summaryrefslogtreecommitdiffstats
path: root/mm/filemap.c
blob: 63a50b7e624c22702aa3de0a79a026e97300dc1b (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
/*
 *	linux/mm/filemap.c
 *
 * Copyright (C) 1994-1999  Linus Torvalds
 */

/*
 * This file handles the generic file mmap semantics used by
 * most "normal" filesystems (but you don't /have/ to use this:
 * the NFS filesystem used to do this differently, for example)
 */
#include <linux/malloc.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/locks.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/smp_lock.h>
#include <linux/blkdev.h>
#include <linux/file.h>
#include <linux/swapctl.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/mm.h>

#include <asm/pgalloc.h>
#include <asm/uaccess.h>

#include <linux/highmem.h>

/*
 * Shared mappings implemented 30.11.1994. It's not fully working yet,
 * though.
 *
 * Shared mappings now work. 15.8.1995  Bruno.
 *
 * finished 'unifying' the page and buffer cache and SMP-threaded the
 * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
 *
 * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
 */

atomic_t page_cache_size = ATOMIC_INIT(0);
unsigned int page_hash_bits;
struct page **page_hash_table;

spinlock_t pagecache_lock = SPIN_LOCK_UNLOCKED;
/*
 * NOTE: to avoid deadlocking you must never acquire the pagecache_lock with
 *       the pagemap_lru_lock held.
 */
spinlock_t pagemap_lru_lock = SPIN_LOCK_UNLOCKED;

#define CLUSTER_PAGES		(1 << page_cluster)
#define CLUSTER_OFFSET(x)	(((x) >> page_cluster) << page_cluster)

void __add_page_to_hash_queue(struct page * page, struct page **p)
{
	atomic_inc(&page_cache_size);
	if((page->next_hash = *p) != NULL)
		(*p)->pprev_hash = &page->next_hash;
	*p = page;
	page->pprev_hash = p;
	if (page->buffers)
		PAGE_BUG(page);
}

static void remove_page_from_hash_queue(struct page * page)
{
	if(page->pprev_hash) {
		if(page->next_hash)
			page->next_hash->pprev_hash = page->pprev_hash;
		*page->pprev_hash = page->next_hash;
		page->pprev_hash = NULL;
	}
	atomic_dec(&page_cache_size);
}

/*
 * Remove a page from the page cache and free it. Caller has to make
 * sure the page is locked and that nobody else uses it - or that usage
 * is safe.
 */
void remove_inode_page(struct page *page)
{
	if (!PageLocked(page))
		PAGE_BUG(page);

	spin_lock(&pagecache_lock);
	remove_page_from_inode_queue(page);
	remove_page_from_hash_queue(page);
	page->mapping = NULL;
	spin_unlock(&pagecache_lock);
}

void invalidate_inode_pages(struct inode * inode)
{
	struct list_head *head, *curr;
	struct page * page;

	head = &inode->i_data.pages;
	spin_lock(&pagecache_lock);
	curr = head->next;

	while (curr != head) {
		page = list_entry(curr, struct page, list);
		curr = curr->next;

		/* We cannot invalidate a locked page */
		if (PageLocked(page))
			continue;

		lru_cache_del(page);

		remove_page_from_inode_queue(page);
		remove_page_from_hash_queue(page);
		page->mapping = NULL;
		page_cache_release(page);
	}
	spin_unlock(&pagecache_lock);
}

/*
 * Truncate the page cache at a set offset, removing the pages
 * that are beyond that offset (and zeroing out partial pages).
 */
void truncate_inode_pages(struct inode * inode, loff_t lstart)
{
	struct list_head *head, *curr;
	struct page * page;
	unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
	unsigned long start;

	start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

repeat:
	head = &inode->i_data.pages;
	spin_lock(&pagecache_lock);
	curr = head->next;
	while (curr != head) {
		unsigned long offset;

		page = list_entry(curr, struct page, list);
		curr = curr->next;

		offset = page->index;

		/* page wholly truncated - free it */
		if (offset >= start) {
			get_page(page);
			spin_unlock(&pagecache_lock);

			lock_page(page);

			if (!page->buffers || block_flushpage(page, 0))
				lru_cache_del(page);

			/*
			 * We remove the page from the page cache
			 * _after_ we have destroyed all buffer-cache
			 * references to it. Otherwise some other process
			 * might think this inode page is not in the
			 * page cache and creates a buffer-cache alias
			 * to it causing all sorts of fun problems ...
			 */
			remove_inode_page(page);

			UnlockPage(page);
			page_cache_release(page);
			page_cache_release(page);

			/*
			 * We have done things without the pagecache lock,
			 * so we'll have to repeat the scan.
			 * It's not possible to deadlock here because
			 * we are guaranteed to make progress. (ie. we have
			 * just removed a page)
			 */
			goto repeat;
		}
		/*
		 * there is only one partial page possible.
		 */
		if (!partial)
			continue;

		/* and it's the one preceeding the first wholly truncated page */
		if ((offset + 1) != start)
			continue;

		/* partial truncate, clear end of page */
		get_page(page);
		spin_unlock(&pagecache_lock);

		lock_page(page);

		memclear_highpage_flush(page, partial, PAGE_CACHE_SIZE-partial);
		if (page->buffers)
			block_flushpage(page, partial);

		partial = 0;

		/*
		 * we have dropped the spinlock so we have to
		 * restart.
		 */
		UnlockPage(page);
		page_cache_release(page);
		goto repeat;
	}
	spin_unlock(&pagecache_lock);
}

int shrink_mmap(int priority, int gfp_mask, zone_t *zone)
{
	int ret = 0, count;
	LIST_HEAD(young);
	LIST_HEAD(old);
	LIST_HEAD(forget);
	struct list_head * page_lru, * dispose;
	struct page * page;

	count = nr_lru_pages / (priority+1);

	spin_lock(&pagemap_lru_lock);

	while (count > 0 && (page_lru = lru_cache.prev) != &lru_cache) {
		page = list_entry(page_lru, struct page, lru);
		list_del(page_lru);

		dispose = &lru_cache;
		if (test_and_clear_bit(PG_referenced, &page->flags))
			/* Roll the page at the top of the lru list,
			 * we could also be more aggressive putting
			 * the page in the young-dispose-list, so
			 * avoiding to free young pages in each pass.
			 */
			goto dispose_continue;

		dispose = &old;
		/* don't account passes over not DMA pages */
		if (zone && (!memclass(page->zone, zone)))
			goto dispose_continue;

		count--;

		dispose = &young;
		if (TryLockPage(page))
			goto dispose_continue;

		/* Release the pagemap_lru lock even if the page is not yet
		   queued in any lru queue since we have just locked down
		   the page so nobody else may SMP race with us running
		   a lru_cache_del() (lru_cache_del() always run with the
		   page locked down ;). */
		spin_unlock(&pagemap_lru_lock);

		/* avoid unscalable SMP locking */
		if (!page->buffers && page_count(page) > 1)
			goto unlock_noput_continue;

		/* Take the pagecache_lock spinlock held to avoid
		   other tasks to notice the page while we are looking at its
		   page count. If it's a pagecache-page we'll free it
		   in one atomic transaction after checking its page count. */
		spin_lock(&pagecache_lock);

		/* avoid freeing the page while it's locked */
		get_page(page);

		/* Is it a buffer page? */
		if (page->buffers) {
			spin_unlock(&pagecache_lock);
			if (!try_to_free_buffers(page))
				goto unlock_continue;
			/* page was locked, inode can't go away under us */
			if (!page->mapping) {
				atomic_dec(&buffermem_pages);
				goto made_buffer_progress;
			}
			spin_lock(&pagecache_lock);
		}

		/*
		 * We can't free pages unless there's just one user
		 * (count == 2 because we added one ourselves above).
		 */
		if (page_count(page) != 2)
			goto cache_unlock_continue;

		/*
		 * Is it a page swap page? If so, we want to
		 * drop it if it is no longer used, even if it
		 * were to be marked referenced..
		 */
		if (PageSwapCache(page)) {
			spin_unlock(&pagecache_lock);
			__delete_from_swap_cache(page);
			goto made_inode_progress;
		}	

		/* is it a page-cache page? */
		if (page->mapping) {
			if (!pgcache_under_min())
			{
				remove_page_from_inode_queue(page);
				remove_page_from_hash_queue(page);
				page->mapping = NULL;
				spin_unlock(&pagecache_lock);
				goto made_inode_progress;
			}
			goto cache_unlock_continue;
		}

		dispose = &forget;
		printk(KERN_ERR "shrink_mmap: unknown LRU page!\n");

cache_unlock_continue:
		spin_unlock(&pagecache_lock);
unlock_continue:
		UnlockPage(page);
		put_page(page);
dispose_relock_continue:
		/* even if the dispose list is local, a truncate_inode_page()
		   may remove a page from its queue so always
		   synchronize with the lru lock while accesing the
		   page->lru field */
		spin_lock(&pagemap_lru_lock);
		list_add(page_lru, dispose);
		continue;

unlock_noput_continue:
		UnlockPage(page);
		goto dispose_relock_continue;

dispose_continue:
		list_add(page_lru, dispose);
	}
	goto out;

made_inode_progress:
	page_cache_release(page);
made_buffer_progress:
	UnlockPage(page);
	put_page(page);
	ret = 1;
	spin_lock(&pagemap_lru_lock);
	/* nr_lru_pages needs the spinlock */
	nr_lru_pages--;

out:
	list_splice(&young, &lru_cache);
	list_splice(&old, lru_cache.prev);

	spin_unlock(&pagemap_lru_lock);

	return ret;
}

static inline struct page * __find_page_nolock(struct address_space *mapping, unsigned long offset, struct page *page)
{
	goto inside;

	for (;;) {
		page = page->next_hash;
inside:
		if (!page)
			goto not_found;
		if (page->mapping != mapping)
			continue;
		if (page->index == offset)
			break;
	}
	set_bit(PG_referenced, &page->flags);
not_found:
	return page;
}

/*
 * By the time this is called, the page is locked and
 * we don't have to worry about any races any more.
 *
 * Start the IO..
 */
static int writeout_one_page(struct page *page)
{
	struct buffer_head *bh, *head = page->buffers;

	bh = head;
	do {
		if (buffer_locked(bh) || !buffer_dirty(bh) || !buffer_uptodate(bh))
			continue;

		bh->b_flushtime = 0;
		ll_rw_block(WRITE, 1, &bh);	
	} while ((bh = bh->b_this_page) != head);
	return 0;
}

static int waitfor_one_page(struct page *page)
{
	int error = 0;
	struct buffer_head *bh, *head = page->buffers;

	bh = head;
	do {
		wait_on_buffer(bh);
		if (buffer_req(bh) && !buffer_uptodate(bh))
			error = -EIO;
	} while ((bh = bh->b_this_page) != head);
	return error;
}

static int do_buffer_fdatasync(struct inode *inode, unsigned long start, unsigned long end, int (*fn)(struct page *))
{
	struct list_head *head, *curr;
	struct page *page;
	int retval = 0;

	head = &inode->i_data.pages;

	spin_lock(&pagecache_lock);
	curr = head->next;
	while (curr != head) {
		page = list_entry(curr, struct page, list);
		curr = curr->next;
		if (!page->buffers)
			continue;
		if (page->index >= end)
			continue;
		if (page->index < start)
			continue;

		get_page(page);
		spin_unlock(&pagecache_lock);
		lock_page(page);

		/* The buffers could have been free'd while we waited for the page lock */
		if (page->buffers)
			retval |= fn(page);

		UnlockPage(page);
		spin_lock(&pagecache_lock);
		curr = page->list.next;
		page_cache_release(page);
	}
	spin_unlock(&pagecache_lock);

	return retval;
}

/*
 * Two-stage data sync: first start the IO, then go back and
 * collect the information..
 */
int generic_buffer_fdatasync(struct inode *inode, unsigned long start_idx, unsigned long end_idx)
{
	int retval;

	retval = do_buffer_fdatasync(inode, start_idx, end_idx, writeout_one_page);
	retval |= do_buffer_fdatasync(inode, start_idx, end_idx, waitfor_one_page);
	return retval;
}

/*
 * This adds a page to the page cache, starting out as locked,
 * owned by us, referenced, but not uptodate and with no errors.
 */
static inline void __add_to_page_cache(struct page * page,
	struct address_space *mapping, unsigned long offset,
	struct page **hash)
{
	struct page *alias;
	unsigned long flags;

	flags = page->flags & ~((1 << PG_uptodate) | (1 << PG_error) | (1 << PG_referenced));
	page->flags = flags | (1 << PG_locked);
	get_page(page);
	page->index = offset;
	add_page_to_inode_queue(mapping, page);
	__add_page_to_hash_queue(page, hash);
	lru_cache_add(page);
	alias = __find_page_nolock(mapping, offset, *hash);
	if (alias != page)
		BUG();
}

void add_to_page_cache(struct page * page, struct address_space * mapping, unsigned long offset)
{
	spin_lock(&pagecache_lock);
	__add_to_page_cache(page, mapping, offset, page_hash(mapping, offset));
	spin_unlock(&pagecache_lock);
}

static int add_to_page_cache_unique(struct page * page,
	struct address_space *mapping, unsigned long offset,
	struct page **hash)
{
	int err;
	struct page *alias;

	spin_lock(&pagecache_lock);
	alias = __find_page_nolock(mapping, offset, *hash);

	err = 1;
	if (!alias) {
		__add_to_page_cache(page,mapping,offset,hash);
		err = 0;
	}

	spin_unlock(&pagecache_lock);
	return err;
}

/*
 * This adds the requested page to the page cache if it isn't already there,
 * and schedules an I/O to read in its contents from disk.
 */
static inline int page_cache_read(struct file * file, unsigned long offset) 
{
	struct inode *inode = file->f_dentry->d_inode;
	struct page **hash = page_hash(&inode->i_data, offset);
	struct page *page; 

	spin_lock(&pagecache_lock);
	page = __find_page_nolock(&inode->i_data, offset, *hash); 
	spin_unlock(&pagecache_lock);
	if (page)
		return 0;

	page = page_cache_alloc();
	if (!page)
		return -ENOMEM;

	if (!add_to_page_cache_unique(page, &inode->i_data, offset, hash)) {
		int error = inode->i_op->readpage(file->f_dentry, page);
		page_cache_release(page);
		return error;
	}
	/*
	 * We arrive here in the unlikely event that someone 
	 * raced with us and added our page to the cache first.
	 */
	page_cache_free(page);
	return 0;
}

/*
 * Read in an entire cluster at once.  A cluster is usually a 64k-
 * aligned block that includes the page requested in "offset."
 */
static int read_cluster_nonblocking(struct file * file, unsigned long offset,
	unsigned long filesize)
{
	unsigned long pages = CLUSTER_PAGES;

	offset = CLUSTER_OFFSET(offset);
	while ((pages-- > 0) && (offset < filesize)) {
		int error = page_cache_read(file, offset);
		if (error < 0)
			return error;
		offset ++;
	}

	return 0;
}

/* 
 * Wait for a page to get unlocked.
 *
 * This must be called with the caller "holding" the page,
 * ie with increased "page->count" so that the page won't
 * go away during the wait..
 */
void ___wait_on_page(struct page *page)
{
	struct task_struct *tsk = current;
	DECLARE_WAITQUEUE(wait, tsk);

	add_wait_queue(&page->wait, &wait);
	do {
		run_task_queue(&tq_disk);
		set_task_state(tsk, TASK_UNINTERRUPTIBLE);
		if (!PageLocked(page))
			break;
		schedule();
	} while (PageLocked(page));
	tsk->state = TASK_RUNNING;
	remove_wait_queue(&page->wait, &wait);
}

/*
 * Get an exclusive lock on the page..
 */
void lock_page(struct page *page)
{
	while (TryLockPage(page))
		___wait_on_page(page);
}


/*
 * a rather lightweight function, finding and getting a reference to a
 * hashed page atomically, waiting for it if it's locked.
 */
struct page * __find_get_page (struct address_space *mapping,
				unsigned long offset, struct page **hash)
{
	struct page *page;

	/*
	 * We scan the hash list read-only. Addition to and removal from
	 * the hash-list needs a held write-lock.
	 */
repeat:
	spin_lock(&pagecache_lock);
	page = __find_page_nolock(mapping, offset, *hash);
	if (page)
		get_page(page);
	spin_unlock(&pagecache_lock);

	/* Found the page, sleep if locked. */
	if (page && PageLocked(page)) {
		struct task_struct *tsk = current;
		DECLARE_WAITQUEUE(wait, tsk);

		run_task_queue(&tq_disk);

		__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
		add_wait_queue(&page->wait, &wait);

		if (PageLocked(page))
			schedule();
		__set_task_state(tsk, TASK_RUNNING);
		remove_wait_queue(&page->wait, &wait);

		/*
		 * The page might have been unhashed meanwhile. It's
		 * not freed though because we hold a reference to it.
		 * If this is the case then it will be freed _here_,
		 * and we recheck the hash anyway.
		 */
		page_cache_release(page);
		goto repeat;
	}
	/*
	 * It's not locked so we can return the page and we hold
	 * a reference to it.
	 */
	return page;
}

/*
 * Get the lock to a page atomically.
 */
struct page * __find_lock_page (struct address_space *mapping,
				unsigned long offset, struct page **hash)
{
	struct page *page;

	/*
	 * We scan the hash list read-only. Addition to and removal from
	 * the hash-list needs a held write-lock.
	 */
repeat:
	spin_lock(&pagecache_lock);
	page = __find_page_nolock(mapping, offset, *hash);
	if (page)
		get_page(page);
	spin_unlock(&pagecache_lock);

	/* Found the page, sleep if locked. */
	if (page && TryLockPage(page)) {
		struct task_struct *tsk = current;
		DECLARE_WAITQUEUE(wait, tsk);

		run_task_queue(&tq_disk);

		__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
		add_wait_queue(&page->wait, &wait);

		if (PageLocked(page))
			schedule();
		__set_task_state(tsk, TASK_RUNNING);
		remove_wait_queue(&page->wait, &wait);

		/*
		 * The page might have been unhashed meanwhile. It's
		 * not freed though because we hold a reference to it.
		 * If this is the case then it will be freed _here_,
		 * and we recheck the hash anyway.
		 */
		page_cache_release(page);
		goto repeat;
	}
	/*
	 * It's not locked so we can return the page and we hold
	 * a reference to it.
	 */
	return page;
}

#if 0
#define PROFILE_READAHEAD
#define DEBUG_READAHEAD
#endif

/*
 * Read-ahead profiling information
 * --------------------------------
 * Every PROFILE_MAXREADCOUNT, the following information is written 
 * to the syslog:
 *   Percentage of asynchronous read-ahead.
 *   Average of read-ahead fields context value.
 * If DEBUG_READAHEAD is defined, a snapshot of these fields is written 
 * to the syslog.
 */

#ifdef PROFILE_READAHEAD

#define PROFILE_MAXREADCOUNT 1000

static unsigned long total_reada;
static unsigned long total_async;
static unsigned long total_ramax;
static unsigned long total_ralen;
static unsigned long total_rawin;

static void profile_readahead(int async, struct file *filp)
{
	unsigned long flags;

	++total_reada;
	if (async)
		++total_async;

	total_ramax	+= filp->f_ramax;
	total_ralen	+= filp->f_ralen;
	total_rawin	+= filp->f_rawin;

	if (total_reada > PROFILE_MAXREADCOUNT) {
		save_flags(flags);
		cli();
		if (!(total_reada > PROFILE_MAXREADCOUNT)) {
			restore_flags(flags);
			return;
		}

		printk("Readahead average:  max=%ld, len=%ld, win=%ld, async=%ld%%\n",
			total_ramax/total_reada,
			total_ralen/total_reada,
			total_rawin/total_reada,
			(total_async*100)/total_reada);
#ifdef DEBUG_READAHEAD
		printk("Readahead snapshot: max=%ld, len=%ld, win=%ld, raend=%Ld\n",
			filp->f_ramax, filp->f_ralen, filp->f_rawin, filp->f_raend);
#endif

		total_reada	= 0;
		total_async	= 0;
		total_ramax	= 0;
		total_ralen	= 0;
		total_rawin	= 0;

		restore_flags(flags);
	}
}
#endif  /* defined PROFILE_READAHEAD */

/*
 * Read-ahead context:
 * -------------------
 * The read ahead context fields of the "struct file" are the following:
 * - f_raend : position of the first byte after the last page we tried to
 *	       read ahead.
 * - f_ramax : current read-ahead maximum size.
 * - f_ralen : length of the current IO read block we tried to read-ahead.
 * - f_rawin : length of the current read-ahead window.
 *		if last read-ahead was synchronous then
 *			f_rawin = f_ralen
 *		otherwise (was asynchronous)
 *			f_rawin = previous value of f_ralen + f_ralen
 *
 * Read-ahead limits:
 * ------------------
 * MIN_READAHEAD   : minimum read-ahead size when read-ahead.
 * MAX_READAHEAD   : maximum read-ahead size when read-ahead.
 *
 * Synchronous read-ahead benefits:
 * --------------------------------
 * Using reasonable IO xfer length from peripheral devices increase system 
 * performances.
 * Reasonable means, in this context, not too large but not too small.
 * The actual maximum value is:
 *	MAX_READAHEAD + PAGE_CACHE_SIZE = 76k is CONFIG_READA_SMALL is undefined
 *      and 32K if defined (4K page size assumed).
 *
 * Asynchronous read-ahead benefits:
 * ---------------------------------
 * Overlapping next read request and user process execution increase system 
 * performance.
 *
 * Read-ahead risks:
 * -----------------
 * We have to guess which further data are needed by the user process.
 * If these data are often not really needed, it's bad for system 
 * performances.
 * However, we know that files are often accessed sequentially by 
 * application programs and it seems that it is possible to have some good 
 * strategy in that guessing.
 * We only try to read-ahead files that seems to be read sequentially.
 *
 * Asynchronous read-ahead risks:
 * ------------------------------
 * In order to maximize overlapping, we must start some asynchronous read 
 * request from the device, as soon as possible.
 * We must be very careful about:
 * - The number of effective pending IO read requests.
 *   ONE seems to be the only reasonable value.
 * - The total memory pool usage for the file access stream.
 *   This maximum memory usage is implicitly 2 IO read chunks:
 *   2*(MAX_READAHEAD + PAGE_CACHE_SIZE) = 156K if CONFIG_READA_SMALL is undefined,
 *   64k if defined (4K page size assumed).
 */

static inline int get_max_readahead(struct inode * inode)
{
	if (!inode->i_dev || !max_readahead[MAJOR(inode->i_dev)])
		return MAX_READAHEAD;
	return max_readahead[MAJOR(inode->i_dev)][MINOR(inode->i_dev)];
}

static void generic_file_readahead(int reada_ok,
	struct file * filp, struct inode * inode,
	struct page * page)
{
	unsigned long end_index = inode->i_size >> PAGE_CACHE_SHIFT;
	unsigned long index = page->index;
	unsigned long max_ahead, ahead;
	unsigned long raend;
	int max_readahead = get_max_readahead(inode);

	raend = filp->f_raend;
	max_ahead = 0;

/*
 * The current page is locked.
 * If the current position is inside the previous read IO request, do not
 * try to reread previously read ahead pages.
 * Otherwise decide or not to read ahead some pages synchronously.
 * If we are not going to read ahead, set the read ahead context for this 
 * page only.
 */
	if (PageLocked(page)) {
		if (!filp->f_ralen || index >= raend || index + filp->f_ralen < raend) {
			raend = index;
			if (raend < end_index)
				max_ahead = filp->f_ramax;
			filp->f_rawin = 0;
			filp->f_ralen = 1;
			if (!max_ahead) {
				filp->f_raend  = index + filp->f_ralen;
				filp->f_rawin += filp->f_ralen;
			}
		}
	}
/*
 * The current page is not locked.
 * If we were reading ahead and,
 * if the current max read ahead size is not zero and,
 * if the current position is inside the last read-ahead IO request,
 *   it is the moment to try to read ahead asynchronously.
 * We will later force unplug device in order to force asynchronous read IO.
 */
	else if (reada_ok && filp->f_ramax && raend >= 1 &&
		 index <= raend && index + filp->f_ralen >= raend) {
/*
 * Add ONE page to max_ahead in order to try to have about the same IO max size
 * as synchronous read-ahead (MAX_READAHEAD + 1)*PAGE_CACHE_SIZE.
 * Compute the position of the last page we have tried to read in order to 
 * begin to read ahead just at the next page.
 */
		raend -= 1;
		if (raend < end_index)
			max_ahead = filp->f_ramax + 1;

		if (max_ahead) {
			filp->f_rawin = filp->f_ralen;
			filp->f_ralen = 0;
			reada_ok      = 2;
		}
	}
/*
 * Try to read ahead pages.
 * We hope that ll_rw_blk() plug/unplug, coalescence, requests sort and the
 * scheduler, will work enough for us to avoid too bad actuals IO requests.
 */
	ahead = 0;
	while (ahead < max_ahead) {
		ahead ++;
		if ((raend + ahead) >= end_index)
			break;
		if (page_cache_read(filp, raend + ahead) < 0)
			break;
	}
/*
 * If we tried to read ahead some pages,
 * If we tried to read ahead asynchronously,
 *   Try to force unplug of the device in order to start an asynchronous
 *   read IO request.
 * Update the read-ahead context.
 * Store the length of the current read-ahead window.
 * Double the current max read ahead size.
 *   That heuristic avoid to do some large IO for files that are not really
 *   accessed sequentially.
 */
	if (ahead) {
		if (reada_ok == 2) {
			run_task_queue(&tq_disk);
		}

		filp->f_ralen += ahead;
		filp->f_rawin += filp->f_ralen;
		filp->f_raend = raend + ahead + 1;

		filp->f_ramax += filp->f_ramax;

		if (filp->f_ramax > max_readahead)
			filp->f_ramax = max_readahead;

#ifdef PROFILE_READAHEAD
		profile_readahead((reada_ok == 2), filp);
#endif
	}

	return;
}


/*
 * This is a generic file read routine, and uses the
 * inode->i_op->readpage() function for the actual low-level
 * stuff.
 *
 * This is really ugly. But the goto's actually try to clarify some
 * of the logic when it comes to error handling etc.
 */
void do_generic_file_read(struct file * filp, loff_t *ppos, read_descriptor_t * desc, read_actor_t actor)
{
	struct dentry *dentry = filp->f_dentry;
	struct inode *inode = dentry->d_inode;
	unsigned long index, offset;
	struct page *cached_page;
	int reada_ok;
	int error;
	int max_readahead = get_max_readahead(inode);

	cached_page = NULL;
	index = *ppos >> PAGE_CACHE_SHIFT;
	offset = *ppos & ~PAGE_CACHE_MASK;

/*
 * If the current position is outside the previous read-ahead window, 
 * we reset the current read-ahead context and set read ahead max to zero
 * (will be set to just needed value later),
 * otherwise, we assume that the file accesses are sequential enough to
 * continue read-ahead.
 */
	if (index > filp->f_raend || index + filp->f_rawin < filp->f_raend) {
		reada_ok = 0;
		filp->f_raend = 0;
		filp->f_ralen = 0;
		filp->f_ramax = 0;
		filp->f_rawin = 0;
	} else {
		reada_ok = 1;
	}
/*
 * Adjust the current value of read-ahead max.
 * If the read operation stay in the first half page, force no readahead.
 * Otherwise try to increase read ahead max just enough to do the read request.
 * Then, at least MIN_READAHEAD if read ahead is ok,
 * and at most MAX_READAHEAD in all cases.
 */
	if (!index && offset + desc->count <= (PAGE_CACHE_SIZE >> 1)) {
		filp->f_ramax = 0;
	} else {
		unsigned long needed;

		needed = ((offset + desc->count) >> PAGE_CACHE_SHIFT) + 1;

		if (filp->f_ramax < needed)
			filp->f_ramax = needed;

		if (reada_ok && filp->f_ramax < MIN_READAHEAD)
				filp->f_ramax = MIN_READAHEAD;
		if (filp->f_ramax > max_readahead)
			filp->f_ramax = max_readahead;
	}

	for (;;) {
		struct page *page, **hash;
		unsigned long end_index, nr;

		end_index = inode->i_size >> PAGE_CACHE_SHIFT;
		if (index > end_index)
			break;
		nr = PAGE_CACHE_SIZE;
		if (index == end_index) {
			nr = inode->i_size & ~PAGE_CACHE_MASK;
			if (nr <= offset)
				break;
		}

		nr = nr - offset;

		/*
		 * Try to find the data in the page cache..
		 */
		hash = page_hash(&inode->i_data, index);

		spin_lock(&pagecache_lock);
		page = __find_page_nolock(&inode->i_data, index, *hash);
		if (!page)
			goto no_cached_page;
found_page:
		get_page(page);
		spin_unlock(&pagecache_lock);

		if (!Page_Uptodate(page))
			goto page_not_up_to_date;
page_ok:
		/*
		 * Ok, we have the page, and it's up-to-date, so
		 * now we can copy it to user space...
		 *
		 * The actor routine returns how many bytes were actually used..
		 * NOTE! This may not be the same as how much of a user buffer
		 * we filled up (we may be padding etc), so we can only update
		 * "pos" here (the actor routine has to update the user buffer
		 * pointers and the remaining count).
		 */
		nr = actor(desc, page, offset, nr);
		offset += nr;
		index += offset >> PAGE_CACHE_SHIFT;
		offset &= ~PAGE_CACHE_MASK;
	
		page_cache_release(page);
		if (nr && desc->count)
			continue;
		break;

/*
 * Ok, the page was not immediately readable, so let's try to read ahead while we're at it..
 */
page_not_up_to_date:
		generic_file_readahead(reada_ok, filp, inode, page);

		if (Page_Uptodate(page))
			goto page_ok;

		/* Get exclusive access to the page ... */
		lock_page(page);
		if (Page_Uptodate(page)) {
			UnlockPage(page);
			goto page_ok;
		}

readpage:
		/* ... and start the actual read. The read will unlock the page. */
		error = inode->i_op->readpage(filp->f_dentry, page);

		if (!error) {
			if (Page_Uptodate(page))
				goto page_ok;

			/* Again, try some read-ahead while waiting for the page to finish.. */
			generic_file_readahead(reada_ok, filp, inode, page);
			wait_on_page(page);
			if (Page_Uptodate(page))
				goto page_ok;
			error = -EIO;
		}

		/* UHHUH! A synchronous read error occurred. Report it */
		desc->error = error;
		page_cache_release(page);
		break;

no_cached_page:
		/*
		 * Ok, it wasn't cached, so we need to create a new
		 * page..
		 *
		 * We get here with the page cache lock held.
		 */
		if (!cached_page) {
			spin_unlock(&pagecache_lock);
			cached_page = page_cache_alloc();
			if (!cached_page) {
				desc->error = -ENOMEM;
				break;
			}

			/*
			 * Somebody may have added the page while we
			 * dropped the page cache lock. Check for that.
			 */
			spin_lock(&pagecache_lock);
			page = __find_page_nolock(&inode->i_data, index, *hash);
			if (page)
				goto found_page;
		}

		/*
		 * Ok, add the new page to the hash-queues...
		 */
		page = cached_page;
		__add_to_page_cache(page, &inode->i_data, index, hash);
		spin_unlock(&pagecache_lock);
		cached_page = NULL;

		goto readpage;
	}

	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
	filp->f_reada = 1;
	if (cached_page)
		page_cache_free(cached_page);
	UPDATE_ATIME(inode);
}

static int file_read_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size)
{
	unsigned long kaddr;
	unsigned long left, count = desc->count;

	if (size > count)
		size = count;

	kaddr = kmap(page);
	left = __copy_to_user(desc->buf, (void *)(kaddr + offset), size);
	kunmap(page);
	
	if (left) {
		size -= left;
		desc->error = -EFAULT;
	}
	desc->count = count - size;
	desc->written += size;
	desc->buf += size;
	return size;
}

/*
 * This is the "read()" routine for all filesystems
 * that can use the page cache directly.
 */
ssize_t generic_file_read(struct file * filp, char * buf, size_t count, loff_t *ppos)
{
	ssize_t retval;

	retval = -EFAULT;
	if (access_ok(VERIFY_WRITE, buf, count)) {
		retval = 0;

		if (count) {
			read_descriptor_t desc;

			desc.written = 0;
			desc.count = count;
			desc.buf = buf;
			desc.error = 0;
			do_generic_file_read(filp, ppos, &desc, file_read_actor);

			retval = desc.written;
			if (!retval)
				retval = desc.error;
		}
	}
	return retval;
}

static int file_send_actor(read_descriptor_t * desc, struct page *page, unsigned long offset , unsigned long size)
{
	unsigned long kaddr;
	ssize_t written;
	unsigned long count = desc->count;
	struct file *file = (struct file *) desc->buf;
	mm_segment_t old_fs;

	if (size > count)
		size = count;
	old_fs = get_fs();
	set_fs(KERNEL_DS);

	kaddr = kmap(page);
	written = file->f_op->write(file, (char *)kaddr + offset,
						 size, &file->f_pos);
	kunmap(page);
	set_fs(old_fs);
	if (written < 0) {
		desc->error = written;
		written = 0;
	}
	desc->count = count - written;
	desc->written += written;
	return written;
}

asmlinkage ssize_t sys_sendfile(int out_fd, int in_fd, off_t *offset, size_t count)
{
	ssize_t retval;
	struct file * in_file, * out_file;
	struct inode * in_inode, * out_inode;

	/*
	 * Get input file, and verify that it is ok..
	 */
	retval = -EBADF;
	in_file = fget(in_fd);
	if (!in_file)
		goto out;
	if (!(in_file->f_mode & FMODE_READ))
		goto fput_in;
	retval = -EINVAL;
	in_inode = in_file->f_dentry->d_inode;
	if (!in_inode)
		goto fput_in;
	if (!in_inode->i_op || !in_inode->i_op->readpage)
		goto fput_in;
	retval = locks_verify_area(FLOCK_VERIFY_READ, in_inode, in_file, in_file->f_pos, count);
	if (retval)
		goto fput_in;

	/*
	 * Get output file, and verify that it is ok..
	 */
	retval = -EBADF;
	out_file = fget(out_fd);
	if (!out_file)
		goto fput_in;
	if (!(out_file->f_mode & FMODE_WRITE))
		goto fput_out;
	retval = -EINVAL;
	if (!out_file->f_op || !out_file->f_op->write)
		goto fput_out;
	out_inode = out_file->f_dentry->d_inode;
	if (!out_inode)
		goto fput_out;
	retval = locks_verify_area(FLOCK_VERIFY_WRITE, out_inode, out_file, out_file->f_pos, count);
	if (retval)
		goto fput_out;

	retval = 0;
	if (count) {
		read_descriptor_t desc;
		loff_t pos = 0, *ppos;

		retval = -EFAULT;
		ppos = &in_file->f_pos;
		if (offset) {
			if (get_user(pos, offset))
				goto fput_out;
			ppos = &pos;
		}

		desc.written = 0;
		desc.count = count;
		desc.buf = (char *) out_file;
		desc.error = 0;
		do_generic_file_read(in_file, ppos, &desc, file_send_actor);

		retval = desc.written;
		if (!retval)
			retval = desc.error;
		if (offset)
			put_user(pos, offset);
	}

fput_out:
	fput(out_file);
fput_in:
	fput(in_file);
out:
	return retval;
}

/*
 * filemap_nopage() is invoked via the vma operations vector for a
 * mapped memory region to read in file data during a page fault.
 *
 * The goto's are kind of ugly, but this streamlines the normal case of having
 * it in the page cache, and handles the special cases reasonably without
 * having a lot of duplicated code.
 */
struct page * filemap_nopage(struct vm_area_struct * area,
	unsigned long address, int no_share)
{
	int error;
	struct file *file = area->vm_file;
	struct dentry *dentry = file->f_dentry;
	struct inode *inode = dentry->d_inode;
	struct page *page, **hash, *old_page;
	unsigned long size = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

	unsigned long pgoff = ((address - area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;

	/*
	 * Semantics for shared and private memory areas are different
	 * past the end of the file. A shared mapping past the last page
	 * of the file is an error and results in a SIGBUS, while a
	 * private mapping just maps in a zero page.
	 */
	if ((pgoff >= size) &&
		(area->vm_flags & VM_SHARED) && (area->vm_mm == current->mm))
		return NULL;

	/*
	 * Do we have something in the page cache already?
	 */
	hash = page_hash(&inode->i_data, pgoff);
retry_find:
	page = __find_get_page(&inode->i_data, pgoff, hash);
	if (!page)
		goto no_cached_page;

	/*
	 * Ok, found a page in the page cache, now we need to check
	 * that it's up-to-date.
	 */
	if (!Page_Uptodate(page))
		goto page_not_uptodate;

success:
	/*
	 * Found the page and have a reference on it, need to check sharing
	 * and possibly copy it over to another page..
	 */
	old_page = page;
	if (no_share) {
		struct page *new_page = page_cache_alloc();

		if (new_page) {
			copy_highpage(new_page, old_page);
			flush_page_to_ram(new_page);
		} else
			new_page = NOPAGE_OOM;
		page_cache_release(page);
		return new_page;
	}
		
	flush_page_to_ram(old_page);
	return old_page;

no_cached_page:
	/*
	 * If the requested offset is within our file, try to read a whole 
	 * cluster of pages at once.
	 *
	 * Otherwise, we're off the end of a privately mapped file,
	 * so we need to map a zero page.
	 */
	if (pgoff < size)
		error = read_cluster_nonblocking(file, pgoff, size);
	else
		error = page_cache_read(file, pgoff);

	/*
	 * The page we want has now been added to the page cache.
	 * In the unlikely event that someone removed it in the
	 * meantime, we'll just come back here and read it again.
	 */
	if (error >= 0)
		goto retry_find;

	/*
	 * An error return from page_cache_read can result if the
	 * system is low on memory, or a problem occurs while trying
	 * to schedule I/O.
	 */
	if (error == -ENOMEM)
		return NOPAGE_OOM;
	return NULL;

page_not_uptodate:
	lock_page(page);
	if (Page_Uptodate(page)) {
		UnlockPage(page);
		goto success;
	}

	if (!inode->i_op->readpage(file->f_dentry, page)) {
		wait_on_page(page);
		if (Page_Uptodate(page))
			goto success;
	}

	/*
	 * Umm, take care of errors if the page isn't up-to-date.
	 * Try to re-read it _once_. We do this synchronously,
	 * because there really aren't any performance issues here
	 * and we need to check for errors.
	 */
	lock_page(page);
	if (Page_Uptodate(page)) {
		UnlockPage(page);
		goto success;
	}
	ClearPageError(page);
	if (!inode->i_op->readpage(file->f_dentry, page)) {
		wait_on_page(page);
		if (Page_Uptodate(page))
			goto success;
	}

	/*
	 * Things didn't work out. Return zero to tell the
	 * mm layer so, possibly freeing the page cache page first.
	 */
	page_cache_release(page);
	return NULL;
}

/*
 * Tries to write a shared mapped page to its backing store. May return -EIO
 * if the disk is full.
 */
static inline int do_write_page(struct inode * inode, struct file * file,
	struct page * page, unsigned long index)
{
	int retval;
	int (*writepage) (struct dentry *, struct page *);

	/* refuse to extend file size.. */
	if (S_ISREG(inode->i_mode)) {
		unsigned long size_idx = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

		/* Ho humm.. We should have tested for this earlier */
		if (size_idx <= index)
			return -EIO;
	}
	writepage = inode->i_op->writepage;
	lock_page(page);

	retval = writepage(file->f_dentry, page);

	UnlockPage(page);
	return retval;
}

static int filemap_write_page(struct file *file,
			      unsigned long index,
			      struct page * page,
			      int wait)
{
	int result;
	struct dentry * dentry;
	struct inode * inode;

	dentry = file->f_dentry;
	inode = dentry->d_inode;

	/*
	 * If a task terminates while we're swapping the page, the vma and
	 * and file could be released: try_to_swap_out has done a get_file.
	 * vma/file is guaranteed to exist in the unmap/sync cases because
	 * mmap_sem is held.
	 */
	result = do_write_page(inode, file, page, index);
	return result;
}


/*
 * The page cache takes care of races between somebody
 * trying to swap something out and swap something in
 * at the same time..
 */
extern void wakeup_bdflush(int);
int filemap_swapout(struct page * page, struct file * file)
{
	int retval = filemap_write_page(file, page->index, page, 0);
	wakeup_bdflush(0);
	return retval;
}

static inline int filemap_sync_pte(pte_t * ptep, struct vm_area_struct *vma,
	unsigned long address, unsigned int flags)
{
	unsigned long pgoff;
	pte_t pte = *ptep;
	struct page *page;
	int error;

	if (!(flags & MS_INVALIDATE)) {
		if (!pte_present(pte))
			return 0;
		if (!pte_dirty(pte))
			return 0;
		flush_page_to_ram(pte_page(pte));
		flush_cache_page(vma, address);
		set_pte(ptep, pte_mkclean(pte));
		flush_tlb_page(vma, address);
		page = pte_page(pte);
		get_page(page);
	} else {
		if (pte_none(pte))
			return 0;
		flush_cache_page(vma, address);
		pte_clear(ptep);
		flush_tlb_page(vma, address);
		if (!pte_present(pte)) {
			swap_free(pte_to_swp_entry(pte));
			return 0;
		}
		page = pte_page(pte);
		if (!pte_dirty(pte) || flags == MS_INVALIDATE) {
			page_cache_free(page);
			return 0;
		}
	}
	pgoff = (address - vma->vm_start) >> PAGE_CACHE_SHIFT;
	pgoff += vma->vm_pgoff;
	if (page->index != pgoff) {
		printk("weirdness: pgoff=%lu index=%lu address=%lu vm_start=%lu vm_pgoff=%lu\n",
			pgoff, page->index, address, vma->vm_start, vma->vm_pgoff);
	}
	error = filemap_write_page(vma->vm_file, pgoff, page, 1);
	page_cache_free(page);
	return error;
}

static inline int filemap_sync_pte_range(pmd_t * pmd,
	unsigned long address, unsigned long size, 
	struct vm_area_struct *vma, unsigned long offset, unsigned int flags)
{
	pte_t * pte;
	unsigned long end;
	int error;

	if (pmd_none(*pmd))
		return 0;
	if (pmd_bad(*pmd)) {
		pmd_ERROR(*pmd);
		pmd_clear(pmd);
		return 0;
	}
	pte = pte_offset(pmd, address);
	offset += address & PMD_MASK;
	address &= ~PMD_MASK;
	end = address + size;
	if (end > PMD_SIZE)
		end = PMD_SIZE;
	error = 0;
	do {
		error |= filemap_sync_pte(pte, vma, address + offset, flags);
		address += PAGE_SIZE;
		pte++;
	} while (address && (address < end));
	return error;
}

static inline int filemap_sync_pmd_range(pgd_t * pgd,
	unsigned long address, unsigned long size, 
	struct vm_area_struct *vma, unsigned int flags)
{
	pmd_t * pmd;
	unsigned long offset, end;
	int error;

	if (pgd_none(*pgd))
		return 0;
	if (pgd_bad(*pgd)) {
		pgd_ERROR(*pgd);
		pgd_clear(pgd);
		return 0;
	}
	pmd = pmd_offset(pgd, address);
	offset = address & PGDIR_MASK;
	address &= ~PGDIR_MASK;
	end = address + size;
	if (end > PGDIR_SIZE)
		end = PGDIR_SIZE;
	error = 0;
	do {
		error |= filemap_sync_pte_range(pmd, address, end - address, vma, offset, flags);
		address = (address + PMD_SIZE) & PMD_MASK;
		pmd++;
	} while (address && (address < end));
	return error;
}

int filemap_sync(struct vm_area_struct * vma, unsigned long address,
	size_t size, unsigned int flags)
{
	pgd_t * dir;
	unsigned long end = address + size;
	int error = 0;

	dir = pgd_offset(vma->vm_mm, address);
	flush_cache_range(vma->vm_mm, end - size, end);
	if (address >= end)
		BUG();
	do {
		error |= filemap_sync_pmd_range(dir, address, end - address, vma, flags);
		address = (address + PGDIR_SIZE) & PGDIR_MASK;
		dir++;
	} while (address && (address < end));
	flush_tlb_range(vma->vm_mm, end - size, end);
	return error;
}

/*
 * This handles (potentially partial) area unmaps..
 */
static void filemap_unmap(struct vm_area_struct *vma, unsigned long start, size_t len)
{
	lock_kernel();
	filemap_sync(vma, start, len, MS_ASYNC);
	unlock_kernel();
}

/*
 * Shared mappings need to be able to do the right thing at
 * close/unmap/sync. They will also use the private file as
 * backing-store for swapping..
 */
static struct vm_operations_struct file_shared_mmap = {
	NULL,			/* no special open */
	NULL,			/* no special close */
	filemap_unmap,		/* unmap - we need to sync the pages */
	NULL,			/* no special protect */
	filemap_sync,		/* sync */
	NULL,			/* advise */
	filemap_nopage,		/* nopage */
	NULL,			/* wppage */
	filemap_swapout		/* swapout */
};

/*
 * Private mappings just need to be able to load in the map.
 *
 * (This is actually used for shared mappings as well, if we
 * know they can't ever get write permissions..)
 */
static struct vm_operations_struct file_private_mmap = {
	NULL,			/* open */
	NULL,			/* close */
	NULL,			/* unmap */
	NULL,			/* protect */
	NULL,			/* sync */
	NULL,			/* advise */
	filemap_nopage,		/* nopage */
	NULL,			/* wppage */
	NULL			/* swapout */
};

/* This is used for a general mmap of a disk file */

int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
{
	struct vm_operations_struct * ops;
	struct inode *inode = file->f_dentry->d_inode;

	ops = &file_private_mmap;
	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) {
		if (!inode->i_op || !inode->i_op->writepage)
			return -EINVAL;
		ops = &file_shared_mmap;
	}
	if (!inode->i_sb || !S_ISREG(inode->i_mode))
		return -EACCES;
	if (!inode->i_op || !inode->i_op->readpage)
		return -ENOEXEC;
	UPDATE_ATIME(inode);
	vma->vm_ops = ops;
	return 0;
}


/*
 * The msync() system call.
 */

static int msync_interval(struct vm_area_struct * vma,
	unsigned long start, unsigned long end, int flags)
{
	if (vma->vm_file && vma->vm_ops && vma->vm_ops->sync) {
		int error;
		error = vma->vm_ops->sync(vma, start, end-start, flags);
		if (!error && (flags & MS_SYNC)) {
			struct file * file = vma->vm_file;
			if (file) {
				struct dentry * dentry = file->f_dentry;
				error = file_fsync(file, dentry);
			}
		}
		return error;
	}
	return 0;
}

asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
{
	unsigned long end;
	struct vm_area_struct * vma;
	int unmapped_error, error = -EINVAL;

	down(&current->mm->mmap_sem);
	lock_kernel();
	if (start & ~PAGE_MASK)
		goto out;
	len = (len + ~PAGE_MASK) & PAGE_MASK;
	end = start + len;
	if (end < start)
		goto out;
	if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
		goto out;
	error = 0;
	if (end == start)
		goto out;
	/*
	 * If the interval [start,end) covers some unmapped address ranges,
	 * just ignore them, but return -EFAULT at the end.
	 */
	vma = find_vma(current->mm, start);
	unmapped_error = 0;
	for (;;) {
		/* Still start < end. */
		error = -EFAULT;
		if (!vma)
			goto out;
		/* Here start < vma->vm_end. */
		if (start < vma->vm_start) {
			unmapped_error = -EFAULT;
			start = vma->vm_start;
		}
		/* Here vma->vm_start <= start < vma->vm_end. */
		if (end <= vma->vm_end) {
			if (start < end) {
				error = msync_interval(vma, start, end, flags);
				if (error)
					goto out;
			}
			error = unmapped_error;
			goto out;
		}
		/* Here vma->vm_start <= start < vma->vm_end < end. */
		error = msync_interval(vma, start, vma->vm_end, flags);
		if (error)
			goto out;
		start = vma->vm_end;
		vma = vma->vm_next;
	}
out:
	unlock_kernel();
	up(&current->mm->mmap_sem);
	return error;
}

struct page *read_cache_page(struct address_space *mapping,
				unsigned long index,
				int (*filler)(void *,struct page*),
				void *data)
{
	struct page **hash = page_hash(mapping, index);
	struct page *page, *cached_page = NULL;
	int err;
repeat:
	page = __find_get_page(mapping, index, hash);
	if (!page) {
		if (!cached_page) {
			cached_page = page_cache_alloc();
			if (!cached_page)
				return ERR_PTR(-ENOMEM);
		}
		page = cached_page;
		if (add_to_page_cache_unique(page, mapping, index, hash))
			goto repeat;
		cached_page = NULL;
		err = filler(data, page);
		if (err < 0) {
			page_cache_release(page);
			page = ERR_PTR(err);
		}
	}
	if (cached_page)
		page_cache_free(cached_page);
	return page;
}

static inline struct page * __grab_cache_page(struct address_space *mapping,
				unsigned long index, struct page **cached_page)
{
	struct page *page, **hash = page_hash(mapping, index);
repeat:
	page = __find_lock_page(mapping, index, hash);
	if (!page) {
		if (!*cached_page) {
			*cached_page = page_cache_alloc();
			if (!*cached_page)
				return NULL;
		}
		page = *cached_page;
		if (add_to_page_cache_unique(page, mapping, index, hash))
			goto repeat;
		*cached_page = NULL;
	}
	return page;
}

/*
 * Returns locked page at given index in given cache, creating it if needed.
 */

struct page *grab_cache_page(struct address_space *mapping, unsigned long index)
{
	struct page *cached_page = NULL;
	struct page *page = __grab_cache_page(mapping,index,&cached_page);
	if (cached_page)
		page_cache_free(cached_page);
	return page;
}

/*
 * Write to a file through the page cache. This is mainly for the
 * benefit of NFS and possibly other network-based file systems.
 *
 * We currently put everything into the page cache prior to writing it.
 * This is not a problem when writing full pages. With partial pages,
 * however, we first have to read the data into the cache, then
 * dirty the page, and finally schedule it for writing. Alternatively, we
 * could write-through just the portion of data that would go into that
 * page, but that would kill performance for applications that write data
 * line by line, and it's prone to race conditions.
 *
 * Note that this routine doesn't try to keep track of dirty pages. Each
 * file system has to do this all by itself, unfortunately.
 *							okir@monad.swb.de
 */
ssize_t
generic_file_write(struct file *file, const char *buf,
		   size_t count, loff_t *ppos,
		   writepage_t write_one_page)
{
	struct dentry	*dentry = file->f_dentry; 
	struct inode	*inode = dentry->d_inode; 
	unsigned long	limit = current->rlim[RLIMIT_FSIZE].rlim_cur;
	loff_t		pos;
	struct page	*page, *cached_page;
	unsigned long	written;
	long		status;
	int		err;

	cached_page = NULL;

	down(&inode->i_sem);

	pos = *ppos;
	err = -EINVAL;
	if (pos < 0)
		goto out;

	err = file->f_error;
	if (err) {
		file->f_error = 0;
		goto out;
	}

	written = 0;

	if (file->f_flags & O_APPEND)
		pos = inode->i_size;

	/*
	 * Check whether we've reached the file size limit.
	 */
	err = -EFBIG;
	if (limit != RLIM_INFINITY) {
		if (pos >= limit) {
			send_sig(SIGXFSZ, current, 0);
			goto out;
		}
		if (count > limit - pos) {
			send_sig(SIGXFSZ, current, 0);
			count = limit - pos;
		}
	}

	status  = 0;

	while (count) {
		unsigned long bytes, index, offset;

		/*
		 * Try to find the page in the cache. If it isn't there,
		 * allocate a free page.
		 */
		offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
		index = pos >> PAGE_CACHE_SHIFT;
		bytes = PAGE_CACHE_SIZE - offset;
		if (bytes > count)
			bytes = count;

		status = -ENOMEM;	/* we'll assign it later anyway */
		page = __grab_cache_page(&inode->i_data, index, &cached_page);
		if (!page)
			break;

		/* We have exclusive IO access to the page.. */
		if (!PageLocked(page)) {
			PAGE_BUG(page);
		}

		status = write_one_page(file, page, offset, bytes, buf);

		if (status >= 0) {
			written += status;
			count -= status;
			pos += status;
			buf += status;
			if (pos > inode->i_size)
				inode->i_size = pos;
		}
		/* Mark it unlocked again and drop the page.. */
		UnlockPage(page);
		page_cache_release(page);

		if (status < 0)
			break;
	}
	*ppos = pos;

	if (cached_page)
		page_cache_free(cached_page);

	err = written ? written : status;
out:
	up(&inode->i_sem);
	return err;
}

void __init page_cache_init(unsigned long mempages)
{
	unsigned long htable_size, order;

	htable_size = mempages;
	htable_size *= sizeof(struct page *);
	for(order = 0; (PAGE_SIZE << order) < htable_size; order++)
		;

	do {
		unsigned long tmp = (PAGE_SIZE << order) / sizeof(struct page *);

		page_hash_bits = 0;
		while((tmp >>= 1UL) != 0UL)
			page_hash_bits++;

		page_hash_table = (struct page **)
			__get_free_pages(GFP_ATOMIC, order);
	} while(page_hash_table == NULL && --order > 0);

	printk("Page-cache hash table entries: %d (order: %ld, %ld bytes)\n",
	       (1 << page_hash_bits), order, (PAGE_SIZE << order));
	if (!page_hash_table)
		panic("Failed to allocate page hash table\n");
	memset((void *)page_hash_table, 0, PAGE_HASH_SIZE * sizeof(struct page *));
}