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1 : : // SPDX-License-Identifier: GPL-2.0-only
2 : : /*
3 : : * mm/readahead.c - address_space-level file readahead.
4 : : *
5 : : * Copyright (C) 2002, Linus Torvalds
6 : : *
7 : : * 09Apr2002 Andrew Morton
8 : : * Initial version.
9 : : */
10 : :
11 : : #include <linux/kernel.h>
12 : : #include <linux/dax.h>
13 : : #include <linux/gfp.h>
14 : : #include <linux/export.h>
15 : : #include <linux/blkdev.h>
16 : : #include <linux/backing-dev.h>
17 : : #include <linux/task_io_accounting_ops.h>
18 : : #include <linux/pagevec.h>
19 : : #include <linux/pagemap.h>
20 : : #include <linux/syscalls.h>
21 : : #include <linux/file.h>
22 : : #include <linux/mm_inline.h>
23 : : #include <linux/blk-cgroup.h>
24 : : #include <linux/fadvise.h>
25 : :
26 : : #include "internal.h"
27 : :
28 : : /*
29 : : * Initialise a struct file's readahead state. Assumes that the caller has
30 : : * memset *ra to zero.
31 : : */
32 : : void
33 : 5085910 : file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
34 : : {
35 : 5085910 : ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
36 : 5072561 : ra->prev_pos = -1;
37 : 5072561 : }
38 : : EXPORT_SYMBOL_GPL(file_ra_state_init);
39 : :
40 : : /*
41 : : * see if a page needs releasing upon read_cache_pages() failure
42 : : * - the caller of read_cache_pages() may have set PG_private or PG_fscache
43 : : * before calling, such as the NFS fs marking pages that are cached locally
44 : : * on disk, thus we need to give the fs a chance to clean up in the event of
45 : : * an error
46 : : */
47 : 0 : static void read_cache_pages_invalidate_page(struct address_space *mapping,
48 : : struct page *page)
49 : : {
50 [ # # ]: 0 : if (page_has_private(page)) {
51 [ # # ]: 0 : if (!trylock_page(page))
52 : 0 : BUG();
53 : 0 : page->mapping = mapping;
54 : 0 : do_invalidatepage(page, 0, PAGE_SIZE);
55 : 0 : page->mapping = NULL;
56 : 0 : unlock_page(page);
57 : : }
58 : 0 : put_page(page);
59 : 0 : }
60 : :
61 : : /*
62 : : * release a list of pages, invalidating them first if need be
63 : : */
64 : 0 : static void read_cache_pages_invalidate_pages(struct address_space *mapping,
65 : : struct list_head *pages)
66 : : {
67 : : struct page *victim;
68 : :
69 [ # # ]: 0 : while (!list_empty(pages)) {
70 : 0 : victim = lru_to_page(pages);
71 : : list_del(&victim->lru);
72 : 0 : read_cache_pages_invalidate_page(mapping, victim);
73 : : }
74 : 0 : }
75 : :
76 : : /**
77 : : * read_cache_pages - populate an address space with some pages & start reads against them
78 : : * @mapping: the address_space
79 : : * @pages: The address of a list_head which contains the target pages. These
80 : : * pages have their ->index populated and are otherwise uninitialised.
81 : : * @filler: callback routine for filling a single page.
82 : : * @data: private data for the callback routine.
83 : : *
84 : : * Hides the details of the LRU cache etc from the filesystems.
85 : : *
86 : : * Returns: %0 on success, error return by @filler otherwise
87 : : */
88 : 0 : int read_cache_pages(struct address_space *mapping, struct list_head *pages,
89 : : int (*filler)(void *, struct page *), void *data)
90 : : {
91 : : struct page *page;
92 : : int ret = 0;
93 : :
94 [ # # ]: 0 : while (!list_empty(pages)) {
95 : 0 : page = lru_to_page(pages);
96 : : list_del(&page->lru);
97 [ # # ]: 0 : if (add_to_page_cache_lru(page, mapping, page->index,
98 : : readahead_gfp_mask(mapping))) {
99 : 0 : read_cache_pages_invalidate_page(mapping, page);
100 : 0 : continue;
101 : : }
102 : 0 : put_page(page);
103 : :
104 : 0 : ret = filler(data, page);
105 [ # # ]: 0 : if (unlikely(ret)) {
106 : 0 : read_cache_pages_invalidate_pages(mapping, pages);
107 : 0 : break;
108 : : }
109 : : task_io_account_read(PAGE_SIZE);
110 : : }
111 : 0 : return ret;
112 : : }
113 : :
114 : : EXPORT_SYMBOL(read_cache_pages);
115 : :
116 : 758775 : static int read_pages(struct address_space *mapping, struct file *filp,
117 : : struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
118 : : {
119 : : struct blk_plug plug;
120 : : unsigned page_idx;
121 : : int ret;
122 : :
123 : 758775 : blk_start_plug(&plug);
124 : :
125 [ - + ]: 758758 : if (mapping->a_ops->readpages) {
126 : 758758 : ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
127 : : /* Clean up the remaining pages */
128 : 758386 : put_pages_list(pages);
129 : 756473 : goto out;
130 : : }
131 : :
132 [ # # ]: 0 : for (page_idx = 0; page_idx < nr_pages; page_idx++) {
133 : 0 : struct page *page = lru_to_page(pages);
134 : : list_del(&page->lru);
135 [ # # ]: 0 : if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
136 : 0 : mapping->a_ops->readpage(filp, page);
137 : 0 : put_page(page);
138 : : }
139 : : ret = 0;
140 : :
141 : : out:
142 : 756473 : blk_finish_plug(&plug);
143 : :
144 : 759296 : return ret;
145 : : }
146 : :
147 : : /*
148 : : * __do_page_cache_readahead() actually reads a chunk of disk. It allocates
149 : : * the pages first, then submits them for I/O. This avoids the very bad
150 : : * behaviour which would occur if page allocations are causing VM writeback.
151 : : * We really don't want to intermingle reads and writes like that.
152 : : *
153 : : * Returns the number of pages requested, or the maximum amount of I/O allowed.
154 : : */
155 : 882645 : unsigned int __do_page_cache_readahead(struct address_space *mapping,
156 : : struct file *filp, pgoff_t offset, unsigned long nr_to_read,
157 : : unsigned long lookahead_size)
158 : : {
159 : 882645 : struct inode *inode = mapping->host;
160 : : struct page *page;
161 : : unsigned long end_index; /* The last page we want to read */
162 : 882645 : LIST_HEAD(page_pool);
163 : : int page_idx;
164 : : unsigned int nr_pages = 0;
165 : : loff_t isize = i_size_read(inode);
166 : : gfp_t gfp_mask = readahead_gfp_mask(mapping);
167 : :
168 [ + + ]: 882268 : if (isize == 0)
169 : : goto out;
170 : :
171 : 882275 : end_index = ((isize - 1) >> PAGE_SHIFT);
172 : :
173 : : /*
174 : : * Preallocate as many pages as we will need.
175 : : */
176 [ + + ]: 10161350 : for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
177 : 9683262 : pgoff_t page_offset = offset + page_idx;
178 : :
179 [ + + ]: 9683262 : if (page_offset > end_index)
180 : : break;
181 : :
182 : 9278560 : page = xa_load(&mapping->i_pages, page_offset);
183 [ + + + + ]: 11581907 : if (page && !xa_is_value(page)) {
184 : : /*
185 : : * Page already present? Kick off the current batch of
186 : : * contiguous pages before continuing with the next
187 : : * batch.
188 : : */
189 [ + + ]: 2301485 : if (nr_pages)
190 : 113617 : read_pages(mapping, filp, &page_pool, nr_pages,
191 : : gfp_mask);
192 : : nr_pages = 0;
193 : 2300933 : continue;
194 : : }
195 : :
196 : : page = __page_cache_alloc(gfp_mask);
197 [ + + ]: 6978522 : if (!page)
198 : : break;
199 : 6978097 : page->index = page_offset;
200 : 6978097 : list_add(&page->lru, &page_pool);
201 [ + + ]: 6978097 : if (page_idx == nr_to_read - lookahead_size)
202 : : SetPageReadahead(page);
203 : 6978142 : nr_pages++;
204 : : }
205 : :
206 : : /*
207 : : * Now start the IO. We ignore I/O errors - if the page is not
208 : : * uptodate then the caller will launch readpage again, and
209 : : * will then handle the error.
210 : : */
211 [ + + ]: 883215 : if (nr_pages)
212 : 645410 : read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
213 [ - + ]: 882681 : BUG_ON(!list_empty(&page_pool));
214 : : out:
215 : 882674 : return nr_pages;
216 : : }
217 : :
218 : : /*
219 : : * Chunk the readahead into 2 megabyte units, so that we don't pin too much
220 : : * memory at once.
221 : : */
222 : 141974 : int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
223 : : pgoff_t offset, unsigned long nr_to_read)
224 : : {
225 : 141974 : struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
226 : : struct file_ra_state *ra = &filp->f_ra;
227 : : unsigned long max_pages;
228 : :
229 [ - + # # ]: 141971 : if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
230 : : return -EINVAL;
231 : :
232 : : /*
233 : : * If the request exceeds the readahead window, allow the read to
234 : : * be up to the optimal hardware IO size
235 : : */
236 : 141977 : max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
237 : 141977 : nr_to_read = min(nr_to_read, max_pages);
238 [ + + ]: 425932 : while (nr_to_read) {
239 : : unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
240 : :
241 [ + - ]: 141970 : if (this_chunk > nr_to_read)
242 : : this_chunk = nr_to_read;
243 : 141970 : __do_page_cache_readahead(mapping, filp, offset, this_chunk, 0);
244 : :
245 : 141978 : offset += this_chunk;
246 : 141978 : nr_to_read -= this_chunk;
247 : : }
248 : : return 0;
249 : : }
250 : :
251 : : /*
252 : : * Set the initial window size, round to next power of 2 and square
253 : : * for small size, x 4 for medium, and x 2 for large
254 : : * for 128k (32 page) max ra
255 : : * 1-8 page = 32k initial, > 8 page = 128k initial
256 : : */
257 : 290543 : static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
258 : : {
259 [ + + - + : 290543 : unsigned long newsize = roundup_pow_of_two(size);
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# # # # #
# ]
260 : :
261 [ + + ]: 290543 : if (newsize <= max / 32)
262 : 264276 : newsize = newsize * 4;
263 [ + + ]: 26267 : else if (newsize <= max / 4)
264 : 20496 : newsize = newsize * 2;
265 : : else
266 : : newsize = max;
267 : :
268 : 290543 : return newsize;
269 : : }
270 : :
271 : : /*
272 : : * Get the previous window size, ramp it up, and
273 : : * return it as the new window size.
274 : : */
275 : : static unsigned long get_next_ra_size(struct file_ra_state *ra,
276 : : unsigned long max)
277 : : {
278 : : unsigned long cur = ra->size;
279 : :
280 [ + + - + : 222683 : if (cur < max / 16)
- + ]
281 : 816 : return 4 * cur;
282 [ + + + + : 221867 : if (cur <= max / 2)
+ + ]
283 : 77063 : return 2 * cur;
284 : : return max;
285 : : }
286 : :
287 : : /*
288 : : * On-demand readahead design.
289 : : *
290 : : * The fields in struct file_ra_state represent the most-recently-executed
291 : : * readahead attempt:
292 : : *
293 : : * |<----- async_size ---------|
294 : : * |------------------- size -------------------->|
295 : : * |==================#===========================|
296 : : * ^start ^page marked with PG_readahead
297 : : *
298 : : * To overlap application thinking time and disk I/O time, we do
299 : : * `readahead pipelining': Do not wait until the application consumed all
300 : : * readahead pages and stalled on the missing page at readahead_index;
301 : : * Instead, submit an asynchronous readahead I/O as soon as there are
302 : : * only async_size pages left in the readahead window. Normally async_size
303 : : * will be equal to size, for maximum pipelining.
304 : : *
305 : : * In interleaved sequential reads, concurrent streams on the same fd can
306 : : * be invalidating each other's readahead state. So we flag the new readahead
307 : : * page at (start+size-async_size) with PG_readahead, and use it as readahead
308 : : * indicator. The flag won't be set on already cached pages, to avoid the
309 : : * readahead-for-nothing fuss, saving pointless page cache lookups.
310 : : *
311 : : * prev_pos tracks the last visited byte in the _previous_ read request.
312 : : * It should be maintained by the caller, and will be used for detecting
313 : : * small random reads. Note that the readahead algorithm checks loosely
314 : : * for sequential patterns. Hence interleaved reads might be served as
315 : : * sequential ones.
316 : : *
317 : : * There is a special-case: if the first page which the application tries to
318 : : * read happens to be the first page of the file, it is assumed that a linear
319 : : * read is about to happen and the window is immediately set to the initial size
320 : : * based on I/O request size and the max_readahead.
321 : : *
322 : : * The code ramps up the readahead size aggressively at first, but slow down as
323 : : * it approaches max_readhead.
324 : : */
325 : :
326 : : /*
327 : : * Count contiguously cached pages from @offset-1 to @offset-@max,
328 : : * this count is a conservative estimation of
329 : : * - length of the sequential read sequence, or
330 : : * - thrashing threshold in memory tight systems
331 : : */
332 : 48045 : static pgoff_t count_history_pages(struct address_space *mapping,
333 : : pgoff_t offset, unsigned long max)
334 : : {
335 : : pgoff_t head;
336 : :
337 : : rcu_read_lock();
338 : 48197 : head = page_cache_prev_miss(mapping, offset - 1, max);
339 : : rcu_read_unlock();
340 : :
341 : 48108 : return offset - 1 - head;
342 : : }
343 : :
344 : : /*
345 : : * page cache context based read-ahead
346 : : */
347 : 48104 : static int try_context_readahead(struct address_space *mapping,
348 : : struct file_ra_state *ra,
349 : : pgoff_t offset,
350 : : unsigned long req_size,
351 : : unsigned long max)
352 : : {
353 : : pgoff_t size;
354 : :
355 : 48104 : size = count_history_pages(mapping, offset, max);
356 : :
357 : : /*
358 : : * not enough history pages:
359 : : * it could be a random read
360 : : */
361 [ + + ]: 48109 : if (size <= req_size)
362 : : return 0;
363 : :
364 : : /*
365 : : * starts from beginning of file:
366 : : * it is a strong indication of long-run stream (or whole-file-read)
367 : : */
368 [ + + ]: 21 : if (size >= offset)
369 : 20 : size *= 2;
370 : :
371 : 21 : ra->start = offset;
372 : 21 : ra->size = min(size + req_size, max);
373 : 21 : ra->async_size = 1;
374 : :
375 : 21 : return 1;
376 : : }
377 : :
378 : : /*
379 : : * A minimal readahead algorithm for trivial sequential/random reads.
380 : : */
381 : : static unsigned long
382 : 554839 : ondemand_readahead(struct address_space *mapping,
383 : : struct file_ra_state *ra, struct file *filp,
384 : : bool hit_readahead_marker, pgoff_t offset,
385 : : unsigned long req_size)
386 : : {
387 : 554839 : struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
388 : 554490 : unsigned long max_pages = ra->ra_pages;
389 : : unsigned long add_pages;
390 : : pgoff_t prev_offset;
391 : :
392 : : /*
393 : : * If the request exceeds the readahead window, allow the read to
394 : : * be up to the optimal hardware IO size
395 : : */
396 [ + + + + ]: 554490 : if (req_size > max_pages && bdi->io_pages > max_pages)
397 : 7237 : max_pages = min(req_size, bdi->io_pages);
398 : :
399 : : /*
400 : : * start of file
401 : : */
402 [ + + ]: 554490 : if (!offset)
403 : : goto initial_readahead;
404 : :
405 : : /*
406 : : * It's the expected callback offset, assume sequential access.
407 : : * Ramp up sizes, and push forward the readahead window.
408 : : */
409 [ + + + + ]: 264842 : if ((offset == (ra->start + ra->size - ra->async_size) ||
410 : : offset == (ra->start + ra->size))) {
411 : 97480 : ra->start += ra->size;
412 : 97480 : ra->size = get_next_ra_size(ra, max_pages);
413 : 97480 : ra->async_size = ra->size;
414 : 97480 : goto readit;
415 : : }
416 : :
417 : : /*
418 : : * Hit a marked page without valid readahead state.
419 : : * E.g. interleaved reads.
420 : : * Query the pagecache for async_size, which normally equals to
421 : : * readahead size. Ramp it up and use it as the new readahead size.
422 : : */
423 [ + + ]: 167362 : if (hit_readahead_marker) {
424 : : pgoff_t start;
425 : :
426 : : rcu_read_lock();
427 : 119233 : start = page_cache_next_miss(mapping, offset + 1, max_pages);
428 : : rcu_read_unlock();
429 : :
430 [ + + + - ]: 119356 : if (!start || start - offset > max_pages)
431 : : return 0;
432 : :
433 : 119368 : ra->start = start;
434 : 119368 : ra->size = start - offset; /* old async_size */
435 : 119368 : ra->size += req_size;
436 : 119368 : ra->size = get_next_ra_size(ra, max_pages);
437 : 119368 : ra->async_size = ra->size;
438 : 119368 : goto readit;
439 : : }
440 : :
441 : : /*
442 : : * oversize read
443 : : */
444 [ + + ]: 48302 : if (req_size > max_pages)
445 : : goto initial_readahead;
446 : :
447 : : /*
448 : : * sequential cache miss
449 : : * trivial case: (offset - prev_offset) == 1
450 : : * unaligned reads: (offset - prev_offset) == 0
451 : : */
452 : 48408 : prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
453 [ + + ]: 48408 : if (offset - prev_offset <= 1UL)
454 : : goto initial_readahead;
455 : :
456 : : /*
457 : : * Query the page cache and look for the traces(cached history pages)
458 : : * that a sequential stream would leave behind.
459 : : */
460 [ + + ]: 48171 : if (try_context_readahead(mapping, ra, offset, req_size, max_pages))
461 : : goto readit;
462 : :
463 : : /*
464 : : * standalone, small random read
465 : : * Read as is, and do not pollute the readahead state.
466 : : */
467 : 48095 : return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
468 : :
469 : : initial_readahead:
470 : 289779 : ra->start = offset;
471 : 289779 : ra->size = get_init_ra_size(req_size, max_pages);
472 [ + + ]: 291043 : ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
473 : :
474 : : readit:
475 : : /*
476 : : * Will this read hit the readahead marker made by itself?
477 : : * If so, trigger the readahead marker hit now, and merge
478 : : * the resulted next readahead window into the current one.
479 : : * Take care of maximum IO pages as above.
480 : : */
481 [ + + + + ]: 507893 : if (offset == ra->start && ra->size == ra->async_size) {
482 : : add_pages = get_next_ra_size(ra, max_pages);
483 [ + + ]: 5835 : if (ra->size + add_pages <= max_pages) {
484 : 5149 : ra->async_size = add_pages;
485 : 5149 : ra->size += add_pages;
486 : : } else {
487 : 686 : ra->size = max_pages;
488 : 686 : ra->async_size = max_pages >> 1;
489 : : }
490 : : }
491 : :
492 : 507983 : return ra_submit(ra, mapping, filp);
493 : : }
494 : :
495 : : /**
496 : : * page_cache_sync_readahead - generic file readahead
497 : : * @mapping: address_space which holds the pagecache and I/O vectors
498 : : * @ra: file_ra_state which holds the readahead state
499 : : * @filp: passed on to ->readpage() and ->readpages()
500 : : * @offset: start offset into @mapping, in pagecache page-sized units
501 : : * @req_size: hint: total size of the read which the caller is performing in
502 : : * pagecache pages
503 : : *
504 : : * page_cache_sync_readahead() should be called when a cache miss happened:
505 : : * it will submit the read. The readahead logic may decide to piggyback more
506 : : * pages onto the read request if access patterns suggest it will improve
507 : : * performance.
508 : : */
509 : 471630 : void page_cache_sync_readahead(struct address_space *mapping,
510 : : struct file_ra_state *ra, struct file *filp,
511 : : pgoff_t offset, unsigned long req_size)
512 : : {
513 : : /* no read-ahead */
514 [ + + ]: 471630 : if (!ra->ra_pages)
515 : : return;
516 : :
517 [ + + ]: 470892 : if (blk_cgroup_congested())
518 : : return;
519 : :
520 : : /* be dumb */
521 [ + + + + ]: 471609 : if (filp && (filp->f_mode & FMODE_RANDOM)) {
522 : 127074 : force_page_cache_readahead(mapping, filp, offset, req_size);
523 : 127074 : return;
524 : : }
525 : :
526 : : /* do read-ahead */
527 : 344535 : ondemand_readahead(mapping, ra, filp, false, offset, req_size);
528 : : }
529 : : EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
530 : :
531 : : /**
532 : : * page_cache_async_readahead - file readahead for marked pages
533 : : * @mapping: address_space which holds the pagecache and I/O vectors
534 : : * @ra: file_ra_state which holds the readahead state
535 : : * @filp: passed on to ->readpage() and ->readpages()
536 : : * @page: the page at @offset which has the PG_readahead flag set
537 : : * @offset: start offset into @mapping, in pagecache page-sized units
538 : : * @req_size: hint: total size of the read which the caller is performing in
539 : : * pagecache pages
540 : : *
541 : : * page_cache_async_readahead() should be called when a page is used which
542 : : * has the PG_readahead flag; this is a marker to suggest that the application
543 : : * has used up enough of the readahead window that we should start pulling in
544 : : * more pages.
545 : : */
546 : : void
547 : 211438 : page_cache_async_readahead(struct address_space *mapping,
548 : : struct file_ra_state *ra, struct file *filp,
549 : : struct page *page, pgoff_t offset,
550 : : unsigned long req_size)
551 : : {
552 : : /* no read-ahead */
553 [ + + ]: 211438 : if (!ra->ra_pages)
554 : : return;
555 : :
556 : : /*
557 : : * Same bit is used for PG_readahead and PG_reclaim.
558 : : */
559 [ + + ]: 211324 : if (PageWriteback(page))
560 : : return;
561 : :
562 : : ClearPageReadahead(page);
563 : :
564 : : /*
565 : : * Defer asynchronous read-ahead on IO congestion.
566 : : */
567 [ + + ]: 422731 : if (inode_read_congested(mapping->host))
568 : : return;
569 : :
570 [ + + ]: 210818 : if (blk_cgroup_congested())
571 : : return;
572 : :
573 : : /* do read-ahead */
574 : 210984 : ondemand_readahead(mapping, ra, filp, true, offset, req_size);
575 : : }
576 : : EXPORT_SYMBOL_GPL(page_cache_async_readahead);
577 : :
578 : 0 : ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
579 : : {
580 : : ssize_t ret;
581 : : struct fd f;
582 : :
583 : : ret = -EBADF;
584 : 0 : f = fdget(fd);
585 [ # # # # ]: 0 : if (!f.file || !(f.file->f_mode & FMODE_READ))
586 : : goto out;
587 : :
588 : : /*
589 : : * The readahead() syscall is intended to run only on files
590 : : * that can execute readahead. If readahead is not possible
591 : : * on this file, then we must return -EINVAL.
592 : : */
593 : : ret = -EINVAL;
594 [ # # # # : 0 : if (!f.file->f_mapping || !f.file->f_mapping->a_ops ||
# # ]
595 : 0 : !S_ISREG(file_inode(f.file)->i_mode))
596 : : goto out;
597 : :
598 : 0 : ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED);
599 : : out:
600 : : fdput(f);
601 : 0 : return ret;
602 : : }
603 : :
604 : 0 : SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
605 : : {
606 : 0 : return ksys_readahead(fd, offset, count);
607 : : }
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