Root/
1 | /* |
2 | * mm/readahead.c - address_space-level file readahead. |
3 | * |
4 | * Copyright (C) 2002, Linus Torvalds |
5 | * |
6 | * 09Apr2002 Andrew Morton |
7 | * Initial version. |
8 | */ |
9 | |
10 | #include <linux/kernel.h> |
11 | #include <linux/fs.h> |
12 | #include <linux/gfp.h> |
13 | #include <linux/mm.h> |
14 | #include <linux/module.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 | |
21 | /* |
22 | * Initialise a struct file's readahead state. Assumes that the caller has |
23 | * memset *ra to zero. |
24 | */ |
25 | void |
26 | file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) |
27 | { |
28 | ra->ra_pages = mapping->backing_dev_info->ra_pages; |
29 | ra->prev_pos = -1; |
30 | } |
31 | EXPORT_SYMBOL_GPL(file_ra_state_init); |
32 | |
33 | #define list_to_page(head) (list_entry((head)->prev, struct page, lru)) |
34 | |
35 | /* |
36 | * see if a page needs releasing upon read_cache_pages() failure |
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 |
41 | */ |
42 | static void read_cache_pages_invalidate_page(struct address_space *mapping, |
43 | struct page *page) |
44 | { |
45 | if (page_has_private(page)) { |
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 | */ |
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)) { |
65 | victim = list_to_page(pages); |
66 | list_del(&victim->lru); |
67 | read_cache_pages_invalidate_page(mapping, victim); |
68 | } |
69 | } |
70 | |
71 | /** |
72 | * read_cache_pages - populate an address space with some pages & start reads against them |
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; |
85 | int ret = 0; |
86 | |
87 | while (!list_empty(pages)) { |
88 | page = list_to_page(pages); |
89 | list_del(&page->lru); |
90 | if (add_to_page_cache_lru(page, mapping, |
91 | page->index, GFP_KERNEL)) { |
92 | read_cache_pages_invalidate_page(mapping, page); |
93 | continue; |
94 | } |
95 | page_cache_release(page); |
96 | |
97 | ret = filler(data, page); |
98 | if (unlikely(ret)) { |
99 | read_cache_pages_invalidate_pages(mapping, pages); |
100 | break; |
101 | } |
102 | task_io_account_read(PAGE_CACHE_SIZE); |
103 | } |
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 | { |
112 | struct blk_plug plug; |
113 | unsigned page_idx; |
114 | int ret; |
115 | |
116 | blk_start_plug(&plug); |
117 | |
118 | if (mapping->a_ops->readpages) { |
119 | ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages); |
120 | /* Clean up the remaining pages */ |
121 | put_pages_list(pages); |
122 | goto out; |
123 | } |
124 | |
125 | for (page_idx = 0; page_idx < nr_pages; page_idx++) { |
126 | struct page *page = list_to_page(pages); |
127 | list_del(&page->lru); |
128 | if (!add_to_page_cache_lru(page, mapping, |
129 | page->index, GFP_KERNEL)) { |
130 | mapping->a_ops->readpage(filp, page); |
131 | } |
132 | page_cache_release(page); |
133 | } |
134 | ret = 0; |
135 | |
136 | out: |
137 | blk_finish_plug(&plug); |
138 | |
139 | return ret; |
140 | } |
141 | |
142 | /* |
143 | * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all |
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. |
149 | */ |
150 | static int |
151 | __do_page_cache_readahead(struct address_space *mapping, struct file *filp, |
152 | pgoff_t offset, unsigned long nr_to_read, |
153 | unsigned long lookahead_size) |
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 | |
166 | end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); |
167 | |
168 | /* |
169 | * Preallocate as many pages as we will need. |
170 | */ |
171 | for (page_idx = 0; page_idx < nr_to_read; page_idx++) { |
172 | pgoff_t page_offset = offset + page_idx; |
173 | |
174 | if (page_offset > end_index) |
175 | break; |
176 | |
177 | rcu_read_lock(); |
178 | page = radix_tree_lookup(&mapping->page_tree, page_offset); |
179 | rcu_read_unlock(); |
180 | if (page) |
181 | continue; |
182 | |
183 | page = page_cache_alloc_readahead(mapping); |
184 | if (!page) |
185 | break; |
186 | page->index = page_offset; |
187 | list_add(&page->lru, &page_pool); |
188 | if (page_idx == nr_to_read - lookahead_size) |
189 | SetPageReadahead(page); |
190 | ret++; |
191 | } |
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)); |
201 | out: |
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 | */ |
209 | int force_page_cache_readahead(struct address_space *mapping, struct file *filp, |
210 | pgoff_t offset, unsigned long nr_to_read) |
211 | { |
212 | int ret = 0; |
213 | |
214 | if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) |
215 | return -EINVAL; |
216 | |
217 | nr_to_read = max_sane_readahead(nr_to_read); |
218 | while (nr_to_read) { |
219 | int err; |
220 | |
221 | unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE; |
222 | |
223 | if (this_chunk > nr_to_read) |
224 | this_chunk = nr_to_read; |
225 | err = __do_page_cache_readahead(mapping, filp, |
226 | offset, this_chunk, 0); |
227 | if (err < 0) { |
228 | ret = err; |
229 | break; |
230 | } |
231 | ret += err; |
232 | offset += this_chunk; |
233 | nr_to_read -= this_chunk; |
234 | } |
235 | return ret; |
236 | } |
237 | |
238 | /* |
239 | * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a |
240 | * sensible upper limit. |
241 | */ |
242 | unsigned long max_sane_readahead(unsigned long nr) |
243 | { |
244 | return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE) |
245 | + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2); |
246 | } |
247 | |
248 | /* |
249 | * Submit IO for the read-ahead request in file_ra_state. |
250 | */ |
251 | unsigned long ra_submit(struct file_ra_state *ra, |
252 | struct address_space *mapping, struct file *filp) |
253 | { |
254 | int actual; |
255 | |
256 | actual = __do_page_cache_readahead(mapping, filp, |
257 | ra->start, ra->size, ra->async_size); |
258 | |
259 | return actual; |
260 | } |
261 | |
262 | /* |
263 | * Set the initial window size, round to next power of 2 and square |
264 | * for small size, x 4 for medium, and x 2 for large |
265 | * for 128k (32 page) max ra |
266 | * 1-8 page = 32k initial, > 8 page = 128k initial |
267 | */ |
268 | static unsigned long get_init_ra_size(unsigned long size, unsigned long max) |
269 | { |
270 | unsigned long newsize = roundup_pow_of_two(size); |
271 | |
272 | if (newsize <= max / 32) |
273 | newsize = newsize * 4; |
274 | else if (newsize <= max / 4) |
275 | newsize = newsize * 2; |
276 | else |
277 | newsize = max; |
278 | |
279 | return newsize; |
280 | } |
281 | |
282 | /* |
283 | * Get the previous window size, ramp it up, and |
284 | * return it as the new window size. |
285 | */ |
286 | static unsigned long get_next_ra_size(struct file_ra_state *ra, |
287 | unsigned long max) |
288 | { |
289 | unsigned long cur = ra->size; |
290 | unsigned long newsize; |
291 | |
292 | if (cur < max / 16) |
293 | newsize = 4 * cur; |
294 | else |
295 | newsize = 2 * cur; |
296 | |
297 | return min(newsize, max); |
298 | } |
299 | |
300 | /* |
301 | * On-demand readahead design. |
302 | * |
303 | * The fields in struct file_ra_state represent the most-recently-executed |
304 | * readahead attempt: |
305 | * |
306 | * |<----- async_size ---------| |
307 | * |------------------- size -------------------->| |
308 | * |==================#===========================| |
309 | * ^start ^page marked with PG_readahead |
310 | * |
311 | * To overlap application thinking time and disk I/O time, we do |
312 | * `readahead pipelining': Do not wait until the application consumed all |
313 | * readahead pages and stalled on the missing page at readahead_index; |
314 | * Instead, submit an asynchronous readahead I/O as soon as there are |
315 | * only async_size pages left in the readahead window. Normally async_size |
316 | * will be equal to size, for maximum pipelining. |
317 | * |
318 | * In interleaved sequential reads, concurrent streams on the same fd can |
319 | * be invalidating each other's readahead state. So we flag the new readahead |
320 | * page at (start+size-async_size) with PG_readahead, and use it as readahead |
321 | * indicator. The flag won't be set on already cached pages, to avoid the |
322 | * readahead-for-nothing fuss, saving pointless page cache lookups. |
323 | * |
324 | * prev_pos tracks the last visited byte in the _previous_ read request. |
325 | * It should be maintained by the caller, and will be used for detecting |
326 | * small random reads. Note that the readahead algorithm checks loosely |
327 | * for sequential patterns. Hence interleaved reads might be served as |
328 | * sequential ones. |
329 | * |
330 | * There is a special-case: if the first page which the application tries to |
331 | * read happens to be the first page of the file, it is assumed that a linear |
332 | * read is about to happen and the window is immediately set to the initial size |
333 | * based on I/O request size and the max_readahead. |
334 | * |
335 | * The code ramps up the readahead size aggressively at first, but slow down as |
336 | * it approaches max_readhead. |
337 | */ |
338 | |
339 | /* |
340 | * Count contiguously cached pages from @offset-1 to @offset-@max, |
341 | * this count is a conservative estimation of |
342 | * - length of the sequential read sequence, or |
343 | * - thrashing threshold in memory tight systems |
344 | */ |
345 | static pgoff_t count_history_pages(struct address_space *mapping, |
346 | struct file_ra_state *ra, |
347 | pgoff_t offset, unsigned long max) |
348 | { |
349 | pgoff_t head; |
350 | |
351 | rcu_read_lock(); |
352 | head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max); |
353 | rcu_read_unlock(); |
354 | |
355 | return offset - 1 - head; |
356 | } |
357 | |
358 | /* |
359 | * page cache context based read-ahead |
360 | */ |
361 | static int try_context_readahead(struct address_space *mapping, |
362 | struct file_ra_state *ra, |
363 | pgoff_t offset, |
364 | unsigned long req_size, |
365 | unsigned long max) |
366 | { |
367 | pgoff_t size; |
368 | |
369 | size = count_history_pages(mapping, ra, offset, max); |
370 | |
371 | /* |
372 | * no history pages: |
373 | * it could be a random read |
374 | */ |
375 | if (!size) |
376 | return 0; |
377 | |
378 | /* |
379 | * starts from beginning of file: |
380 | * it is a strong indication of long-run stream (or whole-file-read) |
381 | */ |
382 | if (size >= offset) |
383 | size *= 2; |
384 | |
385 | ra->start = offset; |
386 | ra->size = get_init_ra_size(size + req_size, max); |
387 | ra->async_size = ra->size; |
388 | |
389 | return 1; |
390 | } |
391 | |
392 | /* |
393 | * A minimal readahead algorithm for trivial sequential/random reads. |
394 | */ |
395 | static unsigned long |
396 | ondemand_readahead(struct address_space *mapping, |
397 | struct file_ra_state *ra, struct file *filp, |
398 | bool hit_readahead_marker, pgoff_t offset, |
399 | unsigned long req_size) |
400 | { |
401 | unsigned long max = max_sane_readahead(ra->ra_pages); |
402 | |
403 | /* |
404 | * start of file |
405 | */ |
406 | if (!offset) |
407 | goto initial_readahead; |
408 | |
409 | /* |
410 | * It's the expected callback offset, assume sequential access. |
411 | * Ramp up sizes, and push forward the readahead window. |
412 | */ |
413 | if ((offset == (ra->start + ra->size - ra->async_size) || |
414 | offset == (ra->start + ra->size))) { |
415 | ra->start += ra->size; |
416 | ra->size = get_next_ra_size(ra, max); |
417 | ra->async_size = ra->size; |
418 | goto readit; |
419 | } |
420 | |
421 | /* |
422 | * Hit a marked page without valid readahead state. |
423 | * E.g. interleaved reads. |
424 | * Query the pagecache for async_size, which normally equals to |
425 | * readahead size. Ramp it up and use it as the new readahead size. |
426 | */ |
427 | if (hit_readahead_marker) { |
428 | pgoff_t start; |
429 | |
430 | rcu_read_lock(); |
431 | start = radix_tree_next_hole(&mapping->page_tree, offset+1,max); |
432 | rcu_read_unlock(); |
433 | |
434 | if (!start || start - offset > max) |
435 | return 0; |
436 | |
437 | ra->start = start; |
438 | ra->size = start - offset; /* old async_size */ |
439 | ra->size += req_size; |
440 | ra->size = get_next_ra_size(ra, max); |
441 | ra->async_size = ra->size; |
442 | goto readit; |
443 | } |
444 | |
445 | /* |
446 | * oversize read |
447 | */ |
448 | if (req_size > max) |
449 | goto initial_readahead; |
450 | |
451 | /* |
452 | * sequential cache miss |
453 | */ |
454 | if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL) |
455 | goto initial_readahead; |
456 | |
457 | /* |
458 | * Query the page cache and look for the traces(cached history pages) |
459 | * that a sequential stream would leave behind. |
460 | */ |
461 | if (try_context_readahead(mapping, ra, offset, req_size, max)) |
462 | goto readit; |
463 | |
464 | /* |
465 | * standalone, small random read |
466 | * Read as is, and do not pollute the readahead state. |
467 | */ |
468 | return __do_page_cache_readahead(mapping, filp, offset, req_size, 0); |
469 | |
470 | initial_readahead: |
471 | ra->start = offset; |
472 | ra->size = get_init_ra_size(req_size, max); |
473 | ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; |
474 | |
475 | readit: |
476 | /* |
477 | * Will this read hit the readahead marker made by itself? |
478 | * If so, trigger the readahead marker hit now, and merge |
479 | * the resulted next readahead window into the current one. |
480 | */ |
481 | if (offset == ra->start && ra->size == ra->async_size) { |
482 | ra->async_size = get_next_ra_size(ra, max); |
483 | ra->size += ra->async_size; |
484 | } |
485 | |
486 | return ra_submit(ra, mapping, filp); |
487 | } |
488 | |
489 | /** |
490 | * page_cache_sync_readahead - generic file readahead |
491 | * @mapping: address_space which holds the pagecache and I/O vectors |
492 | * @ra: file_ra_state which holds the readahead state |
493 | * @filp: passed on to ->readpage() and ->readpages() |
494 | * @offset: start offset into @mapping, in pagecache page-sized units |
495 | * @req_size: hint: total size of the read which the caller is performing in |
496 | * pagecache pages |
497 | * |
498 | * page_cache_sync_readahead() should be called when a cache miss happened: |
499 | * it will submit the read. The readahead logic may decide to piggyback more |
500 | * pages onto the read request if access patterns suggest it will improve |
501 | * performance. |
502 | */ |
503 | void page_cache_sync_readahead(struct address_space *mapping, |
504 | struct file_ra_state *ra, struct file *filp, |
505 | pgoff_t offset, unsigned long req_size) |
506 | { |
507 | /* no read-ahead */ |
508 | if (!ra->ra_pages) |
509 | return; |
510 | |
511 | /* be dumb */ |
512 | if (filp && (filp->f_mode & FMODE_RANDOM)) { |
513 | force_page_cache_readahead(mapping, filp, offset, req_size); |
514 | return; |
515 | } |
516 | |
517 | /* do read-ahead */ |
518 | ondemand_readahead(mapping, ra, filp, false, offset, req_size); |
519 | } |
520 | EXPORT_SYMBOL_GPL(page_cache_sync_readahead); |
521 | |
522 | /** |
523 | * page_cache_async_readahead - file readahead for marked pages |
524 | * @mapping: address_space which holds the pagecache and I/O vectors |
525 | * @ra: file_ra_state which holds the readahead state |
526 | * @filp: passed on to ->readpage() and ->readpages() |
527 | * @page: the page at @offset which has the PG_readahead flag set |
528 | * @offset: start offset into @mapping, in pagecache page-sized units |
529 | * @req_size: hint: total size of the read which the caller is performing in |
530 | * pagecache pages |
531 | * |
532 | * page_cache_async_readahead() should be called when a page is used which |
533 | * has the PG_readahead flag; this is a marker to suggest that the application |
534 | * has used up enough of the readahead window that we should start pulling in |
535 | * more pages. |
536 | */ |
537 | void |
538 | page_cache_async_readahead(struct address_space *mapping, |
539 | struct file_ra_state *ra, struct file *filp, |
540 | struct page *page, pgoff_t offset, |
541 | unsigned long req_size) |
542 | { |
543 | /* no read-ahead */ |
544 | if (!ra->ra_pages) |
545 | return; |
546 | |
547 | /* |
548 | * Same bit is used for PG_readahead and PG_reclaim. |
549 | */ |
550 | if (PageWriteback(page)) |
551 | return; |
552 | |
553 | ClearPageReadahead(page); |
554 | |
555 | /* |
556 | * Defer asynchronous read-ahead on IO congestion. |
557 | */ |
558 | if (bdi_read_congested(mapping->backing_dev_info)) |
559 | return; |
560 | |
561 | /* do read-ahead */ |
562 | ondemand_readahead(mapping, ra, filp, true, offset, req_size); |
563 | } |
564 | EXPORT_SYMBOL_GPL(page_cache_async_readahead); |
565 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9