	DEFINE_WB_COMPLETION_ONSTACK(done);
	struct wb_writeback_work work = {
		.sb		= sb,
		.sync_mode	= WB_SYNC_ALL,
		.nr_pages	= LONG_MAX,
		.range_cyclic	= 0,
		.done		= &done,
		.reason		= WB_REASON_SYNC,
		.for_sync	= 1,
	};
	struct backing_dev_info *bdi = sb->s_bdi;

	/*
	 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
	 * inodes under writeback and I_DIRTY_TIME inodes ignored by
	 * bdi_has_dirty() need to be written out too.
	 */
	if (bdi == &noop_backing_dev_info)
		return;
	WARN_ON(!rwsem_is_locked(&sb->s_umount));

	bdi_split_work_to_wbs(bdi, &work, false);
	wb_wait_for_completion(bdi, &done);

	wait_sb_inodes(sb);
}
EXPORT_SYMBOL(sync_inodes_sb);

/**
 * write_inode_now	-	write an inode to disk
 * @inode: inode to write to disk
 * @sync: whether the write should be synchronous or not
 *
 * This function commits an inode to disk immediately if it is dirty. This is
 * primarily needed by knfsd.
 *
 * The caller must either have a ref on the inode or must have set I_WILL_FREE.
 */
int write_inode_now(struct inode *inode, int sync)
{
	struct writeback_control wbc = {
		.nr_to_write = LONG_MAX,
		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
		.range_start = 0,
		.range_end = LLONG_MAX,
	};

	if (!mapping_cap_writeback_dirty(inode->i_mapping))
		wbc.nr_to_write = 0;

	might_sleep();
	return writeback_single_inode(inode, &wbc);
}
EXPORT_SYMBOL(write_inode_now);

/**
 * sync_inode - write an inode and its pages to disk.
 * @inode: the inode to sync
 * @wbc: controls the writeback mode
 *
 * sync_inode() will write an inode and its pages to disk.  It will also
 * correctly update the inode on its superblock's dirty inode lists and will
 * update inode->i_state.
 *
 * The caller must have a ref on the inode.
 */
int sync_inode(struct inode *inode, struct writeback_control *wbc)
{
	return writeback_single_inode(inode, wbc);
}
EXPORT_SYMBOL(sync_inode);

/**
 * sync_inode_metadata - write an inode to disk
 * @inode: the inode to sync
 * @wait: wait for I/O to complete.
 *
 * Write an inode to disk and adjust its dirty state after completion.
 *
 * Note: only writes the actual inode, no associated data or other metadata.
 */
int sync_inode_metadata(struct inode *inode, int wait)
{
	struct writeback_control wbc = {
		.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
		.nr_to_write = 0, /* metadata-only */
	};

	return sync_inode(inode, &wbc);
}
EXPORT_SYMBOL(sync_inode_metadata);