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Commit | Line | Data |
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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> | |
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> | |
1da177e4 | 20 | |
29f175d1 FF |
21 | #include "internal.h" |
22 | ||
1da177e4 LT |
23 | /* |
24 | * Initialise a struct file's readahead state. Assumes that the caller has | |
25 | * memset *ra to zero. | |
26 | */ | |
27 | void | |
28 | file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) | |
29 | { | |
de1414a6 | 30 | ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages; |
f4e6b498 | 31 | ra->prev_pos = -1; |
1da177e4 | 32 | } |
d41cc702 | 33 | EXPORT_SYMBOL_GPL(file_ra_state_init); |
1da177e4 | 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 | */ |
42 | static 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; | |
d47992f8 | 49 | do_invalidatepage(page, 0, PAGE_CACHE_SIZE); |
03fb3d2a DH |
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 | */ | |
59 | static 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)) { | |
c8ad6302 | 65 | victim = lru_to_page(pages); |
03fb3d2a DH |
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 | */ | |
81 | int 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 | 87 | while (!list_empty(pages)) { |
c8ad6302 | 88 | page = lru_to_page(pages); |
1da177e4 | 89 | list_del(&page->lru); |
063d99b4 | 90 | if (add_to_page_cache_lru(page, mapping, page->index, |
c62d2555 | 91 | mapping_gfp_constraint(mapping, 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 | ||
107 | EXPORT_SYMBOL(read_cache_pages); | |
108 | ||
109 | static int read_pages(struct address_space *mapping, struct file *filp, | |
110 | struct list_head *pages, unsigned nr_pages) | |
111 | { | |
5b417b18 | 112 | struct blk_plug plug; |
1da177e4 | 113 | unsigned page_idx; |
994fc28c | 114 | int ret; |
1da177e4 | 115 | |
5b417b18 JA |
116 | blk_start_plug(&plug); |
117 | ||
1da177e4 LT |
118 | if (mapping->a_ops->readpages) { |
119 | ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages); | |
029e332e OH |
120 | /* Clean up the remaining pages */ |
121 | put_pages_list(pages); | |
1da177e4 LT |
122 | goto out; |
123 | } | |
124 | ||
1da177e4 | 125 | for (page_idx = 0; page_idx < nr_pages; page_idx++) { |
c8ad6302 | 126 | struct page *page = lru_to_page(pages); |
1da177e4 | 127 | list_del(&page->lru); |
063d99b4 | 128 | if (!add_to_page_cache_lru(page, mapping, page->index, |
c62d2555 | 129 | mapping_gfp_constraint(mapping, GFP_KERNEL))) { |
9f1a3cfc | 130 | mapping->a_ops->readpage(filp, page); |
eb2be189 NP |
131 | } |
132 | page_cache_release(page); | |
1da177e4 | 133 | } |
994fc28c | 134 | ret = 0; |
5b417b18 | 135 | |
1da177e4 | 136 | out: |
5b417b18 JA |
137 | blk_finish_plug(&plug); |
138 | ||
1da177e4 LT |
139 | return ret; |
140 | } | |
141 | ||
1da177e4 | 142 | /* |
d30a1100 | 143 | * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all |
1da177e4 LT |
144 | * the pages first, then submits them all for I/O. This avoids the very bad |
145 | * behaviour which would occur if page allocations are causing VM writeback. | |
146 | * We really don't want to intermingle reads and writes like that. | |
147 | * | |
148 | * Returns the number of pages requested, or the maximum amount of I/O allowed. | |
1da177e4 | 149 | */ |
29f175d1 | 150 | int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, |
46fc3e7b FW |
151 | pgoff_t offset, unsigned long nr_to_read, |
152 | unsigned long lookahead_size) | |
1da177e4 LT |
153 | { |
154 | struct inode *inode = mapping->host; | |
155 | struct page *page; | |
156 | unsigned long end_index; /* The last page we want to read */ | |
157 | LIST_HEAD(page_pool); | |
158 | int page_idx; | |
159 | int ret = 0; | |
160 | loff_t isize = i_size_read(inode); | |
161 | ||
162 | if (isize == 0) | |
163 | goto out; | |
164 | ||
46fc3e7b | 165 | end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); |
1da177e4 LT |
166 | |
167 | /* | |
168 | * Preallocate as many pages as we will need. | |
169 | */ | |
1da177e4 | 170 | for (page_idx = 0; page_idx < nr_to_read; page_idx++) { |
7361f4d8 | 171 | pgoff_t page_offset = offset + page_idx; |
c743d96b | 172 | |
1da177e4 LT |
173 | if (page_offset > end_index) |
174 | break; | |
175 | ||
00128188 | 176 | rcu_read_lock(); |
1da177e4 | 177 | page = radix_tree_lookup(&mapping->page_tree, page_offset); |
00128188 | 178 | rcu_read_unlock(); |
0cd6144a | 179 | if (page && !radix_tree_exceptional_entry(page)) |
1da177e4 LT |
180 | continue; |
181 | ||
7b1de586 | 182 | page = page_cache_alloc_readahead(mapping); |
1da177e4 LT |
183 | if (!page) |
184 | break; | |
185 | page->index = page_offset; | |
186 | list_add(&page->lru, &page_pool); | |
46fc3e7b FW |
187 | if (page_idx == nr_to_read - lookahead_size) |
188 | SetPageReadahead(page); | |
1da177e4 LT |
189 | ret++; |
190 | } | |
1da177e4 LT |
191 | |
192 | /* | |
193 | * Now start the IO. We ignore I/O errors - if the page is not | |
194 | * uptodate then the caller will launch readpage again, and | |
195 | * will then handle the error. | |
196 | */ | |
197 | if (ret) | |
198 | read_pages(mapping, filp, &page_pool, ret); | |
199 | BUG_ON(!list_empty(&page_pool)); | |
200 | out: | |
201 | return ret; | |
202 | } | |
203 | ||
204 | /* | |
205 | * Chunk the readahead into 2 megabyte units, so that we don't pin too much | |
206 | * memory at once. | |
207 | */ | |
208 | int force_page_cache_readahead(struct address_space *mapping, struct file *filp, | |
7361f4d8 | 209 | pgoff_t offset, unsigned long nr_to_read) |
1da177e4 | 210 | { |
1da177e4 LT |
211 | if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) |
212 | return -EINVAL; | |
213 | ||
600e19af | 214 | nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages); |
1da177e4 LT |
215 | while (nr_to_read) { |
216 | int err; | |
217 | ||
218 | unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE; | |
219 | ||
220 | if (this_chunk > nr_to_read) | |
221 | this_chunk = nr_to_read; | |
222 | err = __do_page_cache_readahead(mapping, filp, | |
46fc3e7b | 223 | offset, this_chunk, 0); |
58d5640e MR |
224 | if (err < 0) |
225 | return err; | |
226 | ||
1da177e4 LT |
227 | offset += this_chunk; |
228 | nr_to_read -= this_chunk; | |
229 | } | |
58d5640e | 230 | return 0; |
1da177e4 LT |
231 | } |
232 | ||
c743d96b FW |
233 | /* |
234 | * Set the initial window size, round to next power of 2 and square | |
235 | * for small size, x 4 for medium, and x 2 for large | |
236 | * for 128k (32 page) max ra | |
237 | * 1-8 page = 32k initial, > 8 page = 128k initial | |
238 | */ | |
239 | static unsigned long get_init_ra_size(unsigned long size, unsigned long max) | |
240 | { | |
241 | unsigned long newsize = roundup_pow_of_two(size); | |
242 | ||
243 | if (newsize <= max / 32) | |
244 | newsize = newsize * 4; | |
245 | else if (newsize <= max / 4) | |
246 | newsize = newsize * 2; | |
247 | else | |
248 | newsize = max; | |
249 | ||
250 | return newsize; | |
251 | } | |
252 | ||
122a21d1 FW |
253 | /* |
254 | * Get the previous window size, ramp it up, and | |
255 | * return it as the new window size. | |
256 | */ | |
c743d96b | 257 | static unsigned long get_next_ra_size(struct file_ra_state *ra, |
122a21d1 FW |
258 | unsigned long max) |
259 | { | |
f9acc8c7 | 260 | unsigned long cur = ra->size; |
122a21d1 FW |
261 | unsigned long newsize; |
262 | ||
263 | if (cur < max / 16) | |
c743d96b | 264 | newsize = 4 * cur; |
122a21d1 | 265 | else |
c743d96b | 266 | newsize = 2 * cur; |
122a21d1 FW |
267 | |
268 | return min(newsize, max); | |
269 | } | |
270 | ||
271 | /* | |
272 | * On-demand readahead design. | |
273 | * | |
274 | * The fields in struct file_ra_state represent the most-recently-executed | |
275 | * readahead attempt: | |
276 | * | |
f9acc8c7 FW |
277 | * |<----- async_size ---------| |
278 | * |------------------- size -------------------->| | |
279 | * |==================#===========================| | |
280 | * ^start ^page marked with PG_readahead | |
122a21d1 FW |
281 | * |
282 | * To overlap application thinking time and disk I/O time, we do | |
283 | * `readahead pipelining': Do not wait until the application consumed all | |
284 | * readahead pages and stalled on the missing page at readahead_index; | |
f9acc8c7 FW |
285 | * Instead, submit an asynchronous readahead I/O as soon as there are |
286 | * only async_size pages left in the readahead window. Normally async_size | |
287 | * will be equal to size, for maximum pipelining. | |
122a21d1 FW |
288 | * |
289 | * In interleaved sequential reads, concurrent streams on the same fd can | |
290 | * be invalidating each other's readahead state. So we flag the new readahead | |
f9acc8c7 | 291 | * page at (start+size-async_size) with PG_readahead, and use it as readahead |
122a21d1 FW |
292 | * indicator. The flag won't be set on already cached pages, to avoid the |
293 | * readahead-for-nothing fuss, saving pointless page cache lookups. | |
294 | * | |
f4e6b498 | 295 | * prev_pos tracks the last visited byte in the _previous_ read request. |
122a21d1 FW |
296 | * It should be maintained by the caller, and will be used for detecting |
297 | * small random reads. Note that the readahead algorithm checks loosely | |
298 | * for sequential patterns. Hence interleaved reads might be served as | |
299 | * sequential ones. | |
300 | * | |
301 | * There is a special-case: if the first page which the application tries to | |
302 | * read happens to be the first page of the file, it is assumed that a linear | |
303 | * read is about to happen and the window is immediately set to the initial size | |
304 | * based on I/O request size and the max_readahead. | |
305 | * | |
306 | * The code ramps up the readahead size aggressively at first, but slow down as | |
307 | * it approaches max_readhead. | |
308 | */ | |
309 | ||
10be0b37 WF |
310 | /* |
311 | * Count contiguously cached pages from @offset-1 to @offset-@max, | |
312 | * this count is a conservative estimation of | |
313 | * - length of the sequential read sequence, or | |
314 | * - thrashing threshold in memory tight systems | |
315 | */ | |
316 | static pgoff_t count_history_pages(struct address_space *mapping, | |
10be0b37 WF |
317 | pgoff_t offset, unsigned long max) |
318 | { | |
319 | pgoff_t head; | |
320 | ||
321 | rcu_read_lock(); | |
e7b563bb | 322 | head = page_cache_prev_hole(mapping, offset - 1, max); |
10be0b37 WF |
323 | rcu_read_unlock(); |
324 | ||
325 | return offset - 1 - head; | |
326 | } | |
327 | ||
328 | /* | |
329 | * page cache context based read-ahead | |
330 | */ | |
331 | static int try_context_readahead(struct address_space *mapping, | |
332 | struct file_ra_state *ra, | |
333 | pgoff_t offset, | |
334 | unsigned long req_size, | |
335 | unsigned long max) | |
336 | { | |
337 | pgoff_t size; | |
338 | ||
3e2faa08 | 339 | size = count_history_pages(mapping, offset, max); |
10be0b37 WF |
340 | |
341 | /* | |
2cad4018 | 342 | * not enough history pages: |
10be0b37 WF |
343 | * it could be a random read |
344 | */ | |
2cad4018 | 345 | if (size <= req_size) |
10be0b37 WF |
346 | return 0; |
347 | ||
348 | /* | |
349 | * starts from beginning of file: | |
350 | * it is a strong indication of long-run stream (or whole-file-read) | |
351 | */ | |
352 | if (size >= offset) | |
353 | size *= 2; | |
354 | ||
355 | ra->start = offset; | |
2cad4018 FW |
356 | ra->size = min(size + req_size, max); |
357 | ra->async_size = 1; | |
10be0b37 WF |
358 | |
359 | return 1; | |
360 | } | |
361 | ||
122a21d1 FW |
362 | /* |
363 | * A minimal readahead algorithm for trivial sequential/random reads. | |
364 | */ | |
365 | static unsigned long | |
366 | ondemand_readahead(struct address_space *mapping, | |
367 | struct file_ra_state *ra, struct file *filp, | |
cf914a7d | 368 | bool hit_readahead_marker, pgoff_t offset, |
122a21d1 FW |
369 | unsigned long req_size) |
370 | { | |
600e19af | 371 | unsigned long max = ra->ra_pages; |
af248a0c | 372 | pgoff_t prev_offset; |
045a2529 WF |
373 | |
374 | /* | |
375 | * start of file | |
376 | */ | |
377 | if (!offset) | |
378 | goto initial_readahead; | |
122a21d1 FW |
379 | |
380 | /* | |
f9acc8c7 | 381 | * It's the expected callback offset, assume sequential access. |
122a21d1 FW |
382 | * Ramp up sizes, and push forward the readahead window. |
383 | */ | |
045a2529 WF |
384 | if ((offset == (ra->start + ra->size - ra->async_size) || |
385 | offset == (ra->start + ra->size))) { | |
f9acc8c7 FW |
386 | ra->start += ra->size; |
387 | ra->size = get_next_ra_size(ra, max); | |
388 | ra->async_size = ra->size; | |
389 | goto readit; | |
122a21d1 FW |
390 | } |
391 | ||
6b10c6c9 FW |
392 | /* |
393 | * Hit a marked page without valid readahead state. | |
394 | * E.g. interleaved reads. | |
395 | * Query the pagecache for async_size, which normally equals to | |
396 | * readahead size. Ramp it up and use it as the new readahead size. | |
397 | */ | |
398 | if (hit_readahead_marker) { | |
399 | pgoff_t start; | |
400 | ||
30002ed2 | 401 | rcu_read_lock(); |
e7b563bb | 402 | start = page_cache_next_hole(mapping, offset + 1, max); |
30002ed2 | 403 | rcu_read_unlock(); |
6b10c6c9 FW |
404 | |
405 | if (!start || start - offset > max) | |
406 | return 0; | |
407 | ||
408 | ra->start = start; | |
409 | ra->size = start - offset; /* old async_size */ | |
160334a0 | 410 | ra->size += req_size; |
6b10c6c9 FW |
411 | ra->size = get_next_ra_size(ra, max); |
412 | ra->async_size = ra->size; | |
413 | goto readit; | |
414 | } | |
415 | ||
122a21d1 | 416 | /* |
045a2529 | 417 | * oversize read |
122a21d1 | 418 | */ |
045a2529 WF |
419 | if (req_size > max) |
420 | goto initial_readahead; | |
421 | ||
422 | /* | |
423 | * sequential cache miss | |
af248a0c DR |
424 | * trivial case: (offset - prev_offset) == 1 |
425 | * unaligned reads: (offset - prev_offset) == 0 | |
045a2529 | 426 | */ |
af248a0c DR |
427 | prev_offset = (unsigned long long)ra->prev_pos >> PAGE_CACHE_SHIFT; |
428 | if (offset - prev_offset <= 1UL) | |
045a2529 WF |
429 | goto initial_readahead; |
430 | ||
10be0b37 WF |
431 | /* |
432 | * Query the page cache and look for the traces(cached history pages) | |
433 | * that a sequential stream would leave behind. | |
434 | */ | |
435 | if (try_context_readahead(mapping, ra, offset, req_size, max)) | |
436 | goto readit; | |
437 | ||
045a2529 WF |
438 | /* |
439 | * standalone, small random read | |
440 | * Read as is, and do not pollute the readahead state. | |
441 | */ | |
442 | return __do_page_cache_readahead(mapping, filp, offset, req_size, 0); | |
443 | ||
444 | initial_readahead: | |
f9acc8c7 FW |
445 | ra->start = offset; |
446 | ra->size = get_init_ra_size(req_size, max); | |
447 | ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; | |
122a21d1 | 448 | |
f9acc8c7 | 449 | readit: |
51daa88e WF |
450 | /* |
451 | * Will this read hit the readahead marker made by itself? | |
452 | * If so, trigger the readahead marker hit now, and merge | |
453 | * the resulted next readahead window into the current one. | |
454 | */ | |
455 | if (offset == ra->start && ra->size == ra->async_size) { | |
456 | ra->async_size = get_next_ra_size(ra, max); | |
457 | ra->size += ra->async_size; | |
458 | } | |
459 | ||
122a21d1 FW |
460 | return ra_submit(ra, mapping, filp); |
461 | } | |
462 | ||
463 | /** | |
cf914a7d | 464 | * page_cache_sync_readahead - generic file readahead |
122a21d1 FW |
465 | * @mapping: address_space which holds the pagecache and I/O vectors |
466 | * @ra: file_ra_state which holds the readahead state | |
467 | * @filp: passed on to ->readpage() and ->readpages() | |
cf914a7d | 468 | * @offset: start offset into @mapping, in pagecache page-sized units |
122a21d1 | 469 | * @req_size: hint: total size of the read which the caller is performing in |
cf914a7d | 470 | * pagecache pages |
122a21d1 | 471 | * |
cf914a7d RR |
472 | * page_cache_sync_readahead() should be called when a cache miss happened: |
473 | * it will submit the read. The readahead logic may decide to piggyback more | |
474 | * pages onto the read request if access patterns suggest it will improve | |
475 | * performance. | |
122a21d1 | 476 | */ |
cf914a7d RR |
477 | void page_cache_sync_readahead(struct address_space *mapping, |
478 | struct file_ra_state *ra, struct file *filp, | |
479 | pgoff_t offset, unsigned long req_size) | |
122a21d1 FW |
480 | { |
481 | /* no read-ahead */ | |
482 | if (!ra->ra_pages) | |
cf914a7d RR |
483 | return; |
484 | ||
0141450f | 485 | /* be dumb */ |
70655c06 | 486 | if (filp && (filp->f_mode & FMODE_RANDOM)) { |
0141450f WF |
487 | force_page_cache_readahead(mapping, filp, offset, req_size); |
488 | return; | |
489 | } | |
490 | ||
cf914a7d RR |
491 | /* do read-ahead */ |
492 | ondemand_readahead(mapping, ra, filp, false, offset, req_size); | |
493 | } | |
494 | EXPORT_SYMBOL_GPL(page_cache_sync_readahead); | |
495 | ||
496 | /** | |
497 | * page_cache_async_readahead - file readahead for marked pages | |
498 | * @mapping: address_space which holds the pagecache and I/O vectors | |
499 | * @ra: file_ra_state which holds the readahead state | |
500 | * @filp: passed on to ->readpage() and ->readpages() | |
501 | * @page: the page at @offset which has the PG_readahead flag set | |
502 | * @offset: start offset into @mapping, in pagecache page-sized units | |
503 | * @req_size: hint: total size of the read which the caller is performing in | |
504 | * pagecache pages | |
505 | * | |
bf8abe8b | 506 | * page_cache_async_readahead() should be called when a page is used which |
f7850d93 | 507 | * has the PG_readahead flag; this is a marker to suggest that the application |
cf914a7d | 508 | * has used up enough of the readahead window that we should start pulling in |
f7850d93 RD |
509 | * more pages. |
510 | */ | |
cf914a7d RR |
511 | void |
512 | page_cache_async_readahead(struct address_space *mapping, | |
513 | struct file_ra_state *ra, struct file *filp, | |
514 | struct page *page, pgoff_t offset, | |
515 | unsigned long req_size) | |
516 | { | |
517 | /* no read-ahead */ | |
518 | if (!ra->ra_pages) | |
519 | return; | |
520 | ||
521 | /* | |
522 | * Same bit is used for PG_readahead and PG_reclaim. | |
523 | */ | |
524 | if (PageWriteback(page)) | |
525 | return; | |
526 | ||
527 | ClearPageReadahead(page); | |
528 | ||
529 | /* | |
530 | * Defer asynchronous read-ahead on IO congestion. | |
531 | */ | |
703c2708 | 532 | if (inode_read_congested(mapping->host)) |
cf914a7d | 533 | return; |
122a21d1 FW |
534 | |
535 | /* do read-ahead */ | |
cf914a7d | 536 | ondemand_readahead(mapping, ra, filp, true, offset, req_size); |
122a21d1 | 537 | } |
cf914a7d | 538 | EXPORT_SYMBOL_GPL(page_cache_async_readahead); |
782182e5 CW |
539 | |
540 | static ssize_t | |
541 | do_readahead(struct address_space *mapping, struct file *filp, | |
542 | pgoff_t index, unsigned long nr) | |
543 | { | |
63d0f0a3 | 544 | if (!mapping || !mapping->a_ops) |
782182e5 CW |
545 | return -EINVAL; |
546 | ||
58d5640e | 547 | return force_page_cache_readahead(mapping, filp, index, nr); |
782182e5 CW |
548 | } |
549 | ||
4a0fd5bf | 550 | SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count) |
782182e5 CW |
551 | { |
552 | ssize_t ret; | |
2903ff01 | 553 | struct fd f; |
782182e5 CW |
554 | |
555 | ret = -EBADF; | |
2903ff01 AV |
556 | f = fdget(fd); |
557 | if (f.file) { | |
558 | if (f.file->f_mode & FMODE_READ) { | |
559 | struct address_space *mapping = f.file->f_mapping; | |
782182e5 CW |
560 | pgoff_t start = offset >> PAGE_CACHE_SHIFT; |
561 | pgoff_t end = (offset + count - 1) >> PAGE_CACHE_SHIFT; | |
562 | unsigned long len = end - start + 1; | |
2903ff01 | 563 | ret = do_readahead(mapping, f.file, start, len); |
782182e5 | 564 | } |
2903ff01 | 565 | fdput(f); |
782182e5 CW |
566 | } |
567 | return ret; | |
568 | } |