blob: dfa9a1a03a116c7659d0d71134a3450a8d69026f [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * mm/readahead.c - address_space-level file readahead.
3 *
4 * Copyright (C) 2002, Linus Torvalds
5 *
Francois Camie1f8e872008-10-15 22:01:59 -07006 * 09Apr2002 Andrew Morton
Linus Torvalds1da177e2005-04-16 15:20:36 -07007 * Initial version.
8 */
9
10#include <linux/kernel.h>
11#include <linux/fs.h>
Tejun Heo5a0e3ad2010-03-24 17:04:11 +090012#include <linux/gfp.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070013#include <linux/mm.h>
14#include <linux/module.h>
15#include <linux/blkdev.h>
16#include <linux/backing-dev.h>
Andrew Morton8bde37f2006-12-10 02:19:40 -080017#include <linux/task_io_accounting_ops.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070018#include <linux/pagevec.h>
Jens Axboef5ff8422007-09-21 09:19:54 +020019#include <linux/pagemap.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070020
Linus Torvalds1da177e2005-04-16 15:20:36 -070021/*
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;
Fengguang Wuf4e6b492007-10-16 01:24:33 -070029 ra->prev_pos = -1;
Linus Torvalds1da177e2005-04-16 15:20:36 -070030}
Steven Whitehoused41cc702006-01-30 08:53:33 +000031EXPORT_SYMBOL_GPL(file_ra_state_init);
Linus Torvalds1da177e2005-04-16 15:20:36 -070032
Linus Torvalds1da177e2005-04-16 15:20:36 -070033#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
34
David Howells03fb3d22009-04-03 16:42:35 +010035/*
36 * see if a page needs releasing upon read_cache_pages() failure
David Howells266cf652009-04-03 16:42:36 +010037 * - 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
David Howells03fb3d22009-04-03 16:42:35 +010041 */
42static void read_cache_pages_invalidate_page(struct address_space *mapping,
43 struct page *page)
44{
David Howells266cf652009-04-03 16:42:36 +010045 if (page_has_private(page)) {
David Howells03fb3d22009-04-03 16:42:35 +010046 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
Linus Torvalds1da177e2005-04-16 15:20:36 -070071/**
Randy Dunlapbd40cdd2006-06-25 05:48:08 -070072 * read_cache_pages - populate an address space with some pages & start reads against them
Linus Torvalds1da177e2005-04-16 15:20:36 -070073 * @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;
Linus Torvalds1da177e2005-04-16 15:20:36 -070085 int ret = 0;
86
Linus Torvalds1da177e2005-04-16 15:20:36 -070087 while (!list_empty(pages)) {
88 page = list_to_page(pages);
89 list_del(&page->lru);
Nick Piggineb2be182007-10-16 01:24:57 -070090 if (add_to_page_cache_lru(page, mapping,
91 page->index, GFP_KERNEL)) {
David Howells03fb3d22009-04-03 16:42:35 +010092 read_cache_pages_invalidate_page(mapping, page);
Linus Torvalds1da177e2005-04-16 15:20:36 -070093 continue;
94 }
Nick Piggineb2be182007-10-16 01:24:57 -070095 page_cache_release(page);
96
Linus Torvalds1da177e2005-04-16 15:20:36 -070097 ret = filler(data, page);
Nick Piggineb2be182007-10-16 01:24:57 -070098 if (unlikely(ret)) {
David Howells03fb3d22009-04-03 16:42:35 +010099 read_cache_pages_invalidate_pages(mapping, pages);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700100 break;
101 }
Andrew Morton8bde37f2006-12-10 02:19:40 -0800102 task_io_account_read(PAGE_CACHE_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104 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;
Zach Brown994fc28c2005-12-15 14:28:17 -0800113 int ret;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114
115 if (mapping->a_ops->readpages) {
116 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
OGAWA Hirofumi029e3322006-11-02 22:07:06 -0800117 /* Clean up the remaining pages */
118 put_pages_list(pages);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119 goto out;
120 }
121
Linus Torvalds1da177e2005-04-16 15:20:36 -0700122 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
123 struct page *page = list_to_page(pages);
124 list_del(&page->lru);
Nick Piggineb2be182007-10-16 01:24:57 -0700125 if (!add_to_page_cache_lru(page, mapping,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126 page->index, GFP_KERNEL)) {
Zach Brown9f1a3cf2006-06-25 05:46:46 -0700127 mapping->a_ops->readpage(filp, page);
Nick Piggineb2be182007-10-16 01:24:57 -0700128 }
129 page_cache_release(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700130 }
Zach Brown994fc28c2005-12-15 14:28:17 -0800131 ret = 0;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700132out:
133 return ret;
134}
135
136/*
Wu Fengguangd30a1102009-06-16 15:31:30 -0700137 * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138 * 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700143 */
144static int
145__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
Fengguang Wu46fc3e72007-07-19 01:47:57 -0700146 pgoff_t offset, unsigned long nr_to_read,
147 unsigned long lookahead_size)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700148{
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
Fengguang Wu46fc3e72007-07-19 01:47:57 -0700160 end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161
162 /*
163 * Preallocate as many pages as we will need.
164 */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
Andrew Morton7361f4d2005-11-07 00:59:28 -0800166 pgoff_t page_offset = offset + page_idx;
Fengguang Wuc743d962007-07-19 01:48:04 -0700167
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168 if (page_offset > end_index)
169 break;
170
Nick Piggin00128182007-10-16 01:24:40 -0700171 rcu_read_lock();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700172 page = radix_tree_lookup(&mapping->page_tree, page_offset);
Nick Piggin00128182007-10-16 01:24:40 -0700173 rcu_read_unlock();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174 if (page)
175 continue;
176
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177 page = page_cache_alloc_cold(mapping);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178 if (!page)
179 break;
180 page->index = page_offset;
181 list_add(&page->lru, &page_pool);
Fengguang Wu46fc3e72007-07-19 01:47:57 -0700182 if (page_idx == nr_to_read - lookahead_size)
183 SetPageReadahead(page);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700184 ret++;
185 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
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,
Andrew Morton7361f4d2005-11-07 00:59:28 -0800204 pgoff_t offset, unsigned long nr_to_read)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700205{
206 int ret = 0;
207
208 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
209 return -EINVAL;
210
Wu Fengguangf7e839d2009-06-16 15:31:20 -0700211 nr_to_read = max_sane_readahead(nr_to_read);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212 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,
Fengguang Wu46fc3e72007-07-19 01:47:57 -0700220 offset, this_chunk, 0);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700221 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
232/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233 * 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{
Rik van Riel4f98a2f2008-10-18 20:26:32 -0700238 return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
Christoph Lameter05a04162007-02-10 01:43:05 -0800239 + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700240}
Fengguang Wu5ce11102007-07-19 01:47:59 -0700241
242/*
243 * Submit IO for the read-ahead request in file_ra_state.
244 */
Wu Fengguangd30a1102009-06-16 15:31:30 -0700245unsigned long ra_submit(struct file_ra_state *ra,
Fengguang Wu5ce11102007-07-19 01:47:59 -0700246 struct address_space *mapping, struct file *filp)
247{
Fengguang Wu5ce11102007-07-19 01:47:59 -0700248 int actual;
249
Fengguang Wu5ce11102007-07-19 01:47:59 -0700250 actual = __do_page_cache_readahead(mapping, filp,
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700251 ra->start, ra->size, ra->async_size);
Fengguang Wu5ce11102007-07-19 01:47:59 -0700252
253 return actual;
254}
Fengguang Wu122a21d2007-07-19 01:48:01 -0700255
256/*
Fengguang Wuc743d962007-07-19 01:48:04 -0700257 * 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
276/*
Fengguang Wu122a21d2007-07-19 01:48:01 -0700277 * Get the previous window size, ramp it up, and
278 * return it as the new window size.
279 */
Fengguang Wuc743d962007-07-19 01:48:04 -0700280static unsigned long get_next_ra_size(struct file_ra_state *ra,
Fengguang Wu122a21d2007-07-19 01:48:01 -0700281 unsigned long max)
282{
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700283 unsigned long cur = ra->size;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700284 unsigned long newsize;
285
286 if (cur < max / 16)
Fengguang Wuc743d962007-07-19 01:48:04 -0700287 newsize = 4 * cur;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700288 else
Fengguang Wuc743d962007-07-19 01:48:04 -0700289 newsize = 2 * cur;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700290
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 *
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700300 * |<----- async_size ---------|
301 * |------------------- size -------------------->|
302 * |==================#===========================|
303 * ^start ^page marked with PG_readahead
Fengguang Wu122a21d2007-07-19 01:48:01 -0700304 *
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;
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700308 * 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.
Fengguang Wu122a21d2007-07-19 01:48:01 -0700311 *
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
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700314 * page at (start+size-async_size) with PG_readahead, and use it as readahead
Fengguang Wu122a21d2007-07-19 01:48:01 -0700315 * 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 *
Fengguang Wuf4e6b492007-10-16 01:24:33 -0700318 * prev_pos tracks the last visited byte in the _previous_ read request.
Fengguang Wu122a21d2007-07-19 01:48:01 -0700319 * 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
333/*
Wu Fengguang10be0b32009-06-16 15:31:36 -0700334 * 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
386/*
Fengguang Wu122a21d2007-07-19 01:48:01 -0700387 * 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,
Rusty Russellcf914a72007-07-19 01:48:08 -0700392 bool hit_readahead_marker, pgoff_t offset,
Fengguang Wu122a21d2007-07-19 01:48:01 -0700393 unsigned long req_size)
394{
Wu Fengguangfc31d162009-06-16 15:31:21 -0700395 unsigned long max = max_sane_readahead(ra->ra_pages);
Wu Fengguang045a2522009-06-16 15:31:33 -0700396
397 /*
398 * start of file
399 */
400 if (!offset)
401 goto initial_readahead;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700402
403 /*
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700404 * It's the expected callback offset, assume sequential access.
Fengguang Wu122a21d2007-07-19 01:48:01 -0700405 * Ramp up sizes, and push forward the readahead window.
406 */
Wu Fengguang045a2522009-06-16 15:31:33 -0700407 if ((offset == (ra->start + ra->size - ra->async_size) ||
408 offset == (ra->start + ra->size))) {
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700409 ra->start += ra->size;
410 ra->size = get_next_ra_size(ra, max);
411 ra->async_size = ra->size;
412 goto readit;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700413 }
414
Fengguang Wu122a21d2007-07-19 01:48:01 -0700415 /*
Fengguang Wu6b10c6c2007-10-16 01:24:34 -0700416 * 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
Nick Piggin30002ed2008-07-25 19:45:28 -0700424 rcu_read_lock();
Wu Fengguangcaca7cb2009-06-16 15:31:21 -0700425 start = radix_tree_next_hole(&mapping->page_tree, offset+1,max);
Nick Piggin30002ed2008-07-25 19:45:28 -0700426 rcu_read_unlock();
Fengguang Wu6b10c6c2007-10-16 01:24:34 -0700427
428 if (!start || start - offset > max)
429 return 0;
430
431 ra->start = start;
432 ra->size = start - offset; /* old async_size */
Wu Fengguang160334a2009-06-16 15:31:23 -0700433 ra->size += req_size;
Fengguang Wu6b10c6c2007-10-16 01:24:34 -0700434 ra->size = get_next_ra_size(ra, max);
435 ra->async_size = ra->size;
436 goto readit;
437 }
438
439 /*
Wu Fengguang045a2522009-06-16 15:31:33 -0700440 * oversize read
Fengguang Wu122a21d2007-07-19 01:48:01 -0700441 */
Wu Fengguang045a2522009-06-16 15:31:33 -0700442 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
451 /*
Wu Fengguang10be0b32009-06-16 15:31:36 -0700452 * 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
458 /*
Wu Fengguang045a2522009-06-16 15:31:33 -0700459 * 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:
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700465 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;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700468
Fengguang Wuf9acc8c2007-07-19 01:48:08 -0700469readit:
Wu Fengguang51daa882009-06-16 15:31:24 -0700470 /*
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
Fengguang Wu122a21d2007-07-19 01:48:01 -0700480 return ra_submit(ra, mapping, filp);
481}
482
483/**
Rusty Russellcf914a72007-07-19 01:48:08 -0700484 * page_cache_sync_readahead - generic file readahead
Fengguang Wu122a21d2007-07-19 01:48:01 -0700485 * @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()
Rusty Russellcf914a72007-07-19 01:48:08 -0700488 * @offset: start offset into @mapping, in pagecache page-sized units
Fengguang Wu122a21d2007-07-19 01:48:01 -0700489 * @req_size: hint: total size of the read which the caller is performing in
Rusty Russellcf914a72007-07-19 01:48:08 -0700490 * pagecache pages
Fengguang Wu122a21d2007-07-19 01:48:01 -0700491 *
Rusty Russellcf914a72007-07-19 01:48:08 -0700492 * 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.
Fengguang Wu122a21d2007-07-19 01:48:01 -0700496 */
Rusty Russellcf914a72007-07-19 01:48:08 -0700497void 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)
Fengguang Wu122a21d2007-07-19 01:48:01 -0700500{
501 /* no read-ahead */
502 if (!ra->ra_pages)
Rusty Russellcf914a72007-07-19 01:48:08 -0700503 return;
Fengguang Wu122a21d2007-07-19 01:48:01 -0700504
Wu Fengguang01414502010-03-05 13:42:03 -0800505 /* be dumb */
Wu Fengguang70655c02010-04-06 14:34:53 -0700506 if (filp && (filp->f_mode & FMODE_RANDOM)) {
Wu Fengguang01414502010-03-05 13:42:03 -0800507 force_page_cache_readahead(mapping, filp, offset, req_size);
508 return;
509 }
510
Fengguang Wu122a21d2007-07-19 01:48:01 -0700511 /* do read-ahead */
Rusty Russellcf914a72007-07-19 01:48:08 -0700512 ondemand_readahead(mapping, ra, filp, false, offset, req_size);
Fengguang Wu122a21d2007-07-19 01:48:01 -0700513}
Rusty Russellcf914a72007-07-19 01:48:08 -0700514EXPORT_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 *
526 * page_cache_async_ondemand() should be called when a page is used which
Randy Dunlapf7850d92008-03-19 17:01:02 -0700527 * has the PG_readahead flag; this is a marker to suggest that the application
Rusty Russellcf914a72007-07-19 01:48:08 -0700528 * has used up enough of the readahead window that we should start pulling in
Randy Dunlapf7850d92008-03-19 17:01:02 -0700529 * more pages.
530 */
Rusty Russellcf914a72007-07-19 01:48:08 -0700531void
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;
554
555 /* do read-ahead */
556 ondemand_readahead(mapping, ra, filp, true, offset, req_size);
Hisashi Hifumi65a80b42009-12-17 15:27:26 -0800557
558#ifdef CONFIG_BLOCK
559 /*
560 * Normally the current page is !uptodate and lock_page() will be
561 * immediately called to implicitly unplug the device. However this
562 * is not always true for RAID conifgurations, where data arrives
563 * not strictly in their submission order. In this case we need to
564 * explicitly kick off the IO.
565 */
566 if (PageUptodate(page))
567 blk_run_backing_dev(mapping->backing_dev_info, NULL);
568#endif
Rusty Russellcf914a72007-07-19 01:48:08 -0700569}
570EXPORT_SYMBOL_GPL(page_cache_async_readahead);