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 | * | |
6 | * 09Apr2002 akpm@zip.com.au | |
7 | * Initial version. | |
8 | */ | |
9 | ||
10 | #include <linux/kernel.h> | |
11 | #include <linux/fs.h> | |
12 | #include <linux/mm.h> | |
13 | #include <linux/module.h> | |
14 | #include <linux/blkdev.h> | |
15 | #include <linux/backing-dev.h> | |
16 | #include <linux/pagevec.h> | |
17 | ||
18 | void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page) | |
19 | { | |
20 | } | |
21 | EXPORT_SYMBOL(default_unplug_io_fn); | |
22 | ||
23 | struct backing_dev_info default_backing_dev_info = { | |
24 | .ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE, | |
25 | .state = 0, | |
26 | .capabilities = BDI_CAP_MAP_COPY, | |
27 | .unplug_io_fn = default_unplug_io_fn, | |
28 | }; | |
29 | EXPORT_SYMBOL_GPL(default_backing_dev_info); | |
30 | ||
31 | /* | |
32 | * Initialise a struct file's readahead state. Assumes that the caller has | |
33 | * memset *ra to zero. | |
34 | */ | |
35 | void | |
36 | file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) | |
37 | { | |
38 | ra->ra_pages = mapping->backing_dev_info->ra_pages; | |
39 | ra->prev_page = -1; | |
40 | } | |
41 | ||
42 | /* | |
43 | * Return max readahead size for this inode in number-of-pages. | |
44 | */ | |
45 | static inline unsigned long get_max_readahead(struct file_ra_state *ra) | |
46 | { | |
47 | return ra->ra_pages; | |
48 | } | |
49 | ||
50 | static inline unsigned long get_min_readahead(struct file_ra_state *ra) | |
51 | { | |
52 | return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE; | |
53 | } | |
54 | ||
a564da39 ON |
55 | static inline void reset_ahead_window(struct file_ra_state *ra) |
56 | { | |
57 | /* | |
58 | * ... but preserve ahead_start + ahead_size value, | |
59 | * see 'recheck:' label in page_cache_readahead(). | |
60 | * Note: We never use ->ahead_size as rvalue without | |
61 | * checking ->ahead_start != 0 first. | |
62 | */ | |
63 | ra->ahead_size += ra->ahead_start; | |
64 | ra->ahead_start = 0; | |
65 | } | |
66 | ||
1da177e4 LT |
67 | static inline void ra_off(struct file_ra_state *ra) |
68 | { | |
69 | ra->start = 0; | |
70 | ra->flags = 0; | |
71 | ra->size = 0; | |
a564da39 | 72 | reset_ahead_window(ra); |
1da177e4 LT |
73 | return; |
74 | } | |
75 | ||
76 | /* | |
77 | * Set the initial window size, round to next power of 2 and square | |
78 | * for small size, x 4 for medium, and x 2 for large | |
79 | * for 128k (32 page) max ra | |
80 | * 1-8 page = 32k initial, > 8 page = 128k initial | |
81 | */ | |
82 | static unsigned long get_init_ra_size(unsigned long size, unsigned long max) | |
83 | { | |
84 | unsigned long newsize = roundup_pow_of_two(size); | |
85 | ||
aed75ff3 SP |
86 | if (newsize <= max / 32) |
87 | newsize = newsize * 4; | |
1da177e4 | 88 | else if (newsize <= max / 4) |
aed75ff3 | 89 | newsize = newsize * 2; |
1da177e4 LT |
90 | else |
91 | newsize = max; | |
92 | return newsize; | |
93 | } | |
94 | ||
95 | /* | |
96 | * Set the new window size, this is called only when I/O is to be submitted, | |
97 | * not for each call to readahead. If a cache miss occured, reduce next I/O | |
98 | * size, else increase depending on how close to max we are. | |
99 | */ | |
100 | static inline unsigned long get_next_ra_size(struct file_ra_state *ra) | |
101 | { | |
102 | unsigned long max = get_max_readahead(ra); | |
103 | unsigned long min = get_min_readahead(ra); | |
104 | unsigned long cur = ra->size; | |
105 | unsigned long newsize; | |
106 | ||
107 | if (ra->flags & RA_FLAG_MISS) { | |
108 | ra->flags &= ~RA_FLAG_MISS; | |
109 | newsize = max((cur - 2), min); | |
110 | } else if (cur < max / 16) { | |
111 | newsize = 4 * cur; | |
112 | } else { | |
113 | newsize = 2 * cur; | |
114 | } | |
115 | return min(newsize, max); | |
116 | } | |
117 | ||
118 | #define list_to_page(head) (list_entry((head)->prev, struct page, lru)) | |
119 | ||
120 | /** | |
121 | * read_cache_pages - populate an address space with some pages, and | |
122 | * start reads against them. | |
123 | * @mapping: the address_space | |
124 | * @pages: The address of a list_head which contains the target pages. These | |
125 | * pages have their ->index populated and are otherwise uninitialised. | |
126 | * @filler: callback routine for filling a single page. | |
127 | * @data: private data for the callback routine. | |
128 | * | |
129 | * Hides the details of the LRU cache etc from the filesystems. | |
130 | */ | |
131 | int read_cache_pages(struct address_space *mapping, struct list_head *pages, | |
132 | int (*filler)(void *, struct page *), void *data) | |
133 | { | |
134 | struct page *page; | |
135 | struct pagevec lru_pvec; | |
136 | int ret = 0; | |
137 | ||
138 | pagevec_init(&lru_pvec, 0); | |
139 | ||
140 | while (!list_empty(pages)) { | |
141 | page = list_to_page(pages); | |
142 | list_del(&page->lru); | |
143 | if (add_to_page_cache(page, mapping, page->index, GFP_KERNEL)) { | |
144 | page_cache_release(page); | |
145 | continue; | |
146 | } | |
147 | ret = filler(data, page); | |
148 | if (!pagevec_add(&lru_pvec, page)) | |
149 | __pagevec_lru_add(&lru_pvec); | |
150 | if (ret) { | |
151 | while (!list_empty(pages)) { | |
152 | struct page *victim; | |
153 | ||
154 | victim = list_to_page(pages); | |
155 | list_del(&victim->lru); | |
156 | page_cache_release(victim); | |
157 | } | |
158 | break; | |
159 | } | |
160 | } | |
161 | pagevec_lru_add(&lru_pvec); | |
162 | return ret; | |
163 | } | |
164 | ||
165 | EXPORT_SYMBOL(read_cache_pages); | |
166 | ||
167 | static int read_pages(struct address_space *mapping, struct file *filp, | |
168 | struct list_head *pages, unsigned nr_pages) | |
169 | { | |
170 | unsigned page_idx; | |
171 | struct pagevec lru_pvec; | |
994fc28c | 172 | int ret; |
1da177e4 LT |
173 | |
174 | if (mapping->a_ops->readpages) { | |
175 | ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages); | |
176 | goto out; | |
177 | } | |
178 | ||
179 | pagevec_init(&lru_pvec, 0); | |
180 | for (page_idx = 0; page_idx < nr_pages; page_idx++) { | |
181 | struct page *page = list_to_page(pages); | |
182 | list_del(&page->lru); | |
183 | if (!add_to_page_cache(page, mapping, | |
184 | page->index, GFP_KERNEL)) { | |
994fc28c ZB |
185 | ret = mapping->a_ops->readpage(filp, page); |
186 | if (ret != AOP_TRUNCATED_PAGE) { | |
187 | if (!pagevec_add(&lru_pvec, page)) | |
188 | __pagevec_lru_add(&lru_pvec); | |
189 | continue; | |
190 | } /* else fall through to release */ | |
1da177e4 | 191 | } |
994fc28c | 192 | page_cache_release(page); |
1da177e4 LT |
193 | } |
194 | pagevec_lru_add(&lru_pvec); | |
994fc28c | 195 | ret = 0; |
1da177e4 LT |
196 | out: |
197 | return ret; | |
198 | } | |
199 | ||
200 | /* | |
201 | * Readahead design. | |
202 | * | |
203 | * The fields in struct file_ra_state represent the most-recently-executed | |
204 | * readahead attempt: | |
205 | * | |
206 | * start: Page index at which we started the readahead | |
207 | * size: Number of pages in that read | |
208 | * Together, these form the "current window". | |
209 | * Together, start and size represent the `readahead window'. | |
210 | * prev_page: The page which the readahead algorithm most-recently inspected. | |
211 | * It is mainly used to detect sequential file reading. | |
212 | * If page_cache_readahead sees that it is again being called for | |
213 | * a page which it just looked at, it can return immediately without | |
214 | * making any state changes. | |
215 | * ahead_start, | |
216 | * ahead_size: Together, these form the "ahead window". | |
217 | * ra_pages: The externally controlled max readahead for this fd. | |
218 | * | |
219 | * When readahead is in the off state (size == 0), readahead is disabled. | |
220 | * In this state, prev_page is used to detect the resumption of sequential I/O. | |
221 | * | |
222 | * The readahead code manages two windows - the "current" and the "ahead" | |
223 | * windows. The intent is that while the application is walking the pages | |
224 | * in the current window, I/O is underway on the ahead window. When the | |
225 | * current window is fully traversed, it is replaced by the ahead window | |
226 | * and the ahead window is invalidated. When this copying happens, the | |
227 | * new current window's pages are probably still locked. So | |
228 | * we submit a new batch of I/O immediately, creating a new ahead window. | |
229 | * | |
230 | * So: | |
231 | * | |
232 | * ----|----------------|----------------|----- | |
233 | * ^start ^start+size | |
234 | * ^ahead_start ^ahead_start+ahead_size | |
235 | * | |
236 | * ^ When this page is read, we submit I/O for the | |
237 | * ahead window. | |
238 | * | |
239 | * A `readahead hit' occurs when a read request is made against a page which is | |
240 | * the next sequential page. Ahead window calculations are done only when it | |
241 | * is time to submit a new IO. The code ramps up the size agressively at first, | |
242 | * but slow down as it approaches max_readhead. | |
243 | * | |
244 | * Any seek/ramdom IO will result in readahead being turned off. It will resume | |
245 | * at the first sequential access. | |
246 | * | |
247 | * There is a special-case: if the first page which the application tries to | |
248 | * read happens to be the first page of the file, it is assumed that a linear | |
249 | * read is about to happen and the window is immediately set to the initial size | |
250 | * based on I/O request size and the max_readahead. | |
251 | * | |
252 | * This function is to be called for every read request, rather than when | |
253 | * it is time to perform readahead. It is called only once for the entire I/O | |
254 | * regardless of size unless readahead is unable to start enough I/O to satisfy | |
255 | * the request (I/O request > max_readahead). | |
256 | */ | |
257 | ||
258 | /* | |
259 | * do_page_cache_readahead actually reads a chunk of disk. It allocates all | |
260 | * the pages first, then submits them all for I/O. This avoids the very bad | |
261 | * behaviour which would occur if page allocations are causing VM writeback. | |
262 | * We really don't want to intermingle reads and writes like that. | |
263 | * | |
264 | * Returns the number of pages requested, or the maximum amount of I/O allowed. | |
265 | * | |
266 | * do_page_cache_readahead() returns -1 if it encountered request queue | |
267 | * congestion. | |
268 | */ | |
269 | static int | |
270 | __do_page_cache_readahead(struct address_space *mapping, struct file *filp, | |
7361f4d8 | 271 | pgoff_t offset, unsigned long nr_to_read) |
1da177e4 LT |
272 | { |
273 | struct inode *inode = mapping->host; | |
274 | struct page *page; | |
275 | unsigned long end_index; /* The last page we want to read */ | |
276 | LIST_HEAD(page_pool); | |
277 | int page_idx; | |
278 | int ret = 0; | |
279 | loff_t isize = i_size_read(inode); | |
280 | ||
281 | if (isize == 0) | |
282 | goto out; | |
283 | ||
284 | end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); | |
285 | ||
286 | /* | |
287 | * Preallocate as many pages as we will need. | |
288 | */ | |
289 | read_lock_irq(&mapping->tree_lock); | |
290 | for (page_idx = 0; page_idx < nr_to_read; page_idx++) { | |
7361f4d8 | 291 | pgoff_t page_offset = offset + page_idx; |
1da177e4 LT |
292 | |
293 | if (page_offset > end_index) | |
294 | break; | |
295 | ||
296 | page = radix_tree_lookup(&mapping->page_tree, page_offset); | |
297 | if (page) | |
298 | continue; | |
299 | ||
300 | read_unlock_irq(&mapping->tree_lock); | |
301 | page = page_cache_alloc_cold(mapping); | |
302 | read_lock_irq(&mapping->tree_lock); | |
303 | if (!page) | |
304 | break; | |
305 | page->index = page_offset; | |
306 | list_add(&page->lru, &page_pool); | |
307 | ret++; | |
308 | } | |
309 | read_unlock_irq(&mapping->tree_lock); | |
310 | ||
311 | /* | |
312 | * Now start the IO. We ignore I/O errors - if the page is not | |
313 | * uptodate then the caller will launch readpage again, and | |
314 | * will then handle the error. | |
315 | */ | |
316 | if (ret) | |
317 | read_pages(mapping, filp, &page_pool, ret); | |
318 | BUG_ON(!list_empty(&page_pool)); | |
319 | out: | |
320 | return ret; | |
321 | } | |
322 | ||
323 | /* | |
324 | * Chunk the readahead into 2 megabyte units, so that we don't pin too much | |
325 | * memory at once. | |
326 | */ | |
327 | int force_page_cache_readahead(struct address_space *mapping, struct file *filp, | |
7361f4d8 | 328 | pgoff_t offset, unsigned long nr_to_read) |
1da177e4 LT |
329 | { |
330 | int ret = 0; | |
331 | ||
332 | if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) | |
333 | return -EINVAL; | |
334 | ||
335 | while (nr_to_read) { | |
336 | int err; | |
337 | ||
338 | unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE; | |
339 | ||
340 | if (this_chunk > nr_to_read) | |
341 | this_chunk = nr_to_read; | |
342 | err = __do_page_cache_readahead(mapping, filp, | |
343 | offset, this_chunk); | |
344 | if (err < 0) { | |
345 | ret = err; | |
346 | break; | |
347 | } | |
348 | ret += err; | |
349 | offset += this_chunk; | |
350 | nr_to_read -= this_chunk; | |
351 | } | |
352 | return ret; | |
353 | } | |
354 | ||
355 | /* | |
356 | * Check how effective readahead is being. If the amount of started IO is | |
357 | * less than expected then the file is partly or fully in pagecache and | |
358 | * readahead isn't helping. | |
359 | * | |
360 | */ | |
361 | static inline int check_ra_success(struct file_ra_state *ra, | |
362 | unsigned long nr_to_read, unsigned long actual) | |
363 | { | |
364 | if (actual == 0) { | |
365 | ra->cache_hit += nr_to_read; | |
366 | if (ra->cache_hit >= VM_MAX_CACHE_HIT) { | |
367 | ra_off(ra); | |
368 | ra->flags |= RA_FLAG_INCACHE; | |
369 | return 0; | |
370 | } | |
371 | } else { | |
372 | ra->cache_hit=0; | |
373 | } | |
374 | return 1; | |
375 | } | |
376 | ||
377 | /* | |
378 | * This version skips the IO if the queue is read-congested, and will tell the | |
379 | * block layer to abandon the readahead if request allocation would block. | |
380 | * | |
381 | * force_page_cache_readahead() will ignore queue congestion and will block on | |
382 | * request queues. | |
383 | */ | |
384 | int do_page_cache_readahead(struct address_space *mapping, struct file *filp, | |
7361f4d8 | 385 | pgoff_t offset, unsigned long nr_to_read) |
1da177e4 LT |
386 | { |
387 | if (bdi_read_congested(mapping->backing_dev_info)) | |
388 | return -1; | |
389 | ||
390 | return __do_page_cache_readahead(mapping, filp, offset, nr_to_read); | |
391 | } | |
392 | ||
393 | /* | |
394 | * Read 'nr_to_read' pages starting at page 'offset'. If the flag 'block' | |
395 | * is set wait till the read completes. Otherwise attempt to read without | |
396 | * blocking. | |
397 | * Returns 1 meaning 'success' if read is succesfull without switching off | |
398 | * readhaead mode. Otherwise return failure. | |
399 | */ | |
400 | static int | |
401 | blockable_page_cache_readahead(struct address_space *mapping, struct file *filp, | |
7361f4d8 | 402 | pgoff_t offset, unsigned long nr_to_read, |
1da177e4 LT |
403 | struct file_ra_state *ra, int block) |
404 | { | |
405 | int actual; | |
406 | ||
407 | if (!block && bdi_read_congested(mapping->backing_dev_info)) | |
408 | return 0; | |
409 | ||
410 | actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read); | |
411 | ||
412 | return check_ra_success(ra, nr_to_read, actual); | |
413 | } | |
414 | ||
415 | static int make_ahead_window(struct address_space *mapping, struct file *filp, | |
416 | struct file_ra_state *ra, int force) | |
417 | { | |
418 | int block, ret; | |
419 | ||
420 | ra->ahead_size = get_next_ra_size(ra); | |
421 | ra->ahead_start = ra->start + ra->size; | |
422 | ||
423 | block = force || (ra->prev_page >= ra->ahead_start); | |
424 | ret = blockable_page_cache_readahead(mapping, filp, | |
425 | ra->ahead_start, ra->ahead_size, ra, block); | |
426 | ||
427 | if (!ret && !force) { | |
428 | /* A read failure in blocking mode, implies pages are | |
429 | * all cached. So we can safely assume we have taken | |
430 | * care of all the pages requested in this call. | |
431 | * A read failure in non-blocking mode, implies we are | |
432 | * reading more pages than requested in this call. So | |
433 | * we safely assume we have taken care of all the pages | |
434 | * requested in this call. | |
435 | * | |
436 | * Just reset the ahead window in case we failed due to | |
437 | * congestion. The ahead window will any way be closed | |
438 | * in case we failed due to excessive page cache hits. | |
439 | */ | |
a564da39 | 440 | reset_ahead_window(ra); |
1da177e4 LT |
441 | } |
442 | ||
443 | return ret; | |
444 | } | |
445 | ||
7361f4d8 AM |
446 | /** |
447 | * page_cache_readahead - generic adaptive readahead | |
448 | * @mapping: address_space which holds the pagecache and I/O vectors | |
449 | * @ra: file_ra_state which holds the readahead state | |
450 | * @filp: passed on to ->readpage() and ->readpages() | |
451 | * @offset: start offset into @mapping, in PAGE_CACHE_SIZE units | |
452 | * @req_size: hint: total size of the read which the caller is performing in | |
453 | * PAGE_CACHE_SIZE units | |
454 | * | |
455 | * page_cache_readahead() is the main function. If performs the adaptive | |
1da177e4 | 456 | * readahead window size management and submits the readahead I/O. |
7361f4d8 AM |
457 | * |
458 | * Note that @filp is purely used for passing on to the ->readpage[s]() | |
459 | * handler: it may refer to a different file from @mapping (so we may not use | |
460 | * @filp->f_mapping or @filp->f_dentry->d_inode here). | |
461 | * Also, @ra may not be equal to &@filp->f_ra. | |
462 | * | |
1da177e4 LT |
463 | */ |
464 | unsigned long | |
465 | page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, | |
7361f4d8 | 466 | struct file *filp, pgoff_t offset, unsigned long req_size) |
1da177e4 LT |
467 | { |
468 | unsigned long max, newsize; | |
469 | int sequential; | |
470 | ||
471 | /* | |
472 | * We avoid doing extra work and bogusly perturbing the readahead | |
473 | * window expansion logic. | |
474 | */ | |
475 | if (offset == ra->prev_page && --req_size) | |
476 | ++offset; | |
477 | ||
478 | /* Note that prev_page == -1 if it is a first read */ | |
479 | sequential = (offset == ra->prev_page + 1); | |
480 | ra->prev_page = offset; | |
481 | ||
482 | max = get_max_readahead(ra); | |
483 | newsize = min(req_size, max); | |
484 | ||
485 | /* No readahead or sub-page sized read or file already in cache */ | |
486 | if (newsize == 0 || (ra->flags & RA_FLAG_INCACHE)) | |
487 | goto out; | |
488 | ||
489 | ra->prev_page += newsize - 1; | |
490 | ||
491 | /* | |
492 | * Special case - first read at start of file. We'll assume it's | |
493 | * a whole-file read and grow the window fast. Or detect first | |
494 | * sequential access | |
495 | */ | |
496 | if (sequential && ra->size == 0) { | |
497 | ra->size = get_init_ra_size(newsize, max); | |
498 | ra->start = offset; | |
499 | if (!blockable_page_cache_readahead(mapping, filp, offset, | |
500 | ra->size, ra, 1)) | |
501 | goto out; | |
502 | ||
503 | /* | |
504 | * If the request size is larger than our max readahead, we | |
505 | * at least want to be sure that we get 2 IOs in flight and | |
506 | * we know that we will definitly need the new I/O. | |
507 | * once we do this, subsequent calls should be able to overlap | |
508 | * IOs,* thus preventing stalls. so issue the ahead window | |
509 | * immediately. | |
510 | */ | |
511 | if (req_size >= max) | |
512 | make_ahead_window(mapping, filp, ra, 1); | |
513 | ||
514 | goto out; | |
515 | } | |
516 | ||
517 | /* | |
518 | * Now handle the random case: | |
519 | * partial page reads and first access were handled above, | |
520 | * so this must be the next page otherwise it is random | |
521 | */ | |
522 | if (!sequential) { | |
523 | ra_off(ra); | |
524 | blockable_page_cache_readahead(mapping, filp, offset, | |
525 | newsize, ra, 1); | |
526 | goto out; | |
527 | } | |
528 | ||
529 | /* | |
530 | * If we get here we are doing sequential IO and this was not the first | |
531 | * occurence (ie we have an existing window) | |
532 | */ | |
1da177e4 LT |
533 | if (ra->ahead_start == 0) { /* no ahead window yet */ |
534 | if (!make_ahead_window(mapping, filp, ra, 0)) | |
a564da39 | 535 | goto recheck; |
1da177e4 | 536 | } |
a564da39 | 537 | |
1da177e4 LT |
538 | /* |
539 | * Already have an ahead window, check if we crossed into it. | |
540 | * If so, shift windows and issue a new ahead window. | |
541 | * Only return the #pages that are in the current window, so that | |
542 | * we get called back on the first page of the ahead window which | |
543 | * will allow us to submit more IO. | |
544 | */ | |
545 | if (ra->prev_page >= ra->ahead_start) { | |
546 | ra->start = ra->ahead_start; | |
547 | ra->size = ra->ahead_size; | |
548 | make_ahead_window(mapping, filp, ra, 0); | |
a564da39 ON |
549 | recheck: |
550 | /* prev_page shouldn't overrun the ahead window */ | |
551 | ra->prev_page = min(ra->prev_page, | |
552 | ra->ahead_start + ra->ahead_size - 1); | |
1da177e4 LT |
553 | } |
554 | ||
555 | out: | |
556 | return ra->prev_page + 1; | |
557 | } | |
d8733c29 | 558 | EXPORT_SYMBOL_GPL(page_cache_readahead); |
1da177e4 LT |
559 | |
560 | /* | |
561 | * handle_ra_miss() is called when it is known that a page which should have | |
562 | * been present in the pagecache (we just did some readahead there) was in fact | |
563 | * not found. This will happen if it was evicted by the VM (readahead | |
564 | * thrashing) | |
565 | * | |
566 | * Turn on the cache miss flag in the RA struct, this will cause the RA code | |
567 | * to reduce the RA size on the next read. | |
568 | */ | |
569 | void handle_ra_miss(struct address_space *mapping, | |
570 | struct file_ra_state *ra, pgoff_t offset) | |
571 | { | |
572 | ra->flags |= RA_FLAG_MISS; | |
573 | ra->flags &= ~RA_FLAG_INCACHE; | |
3b30bbd9 | 574 | ra->cache_hit = 0; |
1da177e4 LT |
575 | } |
576 | ||
577 | /* | |
578 | * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a | |
579 | * sensible upper limit. | |
580 | */ | |
581 | unsigned long max_sane_readahead(unsigned long nr) | |
582 | { | |
583 | unsigned long active; | |
584 | unsigned long inactive; | |
585 | unsigned long free; | |
586 | ||
587 | __get_zone_counts(&active, &inactive, &free, NODE_DATA(numa_node_id())); | |
588 | return min(nr, (inactive + free) / 2); | |
589 | } |