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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>
11#include <linux/fs.h>
5a0e3ad6 12#include <linux/gfp.h>
1da177e4
LT
13#include <linux/mm.h>
14#include <linux/module.h>
15#include <linux/blkdev.h>
16#include <linux/backing-dev.h>
8bde37f0 17#include <linux/task_io_accounting_ops.h>
1da177e4 18#include <linux/pagevec.h>
f5ff8422 19#include <linux/pagemap.h>
1da177e4 20
1da177e4
LT
21/*
22 * Initialise a struct file's readahead state. Assumes that the caller has
23 * memset *ra to zero.
24 */
25void
26file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
27{
28 ra->ra_pages = mapping->backing_dev_info->ra_pages;
f4e6b498 29 ra->prev_pos = -1;
1da177e4 30}
d41cc702 31EXPORT_SYMBOL_GPL(file_ra_state_init);
1da177e4 32
1da177e4
LT
33#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
34
03fb3d2a
DH
35/*
36 * see if a page needs releasing upon read_cache_pages() failure
266cf658
DH
37 * - the caller of read_cache_pages() may have set PG_private or PG_fscache
38 * before calling, such as the NFS fs marking pages that are cached locally
39 * on disk, thus we need to give the fs a chance to clean up in the event of
40 * an error
03fb3d2a
DH
41 */
42static void read_cache_pages_invalidate_page(struct address_space *mapping,
43 struct page *page)
44{
266cf658 45 if (page_has_private(page)) {
03fb3d2a
DH
46 if (!trylock_page(page))
47 BUG();
48 page->mapping = mapping;
49 do_invalidatepage(page, 0);
50 page->mapping = NULL;
51 unlock_page(page);
52 }
53 page_cache_release(page);
54}
55
56/*
57 * release a list of pages, invalidating them first if need be
58 */
59static void read_cache_pages_invalidate_pages(struct address_space *mapping,
60 struct list_head *pages)
61{
62 struct page *victim;
63
64 while (!list_empty(pages)) {
65 victim = list_to_page(pages);
66 list_del(&victim->lru);
67 read_cache_pages_invalidate_page(mapping, victim);
68 }
69}
70
1da177e4 71/**
bd40cdda 72 * read_cache_pages - populate an address space with some pages & start reads against them
1da177e4
LT
73 * @mapping: the address_space
74 * @pages: The address of a list_head which contains the target pages. These
75 * pages have their ->index populated and are otherwise uninitialised.
76 * @filler: callback routine for filling a single page.
77 * @data: private data for the callback routine.
78 *
79 * Hides the details of the LRU cache etc from the filesystems.
80 */
81int read_cache_pages(struct address_space *mapping, struct list_head *pages,
82 int (*filler)(void *, struct page *), void *data)
83{
84 struct page *page;
1da177e4
LT
85 int ret = 0;
86
1da177e4
LT
87 while (!list_empty(pages)) {
88 page = list_to_page(pages);
89 list_del(&page->lru);
eb2be189
NP
90 if (add_to_page_cache_lru(page, mapping,
91 page->index, GFP_KERNEL)) {
03fb3d2a 92 read_cache_pages_invalidate_page(mapping, page);
1da177e4
LT
93 continue;
94 }
eb2be189
NP
95 page_cache_release(page);
96
1da177e4 97 ret = filler(data, page);
eb2be189 98 if (unlikely(ret)) {
03fb3d2a 99 read_cache_pages_invalidate_pages(mapping, pages);
1da177e4
LT
100 break;
101 }
8bde37f0 102 task_io_account_read(PAGE_CACHE_SIZE);
1da177e4 103 }
1da177e4
LT
104 return ret;
105}
106
107EXPORT_SYMBOL(read_cache_pages);
108
109static int read_pages(struct address_space *mapping, struct file *filp,
110 struct list_head *pages, unsigned nr_pages)
111{
112 unsigned page_idx;
994fc28c 113 int ret;
1da177e4
LT
114
115 if (mapping->a_ops->readpages) {
116 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
029e332e
OH
117 /* Clean up the remaining pages */
118 put_pages_list(pages);
1da177e4
LT
119 goto out;
120 }
121
1da177e4
LT
122 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
123 struct page *page = list_to_page(pages);
124 list_del(&page->lru);
eb2be189 125 if (!add_to_page_cache_lru(page, mapping,
1da177e4 126 page->index, GFP_KERNEL)) {
9f1a3cfc 127 mapping->a_ops->readpage(filp, page);
eb2be189
NP
128 }
129 page_cache_release(page);
1da177e4 130 }
994fc28c 131 ret = 0;
1da177e4
LT
132out:
133 return ret;
134}
135
1da177e4 136/*
d30a1100 137 * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
1da177e4
LT
138 * the pages first, then submits them all for I/O. This avoids the very bad
139 * behaviour which would occur if page allocations are causing VM writeback.
140 * We really don't want to intermingle reads and writes like that.
141 *
142 * Returns the number of pages requested, or the maximum amount of I/O allowed.
1da177e4
LT
143 */
144static int
145__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
46fc3e7b
FW
146 pgoff_t offset, unsigned long nr_to_read,
147 unsigned long lookahead_size)
1da177e4
LT
148{
149 struct inode *inode = mapping->host;
150 struct page *page;
151 unsigned long end_index; /* The last page we want to read */
152 LIST_HEAD(page_pool);
153 int page_idx;
154 int ret = 0;
155 loff_t isize = i_size_read(inode);
156
157 if (isize == 0)
158 goto out;
159
46fc3e7b 160 end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
1da177e4
LT
161
162 /*
163 * Preallocate as many pages as we will need.
164 */
1da177e4 165 for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
7361f4d8 166 pgoff_t page_offset = offset + page_idx;
c743d96b 167
1da177e4
LT
168 if (page_offset > end_index)
169 break;
170
00128188 171 rcu_read_lock();
1da177e4 172 page = radix_tree_lookup(&mapping->page_tree, page_offset);
00128188 173 rcu_read_unlock();
1da177e4
LT
174 if (page)
175 continue;
176
1da177e4 177 page = page_cache_alloc_cold(mapping);
1da177e4
LT
178 if (!page)
179 break;
180 page->index = page_offset;
181 list_add(&page->lru, &page_pool);
46fc3e7b
FW
182 if (page_idx == nr_to_read - lookahead_size)
183 SetPageReadahead(page);
1da177e4
LT
184 ret++;
185 }
1da177e4
LT
186
187 /*
188 * Now start the IO. We ignore I/O errors - if the page is not
189 * uptodate then the caller will launch readpage again, and
190 * will then handle the error.
191 */
192 if (ret)
193 read_pages(mapping, filp, &page_pool, ret);
194 BUG_ON(!list_empty(&page_pool));
195out:
196 return ret;
197}
198
199/*
200 * Chunk the readahead into 2 megabyte units, so that we don't pin too much
201 * memory at once.
202 */
203int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
7361f4d8 204 pgoff_t offset, unsigned long nr_to_read)
1da177e4
LT
205{
206 int ret = 0;
207
208 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
209 return -EINVAL;
210
f7e839dd 211 nr_to_read = max_sane_readahead(nr_to_read);
1da177e4
LT
212 while (nr_to_read) {
213 int err;
214
215 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
216
217 if (this_chunk > nr_to_read)
218 this_chunk = nr_to_read;
219 err = __do_page_cache_readahead(mapping, filp,
46fc3e7b 220 offset, this_chunk, 0);
1da177e4
LT
221 if (err < 0) {
222 ret = err;
223 break;
224 }
225 ret += err;
226 offset += this_chunk;
227 nr_to_read -= this_chunk;
228 }
229 return ret;
230}
231
1da177e4
LT
232/*
233 * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
234 * sensible upper limit.
235 */
236unsigned long max_sane_readahead(unsigned long nr)
237{
4f98a2fe 238 return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
05a0416b 239 + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
1da177e4 240}
5ce1110b
FW
241
242/*
243 * Submit IO for the read-ahead request in file_ra_state.
244 */
d30a1100 245unsigned long ra_submit(struct file_ra_state *ra,
5ce1110b
FW
246 struct address_space *mapping, struct file *filp)
247{
5ce1110b
FW
248 int actual;
249
5ce1110b 250 actual = __do_page_cache_readahead(mapping, filp,
f9acc8c7 251 ra->start, ra->size, ra->async_size);
5ce1110b
FW
252
253 return actual;
254}
122a21d1 255
c743d96b
FW
256/*
257 * Set the initial window size, round to next power of 2 and square
258 * for small size, x 4 for medium, and x 2 for large
259 * for 128k (32 page) max ra
260 * 1-8 page = 32k initial, > 8 page = 128k initial
261 */
262static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
263{
264 unsigned long newsize = roundup_pow_of_two(size);
265
266 if (newsize <= max / 32)
267 newsize = newsize * 4;
268 else if (newsize <= max / 4)
269 newsize = newsize * 2;
270 else
271 newsize = max;
272
273 return newsize;
274}
275
122a21d1
FW
276/*
277 * Get the previous window size, ramp it up, and
278 * return it as the new window size.
279 */
c743d96b 280static unsigned long get_next_ra_size(struct file_ra_state *ra,
122a21d1
FW
281 unsigned long max)
282{
f9acc8c7 283 unsigned long cur = ra->size;
122a21d1
FW
284 unsigned long newsize;
285
286 if (cur < max / 16)
c743d96b 287 newsize = 4 * cur;
122a21d1 288 else
c743d96b 289 newsize = 2 * cur;
122a21d1
FW
290
291 return min(newsize, max);
292}
293
294/*
295 * On-demand readahead design.
296 *
297 * The fields in struct file_ra_state represent the most-recently-executed
298 * readahead attempt:
299 *
f9acc8c7
FW
300 * |<----- async_size ---------|
301 * |------------------- size -------------------->|
302 * |==================#===========================|
303 * ^start ^page marked with PG_readahead
122a21d1
FW
304 *
305 * To overlap application thinking time and disk I/O time, we do
306 * `readahead pipelining': Do not wait until the application consumed all
307 * readahead pages and stalled on the missing page at readahead_index;
f9acc8c7
FW
308 * Instead, submit an asynchronous readahead I/O as soon as there are
309 * only async_size pages left in the readahead window. Normally async_size
310 * will be equal to size, for maximum pipelining.
122a21d1
FW
311 *
312 * In interleaved sequential reads, concurrent streams on the same fd can
313 * be invalidating each other's readahead state. So we flag the new readahead
f9acc8c7 314 * page at (start+size-async_size) with PG_readahead, and use it as readahead
122a21d1
FW
315 * indicator. The flag won't be set on already cached pages, to avoid the
316 * readahead-for-nothing fuss, saving pointless page cache lookups.
317 *
f4e6b498 318 * prev_pos tracks the last visited byte in the _previous_ read request.
122a21d1
FW
319 * It should be maintained by the caller, and will be used for detecting
320 * small random reads. Note that the readahead algorithm checks loosely
321 * for sequential patterns. Hence interleaved reads might be served as
322 * sequential ones.
323 *
324 * There is a special-case: if the first page which the application tries to
325 * read happens to be the first page of the file, it is assumed that a linear
326 * read is about to happen and the window is immediately set to the initial size
327 * based on I/O request size and the max_readahead.
328 *
329 * The code ramps up the readahead size aggressively at first, but slow down as
330 * it approaches max_readhead.
331 */
332
10be0b37
WF
333/*
334 * Count contiguously cached pages from @offset-1 to @offset-@max,
335 * this count is a conservative estimation of
336 * - length of the sequential read sequence, or
337 * - thrashing threshold in memory tight systems
338 */
339static pgoff_t count_history_pages(struct address_space *mapping,
340 struct file_ra_state *ra,
341 pgoff_t offset, unsigned long max)
342{
343 pgoff_t head;
344
345 rcu_read_lock();
346 head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max);
347 rcu_read_unlock();
348
349 return offset - 1 - head;
350}
351
352/*
353 * page cache context based read-ahead
354 */
355static int try_context_readahead(struct address_space *mapping,
356 struct file_ra_state *ra,
357 pgoff_t offset,
358 unsigned long req_size,
359 unsigned long max)
360{
361 pgoff_t size;
362
363 size = count_history_pages(mapping, ra, offset, max);
364
365 /*
366 * no history pages:
367 * it could be a random read
368 */
369 if (!size)
370 return 0;
371
372 /*
373 * starts from beginning of file:
374 * it is a strong indication of long-run stream (or whole-file-read)
375 */
376 if (size >= offset)
377 size *= 2;
378
379 ra->start = offset;
380 ra->size = get_init_ra_size(size + req_size, max);
381 ra->async_size = ra->size;
382
383 return 1;
384}
385
122a21d1
FW
386/*
387 * A minimal readahead algorithm for trivial sequential/random reads.
388 */
389static unsigned long
390ondemand_readahead(struct address_space *mapping,
391 struct file_ra_state *ra, struct file *filp,
cf914a7d 392 bool hit_readahead_marker, pgoff_t offset,
122a21d1
FW
393 unsigned long req_size)
394{
fc31d16a 395 unsigned long max = max_sane_readahead(ra->ra_pages);
045a2529
WF
396
397 /*
398 * start of file
399 */
400 if (!offset)
401 goto initial_readahead;
122a21d1
FW
402
403 /*
f9acc8c7 404 * It's the expected callback offset, assume sequential access.
122a21d1
FW
405 * Ramp up sizes, and push forward the readahead window.
406 */
045a2529
WF
407 if ((offset == (ra->start + ra->size - ra->async_size) ||
408 offset == (ra->start + ra->size))) {
f9acc8c7
FW
409 ra->start += ra->size;
410 ra->size = get_next_ra_size(ra, max);
411 ra->async_size = ra->size;
412 goto readit;
122a21d1
FW
413 }
414
6b10c6c9
FW
415 /*
416 * Hit a marked page without valid readahead state.
417 * E.g. interleaved reads.
418 * Query the pagecache for async_size, which normally equals to
419 * readahead size. Ramp it up and use it as the new readahead size.
420 */
421 if (hit_readahead_marker) {
422 pgoff_t start;
423
30002ed2 424 rcu_read_lock();
caca7cb7 425 start = radix_tree_next_hole(&mapping->page_tree, offset+1,max);
30002ed2 426 rcu_read_unlock();
6b10c6c9
FW
427
428 if (!start || start - offset > max)
429 return 0;
430
431 ra->start = start;
432 ra->size = start - offset; /* old async_size */
160334a0 433 ra->size += req_size;
6b10c6c9
FW
434 ra->size = get_next_ra_size(ra, max);
435 ra->async_size = ra->size;
436 goto readit;
437 }
438
122a21d1 439 /*
045a2529 440 * oversize read
122a21d1 441 */
045a2529
WF
442 if (req_size > max)
443 goto initial_readahead;
444
445 /*
446 * sequential cache miss
447 */
448 if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
449 goto initial_readahead;
450
10be0b37
WF
451 /*
452 * Query the page cache and look for the traces(cached history pages)
453 * that a sequential stream would leave behind.
454 */
455 if (try_context_readahead(mapping, ra, offset, req_size, max))
456 goto readit;
457
045a2529
WF
458 /*
459 * standalone, small random read
460 * Read as is, and do not pollute the readahead state.
461 */
462 return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
463
464initial_readahead:
f9acc8c7
FW
465 ra->start = offset;
466 ra->size = get_init_ra_size(req_size, max);
467 ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
122a21d1 468
f9acc8c7 469readit:
51daa88e
WF
470 /*
471 * Will this read hit the readahead marker made by itself?
472 * If so, trigger the readahead marker hit now, and merge
473 * the resulted next readahead window into the current one.
474 */
475 if (offset == ra->start && ra->size == ra->async_size) {
476 ra->async_size = get_next_ra_size(ra, max);
477 ra->size += ra->async_size;
478 }
479
122a21d1
FW
480 return ra_submit(ra, mapping, filp);
481}
482
483/**
cf914a7d 484 * page_cache_sync_readahead - generic file readahead
122a21d1
FW
485 * @mapping: address_space which holds the pagecache and I/O vectors
486 * @ra: file_ra_state which holds the readahead state
487 * @filp: passed on to ->readpage() and ->readpages()
cf914a7d 488 * @offset: start offset into @mapping, in pagecache page-sized units
122a21d1 489 * @req_size: hint: total size of the read which the caller is performing in
cf914a7d 490 * pagecache pages
122a21d1 491 *
cf914a7d
RR
492 * page_cache_sync_readahead() should be called when a cache miss happened:
493 * it will submit the read. The readahead logic may decide to piggyback more
494 * pages onto the read request if access patterns suggest it will improve
495 * performance.
122a21d1 496 */
cf914a7d
RR
497void page_cache_sync_readahead(struct address_space *mapping,
498 struct file_ra_state *ra, struct file *filp,
499 pgoff_t offset, unsigned long req_size)
122a21d1
FW
500{
501 /* no read-ahead */
502 if (!ra->ra_pages)
cf914a7d
RR
503 return;
504
0141450f 505 /* be dumb */
70655c06 506 if (filp && (filp->f_mode & FMODE_RANDOM)) {
0141450f
WF
507 force_page_cache_readahead(mapping, filp, offset, req_size);
508 return;
509 }
510
cf914a7d
RR
511 /* do read-ahead */
512 ondemand_readahead(mapping, ra, filp, false, offset, req_size);
513}
514EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
515
516/**
517 * page_cache_async_readahead - file readahead for marked pages
518 * @mapping: address_space which holds the pagecache and I/O vectors
519 * @ra: file_ra_state which holds the readahead state
520 * @filp: passed on to ->readpage() and ->readpages()
521 * @page: the page at @offset which has the PG_readahead flag set
522 * @offset: start offset into @mapping, in pagecache page-sized units
523 * @req_size: hint: total size of the read which the caller is performing in
524 * pagecache pages
525 *
bf8abe8b 526 * page_cache_async_readahead() should be called when a page is used which
f7850d93 527 * has the PG_readahead flag; this is a marker to suggest that the application
cf914a7d 528 * has used up enough of the readahead window that we should start pulling in
f7850d93
RD
529 * more pages.
530 */
cf914a7d
RR
531void
532page_cache_async_readahead(struct address_space *mapping,
533 struct file_ra_state *ra, struct file *filp,
534 struct page *page, pgoff_t offset,
535 unsigned long req_size)
536{
537 /* no read-ahead */
538 if (!ra->ra_pages)
539 return;
540
541 /*
542 * Same bit is used for PG_readahead and PG_reclaim.
543 */
544 if (PageWriteback(page))
545 return;
546
547 ClearPageReadahead(page);
548
549 /*
550 * Defer asynchronous read-ahead on IO congestion.
551 */
552 if (bdi_read_congested(mapping->backing_dev_info))
553 return;
122a21d1
FW
554
555 /* do read-ahead */
cf914a7d 556 ondemand_readahead(mapping, ra, filp, true, offset, req_size);
122a21d1 557}
cf914a7d 558EXPORT_SYMBOL_GPL(page_cache_async_readahead);