summaryrefslogtreecommitdiff
path: root/mm/page-writeback.c
blob: d0d466a5c804ca0fa8709dd991dcd62f738cd8a3 (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
// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/page-writeback.c
 *
 * Copyright (C) 2002, Linus Torvalds.
 * Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
 *
 * Contains functions related to writing back dirty pages at the
 * address_space level.
 *
 * 10Apr2002	Andrew Morton
 *		Initial version
 */

#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/init.h>
#include <linux/backing-dev.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/blkdev.h>
#include <linux/mpage.h>
#include <linux/rmap.h>
#include <linux/percpu.h>
#include <linux/smp.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/syscalls.h>
#include <linux/pagevec.h>
#include <linux/timer.h>
#include <linux/sched/rt.h>
#include <linux/sched/signal.h>
#include <linux/mm_inline.h>
#include <trace/events/writeback.h>

#include "internal.h"

/*
 * Sleep at most 200ms at a time in balance_dirty_pages().
 */
#define MAX_PAUSE		max(HZ/5, 1)

/*
 * Try to keep balance_dirty_pages() call intervals higher than this many pages
 * by raising pause time to max_pause when falls below it.
 */
#define DIRTY_POLL_THRESH	(128 >> (PAGE_SHIFT - 10))

/*
 * Estimate write bandwidth at 200ms intervals.
 */
#define BANDWIDTH_INTERVAL	max(HZ/5, 1)

#define RATELIMIT_CALC_SHIFT	10

/*
 * After a CPU has dirtied this many pages, balance_dirty_pages_ratelimited
 * will look to see if it needs to force writeback or throttling.
 */
static long ratelimit_pages = 32;

/* The following parameters are exported via /proc/sys/vm */

/*
 * Start background writeback (via writeback threads) at this percentage
 */
static int dirty_background_ratio = 10;

/*
 * dirty_background_bytes starts at 0 (disabled) so that it is a function of
 * dirty_background_ratio * the amount of dirtyable memory
 */
static unsigned long dirty_background_bytes;

/*
 * free highmem will not be subtracted from the total free memory
 * for calculating free ratios if vm_highmem_is_dirtyable is true
 */
static int vm_highmem_is_dirtyable;

/*
 * The generator of dirty data starts writeback at this percentage
 */
static int vm_dirty_ratio = 20;

/*
 * vm_dirty_bytes starts at 0 (disabled) so that it is a function of
 * vm_dirty_ratio * the amount of dirtyable memory
 */
static unsigned long vm_dirty_bytes;

/*
 * The interval between `kupdate'-style writebacks
 */
unsigned int dirty_writeback_interval = 5 * 100; /* centiseconds */

EXPORT_SYMBOL_GPL(dirty_writeback_interval);

/*
 * The longest time for which data is allowed to remain dirty
 */
unsigned int dirty_expire_interval = 30 * 100; /* centiseconds */

/*
 * Flag that puts the machine in "laptop mode". Doubles as a timeout in jiffies:
 * a full sync is triggered after this time elapses without any disk activity.
 */
int laptop_mode;

EXPORT_SYMBOL(laptop_mode);

/* End of sysctl-exported parameters */

struct wb_domain global_wb_domain;

/* consolidated parameters for balance_dirty_pages() and its subroutines */
struct dirty_throttle_control {
#ifdef CONFIG_CGROUP_WRITEBACK
	struct wb_domain	*dom;
	struct dirty_throttle_control *gdtc;	/* only set in memcg dtc's */
#endif
	struct bdi_writeback	*wb;
	struct fprop_local_percpu *wb_completions;

	unsigned long		avail;		/* dirtyable */
	unsigned long		dirty;		/* file_dirty + write + nfs */
	unsigned long		thresh;		/* dirty threshold */
	unsigned long		bg_thresh;	/* dirty background threshold */

	unsigned long		wb_dirty;	/* per-wb counterparts */
	unsigned long		wb_thresh;
	unsigned long		wb_bg_thresh;

	unsigned long		pos_ratio;
};

/*
 * Length of period for aging writeout fractions of bdis. This is an
 * arbitrarily chosen number. The longer the period, the slower fractions will
 * reflect changes in current writeout rate.
 */
#define VM_COMPLETIONS_PERIOD_LEN (3*HZ)

#ifdef CONFIG_CGROUP_WRITEBACK

#define GDTC_INIT(__wb)		.wb = (__wb),				\
				.dom = &global_wb_domain,		\
				.wb_completions = &(__wb)->completions

#define GDTC_INIT_NO_WB		.dom = &global_wb_domain

#define MDTC_INIT(__wb, __gdtc)	.wb = (__wb),				\
				.dom = mem_cgroup_wb_domain(__wb),	\
				.wb_completions = &(__wb)->memcg_completions, \
				.gdtc = __gdtc

static bool mdtc_valid(struct dirty_throttle_control *dtc)
{
	return dtc->dom;
}

static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
{
	return dtc->dom;
}

static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
{
	return mdtc->gdtc;
}

static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
{
	return &wb->memcg_completions;
}

static void wb_min_max_ratio(struct bdi_writeback *wb,
			     unsigned long *minp, unsigned long *maxp)
{
	unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth);
	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
	unsigned long long min = wb->bdi->min_ratio;
	unsigned long long max = wb->bdi->max_ratio;

	/*
	 * @wb may already be clean by the time control reaches here and
	 * the total may not include its bw.
	 */
	if (this_bw < tot_bw) {
		if (min) {
			min *= this_bw;
			min = div64_ul(min, tot_bw);
		}
		if (max < 100) {
			max *= this_bw;
			max = div64_ul(max, tot_bw);
		}
	}

	*minp = min;
	*maxp = max;
}

#else	/* CONFIG_CGROUP_WRITEBACK */

#define GDTC_INIT(__wb)		.wb = (__wb),                           \
				.wb_completions = &(__wb)->completions
#define GDTC_INIT_NO_WB
#define MDTC_INIT(__wb, __gdtc)

static bool mdtc_valid(struct dirty_throttle_control *dtc)
{
	return false;
}

static struct wb_domain *dtc_dom(struct dirty_throttle_control *dtc)
{
	return &global_wb_domain;
}

static struct dirty_throttle_control *mdtc_gdtc(struct dirty_throttle_control *mdtc)
{
	return NULL;
}

static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb)
{
	return NULL;
}

static void wb_min_max_ratio(struct bdi_writeback *wb,
			     unsigned long *minp, unsigned long *maxp)
{
	*minp = wb->bdi->min_ratio;
	*maxp = wb->bdi->max_ratio;
}

#endif	/* CONFIG_CGROUP_WRITEBACK */

/*
 * In a memory zone, there is a certain amount of pages we consider
 * available for the page cache, which is essentially the number of
 * free and reclaimable pages, minus some zone reserves to protect
 * lowmem and the ability to uphold the zone's watermarks without
 * requiring writeback.
 *
 * This number of dirtyable pages is the base value of which the
 * user-configurable dirty ratio is the effective number of pages that
 * are allowed to be actually dirtied.  Per individual zone, or
 * globally by using the sum of dirtyable pages over all zones.
 *
 * Because the user is allowed to specify the dirty limit globally as
 * absolute number of bytes, calculating the per-zone dirty limit can
 * require translating the configured limit into a percentage of
 * global dirtyable memory first.
 */

/**
 * node_dirtyable_memory - number of dirtyable pages in a node
 * @pgdat: the node
 *
 * Return: the node's number of pages potentially available for dirty
 * page cache.  This is the base value for the per-node dirty limits.
 */
static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
{
	unsigned long nr_pages = 0;
	int z;

	for (z = 0; z < MAX_NR_ZONES; z++) {
		struct zone *zone = pgdat->node_zones + z;

		if (!populated_zone(zone))
			continue;

		nr_pages += zone_page_state(zone, NR_FREE_PAGES);
	}

	/*
	 * Pages reserved for the kernel should not be considered
	 * dirtyable, to prevent a situation where reclaim has to
	 * clean pages in order to balance the zones.
	 */
	nr_pages -= min(nr_pages, pgdat->totalreserve_pages);

	nr_pages += node_page_state(pgdat, NR_INACTIVE_FILE);
	nr_pages += node_page_state(pgdat, NR_ACTIVE_FILE);

	return nr_pages;
}

static unsigned long highmem_dirtyable_memory(unsigned long total)
{
#ifdef CONFIG_HIGHMEM
	int node;
	unsigned long x = 0;
	int i;

	for_each_node_state(node, N_HIGH_MEMORY) {
		for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
			struct zone *z;
			unsigned long nr_pages;

			if (!is_highmem_idx(i))
				continue;

			z = &NODE_DATA(node)->node_zones[i];
			if (!populated_zone(z))
				continue;

			nr_pages = zone_page_state(z, NR_FREE_PAGES);
			/* watch for underflows */
			nr_pages -= min(nr_pages, high_wmark_pages(z));
			nr_pages += zone_page_state(z, NR_ZONE_INACTIVE_FILE);
			nr_pages += zone_page_state(z, NR_ZONE_ACTIVE_FILE);
			x += nr_pages;
		}
	}

	/*
	 * Make sure that the number of highmem pages is never larger
	 * than the number of the total dirtyable memory. This can only
	 * occur in very strange VM situations but we want to make sure
	 * that this does not occur.
	 */
	return min(x, total);
#else
	return 0;
#endif
}

/**
 * global_dirtyable_memory - number of globally dirtyable pages
 *
 * Return: the global number of pages potentially available for dirty
 * page cache.  This is the base value for the global dirty limits.
 */
static unsigned long global_dirtyable_memory(void)
{
	unsigned long x;

	x = global_zone_page_state(NR_FREE_PAGES);
	/*
	 * Pages reserved for the kernel should not be considered
	 * dirtyable, to prevent a situation where reclaim has to
	 * clean pages in order to balance the zones.
	 */
	x -= min(x, totalreserve_pages);

	x += global_node_page_state(NR_INACTIVE_FILE);
	x += global_node_page_state(NR_ACTIVE_FILE);

	if (!vm_highmem_is_dirtyable)
		x -= highmem_dirtyable_memory(x);

	return x + 1;	/* Ensure that we never return 0 */
}

/**
 * domain_dirty_limits - calculate thresh and bg_thresh for a wb_domain
 * @dtc: dirty_throttle_control of interest
 *
 * Calculate @dtc->thresh and ->bg_thresh considering
 * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}.  The caller
 * must ensure that @dtc->avail is set before calling this function.  The
 * dirty limits will be lifted by 1/4 for real-time tasks.
 */
static void domain_dirty_limits(struct dirty_throttle_control *dtc)
{
	const unsigned long available_memory = dtc->avail;
	struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
	unsigned long bytes = vm_dirty_bytes;
	unsigned long bg_bytes = dirty_background_bytes;
	/* convert ratios to per-PAGE_SIZE for higher precision */
	unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
	unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
	unsigned long thresh;
	unsigned long bg_thresh;
	struct task_struct *tsk;

	/* gdtc is !NULL iff @dtc is for memcg domain */
	if (gdtc) {
		unsigned long global_avail = gdtc->avail;

		/*
		 * The byte settings can't be applied directly to memcg
		 * domains.  Convert them to ratios by scaling against
		 * globally available memory.  As the ratios are in
		 * per-PAGE_SIZE, they can be obtained by dividing bytes by
		 * number of pages.
		 */
		if (bytes)
			ratio = min(DIV_ROUND_UP(bytes, global_avail),
				    PAGE_SIZE);
		if (bg_bytes)
			bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
				       PAGE_SIZE);
		bytes = bg_bytes = 0;
	}

	if (bytes)
		thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
	else
		thresh = (ratio * available_memory) / PAGE_SIZE;

	if (bg_bytes)
		bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
	else
		bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;

	if (bg_thresh >= thresh)
		bg_thresh = thresh / 2;
	tsk = current;
	if (rt_task(tsk)) {
		bg_thresh += bg_thresh / 4 + global_wb_domain.dirty_limit / 32;
		thresh += thresh / 4 + global_wb_domain.dirty_limit / 32;
	}
	dtc->thresh = thresh;
	dtc->bg_thresh = bg_thresh;

	/* we should eventually report the domain in the TP */
	if (!gdtc)
		trace_global_dirty_state(bg_thresh, thresh);
}

/**
 * global_dirty_limits - background-writeback and dirty-throttling thresholds
 * @pbackground: out parameter for bg_thresh
 * @pdirty: out parameter for thresh
 *
 * Calculate bg_thresh and thresh for global_wb_domain.  See
 * domain_dirty_limits() for details.
 */
void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
{
	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };

	gdtc.avail = global_dirtyable_memory();
	domain_dirty_limits(&gdtc);

	*pbackground = gdtc.bg_thresh;
	*pdirty = gdtc.thresh;
}

/**
 * node_dirty_limit - maximum number of dirty pages allowed in a node
 * @pgdat: the node
 *
 * Return: the maximum number of dirty pages allowed in a node, based
 * on the node's dirtyable memory.
 */
static unsigned long node_dirty_limit(struct pglist_data *pgdat)
{
	unsigned long node_memory = node_dirtyable_memory(pgdat);
	struct task_struct *tsk = current;
	unsigned long dirty;

	if (vm_dirty_bytes)
		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
			node_memory / global_dirtyable_memory();
	else
		dirty = vm_dirty_ratio * node_memory / 100;

	if (rt_task(tsk))
		dirty += dirty / 4;

	return dirty;
}

/**
 * node_dirty_ok - tells whether a node is within its dirty limits
 * @pgdat: the node to check
 *
 * Return: %true when the dirty pages in @pgdat are within the node's
 * dirty limit, %false if the limit is exceeded.
 */
bool node_dirty_ok(struct pglist_data *pgdat)
{
	unsigned long limit = node_dirty_limit(pgdat);
	unsigned long nr_pages = 0;

	nr_pages += node_page_state(pgdat, NR_FILE_DIRTY);
	nr_pages += node_page_state(pgdat, NR_WRITEBACK);

	return nr_pages <= limit;
}

#ifdef CONFIG_SYSCTL
static int dirty_background_ratio_handler(struct ctl_table *table, int write,
		void *buffer, size_t *lenp, loff_t *ppos)
{
	int ret;

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

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

	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
	if (ret == 0 && write)
		dirty_background_ratio = 0;
	return ret;
}

static int dirty_ratio_handler(struct ctl_table *table, int write, void *buffer,
		size_t *lenp, loff_t *ppos)
{
	int old_ratio = vm_dirty_ratio;
	int ret;

	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
		writeback_set_ratelimit();
		vm_dirty_bytes = 0;
	}
	return ret;
}

static int dirty_bytes_handler(struct ctl_table *table, int write,
		void *buffer, size_t *lenp, loff_t *ppos)
{
	unsigned long old_bytes = vm_dirty_bytes;
	int ret;

	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
	if (ret == 0 && write && vm_dirty_bytes != old_bytes) {
		writeback_set_ratelimit();
		vm_dirty_ratio = 0;
	}
	return ret;
}
#endif

static unsigned long wp_next_time(unsigned long cur_time)
{
	cur_time += VM_COMPLETIONS_PERIOD_LEN;
	/* 0 has a special meaning... */
	if (!cur_time)
		return 1;
	return cur_time;
}

static void wb_domain_writeout_add(struct wb_domain *dom,
				   struct fprop_local_percpu *completions,
				   unsigned int max_prop_frac, long nr)
{
	__fprop_add_percpu_max(&dom->completions, completions,
			       max_prop_frac, nr);
	/* First event after period switching was turned off? */
	if (unlikely(!dom->period_time)) {
		/*
		 * We can race with other __bdi_writeout_inc calls here but
		 * it does not cause any harm since the resulting time when
		 * timer will fire and what is in writeout_period_time will be
		 * roughly the same.
		 */
		dom->period_time = wp_next_time(jiffies);
		mod_timer(&dom->period_timer, dom->period_time);
	}
}

/*
 * Increment @wb's writeout completion count and the global writeout
 * completion count. Called from __folio_end_writeback().
 */
static inline void __wb_writeout_add(struct bdi_writeback *wb, long nr)
{
	struct wb_domain *cgdom;

	wb_stat_mod(wb, WB_WRITTEN, nr);
	wb_domain_writeout_add(&global_wb_domain, &wb->completions,
			       wb->bdi->max_prop_frac, nr);

	cgdom = mem_cgroup_wb_domain(wb);
	if (cgdom)
		wb_domain_writeout_add(cgdom, wb_memcg_completions(wb),
				       wb->bdi->max_prop_frac, nr);
}

void wb_writeout_inc(struct bdi_writeback *wb)
{
	unsigned long flags;

	local_irq_save(flags);
	__wb_writeout_add(wb, 1);
	local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(wb_writeout_inc);

/*
 * On idle system, we can be called long after we scheduled because we use
 * deferred timers so count with missed periods.
 */
static void writeout_period(struct timer_list *t)
{
	struct wb_domain *dom = from_timer(dom, t, period_timer);
	int miss_periods = (jiffies - dom->period_time) /
						 VM_COMPLETIONS_PERIOD_LEN;

	if (fprop_new_period(&dom->completions, miss_periods + 1)) {
		dom->period_time = wp_next_time(dom->period_time +
				miss_periods * VM_COMPLETIONS_PERIOD_LEN);
		mod_timer(&dom->period_timer, dom->period_time);
	} else {
		/*
		 * Aging has zeroed all fractions. Stop wasting CPU on period
		 * updates.
		 */
		dom->period_time = 0;
	}
}

int wb_domain_init(struct wb_domain *dom, gfp_t gfp)
{
	memset(dom, 0, sizeof(*dom));

	spin_lock_init(&dom->lock);

	timer_setup(&dom->period_timer, writeout_period, TIMER_DEFERRABLE);

	dom->dirty_limit_tstamp = jiffies;

	return fprop_global_init(&dom->completions, gfp);
}

#ifdef CONFIG_CGROUP_WRITEBACK
void wb_domain_exit(struct wb_domain *dom)
{
	del_timer_sync(&dom->period_timer);
	fprop_global_destroy(&dom->completions);
}
#endif

/*
 * bdi_min_ratio keeps the sum of the minimum dirty shares of all
 * registered backing devices, which, for obvious reasons, can not
 * exceed 100%.
 */
static unsigned int bdi_min_ratio;

int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
{
	unsigned int delta;
	int ret = 0;

	spin_lock_bh(&bdi_lock);
	if (min_ratio > bdi->max_ratio) {
		ret = -EINVAL;
	} else {
		if (min_ratio < bdi->min_ratio) {
			delta = bdi->min_ratio - min_ratio;
			bdi_min_ratio -= delta;
			bdi->min_ratio = min_ratio;
		} else {
			delta = min_ratio - bdi->min_ratio;
			if (bdi_min_ratio + delta < 100) {
				bdi_min_ratio += delta;
				bdi->min_ratio = min_ratio;
			} else {
				ret = -EINVAL;
			}
		}
	}
	spin_unlock_bh(&bdi_lock);

	return ret;
}

int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
{
	int ret = 0;

	if (max_ratio > 100)
		return -EINVAL;

	spin_lock_bh(&bdi_lock);
	if (bdi->min_ratio > max_ratio) {
		ret = -EINVAL;
	} else {
		bdi->max_ratio = max_ratio;
		bdi->max_prop_frac = (FPROP_FRAC_BASE * max_ratio) / 100;
	}
	spin_unlock_bh(&bdi_lock);

	return ret;
}
EXPORT_SYMBOL(bdi_set_max_ratio);

static unsigned long dirty_freerun_ceiling(unsigned long thresh,
					   unsigned long bg_thresh)
{
	return (thresh + bg_thresh) / 2;
}

static unsigned long hard_dirty_limit(struct wb_domain *dom,
				      unsigned long thresh)
{
	return max(thresh, dom->dirty_limit);
}

/*
 * Memory which can be further allocated to a memcg domain is capped by
 * system-wide clean memory excluding the amount being used in the domain.
 */
static void mdtc_calc_avail(struct dirty_throttle_control *mdtc,
			    unsigned long filepages, unsigned long headroom)
{
	struct dirty_throttle_control *gdtc = mdtc_gdtc(mdtc);
	unsigned long clean = filepages - min(filepages, mdtc->dirty);
	unsigned long global_clean = gdtc->avail - min(gdtc->avail, gdtc->dirty);
	unsigned long other_clean = global_clean - min(global_clean, clean);

	mdtc->avail = filepages + min(headroom, other_clean);
}

/**
 * __wb_calc_thresh - @wb's share of dirty throttling threshold
 * @dtc: dirty_throttle_context of interest
 *
 * Note that balance_dirty_pages() will only seriously take it as a hard limit
 * when sleeping max_pause per page is not enough to keep the dirty pages under
 * control. For example, when the device is completely stalled due to some error
 * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
 * In the other normal situations, it acts more gently by throttling the tasks
 * more (rather than completely block them) when the wb dirty pages go high.
 *
 * It allocates high/low dirty limits to fast/slow devices, in order to prevent
 * - starving fast devices
 * - piling up dirty pages (that will take long time to sync) on slow devices
 *
 * The wb's share of dirty limit will be adapting to its throughput and
 * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
 *
 * Return: @wb's dirty limit in pages. The term "dirty" in the context of
 * dirty balancing includes all PG_dirty and PG_writeback pages.
 */
static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc)
{
	struct wb_domain *dom = dtc_dom(dtc);
	unsigned long thresh = dtc->thresh;
	u64 wb_thresh;
	unsigned long numerator, denominator;
	unsigned long wb_min_ratio, wb_max_ratio;

	/*
	 * Calculate this BDI's share of the thresh ratio.
	 */
	fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
			      &numerator, &denominator);

	wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
	wb_thresh *= numerator;
	wb_thresh = div64_ul(wb_thresh, denominator);

	wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);

	wb_thresh += (thresh * wb_min_ratio) / 100;
	if (wb_thresh > (thresh * wb_max_ratio) / 100)
		wb_thresh = thresh * wb_max_ratio / 100;

	return wb_thresh;
}

unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh)
{
	struct dirty_throttle_control gdtc = { GDTC_INIT(wb),
					       .thresh = thresh };
	return __wb_calc_thresh(&gdtc);
}

/*
 *                           setpoint - dirty 3
 *        f(dirty) := 1.0 + (----------------)
 *                           limit - setpoint
 *
 * it's a 3rd order polynomial that subjects to
 *
 * (1) f(freerun)  = 2.0 => rampup dirty_ratelimit reasonably fast
 * (2) f(setpoint) = 1.0 => the balance point
 * (3) f(limit)    = 0   => the hard limit
 * (4) df/dx      <= 0	 => negative feedback control
 * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
 *     => fast response on large errors; small oscillation near setpoint
 */
static long long pos_ratio_polynom(unsigned long setpoint,
					  unsigned long dirty,
					  unsigned long limit)
{
	long long pos_ratio;
	long x;

	x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
		      (limit - setpoint) | 1);
	pos_ratio = x;
	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
	pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
	pos_ratio += 1 << RATELIMIT_CALC_SHIFT;

	return clamp(pos_ratio, 0LL, 2LL << RATELIMIT_CALC_SHIFT);
}

/*
 * Dirty position control.
 *
 * (o) global/bdi setpoints
 *
 * We want the dirty pages be balanced around the global/wb setpoints.
 * When the number of dirty pages is higher/lower than the setpoint, the
 * dirty position control ratio (and hence task dirty ratelimit) will be
 * decreased/increased to bring the dirty pages back to the setpoint.
 *
 *     pos_ratio = 1 << RATELIMIT_CALC_SHIFT
 *
 *     if (dirty < setpoint) scale up   pos_ratio
 *     if (dirty > setpoint) scale down pos_ratio
 *
 *     if (wb_dirty < wb_setpoint) scale up   pos_ratio
 *     if (wb_dirty > wb_setpoint) scale down pos_ratio
 *
 *     task_ratelimit = dirty_ratelimit * pos_ratio >> RATELIMIT_CALC_SHIFT
 *
 * (o) global control line
 *
 *     ^ pos_ratio
 *     |
 *     |            |<===== global dirty control scope ======>|
 * 2.0  * * * * * * *
 *     |            .*
 *     |            . *
 *     |            .   *
 *     |            .     *
 *     |            .        *
 *     |            .            *
 * 1.0 ................................*
 *     |            .                  .     *
 *     |            .                  .          *
 *     |            .                  .              *
 *     |            .                  .                 *
 *     |            .                  .                    *
 *   0 +------------.------------------.----------------------*------------->
 *           freerun^          setpoint^                 limit^   dirty pages
 *
 * (o) wb control line
 *
 *     ^ pos_ratio
 *     |
 *     |            *
 *     |              *
 *     |                *
 *     |                  *
 *     |                    * |<=========== span ============>|
 * 1.0 .......................*
 *     |                      . *
 *     |                      .   *
 *     |                      .     *
 *     |                      .       *
 *     |                      .         *
 *     |                      .           *
 *     |                      .             *
 *     |                      .               *
 *     |                      .                 *
 *     |                      .                   *
 *     |                      .                     *
 * 1/4 ...............................................* * * * * * * * * * * *
 *     |                      .                         .
 *     |                      .                           .
 *     |                      .                             .
 *   0 +----------------------.-------------------------------.------------->
 *                wb_setpoint^                    x_intercept^
 *
 * The wb control line won't drop below pos_ratio=1/4, so that wb_dirty can
 * be smoothly throttled down to normal if it starts high in situations like
 * - start writing to a slow SD card and a fast disk at the same time. The SD
 *   card's wb_dirty may rush to many times higher than wb_setpoint.
 * - the wb dirty thresh drops quickly due to change of JBOD workload
 */
static void wb_position_ratio(struct dirty_throttle_control *dtc)
{
	struct bdi_writeback *wb = dtc->wb;
	unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth);
	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
	unsigned long wb_thresh = dtc->wb_thresh;
	unsigned long x_intercept;
	unsigned long setpoint;		/* dirty pages' target balance point */
	unsigned long wb_setpoint;
	unsigned long span;
	long long pos_ratio;		/* for scaling up/down the rate limit */
	long x;

	dtc->pos_ratio = 0;

	if (unlikely(dtc->dirty >= limit))
		return;

	/*
	 * global setpoint
	 *
	 * See comment for pos_ratio_polynom().
	 */
	setpoint = (freerun + limit) / 2;
	pos_ratio = pos_ratio_polynom(setpoint, dtc->dirty, limit);

	/*
	 * The strictlimit feature is a tool preventing mistrusted filesystems
	 * from growing a large number of dirty pages before throttling. For
	 * such filesystems balance_dirty_pages always checks wb counters
	 * against wb limits. Even if global "nr_dirty" is under "freerun".
	 * This is especially important for fuse which sets bdi->max_ratio to
	 * 1% by default. Without strictlimit feature, fuse writeback may
	 * consume arbitrary amount of RAM because it is accounted in
	 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
	 *
	 * Here, in wb_position_ratio(), we calculate pos_ratio based on
	 * two values: wb_dirty and wb_thresh. Let's consider an example:
	 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
	 * limits are set by default to 10% and 20% (background and throttle).
	 * Then wb_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
	 * wb_calc_thresh(wb, bg_thresh) is about ~4K pages. wb_setpoint is
	 * about ~6K pages (as the average of background and throttle wb
	 * limits). The 3rd order polynomial will provide positive feedback if
	 * wb_dirty is under wb_setpoint and vice versa.
	 *
	 * Note, that we cannot use global counters in these calculations
	 * because we want to throttle process writing to a strictlimit wb
	 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
	 * in the example above).
	 */
	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
		long long wb_pos_ratio;

		if (dtc->wb_dirty < 8) {
			dtc->pos_ratio = min_t(long long, pos_ratio * 2,
					   2 << RATELIMIT_CALC_SHIFT);
			return;
		}

		if (dtc->wb_dirty >= wb_thresh)
			return;

		wb_setpoint = dirty_freerun_ceiling(wb_thresh,
						    dtc->wb_bg_thresh);

		if (wb_setpoint == 0 || wb_setpoint == wb_thresh)
			return;

		wb_pos_ratio = pos_ratio_polynom(wb_setpoint, dtc->wb_dirty,
						 wb_thresh);

		/*
		 * Typically, for strictlimit case, wb_setpoint << setpoint
		 * and pos_ratio >> wb_pos_ratio. In the other words global
		 * state ("dirty") is not limiting factor and we have to
		 * make decision based on wb counters. But there is an
		 * important case when global pos_ratio should get precedence:
		 * global limits are exceeded (e.g. due to activities on other
		 * wb's) while given strictlimit wb is below limit.
		 *
		 * "pos_ratio * wb_pos_ratio" would work for the case above,
		 * but it would look too non-natural for the case of all
		 * activity in the system coming from a single strictlimit wb
		 * with bdi->max_ratio == 100%.
		 *
		 * Note that min() below somewhat changes the dynamics of the
		 * control system. Normally, pos_ratio value can be well over 3
		 * (when globally we are at freerun and wb is well below wb
		 * setpoint). Now the maximum pos_ratio in the same situation
		 * is 2. We might want to tweak this if we observe the control
		 * system is too slow to adapt.
		 */
		dtc->pos_ratio = min(pos_ratio, wb_pos_ratio);
		return;
	}

	/*
	 * We have computed basic pos_ratio above based on global situation. If
	 * the wb is over/under its share of dirty pages, we want to scale
	 * pos_ratio further down/up. That is done by the following mechanism.
	 */

	/*
	 * wb setpoint
	 *
	 *        f(wb_dirty) := 1.0 + k * (wb_dirty - wb_setpoint)
	 *
	 *                        x_intercept - wb_dirty
	 *                     := --------------------------
	 *                        x_intercept - wb_setpoint
	 *
	 * The main wb control line is a linear function that subjects to
	 *
	 * (1) f(wb_setpoint) = 1.0
	 * (2) k = - 1 / (8 * write_bw)  (in single wb case)
	 *     or equally: x_intercept = wb_setpoint + 8 * write_bw
	 *
	 * For single wb case, the dirty pages are observed to fluctuate
	 * regularly within range
	 *        [wb_setpoint - write_bw/2, wb_setpoint + write_bw/2]
	 * for various filesystems, where (2) can yield in a reasonable 12.5%
	 * fluctuation range for pos_ratio.
	 *
	 * For JBOD case, wb_thresh (not wb_dirty!) could fluctuate up to its
	 * own size, so move the slope over accordingly and choose a slope that
	 * yields 100% pos_ratio fluctuation on suddenly doubled wb_thresh.
	 */
	if (unlikely(wb_thresh > dtc->thresh))
		wb_thresh = dtc->thresh;
	/*
	 * It's very possible that wb_thresh is close to 0 not because the
	 * device is slow, but that it has remained inactive for long time.
	 * Honour such devices a reasonable good (hopefully IO efficient)
	 * threshold, so that the occasional writes won't be blocked and active
	 * writes can rampup the threshold quickly.
	 */
	wb_thresh = max(wb_thresh, (limit - dtc->dirty) / 8);
	/*
	 * scale global setpoint to wb's:
	 *	wb_setpoint = setpoint * wb_thresh / thresh
	 */
	x = div_u64((u64)wb_thresh << 16, dtc->thresh | 1);
	wb_setpoint = setpoint * (u64)x >> 16;
	/*
	 * Use span=(8*write_bw) in single wb case as indicated by
	 * (thresh - wb_thresh ~= 0) and transit to wb_thresh in JBOD case.
	 *
	 *        wb_thresh                    thresh - wb_thresh
	 * span = --------- * (8 * write_bw) + ------------------ * wb_thresh
	 *         thresh                           thresh
	 */
	span = (dtc->thresh - wb_thresh + 8 * write_bw) * (u64)x >> 16;
	x_intercept = wb_setpoint + span;

	if (dtc->wb_dirty < x_intercept - span / 4) {
		pos_ratio = div64_u64(pos_ratio * (x_intercept - dtc->wb_dirty),
				      (x_intercept - wb_setpoint) | 1);
	} else
		pos_ratio /= 4;

	/*
	 * wb reserve area, safeguard against dirty pool underrun and disk idle
	 * It may push the desired control point of global dirty pages higher
	 * than setpoint.
	 */
	x_intercept = wb_thresh / 2;
	if (dtc->wb_dirty < x_intercept) {
		if (dtc->wb_dirty > x_intercept / 8)
			pos_ratio = div_u64(pos_ratio * x_intercept,
					    dtc->wb_dirty);
		else
			pos_ratio *= 8;
	}

	dtc->pos_ratio = pos_ratio;
}

static void wb_update_write_bandwidth(struct bdi_writeback *wb,
				      unsigned long elapsed,
				      unsigned long written)
{
	const unsigned long period = roundup_pow_of_two(3 * HZ);
	unsigned long avg = wb->avg_write_bandwidth;
	unsigned long old = wb->write_bandwidth;
	u64 bw;

	/*
	 * bw = written * HZ / elapsed
	 *
	 *                   bw * elapsed + write_bandwidth * (period - elapsed)
	 * write_bandwidth = ---------------------------------------------------
	 *                                          period
	 *
	 * @written may have decreased due to folio_account_redirty().
	 * Avoid underflowing @bw calculation.
	 */
	bw = written - min(written, wb->written_stamp);
	bw *= HZ;
	if (unlikely(elapsed > period)) {
		bw = div64_ul(bw, elapsed);
		avg = bw;
		goto out;
	}
	bw += (u64)wb->write_bandwidth * (period - elapsed);
	bw >>= ilog2(period);

	/*
	 * one more level of smoothing, for filtering out sudden spikes
	 */
	if (avg > old && old >= (unsigned long)bw)
		avg -= (avg - old) >> 3;

	if (avg < old && old <= (unsigned long)bw)
		avg += (old - avg) >> 3;

out:
	/* keep avg > 0 to guarantee that tot > 0 if there are dirty wbs */
	avg = max(avg, 1LU);
	if (wb_has_dirty_io(wb)) {
		long delta = avg - wb->avg_write_bandwidth;
		WARN_ON_ONCE(atomic_long_add_return(delta,
					&wb->bdi->tot_write_bandwidth) <= 0);
	}
	wb->write_bandwidth = bw;
	WRITE_ONCE(wb->avg_write_bandwidth, avg);
}

static void update_dirty_limit(struct dirty_throttle_control *dtc)
{
	struct wb_domain *dom = dtc_dom(dtc);
	unsigned long thresh = dtc->thresh;
	unsigned long limit = dom->dirty_limit;

	/*
	 * Follow up in one step.
	 */
	if (limit < thresh) {
		limit = thresh;
		goto update;
	}

	/*
	 * Follow down slowly. Use the higher one as the target, because thresh
	 * may drop below dirty. This is exactly the reason to introduce
	 * dom->dirty_limit which is guaranteed to lie above the dirty pages.
	 */
	thresh = max(thresh, dtc->dirty);
	if (limit > thresh) {
		limit -= (limit - thresh) >> 5;
		goto update;
	}
	return;
update:
	dom->dirty_limit = limit;
}

static void domain_update_dirty_limit(struct dirty_throttle_control *dtc,
				      unsigned long now)
{
	struct wb_domain *dom = dtc_dom(dtc);

	/*
	 * check locklessly first to optimize away locking for the most time
	 */
	if (time_before(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL))
		return;

	spin_lock(&dom->lock);
	if (time_after_eq(now, dom->dirty_limit_tstamp + BANDWIDTH_INTERVAL)) {
		update_dirty_limit(dtc);
		dom->dirty_limit_tstamp = now;
	}
	spin_unlock(&dom->lock);
}

/*
 * Maintain wb->dirty_ratelimit, the base dirty throttle rate.
 *
 * Normal wb tasks will be curbed at or below it in long term.
 * Obviously it should be around (write_bw / N) when there are N dd tasks.
 */
static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
				      unsigned long dirtied,
				      unsigned long elapsed)
{
	struct bdi_writeback *wb = dtc->wb;
	unsigned long dirty = dtc->dirty;
	unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh);
	unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh);
	unsigned long setpoint = (freerun + limit) / 2;
	unsigned long write_bw = wb->avg_write_bandwidth;
	unsigned long dirty_ratelimit = wb->dirty_ratelimit;
	unsigned long dirty_rate;
	unsigned long task_ratelimit;
	unsigned long balanced_dirty_ratelimit;
	unsigned long step;
	unsigned long x;
	unsigned long shift;

	/*
	 * The dirty rate will match the writeout rate in long term, except
	 * when dirty pages are truncated by userspace or re-dirtied by FS.
	 */
	dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;

	/*
	 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
	 */
	task_ratelimit = (u64)dirty_ratelimit *
					dtc->pos_ratio >> RATELIMIT_CALC_SHIFT;
	task_ratelimit++; /* it helps rampup dirty_ratelimit from tiny values */

	/*
	 * A linear estimation of the "balanced" throttle rate. The theory is,
	 * if there are N dd tasks, each throttled at task_ratelimit, the wb's
	 * dirty_rate will be measured to be (N * task_ratelimit). So the below
	 * formula will yield the balanced rate limit (write_bw / N).
	 *
	 * Note that the expanded form is not a pure rate feedback:
	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate)		     (1)
	 * but also takes pos_ratio into account:
	 *	rate_(i+1) = rate_(i) * (write_bw / dirty_rate) * pos_ratio  (2)
	 *
	 * (1) is not realistic because pos_ratio also takes part in balancing
	 * the dirty rate.  Consider the state
	 *	pos_ratio = 0.5						     (3)
	 *	rate = 2 * (write_bw / N)				     (4)
	 * If (1) is used, it will stuck in that state! Because each dd will
	 * be throttled at
	 *	task_ratelimit = pos_ratio * rate = (write_bw / N)	     (5)
	 * yielding
	 *	dirty_rate = N * task_ratelimit = write_bw		     (6)
	 * put (6) into (1) we get
	 *	rate_(i+1) = rate_(i)					     (7)
	 *
	 * So we end up using (2) to always keep
	 *	rate_(i+1) ~= (write_bw / N)				     (8)
	 * regardless of the value of pos_ratio. As long as (8) is satisfied,
	 * pos_ratio is able to drive itself to 1.0, which is not only where
	 * the dirty count meet the setpoint, but also where the slope of
	 * pos_ratio is most flat and hence task_ratelimit is least fluctuated.
	 */
	balanced_dirty_ratelimit = div_u64((u64)task_ratelimit * write_bw,
					   dirty_rate | 1);
	/*
	 * balanced_dirty_ratelimit ~= (write_bw / N) <= write_bw
	 */
	if (unlikely(balanced_dirty_ratelimit > write_bw))
		balanced_dirty_ratelimit = write_bw;

	/*
	 * We could safely do this and return immediately:
	 *
	 *	wb->dirty_ratelimit = balanced_dirty_ratelimit;
	 *
	 * However to get a more stable dirty_ratelimit, the below elaborated
	 * code makes use of task_ratelimit to filter out singular points and
	 * limit the step size.
	 *
	 * The below code essentially only uses the relative value of
	 *
	 *	task_ratelimit - dirty_ratelimit
	 *	= (pos_ratio - 1) * dirty_ratelimit
	 *
	 * which reflects the direction and size of dirty position error.
	 */

	/*
	 * dirty_ratelimit will follow balanced_dirty_ratelimit iff
	 * task_ratelimit is on the same side of dirty_ratelimit, too.
	 * For example, when
	 * - dirty_ratelimit > balanced_dirty_ratelimit
	 * - dirty_ratelimit > task_ratelimit (dirty pages are above setpoint)
	 * lowering dirty_ratelimit will help meet both the position and rate
	 * control targets. Otherwise, don't update dirty_ratelimit if it will
	 * only help meet the rate target. After all, what the users ultimately
	 * feel and care are stable dirty rate and small position error.
	 *
	 * |task_ratelimit - dirty_ratelimit| is used to limit the step size
	 * and filter out the singular points of balanced_dirty_ratelimit. Which
	 * keeps jumping around randomly and can even leap far away at times
	 * due to the small 200ms estimation period of dirty_rate (we want to
	 * keep that period small to reduce time lags).
	 */
	step = 0;

	/*
	 * For strictlimit case, calculations above were based on wb counters
	 * and limits (starting from pos_ratio = wb_position_ratio() and up to
	 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
	 * Hence, to calculate "step" properly, we have to use wb_dirty as
	 * "dirty" and wb_setpoint as "setpoint".
	 *
	 * We rampup dirty_ratelimit forcibly if wb_dirty is low because
	 * it's possible that wb_thresh is close to zero due to inactivity
	 * of backing device.
	 */
	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
		dirty = dtc->wb_dirty;
		if (dtc->wb_dirty < 8)
			setpoint = dtc->wb_dirty + 1;
		else
			setpoint = (dtc->wb_thresh + dtc->wb_bg_thresh) / 2;
	}

	if (dirty < setpoint) {
		x = min3(wb->balanced_dirty_ratelimit,
			 balanced_dirty_ratelimit, task_ratelimit);
		if (dirty_ratelimit < x)
			step = x - dirty_ratelimit;
	} else {
		x = max3(wb->balanced_dirty_ratelimit,
			 balanced_dirty_ratelimit, task_ratelimit);
		if (dirty_ratelimit > x)
			step = dirty_ratelimit - x;
	}

	/*
	 * Don't pursue 100% rate matching. It's impossible since the balanced
	 * rate itself is constantly fluctuating. So decrease the track speed
	 * when it gets close to the target. Helps eliminate pointless tremors.
	 */
	shift = dirty_ratelimit / (2 * step + 1);
	if (shift < BITS_PER_LONG)
		step = DIV_ROUND_UP(step >> shift, 8);
	else
		step = 0;

	if (dirty_ratelimit < balanced_dirty_ratelimit)
		dirty_ratelimit += step;
	else
		dirty_ratelimit -= step;

	WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL));
	wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;

	trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit);
}

static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc,
				  struct dirty_throttle_control *mdtc,
				  bool update_ratelimit)
{
	struct bdi_writeback *wb = gdtc->wb;
	unsigned long now = jiffies;
	unsigned long elapsed;
	unsigned long dirtied;
	unsigned long written;

	spin_lock(&wb->list_lock);

	/*
	 * Lockless checks for elapsed time are racy and delayed update after
	 * IO completion doesn't do it at all (to make sure written pages are
	 * accounted reasonably quickly). Make sure elapsed >= 1 to avoid
	 * division errors.
	 */
	elapsed = max(now - wb->bw_time_stamp, 1UL);
	dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
	written = percpu_counter_read(&wb->stat[WB_WRITTEN]);

	if (update_ratelimit) {
		domain_update_dirty_limit(gdtc, now);
		wb_update_dirty_ratelimit(gdtc, dirtied, elapsed);

		/*
		 * @mdtc is always NULL if !CGROUP_WRITEBACK but the
		 * compiler has no way to figure that out.  Help it.
		 */
		if (IS_ENABLED(CONFIG_CGROUP_WRITEBACK) && mdtc) {
			domain_update_dirty_limit(mdtc, now);
			wb_update_dirty_ratelimit(mdtc, dirtied, elapsed);
		}
	}
	wb_update_write_bandwidth(wb, elapsed, written);

	wb->dirtied_stamp = dirtied;
	wb->written_stamp = written;
	WRITE_ONCE(wb->bw_time_stamp, now);
	spin_unlock(&wb->list_lock);
}

void wb_update_bandwidth(struct bdi_writeback *wb)
{
	struct dirty_throttle_control gdtc = { GDTC_INIT(wb) };

	__wb_update_bandwidth(&gdtc, NULL, false);
}

/* Interval after which we consider wb idle and don't estimate bandwidth */
#define WB_BANDWIDTH_IDLE_JIF (HZ)

static void wb_bandwidth_estimate_start(struct bdi_writeback *wb)
{
	unsigned long now = jiffies;
	unsigned long elapsed = now - READ_ONCE(wb->bw_time_stamp);

	if (elapsed > WB_BANDWIDTH_IDLE_JIF &&
	    !atomic_read(&wb->writeback_inodes)) {
		spin_lock(&wb->list_lock);
		wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED);
		wb->written_stamp = wb_stat(wb, WB_WRITTEN);
		WRITE_ONCE(wb->bw_time_stamp, now);
		spin_unlock(&wb->list_lock);
	}
}

/*
 * After a task dirtied this many pages, balance_dirty_pages_ratelimited()
 * will look to see if it needs to start dirty throttling.
 *
 * If dirty_poll_interval is too low, big NUMA machines will call the expensive
 * global_zone_page_state() too often. So scale it near-sqrt to the safety margin
 * (the number of pages we may dirty without exceeding the dirty limits).
 */
static unsigned long dirty_poll_interval(unsigned long dirty,
					 unsigned long thresh)
{
	if (thresh > dirty)
		return 1UL << (ilog2(thresh - dirty) >> 1);

	return 1;
}

static unsigned long wb_max_pause(struct bdi_writeback *wb,
				  unsigned long wb_dirty)
{
	unsigned long bw = READ_ONCE(wb->avg_write_bandwidth);
	unsigned long t;

	/*
	 * Limit pause time for small memory systems. If sleeping for too long
	 * time, a small pool of dirty/writeback pages may go empty and disk go
	 * idle.
	 *
	 * 8 serves as the safety ratio.
	 */
	t = wb_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
	t++;

	return min_t(unsigned long, t, MAX_PAUSE);
}

static long wb_min_pause(struct bdi_writeback *wb,
			 long max_pause,
			 unsigned long task_ratelimit,
			 unsigned long dirty_ratelimit,
			 int *nr_dirtied_pause)
{
	long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth));
	long lo = ilog2(READ_ONCE(wb->dirty_ratelimit));
	long t;		/* target pause */
	long pause;	/* estimated next pause */
	int pages;	/* target nr_dirtied_pause */

	/* target for 10ms pause on 1-dd case */
	t = max(1, HZ / 100);

	/*
	 * Scale up pause time for concurrent dirtiers in order to reduce CPU
	 * overheads.
	 *
	 * (N * 10ms) on 2^N concurrent tasks.
	 */
	if (hi > lo)
		t += (hi - lo) * (10 * HZ) / 1024;

	/*
	 * This is a bit convoluted. We try to base the next nr_dirtied_pause
	 * on the much more stable dirty_ratelimit. However the next pause time
	 * will be computed based on task_ratelimit and the two rate limits may
	 * depart considerably at some time. Especially if task_ratelimit goes
	 * below dirty_ratelimit/2 and the target pause is max_pause, the next
	 * pause time will be max_pause*2 _trimmed down_ to max_pause.  As a
	 * result task_ratelimit won't be executed faithfully, which could
	 * eventually bring down dirty_ratelimit.
	 *
	 * We apply two rules to fix it up:
	 * 1) try to estimate the next pause time and if necessary, use a lower
	 *    nr_dirtied_pause so as not to exceed max_pause. When this happens,
	 *    nr_dirtied_pause will be "dancing" with task_ratelimit.
	 * 2) limit the target pause time to max_pause/2, so that the normal
	 *    small fluctuations of task_ratelimit won't trigger rule (1) and
	 *    nr_dirtied_pause will remain as stable as dirty_ratelimit.
	 */
	t = min(t, 1 + max_pause / 2);
	pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);

	/*
	 * Tiny nr_dirtied_pause is found to hurt I/O performance in the test
	 * case fio-mmap-randwrite-64k, which does 16*{sync read, async write}.
	 * When the 16 consecutive reads are often interrupted by some dirty
	 * throttling pause during the async writes, cfq will go into idles
	 * (deadline is fine). So push nr_dirtied_pause as high as possible
	 * until reaches DIRTY_POLL_THRESH=32 pages.
	 */
	if (pages < DIRTY_POLL_THRESH) {
		t = max_pause;
		pages = dirty_ratelimit * t / roundup_pow_of_two(HZ);
		if (pages > DIRTY_POLL_THRESH) {
			pages = DIRTY_POLL_THRESH;
			t = HZ * DIRTY_POLL_THRESH / dirty_ratelimit;
		}
	}

	pause = HZ * pages / (task_ratelimit + 1);
	if (pause > max_pause) {
		t = max_pause;
		pages = task_ratelimit * t / roundup_pow_of_two(HZ);
	}

	*nr_dirtied_pause = pages;
	/*
	 * The minimal pause time will normally be half the target pause time.
	 */
	return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
}

static inline void wb_dirty_limits(struct dirty_throttle_control *dtc)
{
	struct bdi_writeback *wb = dtc->wb;
	unsigned long wb_reclaimable;

	/*
	 * wb_thresh is not treated as some limiting factor as
	 * dirty_thresh, due to reasons
	 * - in JBOD setup, wb_thresh can fluctuate a lot
	 * - in a system with HDD and USB key, the USB key may somehow
	 *   go into state (wb_dirty >> wb_thresh) either because
	 *   wb_dirty starts high, or because wb_thresh drops low.
	 *   In this case we don't want to hard throttle the USB key
	 *   dirtiers for 100 seconds until wb_dirty drops under
	 *   wb_thresh. Instead the auxiliary wb control line in
	 *   wb_position_ratio() will let the dirtier task progress
	 *   at some rate <= (write_bw / 2) for bringing down wb_dirty.
	 */
	dtc->wb_thresh = __wb_calc_thresh(dtc);
	dtc->wb_bg_thresh = dtc->thresh ?
		div_u64((u64)dtc->wb_thresh * dtc->bg_thresh, dtc->thresh) : 0;

	/*
	 * In order to avoid the stacked BDI deadlock we need
	 * to ensure we accurately count the 'dirty' pages when
	 * the threshold is low.
	 *
	 * Otherwise it would be possible to get thresh+n pages
	 * reported dirty, even though there are thresh-m pages
	 * actually dirty; with m+n sitting in the percpu
	 * deltas.
	 */
	if (dtc->wb_thresh < 2 * wb_stat_error()) {
		wb_reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
		dtc->wb_dirty = wb_reclaimable + wb_stat_sum(wb, WB_WRITEBACK);
	} else {
		wb_reclaimable = wb_stat(wb, WB_RECLAIMABLE);
		dtc->wb_dirty = wb_reclaimable + wb_stat(wb, WB_WRITEBACK);
	}
}

/*
 * balance_dirty_pages() must be called by processes which are generating dirty
 * data.  It looks at the number of dirty pages in the machine and will force
 * the caller to wait once crossing the (background_thresh + dirty_thresh) / 2.
 * If we're over `background_thresh' then the writeback threads are woken to
 * perform some writeout.
 */
static int balance_dirty_pages(struct bdi_writeback *wb,
			       unsigned long pages_dirtied, unsigned int flags)
{
	struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
	struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
	struct dirty_throttle_control * const gdtc = &gdtc_stor;
	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
						     &mdtc_stor : NULL;
	struct dirty_throttle_control *sdtc;
	unsigned long nr_reclaimable;	/* = file_dirty */
	long period;
	long pause;
	long max_pause;
	long min_pause;
	int nr_dirtied_pause;
	bool dirty_exceeded = false;
	unsigned long task_ratelimit;
	unsigned long dirty_ratelimit;
	struct backing_dev_info *bdi = wb->bdi;
	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
	unsigned long start_time = jiffies;
	int ret = 0;

	for (;;) {
		unsigned long now = jiffies;
		unsigned long dirty, thresh, bg_thresh;
		unsigned long m_dirty = 0;	/* stop bogus uninit warnings */
		unsigned long m_thresh = 0;
		unsigned long m_bg_thresh = 0;

		nr_reclaimable = global_node_page_state(NR_FILE_DIRTY);
		gdtc->avail = global_dirtyable_memory();
		gdtc->dirty = nr_reclaimable + global_node_page_state(NR_WRITEBACK);

		domain_dirty_limits(gdtc);

		if (unlikely(strictlimit)) {
			wb_dirty_limits(gdtc);

			dirty = gdtc->wb_dirty;
			thresh = gdtc->wb_thresh;
			bg_thresh = gdtc->wb_bg_thresh;
		} else {
			dirty = gdtc->dirty;
			thresh = gdtc->thresh;
			bg_thresh = gdtc->bg_thresh;
		}

		if (mdtc) {
			unsigned long filepages, headroom, writeback;

			/*
			 * If @wb belongs to !root memcg, repeat the same
			 * basic calculations for the memcg domain.
			 */
			mem_cgroup_wb_stats(wb, &filepages, &headroom,
					    &mdtc->dirty, &writeback);
			mdtc->dirty += writeback;
			mdtc_calc_avail(mdtc, filepages, headroom);

			domain_dirty_limits(mdtc);

			if (unlikely(strictlimit)) {
				wb_dirty_limits(mdtc);
				m_dirty = mdtc->wb_dirty;
				m_thresh = mdtc->wb_thresh;
				m_bg_thresh = mdtc->wb_bg_thresh;
			} else {
				m_dirty = mdtc->dirty;
				m_thresh = mdtc->thresh;
				m_bg_thresh = mdtc->bg_thresh;
			}
		}

		/*
		 * In laptop mode, we wait until hitting the higher threshold
		 * before starting background writeout, and then write out all
		 * the way down to the lower threshold.  So slow writers cause
		 * minimal disk activity.
		 *
		 * In normal mode, we start background writeout at the lower
		 * background_thresh, to keep the amount of dirty memory low.
		 */
		if (!laptop_mode && nr_reclaimable > gdtc->bg_thresh &&
		    !writeback_in_progress(wb))
			wb_start_background_writeback(wb);

		/*
		 * Throttle it only when the background writeback cannot
		 * catch-up. This avoids (excessively) small writeouts
		 * when the wb limits are ramping up in case of !strictlimit.
		 *
		 * In strictlimit case make decision based on the wb counters
		 * and limits. Small writeouts when the wb limits are ramping
		 * up are the price we consciously pay for strictlimit-ing.
		 *
		 * If memcg domain is in effect, @dirty should be under
		 * both global and memcg freerun ceilings.
		 */
		if (dirty <= dirty_freerun_ceiling(thresh, bg_thresh) &&
		    (!mdtc ||
		     m_dirty <= dirty_freerun_ceiling(m_thresh, m_bg_thresh))) {
			unsigned long intv;
			unsigned long m_intv;

free_running:
			intv = dirty_poll_interval(dirty, thresh);
			m_intv = ULONG_MAX;

			current->dirty_paused_when = now;
			current->nr_dirtied = 0;
			if (mdtc)
				m_intv = dirty_poll_interval(m_dirty, m_thresh);
			current->nr_dirtied_pause = min(intv, m_intv);
			break;
		}

		/* Start writeback even when in laptop mode */
		if (unlikely(!writeback_in_progress(wb)))
			wb_start_background_writeback(wb);

		mem_cgroup_flush_foreign(wb);

		/*
		 * Calculate global domain's pos_ratio and select the
		 * global dtc by default.
		 */
		if (!strictlimit) {
			wb_dirty_limits(gdtc);

			if ((current->flags & PF_LOCAL_THROTTLE) &&
			    gdtc->wb_dirty <
			    dirty_freerun_ceiling(gdtc->wb_thresh,
						  gdtc->wb_bg_thresh))
				/*
				 * LOCAL_THROTTLE tasks must not be throttled
				 * when below the per-wb freerun ceiling.
				 */
				goto free_running;
		}

		dirty_exceeded = (gdtc->wb_dirty > gdtc->wb_thresh) &&
			((gdtc->dirty > gdtc->thresh) || strictlimit);

		wb_position_ratio(gdtc);
		sdtc = gdtc;

		if (mdtc) {
			/*
			 * If memcg domain is in effect, calculate its
			 * pos_ratio.  @wb should satisfy constraints from
			 * both global and memcg domains.  Choose the one
			 * w/ lower pos_ratio.
			 */
			if (!strictlimit) {
				wb_dirty_limits(mdtc);

				if ((current->flags & PF_LOCAL_THROTTLE) &&
				    mdtc->wb_dirty <
				    dirty_freerun_ceiling(mdtc->wb_thresh,
							  mdtc->wb_bg_thresh))
					/*
					 * LOCAL_THROTTLE tasks must not be
					 * throttled when below the per-wb
					 * freerun ceiling.
					 */
					goto free_running;
			}
			dirty_exceeded |= (mdtc->wb_dirty > mdtc->wb_thresh) &&
				((mdtc->dirty > mdtc->thresh) || strictlimit);

			wb_position_ratio(mdtc);
			if (mdtc->pos_ratio < gdtc->pos_ratio)
				sdtc = mdtc;
		}

		if (dirty_exceeded != wb->dirty_exceeded)
			wb->dirty_exceeded = dirty_exceeded;

		if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
					   BANDWIDTH_INTERVAL))
			__wb_update_bandwidth(gdtc, mdtc, true);

		/* throttle according to the chosen dtc */
		dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
		task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
							RATELIMIT_CALC_SHIFT;
		max_pause = wb_max_pause(wb, sdtc->wb_dirty);
		min_pause = wb_min_pause(wb, max_pause,
					 task_ratelimit, dirty_ratelimit,
					 &nr_dirtied_pause);

		if (unlikely(task_ratelimit == 0)) {
			period = max_pause;
			pause = max_pause;
			goto pause;
		}
		period = HZ * pages_dirtied / task_ratelimit;
		pause = period;
		if (current->dirty_paused_when)
			pause -= now - current->dirty_paused_when;
		/*
		 * For less than 1s think time (ext3/4 may block the dirtier
		 * for up to 800ms from time to time on 1-HDD; so does xfs,
		 * however at much less frequency), try to compensate it in
		 * future periods by updating the virtual time; otherwise just
		 * do a reset, as it may be a light dirtier.
		 */
		if (pause < min_pause) {
			trace_balance_dirty_pages(wb,
						  sdtc->thresh,
						  sdtc->bg_thresh,
						  sdtc->dirty,
						  sdtc->wb_thresh,
						  sdtc->wb_dirty,
						  dirty_ratelimit,
						  task_ratelimit,
						  pages_dirtied,
						  period,
						  min(pause, 0L),
						  start_time);
			if (pause < -HZ) {
				current->dirty_paused_when = now;
				current->nr_dirtied = 0;
			} else if (period) {
				current->dirty_paused_when += period;
				current->nr_dirtied = 0;
			} else if (current->nr_dirtied_pause <= pages_dirtied)
				current->nr_dirtied_pause += pages_dirtied;
			break;
		}
		if (unlikely(pause > max_pause)) {
			/* for occasional dropped task_ratelimit */
			now += min(pause - max_pause, max_pause);
			pause = max_pause;
		}

pause:
		trace_balance_dirty_pages(wb,
					  sdtc->thresh,
					  sdtc->bg_thresh,
					  sdtc->dirty,
					  sdtc->wb_thresh,
					  sdtc->wb_dirty,
					  dirty_ratelimit,
					  task_ratelimit,
					  pages_dirtied,
					  period,
					  pause,
					  start_time);
		if (flags & BDP_ASYNC) {
			ret = -EAGAIN;
			break;
		}
		__set_current_state(TASK_KILLABLE);
		wb->dirty_sleep = now;
		io_schedule_timeout(pause);

		current->dirty_paused_when = now + pause;
		current->nr_dirtied = 0;
		current->nr_dirtied_pause = nr_dirtied_pause;

		/*
		 * This is typically equal to (dirty < thresh) and can also
		 * keep "1000+ dd on a slow USB stick" under control.
		 */
		if (task_ratelimit)
			break;

		/*
		 * In the case of an unresponsive NFS server and the NFS dirty
		 * pages exceeds dirty_thresh, give the other good wb's a pipe
		 * to go through, so that tasks on them still remain responsive.
		 *
		 * In theory 1 page is enough to keep the consumer-producer
		 * pipe going: the flusher cleans 1 page => the task dirties 1
		 * more page. However wb_dirty has accounting errors.  So use
		 * the larger and more IO friendly wb_stat_error.
		 */
		if (sdtc->wb_dirty <= wb_stat_error())
			break;

		if (fatal_signal_pending(current))
			break;
	}
	return ret;
}

static DEFINE_PER_CPU(int, bdp_ratelimits);

/*
 * Normal tasks are throttled by
 *	loop {
 *		dirty tsk->nr_dirtied_pause pages;
 *		take a snap in balance_dirty_pages();
 *	}
 * However there is a worst case. If every task exit immediately when dirtied
 * (tsk->nr_dirtied_pause - 1) pages, balance_dirty_pages() will never be
 * called to throttle the page dirties. The solution is to save the not yet
 * throttled page dirties in dirty_throttle_leaks on task exit and charge them
 * randomly into the running tasks. This works well for the above worst case,
 * as the new task will pick up and accumulate the old task's leaked dirty
 * count and eventually get throttled.
 */
DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;

/**
 * balance_dirty_pages_ratelimited_flags - Balance dirty memory state.
 * @mapping: address_space which was dirtied.
 * @flags: BDP flags.
 *
 * Processes which are dirtying memory should call in here once for each page
 * which was newly dirtied.  The function will periodically check the system's
 * dirty state and will initiate writeback if needed.
 *
 * See balance_dirty_pages_ratelimited() for details.
 *
 * Return: If @flags contains BDP_ASYNC, it may return -EAGAIN to
 * indicate that memory is out of balance and the caller must wait
 * for I/O to complete.  Otherwise, it will return 0 to indicate
 * that either memory was already in balance, or it was able to sleep
 * until the amount of dirty memory returned to balance.
 */
int balance_dirty_pages_ratelimited_flags(struct address_space *mapping,
					unsigned int flags)
{
	struct inode *inode = mapping->host;
	struct backing_dev_info *bdi = inode_to_bdi(inode);
	struct bdi_writeback *wb = NULL;
	int ratelimit;
	int ret = 0;
	int *p;

	if (!(bdi->capabilities & BDI_CAP_WRITEBACK))
		return ret;

	if (inode_cgwb_enabled(inode))
		wb = wb_get_create_current(bdi, GFP_KERNEL);
	if (!wb)
		wb = &bdi->wb;

	ratelimit = current->nr_dirtied_pause;
	if (wb->dirty_exceeded)
		ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));

	preempt_disable();
	/*
	 * This prevents one CPU to accumulate too many dirtied pages without
	 * calling into balance_dirty_pages(), which can happen when there are
	 * 1000+ tasks, all of them start dirtying pages at exactly the same
	 * time, hence all honoured too large initial task->nr_dirtied_pause.
	 */
	p =  this_cpu_ptr(&bdp_ratelimits);
	if (unlikely(current->nr_dirtied >= ratelimit))
		*p = 0;
	else if (unlikely(*p >= ratelimit_pages)) {
		*p = 0;
		ratelimit = 0;
	}
	/*
	 * Pick up the dirtied pages by the exited tasks. This avoids lots of
	 * short-lived tasks (eg. gcc invocations in a kernel build) escaping
	 * the dirty throttling and livelock other long-run dirtiers.
	 */
	p = this_cpu_ptr(&dirty_throttle_leaks);
	if (*p > 0 && current->nr_dirtied < ratelimit) {
		unsigned long nr_pages_dirtied;
		nr_pages_dirtied = min(*p, ratelimit - current->nr_dirtied);
		*p -= nr_pages_dirtied;
		current->nr_dirtied += nr_pages_dirtied;
	}
	preempt_enable();

	if (unlikely(current->nr_dirtied >= ratelimit))
		ret = balance_dirty_pages(wb, current->nr_dirtied, flags);

	wb_put(wb);
	return ret;
}

/**
 * balance_dirty_pages_ratelimited - balance dirty memory state.
 * @mapping: address_space which was dirtied.
 *
 * Processes which are dirtying memory should call in here once for each page
 * which was newly dirtied.  The function will periodically check the system's
 * dirty state and will initiate writeback if needed.
 *
 * Once we're over the dirty memory limit we decrease the ratelimiting
 * by a lot, to prevent individual processes from overshooting the limit
 * by (ratelimit_pages) each.
 */
void balance_dirty_pages_ratelimited(struct address_space *mapping)
{
	balance_dirty_pages_ratelimited_flags(mapping, 0);
}
EXPORT_SYMBOL(balance_dirty_pages_ratelimited);

/**
 * wb_over_bg_thresh - does @wb need to be written back?
 * @wb: bdi_writeback of interest
 *
 * Determines whether background writeback should keep writing @wb or it's
 * clean enough.
 *
 * Return: %true if writeback should continue.
 */
bool wb_over_bg_thresh(struct bdi_writeback *wb)
{
	struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
	struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
	struct dirty_throttle_control * const gdtc = &gdtc_stor;
	struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
						     &mdtc_stor : NULL;
	unsigned long reclaimable;
	unsigned long thresh;

	/*
	 * Similar to balance_dirty_pages() but ignores pages being written
	 * as we're trying to decide whether to put more under writeback.
	 */
	gdtc->avail = global_dirtyable_memory();
	gdtc->dirty = global_node_page_state(NR_FILE_DIRTY);
	domain_dirty_limits(gdtc);

	if (gdtc->dirty > gdtc->bg_thresh)
		return true;

	thresh = wb_calc_thresh(gdtc->wb, gdtc->bg_thresh);
	if (thresh < 2 * wb_stat_error())
		reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
	else
		reclaimable = wb_stat(wb, WB_RECLAIMABLE);

	if (reclaimable > thresh)
		return true;

	if (mdtc) {
		unsigned long filepages, headroom, writeback;

		mem_cgroup_wb_stats(wb, &filepages, &headroom, &mdtc->dirty,
				    &writeback);
		mdtc_calc_avail(mdtc, filepages, headroom);
		domain_dirty_limits(mdtc);	/* ditto, ignore writeback */

		if (mdtc->dirty > mdtc->bg_thresh)
			return true;

		thresh = wb_calc_thresh(mdtc->wb, mdtc->bg_thresh);
		if (thresh < 2 * wb_stat_error())
			reclaimable = wb_stat_sum(wb, WB_RECLAIMABLE);
		else
			reclaimable = wb_stat(wb, WB_RECLAIMABLE);

		if (reclaimable > thresh)
			return true;
	}

	return false;
}

#ifdef CONFIG_SYSCTL
/*
 * sysctl handler for /proc/sys/vm/dirty_writeback_centisecs
 */
static int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
		void *buffer, size_t *length, loff_t *ppos)
{
	unsigned int old_interval = dirty_writeback_interval;
	int ret;

	ret = proc_dointvec(table, write, buffer, length, ppos);

	/*
	 * Writing 0 to dirty_writeback_interval will disable periodic writeback
	 * and a different non-zero value will wakeup the writeback threads.
	 * wb_wakeup_delayed() would be more appropriate, but it's a pain to
	 * iterate over all bdis and wbs.
	 * The reason we do this is to make the change take effect immediately.
	 */
	if (!ret && write && dirty_writeback_interval &&
		dirty_writeback_interval != old_interval)
		wakeup_flusher_threads(WB_REASON_PERIODIC);

	return ret;
}
#endif

void laptop_mode_timer_fn(struct timer_list *t)
{
	struct backing_dev_info *backing_dev_info =
		from_timer(backing_dev_info, t, laptop_mode_wb_timer);

	wakeup_flusher_threads_bdi(backing_dev_info, WB_REASON_LAPTOP_TIMER);
}

/*
 * We've spun up the disk and we're in laptop mode: schedule writeback
 * of all dirty data a few seconds from now.  If the flush is already scheduled
 * then push it back - the user is still using the disk.
 */
void laptop_io_completion(struct backing_dev_info *info)
{
	mod_timer(&info->laptop_mode_wb_timer, jiffies + laptop_mode);
}

/*
 * We're in laptop mode and we've just synced. The sync's writes will have
 * caused another writeback to be scheduled by laptop_io_completion.
 * Nothing needs to be written back anymore, so we unschedule the writeback.
 */
void laptop_sync_completion(void)
{
	struct backing_dev_info *bdi;

	rcu_read_lock();

	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
		del_timer(&bdi->laptop_mode_wb_timer);

	rcu_read_unlock();
}

/*
 * If ratelimit_pages is too high then we can get into dirty-data overload
 * if a large number of processes all perform writes at the same time.
 *
 * Here we set ratelimit_pages to a level which ensures that when all CPUs are
 * dirtying in parallel, we cannot go more than 3% (1/32) over the dirty memory
 * thresholds.
 */

void writeback_set_ratelimit(void)
{
	struct wb_domain *dom = &global_wb_domain;
	unsigned long background_thresh;
	unsigned long dirty_thresh;

	global_dirty_limits(&background_thresh, &dirty_thresh);
	dom->dirty_limit = dirty_thresh;
	ratelimit_pages = dirty_thresh / (num_online_cpus() * 32);
	if (ratelimit_pages < 16)
		ratelimit_pages = 16;
}

static int page_writeback_cpu_online(unsigned int cpu)
{
	writeback_set_ratelimit();
	return 0;
}

#ifdef CONFIG_SYSCTL

/* this is needed for the proc_doulongvec_minmax of vm_dirty_bytes */
static const unsigned long dirty_bytes_min = 2 * PAGE_SIZE;

static struct ctl_table vm_page_writeback_sysctls[] = {
	{
		.procname   = "dirty_background_ratio",
		.data       = &dirty_background_ratio,
		.maxlen     = sizeof(dirty_background_ratio),
		.mode       = 0644,
		.proc_handler   = dirty_background_ratio_handler,
		.extra1     = SYSCTL_ZERO,
		.extra2     = SYSCTL_ONE_HUNDRED,
	},
	{
		.procname   = "dirty_background_bytes",
		.data       = &dirty_background_bytes,
		.maxlen     = sizeof(dirty_background_bytes),
		.mode       = 0644,
		.proc_handler   = dirty_background_bytes_handler,
		.extra1     = SYSCTL_LONG_ONE,
	},
	{
		.procname   = "dirty_ratio",
		.data       = &vm_dirty_ratio,
		.maxlen     = sizeof(vm_dirty_ratio),
		.mode       = 0644,
		.proc_handler   = dirty_ratio_handler,
		.extra1     = SYSCTL_ZERO,
		.extra2     = SYSCTL_ONE_HUNDRED,
	},
	{
		.procname   = "dirty_bytes",
		.data       = &vm_dirty_bytes,
		.maxlen     = sizeof(vm_dirty_bytes),
		.mode       = 0644,
		.proc_handler   = dirty_bytes_handler,
		.extra1     = (void *)&dirty_bytes_min,
	},
	{
		.procname   = "dirty_writeback_centisecs",
		.data       = &dirty_writeback_interval,
		.maxlen     = sizeof(dirty_writeback_interval),
		.mode       = 0644,
		.proc_handler   = dirty_writeback_centisecs_handler,
	},
	{
		.procname   = "dirty_expire_centisecs",
		.data       = &dirty_expire_interval,
		.maxlen     = sizeof(dirty_expire_interval),
		.mode       = 0644,
		.proc_handler   = proc_dointvec_minmax,
		.extra1     = SYSCTL_ZERO,
	},
#ifdef CONFIG_HIGHMEM
	{
		.procname	= "highmem_is_dirtyable",
		.data		= &vm_highmem_is_dirtyable,
		.maxlen		= sizeof(vm_highmem_is_dirtyable),
		.mode		= 0644,
		.proc_handler	= proc_dointvec_minmax,
		.extra1		= SYSCTL_ZERO,
		.extra2		= SYSCTL_ONE,
	},
#endif
	{
		.procname	= "laptop_mode",
		.data		= &laptop_mode,
		.maxlen		= sizeof(laptop_mode),
		.mode		= 0644,
		.proc_handler	= proc_dointvec_jiffies,
	},
	{}
};
#endif

/*
 * Called early on to tune the page writeback dirty limits.
 *
 * We used to scale dirty pages according to how total memory
 * related to pages that could be allocated for buffers.
 *
 * However, that was when we used "dirty_ratio" to scale with
 * all memory, and we don't do that any more. "dirty_ratio"
 * is now applied to total non-HIGHPAGE memory, and as such we can't
 * get into the old insane situation any more where we had
 * large amounts of dirty pages compared to a small amount of
 * non-HIGHMEM memory.
 *
 * But we might still want to scale the dirty_ratio by how
 * much memory the box has..
 */
void __init page_writeback_init(void)
{
	BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));

	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
			  page_writeback_cpu_online, NULL);
	cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
			  page_writeback_cpu_online);
#ifdef CONFIG_SYSCTL
	register_sysctl_init("vm", vm_page_writeback_sysctls);
#endif
}

/**
 * tag_pages_for_writeback - tag pages to be written by write_cache_pages
 * @mapping: address space structure to write
 * @start: starting page index
 * @end: ending page index (inclusive)
 *
 * This function scans the page range from @start to @end (inclusive) and tags
 * all pages that have DIRTY tag set with a special TOWRITE tag. The idea is
 * that write_cache_pages (or whoever calls this function) will then use
 * TOWRITE tag to identify pages eligible for writeback.  This mechanism is
 * used to avoid livelocking of writeback by a process steadily creating new
 * dirty pages in the file (thus it is important for this function to be quick
 * so that it can tag pages faster than a dirtying process can create them).
 */
void tag_pages_for_writeback(struct address_space *mapping,
			     pgoff_t start, pgoff_t end)
{
	XA_STATE(xas, &mapping->i_pages, start);
	unsigned int tagged = 0;
	void *page;

	xas_lock_irq(&xas);
	xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
		xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
		if (++tagged % XA_CHECK_SCHED)
			continue;

		xas_pause(&xas);
		xas_unlock_irq(&xas);
		cond_resched();
		xas_lock_irq(&xas);
	}
	xas_unlock_irq(&xas);
}
EXPORT_SYMBOL(tag_pages_for_writeback);

/**
 * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 * @writepage: function called for each page
 * @data: data passed to writepage function
 *
 * If a page is already under I/O, write_cache_pages() skips it, even
 * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
 * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
 * and msync() need to guarantee that all the data which was dirty at the time
 * the call was made get new I/O started against them.  If wbc->sync_mode is
 * WB_SYNC_ALL then we were called for data integrity and we must wait for
 * existing IO to complete.
 *
 * To avoid livelocks (when other process dirties new pages), we first tag
 * pages which should be written back with TOWRITE tag and only then start
 * writing them. For data-integrity sync we have to be careful so that we do
 * not miss some pages (e.g., because some other process has cleared TOWRITE
 * tag we set). The rule we follow is that TOWRITE tag can be cleared only
 * by the process clearing the DIRTY tag (and submitting the page for IO).
 *
 * To avoid deadlocks between range_cyclic writeback and callers that hold
 * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
 * we do not loop back to the start of the file. Doing so causes a page
 * lock/page writeback access order inversion - we should only ever lock
 * multiple pages in ascending page->index order, and looping back to the start
 * of the file violates that rule and causes deadlocks.
 *
 * Return: %0 on success, negative error code otherwise
 */
int write_cache_pages(struct address_space *mapping,
		      struct writeback_control *wbc, writepage_t writepage,
		      void *data)
{
	int ret = 0;
	int done = 0;
	int error;
	struct pagevec pvec;
	int nr_pages;
	pgoff_t index;
	pgoff_t end;		/* Inclusive */
	pgoff_t done_index;
	int range_whole = 0;
	xa_mark_t tag;

	pagevec_init(&pvec);
	if (wbc->range_cyclic) {
		index = mapping->writeback_index; /* prev offset */
		end = -1;
	} else {
		index = wbc->range_start >> PAGE_SHIFT;
		end = wbc->range_end >> PAGE_SHIFT;
		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
			range_whole = 1;
	}
	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
		tag_pages_for_writeback(mapping, index, end);
		tag = PAGECACHE_TAG_TOWRITE;
	} else {
		tag = PAGECACHE_TAG_DIRTY;
	}
	done_index = index;
	while (!done && (index <= end)) {
		int i;

		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
				tag);
		if (nr_pages == 0)
			break;

		for (i = 0; i < nr_pages; i++) {
			struct page *page = pvec.pages[i];

			done_index = page->index;

			lock_page(page);

			/*
			 * Page truncated or invalidated. We can freely skip it
			 * then, even for data integrity operations: the page
			 * has disappeared concurrently, so there could be no
			 * real expectation of this data integrity operation
			 * even if there is now a new, dirty page at the same
			 * pagecache address.
			 */
			if (unlikely(page->mapping != mapping)) {
continue_unlock:
				unlock_page(page);
				continue;
			}

			if (!PageDirty(page)) {
				/* someone wrote it for us */
				goto continue_unlock;
			}

			if (PageWriteback(page)) {
				if (wbc->sync_mode != WB_SYNC_NONE)
					wait_on_page_writeback(page);
				else
					goto continue_unlock;
			}

			BUG_ON(PageWriteback(page));
			if (!clear_page_dirty_for_io(page))
				goto continue_unlock;

			trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
			error = (*writepage)(page, wbc, data);
			if (unlikely(error)) {
				/*
				 * Handle errors according to the type of
				 * writeback. There's no need to continue for
				 * background writeback. Just push done_index
				 * past this page so media errors won't choke
				 * writeout for the entire file. For integrity
				 * writeback, we must process the entire dirty
				 * set regardless of errors because the fs may
				 * still have state to clear for each page. In
				 * that case we continue processing and return
				 * the first error.
				 */
				if (error == AOP_WRITEPAGE_ACTIVATE) {
					unlock_page(page);
					error = 0;
				} else if (wbc->sync_mode != WB_SYNC_ALL) {
					ret = error;
					done_index = page->index + 1;
					done = 1;
					break;
				}
				if (!ret)
					ret = error;
			}

			/*
			 * We stop writing back only if we are not doing
			 * integrity sync. In case of integrity sync we have to
			 * keep going until we have written all the pages
			 * we tagged for writeback prior to entering this loop.
			 */
			if (--wbc->nr_to_write <= 0 &&
			    wbc->sync_mode == WB_SYNC_NONE) {
				done = 1;
				break;
			}
		}
		pagevec_release(&pvec);
		cond_resched();
	}

	/*
	 * If we hit the last page and there is more work to be done: wrap
	 * back the index back to the start of the file for the next
	 * time we are called.
	 */
	if (wbc->range_cyclic && !done)
		done_index = 0;
	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
		mapping->writeback_index = done_index;

	return ret;
}
EXPORT_SYMBOL(write_cache_pages);

/*
 * Function used by generic_writepages to call the real writepage
 * function and set the mapping flags on error
 */
static int __writepage(struct page *page, struct writeback_control *wbc,
		       void *data)
{
	struct address_space *mapping = data;
	int ret = mapping->a_ops->writepage(page, wbc);
	mapping_set_error(mapping, ret);
	return ret;
}

/**
 * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
 * @mapping: address space structure to write
 * @wbc: subtract the number of written pages from *@wbc->nr_to_write
 *
 * This is a library function, which implements the writepages()
 * address_space_operation.
 *
 * Return: %0 on success, negative error code otherwise
 */
int generic_writepages(struct address_space *mapping,
		       struct writeback_control *wbc)
{
	struct blk_plug plug;
	int ret;

	/* deal with chardevs and other special file */
	if (!mapping->a_ops->writepage)
		return 0;

	blk_start_plug(&plug);
	ret = write_cache_pages(mapping, wbc, __writepage, mapping);
	blk_finish_plug(&plug);
	return ret;
}

EXPORT_SYMBOL(generic_writepages);

int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
	int ret;
	struct bdi_writeback *wb;

	if (wbc->nr_to_write <= 0)
		return 0;
	wb = inode_to_wb_wbc(mapping->host, wbc);
	wb_bandwidth_estimate_start(wb);
	while (1) {
		if (mapping->a_ops->writepages)
			ret = mapping->a_ops->writepages(mapping, wbc);
		else
			ret = generic_writepages(mapping, wbc);
		if ((ret != -ENOMEM) || (wbc->sync_mode != WB_SYNC_ALL))
			break;

		/*
		 * Lacking an allocation context or the locality or writeback
		 * state of any of the inode's pages, throttle based on
		 * writeback activity on the local node. It's as good a
		 * guess as any.
		 */
		reclaim_throttle(NODE_DATA(numa_node_id()),
			VMSCAN_THROTTLE_WRITEBACK);
	}
	/*
	 * Usually few pages are written by now from those we've just submitted
	 * but if there's constant writeback being submitted, this makes sure
	 * writeback bandwidth is updated once in a while.
	 */
	if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
				   BANDWIDTH_INTERVAL))
		wb_update_bandwidth(wb);
	return ret;
}

/**
 * folio_write_one - write out a single folio and wait on I/O.
 * @folio: The folio to write.
 *
 * The folio must be locked by the caller and will be unlocked upon return.
 *
 * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
 * function returns.
 *
 * Return: %0 on success, negative error code otherwise
 */
int folio_write_one(struct folio *folio)
{
	struct address_space *mapping = folio->mapping;
	int ret = 0;
	struct writeback_control wbc = {
		.sync_mode = WB_SYNC_ALL,
		.nr_to_write = folio_nr_pages(folio),
	};

	BUG_ON(!folio_test_locked(folio));

	folio_wait_writeback(folio);

	if (folio_clear_dirty_for_io(folio)) {
		folio_get(folio);
		ret = mapping->a_ops->writepage(&folio->page, &wbc);
		if (ret == 0)
			folio_wait_writeback(folio);
		folio_put(folio);
	} else {
		folio_unlock(folio);
	}

	if (!ret)
		ret = filemap_check_errors(mapping);
	return ret;
}
EXPORT_SYMBOL(folio_write_one);

/*
 * For address_spaces which do not use buffers nor write back.
 */
bool noop_dirty_folio(struct address_space *mapping, struct folio *folio)
{
	if (!folio_test_dirty(folio))
		return !folio_test_set_dirty(folio);
	return false;
}
EXPORT_SYMBOL(noop_dirty_folio);

/*
 * Helper function for set_page_dirty family.
 *
 * Caller must hold lock_page_memcg().
 *
 * NOTE: This relies on being atomic wrt interrupts.
 */
static void folio_account_dirtied(struct folio *folio,
		struct address_space *mapping)
{
	struct inode *inode = mapping->host;

	trace_writeback_dirty_folio(folio, mapping);

	if (mapping_can_writeback(mapping)) {
		struct bdi_writeback *wb;
		long nr = folio_nr_pages(folio);

		inode_attach_wb(inode, &folio->page);
		wb = inode_to_wb(inode);

		__lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, nr);
		__zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
		__node_stat_mod_folio(folio, NR_DIRTIED, nr);
		wb_stat_mod(wb, WB_RECLAIMABLE, nr);
		wb_stat_mod(wb, WB_DIRTIED, nr);
		task_io_account_write(nr * PAGE_SIZE);
		current->nr_dirtied += nr;
		__this_cpu_add(bdp_ratelimits, nr);

		mem_cgroup_track_foreign_dirty(folio, wb);
	}
}

/*
 * Helper function for deaccounting dirty page without writeback.
 *
 * Caller must hold lock_page_memcg().
 */
void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
{
	long nr = folio_nr_pages(folio);

	lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
	zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
	wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
	task_io_account_cancelled_write(nr * PAGE_SIZE);
}

/*
 * Mark the folio dirty, and set it dirty in the page cache, and mark
 * the inode dirty.
 *
 * If warn is true, then emit a warning if the folio is not uptodate and has
 * not been truncated.
 *
 * The caller must hold lock_page_memcg().  Most callers have the folio
 * locked.  A few have the folio blocked from truncation through other
 * means (eg zap_page_range() has it mapped and is holding the page table
 * lock).  This can also be called from mark_buffer_dirty(), which I
 * cannot prove is always protected against truncate.
 */
void __folio_mark_dirty(struct folio *folio, struct address_space *mapping,
			     int warn)
{
	unsigned long flags;

	xa_lock_irqsave(&mapping->i_pages, flags);
	if (folio->mapping) {	/* Race with truncate? */
		WARN_ON_ONCE(warn && !folio_test_uptodate(folio));
		folio_account_dirtied(folio, mapping);
		__xa_set_mark(&mapping->i_pages, folio_index(folio),
				PAGECACHE_TAG_DIRTY);
	}
	xa_unlock_irqrestore(&mapping->i_pages, flags);
}

/**
 * filemap_dirty_folio - Mark a folio dirty for filesystems which do not use buffer_heads.
 * @mapping: Address space this folio belongs to.
 * @folio: Folio to be marked as dirty.
 *
 * Filesystems which do not use buffer heads should call this function
 * from their set_page_dirty address space operation.  It ignores the
 * contents of folio_get_private(), so if the filesystem marks individual
 * blocks as dirty, the filesystem should handle that itself.
 *
 * This is also sometimes used by filesystems which use buffer_heads when
 * a single buffer is being dirtied: we want to set the folio dirty in
 * that case, but not all the buffers.  This is a "bottom-up" dirtying,
 * whereas block_dirty_folio() is a "top-down" dirtying.
 *
 * The caller must ensure this doesn't race with truncation.  Most will
 * simply hold the folio lock, but e.g. zap_pte_range() calls with the
 * folio mapped and the pte lock held, which also locks out truncation.
 */
bool filemap_dirty_folio(struct address_space *mapping, struct folio *folio)
{
	folio_memcg_lock(folio);
	if (folio_test_set_dirty(folio)) {
		folio_memcg_unlock(folio);
		return false;
	}

	__folio_mark_dirty(folio, mapping, !folio_test_private(folio));
	folio_memcg_unlock(folio);

	if (mapping->host) {
		/* !PageAnon && !swapper_space */
		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
	}
	return true;
}
EXPORT_SYMBOL(filemap_dirty_folio);

/**
 * folio_account_redirty - Manually account for redirtying a page.
 * @folio: The folio which is being redirtied.
 *
 * Most filesystems should call folio_redirty_for_writepage() instead
 * of this fuction.  If your filesystem is doing writeback outside the
 * context of a writeback_control(), it can call this when redirtying
 * a folio, to de-account the dirty counters (NR_DIRTIED, WB_DIRTIED,
 * tsk->nr_dirtied), so that they match the written counters (NR_WRITTEN,
 * WB_WRITTEN) in long term. The mismatches will lead to systematic errors
 * in balanced_dirty_ratelimit and the dirty pages position control.
 */
void folio_account_redirty(struct folio *folio)
{
	struct address_space *mapping = folio->mapping;

	if (mapping && mapping_can_writeback(mapping)) {
		struct inode *inode = mapping->host;
		struct bdi_writeback *wb;
		struct wb_lock_cookie cookie = {};
		long nr = folio_nr_pages(folio);

		wb = unlocked_inode_to_wb_begin(inode, &cookie);
		current->nr_dirtied -= nr;
		node_stat_mod_folio(folio, NR_DIRTIED, -nr);
		wb_stat_mod(wb, WB_DIRTIED, -nr);
		unlocked_inode_to_wb_end(inode, &cookie);
	}
}
EXPORT_SYMBOL(folio_account_redirty);

/**
 * folio_redirty_for_writepage - Decline to write a dirty folio.
 * @wbc: The writeback control.
 * @folio: The folio.
 *
 * When a writepage implementation decides that it doesn't want to write
 * @folio for some reason, it should call this function, unlock @folio and
 * return 0.
 *
 * Return: True if we redirtied the folio.  False if someone else dirtied
 * it first.
 */
bool folio_redirty_for_writepage(struct writeback_control *wbc,
		struct folio *folio)
{
	bool ret;
	long nr = folio_nr_pages(folio);

	wbc->pages_skipped += nr;
	ret = filemap_dirty_folio(folio->mapping, folio);
	folio_account_redirty(folio);

	return ret;
}
EXPORT_SYMBOL(folio_redirty_for_writepage);

/**
 * folio_mark_dirty - Mark a folio as being modified.
 * @folio: The folio.
 *
 * The folio may not be truncated while this function is running.
 * Holding the folio lock is sufficient to prevent truncation, but some
 * callers cannot acquire a sleeping lock.  These callers instead hold
 * the page table lock for a page table which contains at least one page
 * in this folio.  Truncation will block on the page table lock as it
 * unmaps pages before removing the folio from its mapping.
 *
 * Return: True if the folio was newly dirtied, false if it was already dirty.
 */
bool folio_mark_dirty(struct folio *folio)
{
	struct address_space *mapping = folio_mapping(folio);

	if (likely(mapping)) {
		/*
		 * readahead/lru_deactivate_page could remain
		 * PG_readahead/PG_reclaim due to race with folio_end_writeback
		 * About readahead, if the folio is written, the flags would be
		 * reset. So no problem.
		 * About lru_deactivate_page, if the folio is redirtied,
		 * the flag will be reset. So no problem. but if the
		 * folio is used by readahead it will confuse readahead
		 * and make it restart the size rampup process. But it's
		 * a trivial problem.
		 */
		if (folio_test_reclaim(folio))
			folio_clear_reclaim(folio);
		return mapping->a_ops->dirty_folio(mapping, folio);
	}

	return noop_dirty_folio(mapping, folio);
}
EXPORT_SYMBOL(folio_mark_dirty);

/*
 * set_page_dirty() is racy if the caller has no reference against
 * page->mapping->host, and if the page is unlocked.  This is because another
 * CPU could truncate the page off the mapping and then free the mapping.
 *
 * Usually, the page _is_ locked, or the caller is a user-space process which
 * holds a reference on the inode by having an open file.
 *
 * In other cases, the page should be locked before running set_page_dirty().
 */
int set_page_dirty_lock(struct page *page)
{
	int ret;

	lock_page(page);
	ret = set_page_dirty(page);
	unlock_page(page);
	return ret;
}
EXPORT_SYMBOL(set_page_dirty_lock);

/*
 * This cancels just the dirty bit on the kernel page itself, it does NOT
 * actually remove dirty bits on any mmap's that may be around. It also
 * leaves the page tagged dirty, so any sync activity will still find it on
 * the dirty lists, and in particular, clear_page_dirty_for_io() will still
 * look at the dirty bits in the VM.
 *
 * Doing this should *normally* only ever be done when a page is truncated,
 * and is not actually mapped anywhere at all. However, fs/buffer.c does
 * this when it notices that somebody has cleaned out all the buffers on a
 * page without actually doing it through the VM. Can you say "ext3 is
 * horribly ugly"? Thought you could.
 */
void __folio_cancel_dirty(struct folio *folio)
{
	struct address_space *mapping = folio_mapping(folio);

	if (mapping_can_writeback(mapping)) {
		struct inode *inode = mapping->host;
		struct bdi_writeback *wb;
		struct wb_lock_cookie cookie = {};

		folio_memcg_lock(folio);
		wb = unlocked_inode_to_wb_begin(inode, &cookie);

		if (folio_test_clear_dirty(folio))
			folio_account_cleaned(folio, wb);

		unlocked_inode_to_wb_end(inode, &cookie);
		folio_memcg_unlock(folio);
	} else {
		folio_clear_dirty(folio);
	}
}
EXPORT_SYMBOL(__folio_cancel_dirty);

/*
 * Clear a folio's dirty flag, while caring for dirty memory accounting.
 * Returns true if the folio was previously dirty.
 *
 * This is for preparing to put the folio under writeout.  We leave
 * the folio tagged as dirty in the xarray so that a concurrent
 * write-for-sync can discover it via a PAGECACHE_TAG_DIRTY walk.
 * The ->writepage implementation will run either folio_start_writeback()
 * or folio_mark_dirty(), at which stage we bring the folio's dirty flag
 * and xarray dirty tag back into sync.
 *
 * This incoherency between the folio's dirty flag and xarray tag is
 * unfortunate, but it only exists while the folio is locked.
 */
bool folio_clear_dirty_for_io(struct folio *folio)
{
	struct address_space *mapping = folio_mapping(folio);
	bool ret = false;

	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);

	if (mapping && mapping_can_writeback(mapping)) {
		struct inode *inode = mapping->host;
		struct bdi_writeback *wb;
		struct wb_lock_cookie cookie = {};

		/*
		 * Yes, Virginia, this is indeed insane.
		 *
		 * We use this sequence to make sure that
		 *  (a) we account for dirty stats properly
		 *  (b) we tell the low-level filesystem to
		 *      mark the whole folio dirty if it was
		 *      dirty in a pagetable. Only to then
		 *  (c) clean the folio again and return 1 to
		 *      cause the writeback.
		 *
		 * This way we avoid all nasty races with the
		 * dirty bit in multiple places and clearing
		 * them concurrently from different threads.
		 *
		 * Note! Normally the "folio_mark_dirty(folio)"
		 * has no effect on the actual dirty bit - since
		 * that will already usually be set. But we
		 * need the side effects, and it can help us
		 * avoid races.
		 *
		 * We basically use the folio "master dirty bit"
		 * as a serialization point for all the different
		 * threads doing their things.
		 */
		if (folio_mkclean(folio))
			folio_mark_dirty(folio);
		/*
		 * We carefully synchronise fault handlers against
		 * installing a dirty pte and marking the folio dirty
		 * at this point.  We do this by having them hold the
		 * page lock while dirtying the folio, and folios are
		 * always locked coming in here, so we get the desired
		 * exclusion.
		 */
		wb = unlocked_inode_to_wb_begin(inode, &cookie);
		if (folio_test_clear_dirty(folio)) {
			long nr = folio_nr_pages(folio);
			lruvec_stat_mod_folio(folio, NR_FILE_DIRTY, -nr);
			zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
			wb_stat_mod(wb, WB_RECLAIMABLE, -nr);
			ret = true;
		}
		unlocked_inode_to_wb_end(inode, &cookie);
		return ret;
	}
	return folio_test_clear_dirty(folio);
}
EXPORT_SYMBOL(folio_clear_dirty_for_io);

static void wb_inode_writeback_start(struct bdi_writeback *wb)
{
	atomic_inc(&wb->writeback_inodes);
}

static void wb_inode_writeback_end(struct bdi_writeback *wb)
{
	atomic_dec(&wb->writeback_inodes);
	/*
	 * Make sure estimate of writeback throughput gets updated after
	 * writeback completed. We delay the update by BANDWIDTH_INTERVAL
	 * (which is the interval other bandwidth updates use for batching) so
	 * that if multiple inodes end writeback at a similar time, they get
	 * batched into one bandwidth update.
	 */
	queue_delayed_work(bdi_wq, &wb->bw_dwork, BANDWIDTH_INTERVAL);
}

bool __folio_end_writeback(struct folio *folio)
{
	long nr = folio_nr_pages(folio);
	struct address_space *mapping = folio_mapping(folio);
	bool ret;

	folio_memcg_lock(folio);
	if (mapping && mapping_use_writeback_tags(mapping)) {
		struct inode *inode = mapping->host;
		struct backing_dev_info *bdi = inode_to_bdi(inode);
		unsigned long flags;

		xa_lock_irqsave(&mapping->i_pages, flags);
		ret = folio_test_clear_writeback(folio);
		if (ret) {
			__xa_clear_mark(&mapping->i_pages, folio_index(folio),
						PAGECACHE_TAG_WRITEBACK);
			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
				struct bdi_writeback *wb = inode_to_wb(inode);

				wb_stat_mod(wb, WB_WRITEBACK, -nr);
				__wb_writeout_add(wb, nr);
				if (!mapping_tagged(mapping,
						    PAGECACHE_TAG_WRITEBACK))
					wb_inode_writeback_end(wb);
			}
		}

		if (mapping->host && !mapping_tagged(mapping,
						     PAGECACHE_TAG_WRITEBACK))
			sb_clear_inode_writeback(mapping->host);

		xa_unlock_irqrestore(&mapping->i_pages, flags);
	} else {
		ret = folio_test_clear_writeback(folio);
	}
	if (ret) {
		lruvec_stat_mod_folio(folio, NR_WRITEBACK, -nr);
		zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, -nr);
		node_stat_mod_folio(folio, NR_WRITTEN, nr);
	}
	folio_memcg_unlock(folio);
	return ret;
}

bool __folio_start_writeback(struct folio *folio, bool keep_write)
{
	long nr = folio_nr_pages(folio);
	struct address_space *mapping = folio_mapping(folio);
	bool ret;
	int access_ret;

	folio_memcg_lock(folio);
	if (mapping && mapping_use_writeback_tags(mapping)) {
		XA_STATE(xas, &mapping->i_pages, folio_index(folio));
		struct inode *inode = mapping->host;
		struct backing_dev_info *bdi = inode_to_bdi(inode);
		unsigned long flags;

		xas_lock_irqsave(&xas, flags);
		xas_load(&xas);
		ret = folio_test_set_writeback(folio);
		if (!ret) {
			bool on_wblist;

			on_wblist = mapping_tagged(mapping,
						   PAGECACHE_TAG_WRITEBACK);

			xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
			if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
				struct bdi_writeback *wb = inode_to_wb(inode);

				wb_stat_mod(wb, WB_WRITEBACK, nr);
				if (!on_wblist)
					wb_inode_writeback_start(wb);
			}

			/*
			 * We can come through here when swapping
			 * anonymous folios, so we don't necessarily
			 * have an inode to track for sync.
			 */
			if (mapping->host && !on_wblist)
				sb_mark_inode_writeback(mapping->host);
		}
		if (!folio_test_dirty(folio))
			xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
		if (!keep_write)
			xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
		xas_unlock_irqrestore(&xas, flags);
	} else {
		ret = folio_test_set_writeback(folio);
	}
	if (!ret) {
		lruvec_stat_mod_folio(folio, NR_WRITEBACK, nr);
		zone_stat_mod_folio(folio, NR_ZONE_WRITE_PENDING, nr);
	}
	folio_memcg_unlock(folio);
	access_ret = arch_make_folio_accessible(folio);
	/*
	 * If writeback has been triggered on a page that cannot be made
	 * accessible, it is too late to recover here.
	 */
	VM_BUG_ON_FOLIO(access_ret != 0, folio);

	return ret;
}
EXPORT_SYMBOL(__folio_start_writeback);

/**
 * folio_wait_writeback - Wait for a folio to finish writeback.
 * @folio: The folio to wait for.
 *
 * If the folio is currently being written back to storage, wait for the
 * I/O to complete.
 *
 * Context: Sleeps.  Must be called in process context and with
 * no spinlocks held.  Caller should hold a reference on the folio.
 * If the folio is not locked, writeback may start again after writeback
 * has finished.
 */
void folio_wait_writeback(struct folio *folio)
{
	while (folio_test_writeback(folio)) {
		trace_folio_wait_writeback(folio, folio_mapping(folio));
		folio_wait_bit(folio, PG_writeback);
	}
}
EXPORT_SYMBOL_GPL(folio_wait_writeback);

/**
 * folio_wait_writeback_killable - Wait for a folio to finish writeback.
 * @folio: The folio to wait for.
 *
 * If the folio is currently being written back to storage, wait for the
 * I/O to complete or a fatal signal to arrive.
 *
 * Context: Sleeps.  Must be called in process context and with
 * no spinlocks held.  Caller should hold a reference on the folio.
 * If the folio is not locked, writeback may start again after writeback
 * has finished.
 * Return: 0 on success, -EINTR if we get a fatal signal while waiting.
 */
int folio_wait_writeback_killable(struct folio *folio)
{
	while (folio_test_writeback(folio)) {
		trace_folio_wait_writeback(folio, folio_mapping(folio));
		if (folio_wait_bit_killable(folio, PG_writeback))
			return -EINTR;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);

/**
 * folio_wait_stable() - wait for writeback to finish, if necessary.
 * @folio: The folio to wait on.
 *
 * This function determines if the given folio is related to a backing
 * device that requires folio contents to be held stable during writeback.
 * If so, then it will wait for any pending writeback to complete.
 *
 * Context: Sleeps.  Must be called in process context and with
 * no spinlocks held.  Caller should hold a reference on the folio.
 * If the folio is not locked, writeback may start again after writeback
 * has finished.
 */
void folio_wait_stable(struct folio *folio)
{
	if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
		folio_wait_writeback(folio);
}
EXPORT_SYMBOL_GPL(folio_wait_stable);