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CommitLineData
1da177e4
LT
1/*
2 * mm/readahead.c - address_space-level file readahead.
3 *
4 * Copyright (C) 2002, Linus Torvalds
5 *
e1f8e874 6 * 09Apr2002 Andrew Morton
1da177e4
LT
7 * Initial version.
8 */
9
10#include <linux/kernel.h>
5a0e3ad6 11#include <linux/gfp.h>
b95f1b31 12#include <linux/export.h>
1da177e4
LT
13#include <linux/blkdev.h>
14#include <linux/backing-dev.h>
8bde37f0 15#include <linux/task_io_accounting_ops.h>
1da177e4 16#include <linux/pagevec.h>
f5ff8422 17#include <linux/pagemap.h>
782182e5
CW
18#include <linux/syscalls.h>
19#include <linux/file.h>
d72ee911 20#include <linux/mm_inline.h>
1da177e4 21
29f175d1
FF
22#include "internal.h"
23
1da177e4
LT
24/*
25 * Initialise a struct file's readahead state. Assumes that the caller has
26 * memset *ra to zero.
27 */
28void
29file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
30{
de1414a6 31 ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
f4e6b498 32 ra->prev_pos = -1;
1da177e4 33}
d41cc702 34EXPORT_SYMBOL_GPL(file_ra_state_init);
1da177e4 35
03fb3d2a
DH
36/*
37 * see if a page needs releasing upon read_cache_pages() failure
266cf658
DH
38 * - the caller of read_cache_pages() may have set PG_private or PG_fscache
39 * before calling, such as the NFS fs marking pages that are cached locally
40 * on disk, thus we need to give the fs a chance to clean up in the event of
41 * an error
03fb3d2a
DH
42 */
43static void read_cache_pages_invalidate_page(struct address_space *mapping,
44 struct page *page)
45{
266cf658 46 if (page_has_private(page)) {
03fb3d2a
DH
47 if (!trylock_page(page))
48 BUG();
49 page->mapping = mapping;
09cbfeaf 50 do_invalidatepage(page, 0, PAGE_SIZE);
03fb3d2a
DH
51 page->mapping = NULL;
52 unlock_page(page);
53 }
09cbfeaf 54 put_page(page);
03fb3d2a
DH
55}
56
57/*
58 * release a list of pages, invalidating them first if need be
59 */
60static void read_cache_pages_invalidate_pages(struct address_space *mapping,
61 struct list_head *pages)
62{
63 struct page *victim;
64
65 while (!list_empty(pages)) {
c8ad6302 66 victim = lru_to_page(pages);
03fb3d2a
DH
67 list_del(&victim->lru);
68 read_cache_pages_invalidate_page(mapping, victim);
69 }
70}
71
1da177e4 72/**
bd40cdda 73 * read_cache_pages - populate an address space with some pages & start reads against them
1da177e4
LT
74 * @mapping: the address_space
75 * @pages: The address of a list_head which contains the target pages. These
76 * pages have their ->index populated and are otherwise uninitialised.
77 * @filler: callback routine for filling a single page.
78 * @data: private data for the callback routine.
79 *
80 * Hides the details of the LRU cache etc from the filesystems.
81 */
82int read_cache_pages(struct address_space *mapping, struct list_head *pages,
83 int (*filler)(void *, struct page *), void *data)
84{
85 struct page *page;
1da177e4
LT
86 int ret = 0;
87
1da177e4 88 while (!list_empty(pages)) {
c8ad6302 89 page = lru_to_page(pages);
1da177e4 90 list_del(&page->lru);
063d99b4 91 if (add_to_page_cache_lru(page, mapping, page->index,
c62d2555 92 mapping_gfp_constraint(mapping, GFP_KERNEL))) {
03fb3d2a 93 read_cache_pages_invalidate_page(mapping, page);
1da177e4
LT
94 continue;
95 }
09cbfeaf 96 put_page(page);
eb2be189 97
1da177e4 98 ret = filler(data, page);
eb2be189 99 if (unlikely(ret)) {
03fb3d2a 100 read_cache_pages_invalidate_pages(mapping, pages);
1da177e4
LT
101 break;
102 }
09cbfeaf 103 task_io_account_read(PAGE_SIZE);
1da177e4 104 }
1da177e4
LT
105 return ret;
106}
107
108EXPORT_SYMBOL(read_cache_pages);
109
110static int read_pages(struct address_space *mapping, struct file *filp,
111 struct list_head *pages, unsigned nr_pages)
112{
5b417b18 113 struct blk_plug plug;
1da177e4 114 unsigned page_idx;
994fc28c 115 int ret;
1da177e4 116
5b417b18
JA
117 blk_start_plug(&plug);
118
1da177e4
LT
119 if (mapping->a_ops->readpages) {
120 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
029e332e
OH
121 /* Clean up the remaining pages */
122 put_pages_list(pages);
1da177e4
LT
123 goto out;
124 }
125
1da177e4 126 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
c8ad6302 127 struct page *page = lru_to_page(pages);
1da177e4 128 list_del(&page->lru);
063d99b4 129 if (!add_to_page_cache_lru(page, mapping, page->index,
c62d2555 130 mapping_gfp_constraint(mapping, GFP_KERNEL))) {
9f1a3cfc 131 mapping->a_ops->readpage(filp, page);
eb2be189 132 }
09cbfeaf 133 put_page(page);
1da177e4 134 }
994fc28c 135 ret = 0;
5b417b18 136
1da177e4 137out:
5b417b18
JA
138 blk_finish_plug(&plug);
139
1da177e4
LT
140 return ret;
141}
142
1da177e4 143/*
d30a1100 144 * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
1da177e4
LT
145 * the pages first, then submits them all for I/O. This avoids the very bad
146 * behaviour which would occur if page allocations are causing VM writeback.
147 * We really don't want to intermingle reads and writes like that.
148 *
149 * Returns the number of pages requested, or the maximum amount of I/O allowed.
1da177e4 150 */
29f175d1 151int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
46fc3e7b
FW
152 pgoff_t offset, unsigned long nr_to_read,
153 unsigned long lookahead_size)
1da177e4
LT
154{
155 struct inode *inode = mapping->host;
156 struct page *page;
157 unsigned long end_index; /* The last page we want to read */
158 LIST_HEAD(page_pool);
159 int page_idx;
160 int ret = 0;
161 loff_t isize = i_size_read(inode);
162
163 if (isize == 0)
164 goto out;
165
09cbfeaf 166 end_index = ((isize - 1) >> PAGE_SHIFT);
1da177e4
LT
167
168 /*
169 * Preallocate as many pages as we will need.
170 */
1da177e4 171 for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
7361f4d8 172 pgoff_t page_offset = offset + page_idx;
c743d96b 173
1da177e4
LT
174 if (page_offset > end_index)
175 break;
176
00128188 177 rcu_read_lock();
1da177e4 178 page = radix_tree_lookup(&mapping->page_tree, page_offset);
00128188 179 rcu_read_unlock();
0cd6144a 180 if (page && !radix_tree_exceptional_entry(page))
1da177e4
LT
181 continue;
182
7b1de586 183 page = page_cache_alloc_readahead(mapping);
1da177e4
LT
184 if (!page)
185 break;
186 page->index = page_offset;
187 list_add(&page->lru, &page_pool);
46fc3e7b
FW
188 if (page_idx == nr_to_read - lookahead_size)
189 SetPageReadahead(page);
1da177e4
LT
190 ret++;
191 }
1da177e4
LT
192
193 /*
194 * Now start the IO. We ignore I/O errors - if the page is not
195 * uptodate then the caller will launch readpage again, and
196 * will then handle the error.
197 */
198 if (ret)
199 read_pages(mapping, filp, &page_pool, ret);
200 BUG_ON(!list_empty(&page_pool));
201out:
202 return ret;
203}
204
205/*
206 * Chunk the readahead into 2 megabyte units, so that we don't pin too much
207 * memory at once.
208 */
209int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
7361f4d8 210 pgoff_t offset, unsigned long nr_to_read)
1da177e4 211{
1da177e4
LT
212 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
213 return -EINVAL;
214
600e19af 215 nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages);
1da177e4
LT
216 while (nr_to_read) {
217 int err;
218
09cbfeaf 219 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
1da177e4
LT
220
221 if (this_chunk > nr_to_read)
222 this_chunk = nr_to_read;
223 err = __do_page_cache_readahead(mapping, filp,
46fc3e7b 224 offset, this_chunk, 0);
58d5640e
MR
225 if (err < 0)
226 return err;
227
1da177e4
LT
228 offset += this_chunk;
229 nr_to_read -= this_chunk;
230 }
58d5640e 231 return 0;
1da177e4
LT
232}
233
c743d96b
FW
234/*
235 * Set the initial window size, round to next power of 2 and square
236 * for small size, x 4 for medium, and x 2 for large
237 * for 128k (32 page) max ra
238 * 1-8 page = 32k initial, > 8 page = 128k initial
239 */
240static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
241{
242 unsigned long newsize = roundup_pow_of_two(size);
243
244 if (newsize <= max / 32)
245 newsize = newsize * 4;
246 else if (newsize <= max / 4)
247 newsize = newsize * 2;
248 else
249 newsize = max;
250
251 return newsize;
252}
253
122a21d1
FW
254/*
255 * Get the previous window size, ramp it up, and
256 * return it as the new window size.
257 */
c743d96b 258static unsigned long get_next_ra_size(struct file_ra_state *ra,
122a21d1
FW
259 unsigned long max)
260{
f9acc8c7 261 unsigned long cur = ra->size;
122a21d1
FW
262 unsigned long newsize;
263
264 if (cur < max / 16)
c743d96b 265 newsize = 4 * cur;
122a21d1 266 else
c743d96b 267 newsize = 2 * cur;
122a21d1
FW
268
269 return min(newsize, max);
270}
271
272/*
273 * On-demand readahead design.
274 *
275 * The fields in struct file_ra_state represent the most-recently-executed
276 * readahead attempt:
277 *
f9acc8c7
FW
278 * |<----- async_size ---------|
279 * |------------------- size -------------------->|
280 * |==================#===========================|
281 * ^start ^page marked with PG_readahead
122a21d1
FW
282 *
283 * To overlap application thinking time and disk I/O time, we do
284 * `readahead pipelining': Do not wait until the application consumed all
285 * readahead pages and stalled on the missing page at readahead_index;
f9acc8c7
FW
286 * Instead, submit an asynchronous readahead I/O as soon as there are
287 * only async_size pages left in the readahead window. Normally async_size
288 * will be equal to size, for maximum pipelining.
122a21d1
FW
289 *
290 * In interleaved sequential reads, concurrent streams on the same fd can
291 * be invalidating each other's readahead state. So we flag the new readahead
f9acc8c7 292 * page at (start+size-async_size) with PG_readahead, and use it as readahead
122a21d1
FW
293 * indicator. The flag won't be set on already cached pages, to avoid the
294 * readahead-for-nothing fuss, saving pointless page cache lookups.
295 *
f4e6b498 296 * prev_pos tracks the last visited byte in the _previous_ read request.
122a21d1
FW
297 * It should be maintained by the caller, and will be used for detecting
298 * small random reads. Note that the readahead algorithm checks loosely
299 * for sequential patterns. Hence interleaved reads might be served as
300 * sequential ones.
301 *
302 * There is a special-case: if the first page which the application tries to
303 * read happens to be the first page of the file, it is assumed that a linear
304 * read is about to happen and the window is immediately set to the initial size
305 * based on I/O request size and the max_readahead.
306 *
307 * The code ramps up the readahead size aggressively at first, but slow down as
308 * it approaches max_readhead.
309 */
310
10be0b37
WF
311/*
312 * Count contiguously cached pages from @offset-1 to @offset-@max,
313 * this count is a conservative estimation of
314 * - length of the sequential read sequence, or
315 * - thrashing threshold in memory tight systems
316 */
317static pgoff_t count_history_pages(struct address_space *mapping,
10be0b37
WF
318 pgoff_t offset, unsigned long max)
319{
320 pgoff_t head;
321
322 rcu_read_lock();
e7b563bb 323 head = page_cache_prev_hole(mapping, offset - 1, max);
10be0b37
WF
324 rcu_read_unlock();
325
326 return offset - 1 - head;
327}
328
329/*
330 * page cache context based read-ahead
331 */
332static int try_context_readahead(struct address_space *mapping,
333 struct file_ra_state *ra,
334 pgoff_t offset,
335 unsigned long req_size,
336 unsigned long max)
337{
338 pgoff_t size;
339
3e2faa08 340 size = count_history_pages(mapping, offset, max);
10be0b37
WF
341
342 /*
2cad4018 343 * not enough history pages:
10be0b37
WF
344 * it could be a random read
345 */
2cad4018 346 if (size <= req_size)
10be0b37
WF
347 return 0;
348
349 /*
350 * starts from beginning of file:
351 * it is a strong indication of long-run stream (or whole-file-read)
352 */
353 if (size >= offset)
354 size *= 2;
355
356 ra->start = offset;
2cad4018
FW
357 ra->size = min(size + req_size, max);
358 ra->async_size = 1;
10be0b37
WF
359
360 return 1;
361}
362
122a21d1
FW
363/*
364 * A minimal readahead algorithm for trivial sequential/random reads.
365 */
366static unsigned long
367ondemand_readahead(struct address_space *mapping,
368 struct file_ra_state *ra, struct file *filp,
cf914a7d 369 bool hit_readahead_marker, pgoff_t offset,
122a21d1
FW
370 unsigned long req_size)
371{
600e19af 372 unsigned long max = ra->ra_pages;
af248a0c 373 pgoff_t prev_offset;
045a2529
WF
374
375 /*
376 * start of file
377 */
378 if (!offset)
379 goto initial_readahead;
122a21d1
FW
380
381 /*
f9acc8c7 382 * It's the expected callback offset, assume sequential access.
122a21d1
FW
383 * Ramp up sizes, and push forward the readahead window.
384 */
045a2529
WF
385 if ((offset == (ra->start + ra->size - ra->async_size) ||
386 offset == (ra->start + ra->size))) {
f9acc8c7
FW
387 ra->start += ra->size;
388 ra->size = get_next_ra_size(ra, max);
389 ra->async_size = ra->size;
390 goto readit;
122a21d1
FW
391 }
392
6b10c6c9
FW
393 /*
394 * Hit a marked page without valid readahead state.
395 * E.g. interleaved reads.
396 * Query the pagecache for async_size, which normally equals to
397 * readahead size. Ramp it up and use it as the new readahead size.
398 */
399 if (hit_readahead_marker) {
400 pgoff_t start;
401
30002ed2 402 rcu_read_lock();
e7b563bb 403 start = page_cache_next_hole(mapping, offset + 1, max);
30002ed2 404 rcu_read_unlock();
6b10c6c9
FW
405
406 if (!start || start - offset > max)
407 return 0;
408
409 ra->start = start;
410 ra->size = start - offset; /* old async_size */
160334a0 411 ra->size += req_size;
6b10c6c9
FW
412 ra->size = get_next_ra_size(ra, max);
413 ra->async_size = ra->size;
414 goto readit;
415 }
416
122a21d1 417 /*
045a2529 418 * oversize read
122a21d1 419 */
045a2529
WF
420 if (req_size > max)
421 goto initial_readahead;
422
423 /*
424 * sequential cache miss
af248a0c
DR
425 * trivial case: (offset - prev_offset) == 1
426 * unaligned reads: (offset - prev_offset) == 0
045a2529 427 */
09cbfeaf 428 prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
af248a0c 429 if (offset - prev_offset <= 1UL)
045a2529
WF
430 goto initial_readahead;
431
10be0b37
WF
432 /*
433 * Query the page cache and look for the traces(cached history pages)
434 * that a sequential stream would leave behind.
435 */
436 if (try_context_readahead(mapping, ra, offset, req_size, max))
437 goto readit;
438
045a2529
WF
439 /*
440 * standalone, small random read
441 * Read as is, and do not pollute the readahead state.
442 */
443 return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
444
445initial_readahead:
f9acc8c7
FW
446 ra->start = offset;
447 ra->size = get_init_ra_size(req_size, max);
448 ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
122a21d1 449
f9acc8c7 450readit:
51daa88e
WF
451 /*
452 * Will this read hit the readahead marker made by itself?
453 * If so, trigger the readahead marker hit now, and merge
454 * the resulted next readahead window into the current one.
455 */
456 if (offset == ra->start && ra->size == ra->async_size) {
457 ra->async_size = get_next_ra_size(ra, max);
458 ra->size += ra->async_size;
459 }
460
122a21d1
FW
461 return ra_submit(ra, mapping, filp);
462}
463
464/**
cf914a7d 465 * page_cache_sync_readahead - generic file readahead
122a21d1
FW
466 * @mapping: address_space which holds the pagecache and I/O vectors
467 * @ra: file_ra_state which holds the readahead state
468 * @filp: passed on to ->readpage() and ->readpages()
cf914a7d 469 * @offset: start offset into @mapping, in pagecache page-sized units
122a21d1 470 * @req_size: hint: total size of the read which the caller is performing in
cf914a7d 471 * pagecache pages
122a21d1 472 *
cf914a7d
RR
473 * page_cache_sync_readahead() should be called when a cache miss happened:
474 * it will submit the read. The readahead logic may decide to piggyback more
475 * pages onto the read request if access patterns suggest it will improve
476 * performance.
122a21d1 477 */
cf914a7d
RR
478void page_cache_sync_readahead(struct address_space *mapping,
479 struct file_ra_state *ra, struct file *filp,
480 pgoff_t offset, unsigned long req_size)
122a21d1
FW
481{
482 /* no read-ahead */
483 if (!ra->ra_pages)
cf914a7d
RR
484 return;
485
0141450f 486 /* be dumb */
70655c06 487 if (filp && (filp->f_mode & FMODE_RANDOM)) {
0141450f
WF
488 force_page_cache_readahead(mapping, filp, offset, req_size);
489 return;
490 }
491
cf914a7d
RR
492 /* do read-ahead */
493 ondemand_readahead(mapping, ra, filp, false, offset, req_size);
494}
495EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
496
497/**
498 * page_cache_async_readahead - file readahead for marked pages
499 * @mapping: address_space which holds the pagecache and I/O vectors
500 * @ra: file_ra_state which holds the readahead state
501 * @filp: passed on to ->readpage() and ->readpages()
502 * @page: the page at @offset which has the PG_readahead flag set
503 * @offset: start offset into @mapping, in pagecache page-sized units
504 * @req_size: hint: total size of the read which the caller is performing in
505 * pagecache pages
506 *
bf8abe8b 507 * page_cache_async_readahead() should be called when a page is used which
f7850d93 508 * has the PG_readahead flag; this is a marker to suggest that the application
cf914a7d 509 * has used up enough of the readahead window that we should start pulling in
f7850d93
RD
510 * more pages.
511 */
cf914a7d
RR
512void
513page_cache_async_readahead(struct address_space *mapping,
514 struct file_ra_state *ra, struct file *filp,
515 struct page *page, pgoff_t offset,
516 unsigned long req_size)
517{
518 /* no read-ahead */
519 if (!ra->ra_pages)
520 return;
521
522 /*
523 * Same bit is used for PG_readahead and PG_reclaim.
524 */
525 if (PageWriteback(page))
526 return;
527
528 ClearPageReadahead(page);
529
530 /*
531 * Defer asynchronous read-ahead on IO congestion.
532 */
703c2708 533 if (inode_read_congested(mapping->host))
cf914a7d 534 return;
122a21d1
FW
535
536 /* do read-ahead */
cf914a7d 537 ondemand_readahead(mapping, ra, filp, true, offset, req_size);
122a21d1 538}
cf914a7d 539EXPORT_SYMBOL_GPL(page_cache_async_readahead);
782182e5
CW
540
541static ssize_t
542do_readahead(struct address_space *mapping, struct file *filp,
543 pgoff_t index, unsigned long nr)
544{
63d0f0a3 545 if (!mapping || !mapping->a_ops)
782182e5
CW
546 return -EINVAL;
547
58d5640e 548 return force_page_cache_readahead(mapping, filp, index, nr);
782182e5
CW
549}
550
4a0fd5bf 551SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
782182e5
CW
552{
553 ssize_t ret;
2903ff01 554 struct fd f;
782182e5
CW
555
556 ret = -EBADF;
2903ff01
AV
557 f = fdget(fd);
558 if (f.file) {
559 if (f.file->f_mode & FMODE_READ) {
560 struct address_space *mapping = f.file->f_mapping;
09cbfeaf
KS
561 pgoff_t start = offset >> PAGE_SHIFT;
562 pgoff_t end = (offset + count - 1) >> PAGE_SHIFT;
782182e5 563 unsigned long len = end - start + 1;
2903ff01 564 ret = do_readahead(mapping, f.file, start, len);
782182e5 565 }
2903ff01 566 fdput(f);
782182e5
CW
567 }
568 return ret;
569}