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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/gfp.h>
12#include <linux/export.h>
13#include <linux/blkdev.h>
14#include <linux/backing-dev.h>
15#include <linux/task_io_accounting_ops.h>
16#include <linux/pagevec.h>
17#include <linux/pagemap.h>
18#include <linux/syscalls.h>
19#include <linux/file.h>
20#include <linux/mm_inline.h>
21
22#include "internal.h"
23
24/*
25 * Initialise a struct file's readahead state. Assumes that the caller has
26 * memset *ra to zero.
27 */
28void
29file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
30{
31 ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
32 ra->prev_pos = -1;
33}
34EXPORT_SYMBOL_GPL(file_ra_state_init);
35
36/*
37 * see if a page needs releasing upon read_cache_pages() failure
38 * - the caller of read_cache_pages() may have set PG_private or PG_fscache
39 * before calling, such as the NFS fs marking pages that are cached locally
40 * on disk, thus we need to give the fs a chance to clean up in the event of
41 * an error
42 */
43static void read_cache_pages_invalidate_page(struct address_space *mapping,
44 struct page *page)
45{
46 if (page_has_private(page)) {
47 if (!trylock_page(page))
48 BUG();
49 page->mapping = mapping;
50 do_invalidatepage(page, 0, PAGE_SIZE);
51 page->mapping = NULL;
52 unlock_page(page);
53 }
54 put_page(page);
55}
56
57/*
58 * release a list of pages, invalidating them first if need be
59 */
60static void read_cache_pages_invalidate_pages(struct address_space *mapping,
61 struct list_head *pages)
62{
63 struct page *victim;
64
65 while (!list_empty(pages)) {
66 victim = lru_to_page(pages);
67 list_del(&victim->lru);
68 read_cache_pages_invalidate_page(mapping, victim);
69 }
70}
71
72/**
73 * read_cache_pages - populate an address space with some pages & start reads against them
74 * @mapping: the address_space
75 * @pages: The address of a list_head which contains the target pages. These
76 * pages have their ->index populated and are otherwise uninitialised.
77 * @filler: callback routine for filling a single page.
78 * @data: private data for the callback routine.
79 *
80 * Hides the details of the LRU cache etc from the filesystems.
81 */
82int read_cache_pages(struct address_space *mapping, struct list_head *pages,
83 int (*filler)(void *, struct page *), void *data)
84{
85 struct page *page;
86 int ret = 0;
87
88 while (!list_empty(pages)) {
89 page = lru_to_page(pages);
90 list_del(&page->lru);
91 if (add_to_page_cache_lru(page, mapping, page->index,
92 mapping_gfp_constraint(mapping, GFP_KERNEL))) {
93 read_cache_pages_invalidate_page(mapping, page);
94 continue;
95 }
96 put_page(page);
97
98 ret = filler(data, page);
99 if (unlikely(ret)) {
100 read_cache_pages_invalidate_pages(mapping, pages);
101 break;
102 }
103 task_io_account_read(PAGE_SIZE);
104 }
105 return ret;
106}
107
108EXPORT_SYMBOL(read_cache_pages);
109
110static int read_pages(struct address_space *mapping, struct file *filp,
111 struct list_head *pages, unsigned nr_pages)
112{
113 struct blk_plug plug;
114 unsigned page_idx;
115 int ret;
116
117 blk_start_plug(&plug);
118
119 if (mapping->a_ops->readpages) {
120 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
121 /* Clean up the remaining pages */
122 put_pages_list(pages);
123 goto out;
124 }
125
126 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
127 struct page *page = lru_to_page(pages);
128 list_del(&page->lru);
129 if (!add_to_page_cache_lru(page, mapping, page->index,
130 mapping_gfp_constraint(mapping, GFP_KERNEL))) {
131 mapping->a_ops->readpage(filp, page);
132 }
133 put_page(page);
134 }
135 ret = 0;
136
137out:
138 blk_finish_plug(&plug);
139
140 return ret;
141}
142
143/*
144 * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
145 * the pages first, then submits them all for I/O. This avoids the very bad
146 * behaviour which would occur if page allocations are causing VM writeback.
147 * We really don't want to intermingle reads and writes like that.
148 *
149 * Returns the number of pages requested, or the maximum amount of I/O allowed.
150 */
151int __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_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 && !radix_tree_exceptional_entry(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));
201out:
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 */
209int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
210 pgoff_t offset, unsigned long nr_to_read)
211{
212 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
213 return -EINVAL;
214
215 nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages);
216 while (nr_to_read) {
217 int err;
218
219 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
220
221 if (this_chunk > nr_to_read)
222 this_chunk = nr_to_read;
223 err = __do_page_cache_readahead(mapping, filp,
224 offset, this_chunk, 0);
225 if (err < 0)
226 return err;
227
228 offset += this_chunk;
229 nr_to_read -= this_chunk;
230 }
231 return 0;
232}
233
234/*
235 * Set the initial window size, round to next power of 2 and square
236 * for small size, x 4 for medium, and x 2 for large
237 * for 128k (32 page) max ra
238 * 1-8 page = 32k initial, > 8 page = 128k initial
239 */
240static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
241{
242 unsigned long newsize = roundup_pow_of_two(size);
243
244 if (newsize <= max / 32)
245 newsize = newsize * 4;
246 else if (newsize <= max / 4)
247 newsize = newsize * 2;
248 else
249 newsize = max;
250
251 return newsize;
252}
253
254/*
255 * Get the previous window size, ramp it up, and
256 * return it as the new window size.
257 */
258static unsigned long get_next_ra_size(struct file_ra_state *ra,
259 unsigned long max)
260{
261 unsigned long cur = ra->size;
262 unsigned long newsize;
263
264 if (cur < max / 16)
265 newsize = 4 * cur;
266 else
267 newsize = 2 * cur;
268
269 return min(newsize, max);
270}
271
272/*
273 * On-demand readahead design.
274 *
275 * The fields in struct file_ra_state represent the most-recently-executed
276 * readahead attempt:
277 *
278 * |<----- async_size ---------|
279 * |------------------- size -------------------->|
280 * |==================#===========================|
281 * ^start ^page marked with PG_readahead
282 *
283 * To overlap application thinking time and disk I/O time, we do
284 * `readahead pipelining': Do not wait until the application consumed all
285 * readahead pages and stalled on the missing page at readahead_index;
286 * Instead, submit an asynchronous readahead I/O as soon as there are
287 * only async_size pages left in the readahead window. Normally async_size
288 * will be equal to size, for maximum pipelining.
289 *
290 * In interleaved sequential reads, concurrent streams on the same fd can
291 * be invalidating each other's readahead state. So we flag the new readahead
292 * page at (start+size-async_size) with PG_readahead, and use it as readahead
293 * indicator. The flag won't be set on already cached pages, to avoid the
294 * readahead-for-nothing fuss, saving pointless page cache lookups.
295 *
296 * prev_pos tracks the last visited byte in the _previous_ read request.
297 * It should be maintained by the caller, and will be used for detecting
298 * small random reads. Note that the readahead algorithm checks loosely
299 * for sequential patterns. Hence interleaved reads might be served as
300 * sequential ones.
301 *
302 * There is a special-case: if the first page which the application tries to
303 * read happens to be the first page of the file, it is assumed that a linear
304 * read is about to happen and the window is immediately set to the initial size
305 * based on I/O request size and the max_readahead.
306 *
307 * The code ramps up the readahead size aggressively at first, but slow down as
308 * it approaches max_readhead.
309 */
310
311/*
312 * Count contiguously cached pages from @offset-1 to @offset-@max,
313 * this count is a conservative estimation of
314 * - length of the sequential read sequence, or
315 * - thrashing threshold in memory tight systems
316 */
317static pgoff_t count_history_pages(struct address_space *mapping,
318 pgoff_t offset, unsigned long max)
319{
320 pgoff_t head;
321
322 rcu_read_lock();
323 head = page_cache_prev_hole(mapping, offset - 1, max);
324 rcu_read_unlock();
325
326 return offset - 1 - head;
327}
328
329/*
330 * page cache context based read-ahead
331 */
332static int try_context_readahead(struct address_space *mapping,
333 struct file_ra_state *ra,
334 pgoff_t offset,
335 unsigned long req_size,
336 unsigned long max)
337{
338 pgoff_t size;
339
340 size = count_history_pages(mapping, offset, max);
341
342 /*
343 * not enough history pages:
344 * it could be a random read
345 */
346 if (size <= req_size)
347 return 0;
348
349 /*
350 * starts from beginning of file:
351 * it is a strong indication of long-run stream (or whole-file-read)
352 */
353 if (size >= offset)
354 size *= 2;
355
356 ra->start = offset;
357 ra->size = min(size + req_size, max);
358 ra->async_size = 1;
359
360 return 1;
361}
362
363/*
364 * A minimal readahead algorithm for trivial sequential/random reads.
365 */
366static unsigned long
367ondemand_readahead(struct address_space *mapping,
368 struct file_ra_state *ra, struct file *filp,
369 bool hit_readahead_marker, pgoff_t offset,
370 unsigned long req_size)
371{
372 unsigned long max = ra->ra_pages;
373 pgoff_t prev_offset;
374
375 /*
376 * start of file
377 */
378 if (!offset)
379 goto initial_readahead;
380
381 /*
382 * It's the expected callback offset, assume sequential access.
383 * Ramp up sizes, and push forward the readahead window.
384 */
385 if ((offset == (ra->start + ra->size - ra->async_size) ||
386 offset == (ra->start + ra->size))) {
387 ra->start += ra->size;
388 ra->size = get_next_ra_size(ra, max);
389 ra->async_size = ra->size;
390 goto readit;
391 }
392
393 /*
394 * Hit a marked page without valid readahead state.
395 * E.g. interleaved reads.
396 * Query the pagecache for async_size, which normally equals to
397 * readahead size. Ramp it up and use it as the new readahead size.
398 */
399 if (hit_readahead_marker) {
400 pgoff_t start;
401
402 rcu_read_lock();
403 start = page_cache_next_hole(mapping, offset + 1, max);
404 rcu_read_unlock();
405
406 if (!start || start - offset > max)
407 return 0;
408
409 ra->start = start;
410 ra->size = start - offset; /* old async_size */
411 ra->size += req_size;
412 ra->size = get_next_ra_size(ra, max);
413 ra->async_size = ra->size;
414 goto readit;
415 }
416
417 /*
418 * oversize read
419 */
420 if (req_size > max)
421 goto initial_readahead;
422
423 /*
424 * sequential cache miss
425 * trivial case: (offset - prev_offset) == 1
426 * unaligned reads: (offset - prev_offset) == 0
427 */
428 prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
429 if (offset - prev_offset <= 1UL)
430 goto initial_readahead;
431
432 /*
433 * Query the page cache and look for the traces(cached history pages)
434 * that a sequential stream would leave behind.
435 */
436 if (try_context_readahead(mapping, ra, offset, req_size, max))
437 goto readit;
438
439 /*
440 * standalone, small random read
441 * Read as is, and do not pollute the readahead state.
442 */
443 return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
444
445initial_readahead:
446 ra->start = offset;
447 ra->size = get_init_ra_size(req_size, max);
448 ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
449
450readit:
451 /*
452 * Will this read hit the readahead marker made by itself?
453 * If so, trigger the readahead marker hit now, and merge
454 * the resulted next readahead window into the current one.
455 */
456 if (offset == ra->start && ra->size == ra->async_size) {
457 ra->async_size = get_next_ra_size(ra, max);
458 ra->size += ra->async_size;
459 }
460
461 return ra_submit(ra, mapping, filp);
462}
463
464/**
465 * page_cache_sync_readahead - generic file readahead
466 * @mapping: address_space which holds the pagecache and I/O vectors
467 * @ra: file_ra_state which holds the readahead state
468 * @filp: passed on to ->readpage() and ->readpages()
469 * @offset: start offset into @mapping, in pagecache page-sized units
470 * @req_size: hint: total size of the read which the caller is performing in
471 * pagecache pages
472 *
473 * page_cache_sync_readahead() should be called when a cache miss happened:
474 * it will submit the read. The readahead logic may decide to piggyback more
475 * pages onto the read request if access patterns suggest it will improve
476 * performance.
477 */
478void page_cache_sync_readahead(struct address_space *mapping,
479 struct file_ra_state *ra, struct file *filp,
480 pgoff_t offset, unsigned long req_size)
481{
482 /* no read-ahead */
483 if (!ra->ra_pages)
484 return;
485
486 /* be dumb */
487 if (filp && (filp->f_mode & FMODE_RANDOM)) {
488 force_page_cache_readahead(mapping, filp, offset, req_size);
489 return;
490 }
491
492 /* do read-ahead */
493 ondemand_readahead(mapping, ra, filp, false, offset, req_size);
494}
495EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
496
497/**
498 * page_cache_async_readahead - file readahead for marked pages
499 * @mapping: address_space which holds the pagecache and I/O vectors
500 * @ra: file_ra_state which holds the readahead state
501 * @filp: passed on to ->readpage() and ->readpages()
502 * @page: the page at @offset which has the PG_readahead flag set
503 * @offset: start offset into @mapping, in pagecache page-sized units
504 * @req_size: hint: total size of the read which the caller is performing in
505 * pagecache pages
506 *
507 * page_cache_async_readahead() should be called when a page is used which
508 * has the PG_readahead flag; this is a marker to suggest that the application
509 * has used up enough of the readahead window that we should start pulling in
510 * more pages.
511 */
512void
513page_cache_async_readahead(struct address_space *mapping,
514 struct file_ra_state *ra, struct file *filp,
515 struct page *page, pgoff_t offset,
516 unsigned long req_size)
517{
518 /* no read-ahead */
519 if (!ra->ra_pages)
520 return;
521
522 /*
523 * Same bit is used for PG_readahead and PG_reclaim.
524 */
525 if (PageWriteback(page))
526 return;
527
528 ClearPageReadahead(page);
529
530 /*
531 * Defer asynchronous read-ahead on IO congestion.
532 */
533 if (inode_read_congested(mapping->host))
534 return;
535
536 /* do read-ahead */
537 ondemand_readahead(mapping, ra, filp, true, offset, req_size);
538}
539EXPORT_SYMBOL_GPL(page_cache_async_readahead);
540
541static ssize_t
542do_readahead(struct address_space *mapping, struct file *filp,
543 pgoff_t index, unsigned long nr)
544{
545 if (!mapping || !mapping->a_ops)
546 return -EINVAL;
547
548 return force_page_cache_readahead(mapping, filp, index, nr);
549}
550
551SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
552{
553 ssize_t ret;
554 struct fd f;
555
556 ret = -EBADF;
557 f = fdget(fd);
558 if (f.file) {
559 if (f.file->f_mode & FMODE_READ) {
560 struct address_space *mapping = f.file->f_mapping;
561 pgoff_t start = offset >> PAGE_SHIFT;
562 pgoff_t end = (offset + count - 1) >> PAGE_SHIFT;
563 unsigned long len = end - start + 1;
564 ret = do_readahead(mapping, f.file, start, len);
565 }
566 fdput(f);
567 }
568 return ret;
569}
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#include <linux/sched/mm.h>
26
27#include "internal.h"
28
29/*
30 * Initialise a struct file's readahead state. Assumes that the caller has
31 * memset *ra to zero.
32 */
33void
34file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
35{
36 ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
37 ra->prev_pos = -1;
38}
39EXPORT_SYMBOL_GPL(file_ra_state_init);
40
41/*
42 * see if a page needs releasing upon read_cache_pages() failure
43 * - the caller of read_cache_pages() may have set PG_private or PG_fscache
44 * before calling, such as the NFS fs marking pages that are cached locally
45 * on disk, thus we need to give the fs a chance to clean up in the event of
46 * an error
47 */
48static void read_cache_pages_invalidate_page(struct address_space *mapping,
49 struct page *page)
50{
51 if (page_has_private(page)) {
52 if (!trylock_page(page))
53 BUG();
54 page->mapping = mapping;
55 do_invalidatepage(page, 0, PAGE_SIZE);
56 page->mapping = NULL;
57 unlock_page(page);
58 }
59 put_page(page);
60}
61
62/*
63 * release a list of pages, invalidating them first if need be
64 */
65static void read_cache_pages_invalidate_pages(struct address_space *mapping,
66 struct list_head *pages)
67{
68 struct page *victim;
69
70 while (!list_empty(pages)) {
71 victim = lru_to_page(pages);
72 list_del(&victim->lru);
73 read_cache_pages_invalidate_page(mapping, victim);
74 }
75}
76
77/**
78 * read_cache_pages - populate an address space with some pages & start reads against them
79 * @mapping: the address_space
80 * @pages: The address of a list_head which contains the target pages. These
81 * pages have their ->index populated and are otherwise uninitialised.
82 * @filler: callback routine for filling a single page.
83 * @data: private data for the callback routine.
84 *
85 * Hides the details of the LRU cache etc from the filesystems.
86 *
87 * Returns: %0 on success, error return by @filler otherwise
88 */
89int read_cache_pages(struct address_space *mapping, struct list_head *pages,
90 int (*filler)(void *, struct page *), void *data)
91{
92 struct page *page;
93 int ret = 0;
94
95 while (!list_empty(pages)) {
96 page = lru_to_page(pages);
97 list_del(&page->lru);
98 if (add_to_page_cache_lru(page, mapping, page->index,
99 readahead_gfp_mask(mapping))) {
100 read_cache_pages_invalidate_page(mapping, page);
101 continue;
102 }
103 put_page(page);
104
105 ret = filler(data, page);
106 if (unlikely(ret)) {
107 read_cache_pages_invalidate_pages(mapping, pages);
108 break;
109 }
110 task_io_account_read(PAGE_SIZE);
111 }
112 return ret;
113}
114
115EXPORT_SYMBOL(read_cache_pages);
116
117static void read_pages(struct readahead_control *rac, struct list_head *pages,
118 bool skip_page)
119{
120 const struct address_space_operations *aops = rac->mapping->a_ops;
121 struct page *page;
122 struct blk_plug plug;
123
124 if (!readahead_count(rac))
125 goto out;
126
127 blk_start_plug(&plug);
128
129 if (aops->readahead) {
130 aops->readahead(rac);
131 /* Clean up the remaining pages */
132 while ((page = readahead_page(rac))) {
133 unlock_page(page);
134 put_page(page);
135 }
136 } else if (aops->readpages) {
137 aops->readpages(rac->file, rac->mapping, pages,
138 readahead_count(rac));
139 /* Clean up the remaining pages */
140 put_pages_list(pages);
141 rac->_index += rac->_nr_pages;
142 rac->_nr_pages = 0;
143 } else {
144 while ((page = readahead_page(rac))) {
145 aops->readpage(rac->file, page);
146 put_page(page);
147 }
148 }
149
150 blk_finish_plug(&plug);
151
152 BUG_ON(!list_empty(pages));
153 BUG_ON(readahead_count(rac));
154
155out:
156 if (skip_page)
157 rac->_index++;
158}
159
160/**
161 * page_cache_ra_unbounded - Start unchecked readahead.
162 * @ractl: Readahead control.
163 * @nr_to_read: The number of pages to read.
164 * @lookahead_size: Where to start the next readahead.
165 *
166 * This function is for filesystems to call when they want to start
167 * readahead beyond a file's stated i_size. This is almost certainly
168 * not the function you want to call. Use page_cache_async_readahead()
169 * or page_cache_sync_readahead() instead.
170 *
171 * Context: File is referenced by caller. Mutexes may be held by caller.
172 * May sleep, but will not reenter filesystem to reclaim memory.
173 */
174void page_cache_ra_unbounded(struct readahead_control *ractl,
175 unsigned long nr_to_read, unsigned long lookahead_size)
176{
177 struct address_space *mapping = ractl->mapping;
178 unsigned long index = readahead_index(ractl);
179 LIST_HEAD(page_pool);
180 gfp_t gfp_mask = readahead_gfp_mask(mapping);
181 unsigned long i;
182
183 /*
184 * Partway through the readahead operation, we will have added
185 * locked pages to the page cache, but will not yet have submitted
186 * them for I/O. Adding another page may need to allocate memory,
187 * which can trigger memory reclaim. Telling the VM we're in
188 * the middle of a filesystem operation will cause it to not
189 * touch file-backed pages, preventing a deadlock. Most (all?)
190 * filesystems already specify __GFP_NOFS in their mapping's
191 * gfp_mask, but let's be explicit here.
192 */
193 unsigned int nofs = memalloc_nofs_save();
194
195 /*
196 * Preallocate as many pages as we will need.
197 */
198 for (i = 0; i < nr_to_read; i++) {
199 struct page *page = xa_load(&mapping->i_pages, index + i);
200
201 if (page && !xa_is_value(page)) {
202 /*
203 * Page already present? Kick off the current batch
204 * of contiguous pages before continuing with the
205 * next batch. This page may be the one we would
206 * have intended to mark as Readahead, but we don't
207 * have a stable reference to this page, and it's
208 * not worth getting one just for that.
209 */
210 read_pages(ractl, &page_pool, true);
211 i = ractl->_index + ractl->_nr_pages - index - 1;
212 continue;
213 }
214
215 page = __page_cache_alloc(gfp_mask);
216 if (!page)
217 break;
218 if (mapping->a_ops->readpages) {
219 page->index = index + i;
220 list_add(&page->lru, &page_pool);
221 } else if (add_to_page_cache_lru(page, mapping, index + i,
222 gfp_mask) < 0) {
223 put_page(page);
224 read_pages(ractl, &page_pool, true);
225 i = ractl->_index + ractl->_nr_pages - index - 1;
226 continue;
227 }
228 if (i == nr_to_read - lookahead_size)
229 SetPageReadahead(page);
230 ractl->_nr_pages++;
231 }
232
233 /*
234 * Now start the IO. We ignore I/O errors - if the page is not
235 * uptodate then the caller will launch readpage again, and
236 * will then handle the error.
237 */
238 read_pages(ractl, &page_pool, false);
239 memalloc_nofs_restore(nofs);
240}
241EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
242
243/*
244 * do_page_cache_ra() actually reads a chunk of disk. It allocates
245 * the pages first, then submits them for I/O. This avoids the very bad
246 * behaviour which would occur if page allocations are causing VM writeback.
247 * We really don't want to intermingle reads and writes like that.
248 */
249void do_page_cache_ra(struct readahead_control *ractl,
250 unsigned long nr_to_read, unsigned long lookahead_size)
251{
252 struct inode *inode = ractl->mapping->host;
253 unsigned long index = readahead_index(ractl);
254 loff_t isize = i_size_read(inode);
255 pgoff_t end_index; /* The last page we want to read */
256
257 if (isize == 0)
258 return;
259
260 end_index = (isize - 1) >> PAGE_SHIFT;
261 if (index > end_index)
262 return;
263 /* Don't read past the page containing the last byte of the file */
264 if (nr_to_read > end_index - index)
265 nr_to_read = end_index - index + 1;
266
267 page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size);
268}
269
270/*
271 * Chunk the readahead into 2 megabyte units, so that we don't pin too much
272 * memory at once.
273 */
274void force_page_cache_ra(struct readahead_control *ractl,
275 unsigned long nr_to_read)
276{
277 struct address_space *mapping = ractl->mapping;
278 struct file_ra_state *ra = ractl->ra;
279 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
280 unsigned long max_pages, index;
281
282 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
283 !mapping->a_ops->readahead))
284 return;
285
286 /*
287 * If the request exceeds the readahead window, allow the read to
288 * be up to the optimal hardware IO size
289 */
290 index = readahead_index(ractl);
291 max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
292 nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
293 while (nr_to_read) {
294 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
295
296 if (this_chunk > nr_to_read)
297 this_chunk = nr_to_read;
298 ractl->_index = index;
299 do_page_cache_ra(ractl, this_chunk, 0);
300
301 index += this_chunk;
302 nr_to_read -= this_chunk;
303 }
304}
305
306/*
307 * Set the initial window size, round to next power of 2 and square
308 * for small size, x 4 for medium, and x 2 for large
309 * for 128k (32 page) max ra
310 * 1-8 page = 32k initial, > 8 page = 128k initial
311 */
312static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
313{
314 unsigned long newsize = roundup_pow_of_two(size);
315
316 if (newsize <= max / 32)
317 newsize = newsize * 4;
318 else if (newsize <= max / 4)
319 newsize = newsize * 2;
320 else
321 newsize = max;
322
323 return newsize;
324}
325
326/*
327 * Get the previous window size, ramp it up, and
328 * return it as the new window size.
329 */
330static unsigned long get_next_ra_size(struct file_ra_state *ra,
331 unsigned long max)
332{
333 unsigned long cur = ra->size;
334
335 if (cur < max / 16)
336 return 4 * cur;
337 if (cur <= max / 2)
338 return 2 * cur;
339 return max;
340}
341
342/*
343 * On-demand readahead design.
344 *
345 * The fields in struct file_ra_state represent the most-recently-executed
346 * readahead attempt:
347 *
348 * |<----- async_size ---------|
349 * |------------------- size -------------------->|
350 * |==================#===========================|
351 * ^start ^page marked with PG_readahead
352 *
353 * To overlap application thinking time and disk I/O time, we do
354 * `readahead pipelining': Do not wait until the application consumed all
355 * readahead pages and stalled on the missing page at readahead_index;
356 * Instead, submit an asynchronous readahead I/O as soon as there are
357 * only async_size pages left in the readahead window. Normally async_size
358 * will be equal to size, for maximum pipelining.
359 *
360 * In interleaved sequential reads, concurrent streams on the same fd can
361 * be invalidating each other's readahead state. So we flag the new readahead
362 * page at (start+size-async_size) with PG_readahead, and use it as readahead
363 * indicator. The flag won't be set on already cached pages, to avoid the
364 * readahead-for-nothing fuss, saving pointless page cache lookups.
365 *
366 * prev_pos tracks the last visited byte in the _previous_ read request.
367 * It should be maintained by the caller, and will be used for detecting
368 * small random reads. Note that the readahead algorithm checks loosely
369 * for sequential patterns. Hence interleaved reads might be served as
370 * sequential ones.
371 *
372 * There is a special-case: if the first page which the application tries to
373 * read happens to be the first page of the file, it is assumed that a linear
374 * read is about to happen and the window is immediately set to the initial size
375 * based on I/O request size and the max_readahead.
376 *
377 * The code ramps up the readahead size aggressively at first, but slow down as
378 * it approaches max_readhead.
379 */
380
381/*
382 * Count contiguously cached pages from @index-1 to @index-@max,
383 * this count is a conservative estimation of
384 * - length of the sequential read sequence, or
385 * - thrashing threshold in memory tight systems
386 */
387static pgoff_t count_history_pages(struct address_space *mapping,
388 pgoff_t index, unsigned long max)
389{
390 pgoff_t head;
391
392 rcu_read_lock();
393 head = page_cache_prev_miss(mapping, index - 1, max);
394 rcu_read_unlock();
395
396 return index - 1 - head;
397}
398
399/*
400 * page cache context based read-ahead
401 */
402static int try_context_readahead(struct address_space *mapping,
403 struct file_ra_state *ra,
404 pgoff_t index,
405 unsigned long req_size,
406 unsigned long max)
407{
408 pgoff_t size;
409
410 size = count_history_pages(mapping, index, max);
411
412 /*
413 * not enough history pages:
414 * it could be a random read
415 */
416 if (size <= req_size)
417 return 0;
418
419 /*
420 * starts from beginning of file:
421 * it is a strong indication of long-run stream (or whole-file-read)
422 */
423 if (size >= index)
424 size *= 2;
425
426 ra->start = index;
427 ra->size = min(size + req_size, max);
428 ra->async_size = 1;
429
430 return 1;
431}
432
433/*
434 * A minimal readahead algorithm for trivial sequential/random reads.
435 */
436static void ondemand_readahead(struct readahead_control *ractl,
437 bool hit_readahead_marker, unsigned long req_size)
438{
439 struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
440 struct file_ra_state *ra = ractl->ra;
441 unsigned long max_pages = ra->ra_pages;
442 unsigned long add_pages;
443 unsigned long index = readahead_index(ractl);
444 pgoff_t prev_index;
445
446 /*
447 * If the request exceeds the readahead window, allow the read to
448 * be up to the optimal hardware IO size
449 */
450 if (req_size > max_pages && bdi->io_pages > max_pages)
451 max_pages = min(req_size, bdi->io_pages);
452
453 /*
454 * start of file
455 */
456 if (!index)
457 goto initial_readahead;
458
459 /*
460 * It's the expected callback index, assume sequential access.
461 * Ramp up sizes, and push forward the readahead window.
462 */
463 if ((index == (ra->start + ra->size - ra->async_size) ||
464 index == (ra->start + ra->size))) {
465 ra->start += ra->size;
466 ra->size = get_next_ra_size(ra, max_pages);
467 ra->async_size = ra->size;
468 goto readit;
469 }
470
471 /*
472 * Hit a marked page without valid readahead state.
473 * E.g. interleaved reads.
474 * Query the pagecache for async_size, which normally equals to
475 * readahead size. Ramp it up and use it as the new readahead size.
476 */
477 if (hit_readahead_marker) {
478 pgoff_t start;
479
480 rcu_read_lock();
481 start = page_cache_next_miss(ractl->mapping, index + 1,
482 max_pages);
483 rcu_read_unlock();
484
485 if (!start || start - index > max_pages)
486 return;
487
488 ra->start = start;
489 ra->size = start - index; /* old async_size */
490 ra->size += req_size;
491 ra->size = get_next_ra_size(ra, max_pages);
492 ra->async_size = ra->size;
493 goto readit;
494 }
495
496 /*
497 * oversize read
498 */
499 if (req_size > max_pages)
500 goto initial_readahead;
501
502 /*
503 * sequential cache miss
504 * trivial case: (index - prev_index) == 1
505 * unaligned reads: (index - prev_index) == 0
506 */
507 prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
508 if (index - prev_index <= 1UL)
509 goto initial_readahead;
510
511 /*
512 * Query the page cache and look for the traces(cached history pages)
513 * that a sequential stream would leave behind.
514 */
515 if (try_context_readahead(ractl->mapping, ra, index, req_size,
516 max_pages))
517 goto readit;
518
519 /*
520 * standalone, small random read
521 * Read as is, and do not pollute the readahead state.
522 */
523 do_page_cache_ra(ractl, req_size, 0);
524 return;
525
526initial_readahead:
527 ra->start = index;
528 ra->size = get_init_ra_size(req_size, max_pages);
529 ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
530
531readit:
532 /*
533 * Will this read hit the readahead marker made by itself?
534 * If so, trigger the readahead marker hit now, and merge
535 * the resulted next readahead window into the current one.
536 * Take care of maximum IO pages as above.
537 */
538 if (index == ra->start && ra->size == ra->async_size) {
539 add_pages = get_next_ra_size(ra, max_pages);
540 if (ra->size + add_pages <= max_pages) {
541 ra->async_size = add_pages;
542 ra->size += add_pages;
543 } else {
544 ra->size = max_pages;
545 ra->async_size = max_pages >> 1;
546 }
547 }
548
549 ractl->_index = ra->start;
550 do_page_cache_ra(ractl, ra->size, ra->async_size);
551}
552
553void page_cache_sync_ra(struct readahead_control *ractl,
554 unsigned long req_count)
555{
556 bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
557
558 /*
559 * Even if read-ahead is disabled, issue this request as read-ahead
560 * as we'll need it to satisfy the requested range. The forced
561 * read-ahead will do the right thing and limit the read to just the
562 * requested range, which we'll set to 1 page for this case.
563 */
564 if (!ractl->ra->ra_pages || blk_cgroup_congested()) {
565 if (!ractl->file)
566 return;
567 req_count = 1;
568 do_forced_ra = true;
569 }
570
571 /* be dumb */
572 if (do_forced_ra) {
573 force_page_cache_ra(ractl, req_count);
574 return;
575 }
576
577 /* do read-ahead */
578 ondemand_readahead(ractl, false, req_count);
579}
580EXPORT_SYMBOL_GPL(page_cache_sync_ra);
581
582void page_cache_async_ra(struct readahead_control *ractl,
583 struct page *page, unsigned long req_count)
584{
585 /* no read-ahead */
586 if (!ractl->ra->ra_pages)
587 return;
588
589 /*
590 * Same bit is used for PG_readahead and PG_reclaim.
591 */
592 if (PageWriteback(page))
593 return;
594
595 ClearPageReadahead(page);
596
597 /*
598 * Defer asynchronous read-ahead on IO congestion.
599 */
600 if (inode_read_congested(ractl->mapping->host))
601 return;
602
603 if (blk_cgroup_congested())
604 return;
605
606 /* do read-ahead */
607 ondemand_readahead(ractl, true, req_count);
608}
609EXPORT_SYMBOL_GPL(page_cache_async_ra);
610
611ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
612{
613 ssize_t ret;
614 struct fd f;
615
616 ret = -EBADF;
617 f = fdget(fd);
618 if (!f.file || !(f.file->f_mode & FMODE_READ))
619 goto out;
620
621 /*
622 * The readahead() syscall is intended to run only on files
623 * that can execute readahead. If readahead is not possible
624 * on this file, then we must return -EINVAL.
625 */
626 ret = -EINVAL;
627 if (!f.file->f_mapping || !f.file->f_mapping->a_ops ||
628 !S_ISREG(file_inode(f.file)->i_mode))
629 goto out;
630
631 ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED);
632out:
633 fdput(f);
634 return ret;
635}
636
637SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
638{
639 return ksys_readahead(fd, offset, count);
640}
641
642/**
643 * readahead_expand - Expand a readahead request
644 * @ractl: The request to be expanded
645 * @new_start: The revised start
646 * @new_len: The revised size of the request
647 *
648 * Attempt to expand a readahead request outwards from the current size to the
649 * specified size by inserting locked pages before and after the current window
650 * to increase the size to the new window. This may involve the insertion of
651 * THPs, in which case the window may get expanded even beyond what was
652 * requested.
653 *
654 * The algorithm will stop if it encounters a conflicting page already in the
655 * pagecache and leave a smaller expansion than requested.
656 *
657 * The caller must check for this by examining the revised @ractl object for a
658 * different expansion than was requested.
659 */
660void readahead_expand(struct readahead_control *ractl,
661 loff_t new_start, size_t new_len)
662{
663 struct address_space *mapping = ractl->mapping;
664 struct file_ra_state *ra = ractl->ra;
665 pgoff_t new_index, new_nr_pages;
666 gfp_t gfp_mask = readahead_gfp_mask(mapping);
667
668 new_index = new_start / PAGE_SIZE;
669
670 /* Expand the leading edge downwards */
671 while (ractl->_index > new_index) {
672 unsigned long index = ractl->_index - 1;
673 struct page *page = xa_load(&mapping->i_pages, index);
674
675 if (page && !xa_is_value(page))
676 return; /* Page apparently present */
677
678 page = __page_cache_alloc(gfp_mask);
679 if (!page)
680 return;
681 if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
682 put_page(page);
683 return;
684 }
685
686 ractl->_nr_pages++;
687 ractl->_index = page->index;
688 }
689
690 new_len += new_start - readahead_pos(ractl);
691 new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE);
692
693 /* Expand the trailing edge upwards */
694 while (ractl->_nr_pages < new_nr_pages) {
695 unsigned long index = ractl->_index + ractl->_nr_pages;
696 struct page *page = xa_load(&mapping->i_pages, index);
697
698 if (page && !xa_is_value(page))
699 return; /* Page apparently present */
700
701 page = __page_cache_alloc(gfp_mask);
702 if (!page)
703 return;
704 if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) {
705 put_page(page);
706 return;
707 }
708 ractl->_nr_pages++;
709 if (ra) {
710 ra->size++;
711 ra->async_size++;
712 }
713 }
714}
715EXPORT_SYMBOL(readahead_expand);