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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/dax.h>
12#include <linux/gfp.h>
13#include <linux/export.h>
14#include <linux/blkdev.h>
15#include <linux/backing-dev.h>
16#include <linux/task_io_accounting_ops.h>
17#include <linux/pagevec.h>
18#include <linux/pagemap.h>
19#include <linux/syscalls.h>
20#include <linux/file.h>
21#include <linux/mm_inline.h>
22
23#include "internal.h"
24
25/*
26 * Initialise a struct file's readahead state. Assumes that the caller has
27 * memset *ra to zero.
28 */
29void
30file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
31{
32 ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
33 ra->prev_pos = -1;
34}
35EXPORT_SYMBOL_GPL(file_ra_state_init);
36
37/*
38 * see if a page needs releasing upon read_cache_pages() failure
39 * - the caller of read_cache_pages() may have set PG_private or PG_fscache
40 * before calling, such as the NFS fs marking pages that are cached locally
41 * on disk, thus we need to give the fs a chance to clean up in the event of
42 * an error
43 */
44static void read_cache_pages_invalidate_page(struct address_space *mapping,
45 struct page *page)
46{
47 if (page_has_private(page)) {
48 if (!trylock_page(page))
49 BUG();
50 page->mapping = mapping;
51 do_invalidatepage(page, 0, PAGE_SIZE);
52 page->mapping = NULL;
53 unlock_page(page);
54 }
55 put_page(page);
56}
57
58/*
59 * release a list of pages, invalidating them first if need be
60 */
61static void read_cache_pages_invalidate_pages(struct address_space *mapping,
62 struct list_head *pages)
63{
64 struct page *victim;
65
66 while (!list_empty(pages)) {
67 victim = lru_to_page(pages);
68 list_del(&victim->lru);
69 read_cache_pages_invalidate_page(mapping, victim);
70 }
71}
72
73/**
74 * read_cache_pages - populate an address space with some pages & start reads against them
75 * @mapping: the address_space
76 * @pages: The address of a list_head which contains the target pages. These
77 * pages have their ->index populated and are otherwise uninitialised.
78 * @filler: callback routine for filling a single page.
79 * @data: private data for the callback routine.
80 *
81 * Hides the details of the LRU cache etc from the filesystems.
82 */
83int read_cache_pages(struct address_space *mapping, struct list_head *pages,
84 int (*filler)(struct file *, struct page *), void *data)
85{
86 struct page *page;
87 int ret = 0;
88
89 while (!list_empty(pages)) {
90 page = lru_to_page(pages);
91 list_del(&page->lru);
92 if (add_to_page_cache_lru(page, mapping, page->index,
93 readahead_gfp_mask(mapping))) {
94 read_cache_pages_invalidate_page(mapping, page);
95 continue;
96 }
97 put_page(page);
98
99 ret = filler(data, page);
100 if (unlikely(ret)) {
101 read_cache_pages_invalidate_pages(mapping, pages);
102 break;
103 }
104 task_io_account_read(PAGE_SIZE);
105 }
106 return ret;
107}
108
109EXPORT_SYMBOL(read_cache_pages);
110
111static int read_pages(struct address_space *mapping, struct file *filp,
112 struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
113{
114 struct blk_plug plug;
115 unsigned page_idx;
116 int ret;
117
118 blk_start_plug(&plug);
119
120 if (mapping->a_ops->readpages) {
121 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
122 /* Clean up the remaining pages */
123 put_pages_list(pages);
124 goto out;
125 }
126
127 for (page_idx = 0; page_idx < nr_pages; page_idx++) {
128 struct page *page = lru_to_page(pages);
129 list_del(&page->lru);
130 if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
131 mapping->a_ops->readpage(filp, page);
132 put_page(page);
133 }
134 ret = 0;
135
136out:
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 */
150int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
151 pgoff_t offset, unsigned long nr_to_read,
152 unsigned long lookahead_size)
153{
154 struct inode *inode = mapping->host;
155 struct page *page;
156 unsigned long end_index; /* The last page we want to read */
157 LIST_HEAD(page_pool);
158 int page_idx;
159 int ret = 0;
160 loff_t isize = i_size_read(inode);
161 gfp_t gfp_mask = readahead_gfp_mask(mapping);
162
163#ifdef CONFIG_AMLOGIC_CMA
164 if (filp->f_mode & (FMODE_WRITE | FMODE_WRITE_IOCTL))
165 gfp_mask |= __GFP_WRITE;
166#endif /* CONFIG_AMLOGIC_CMA */
167
168 if (isize == 0)
169 goto out;
170
171 end_index = ((isize - 1) >> PAGE_SHIFT);
172
173 /*
174 * Preallocate as many pages as we will need.
175 */
176 for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
177 pgoff_t page_offset = offset + page_idx;
178
179 if (page_offset > end_index)
180 break;
181
182 rcu_read_lock();
183 page = radix_tree_lookup(&mapping->page_tree, page_offset);
184 rcu_read_unlock();
185 if (page && !radix_tree_exceptional_entry(page))
186 continue;
187
188 page = __page_cache_alloc(gfp_mask);
189 if (!page)
190 break;
191 page->index = page_offset;
192 list_add(&page->lru, &page_pool);
193 if (page_idx == nr_to_read - lookahead_size)
194 SetPageReadahead(page);
195 ret++;
196 }
197
198 /*
199 * Now start the IO. We ignore I/O errors - if the page is not
200 * uptodate then the caller will launch readpage again, and
201 * will then handle the error.
202 */
203 if (ret)
204 read_pages(mapping, filp, &page_pool, ret, gfp_mask);
205 BUG_ON(!list_empty(&page_pool));
206out:
207 return ret;
208}
209
210/*
211 * Chunk the readahead into 2 megabyte units, so that we don't pin too much
212 * memory at once.
213 */
214int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
215 pgoff_t offset, unsigned long nr_to_read)
216{
217 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
218 struct file_ra_state *ra = &filp->f_ra;
219 unsigned long max_pages;
220
221 if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
222 return -EINVAL;
223
224 /*
225 * If the request exceeds the readahead window, allow the read to
226 * be up to the optimal hardware IO size
227 */
228 max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
229 nr_to_read = min(nr_to_read, max_pages);
230 while (nr_to_read) {
231 int err;
232
233 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
234
235 if (this_chunk > nr_to_read)
236 this_chunk = nr_to_read;
237 err = __do_page_cache_readahead(mapping, filp,
238 offset, this_chunk, 0);
239 if (err < 0)
240 return err;
241
242 offset += this_chunk;
243 nr_to_read -= this_chunk;
244 }
245 return 0;
246}
247
248/*
249 * Set the initial window size, round to next power of 2 and square
250 * for small size, x 4 for medium, and x 2 for large
251 * for 128k (32 page) max ra
252 * 1-8 page = 32k initial, > 8 page = 128k initial
253 */
254static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
255{
256 unsigned long newsize = roundup_pow_of_two(size);
257
258 if (newsize <= max / 32)
259 newsize = newsize * 4;
260 else if (newsize <= max / 4)
261 newsize = newsize * 2;
262 else
263 newsize = max;
264
265 return newsize;
266}
267
268/*
269 * Get the previous window size, ramp it up, and
270 * return it as the new window size.
271 */
272static unsigned long get_next_ra_size(struct file_ra_state *ra,
273 unsigned long max)
274{
275 unsigned long cur = ra->size;
276 unsigned long newsize;
277
278 if (cur < max / 16)
279 newsize = 4 * cur;
280 else
281 newsize = 2 * cur;
282
283 return min(newsize, max);
284}
285
286/*
287 * On-demand readahead design.
288 *
289 * The fields in struct file_ra_state represent the most-recently-executed
290 * readahead attempt:
291 *
292 * |<----- async_size ---------|
293 * |------------------- size -------------------->|
294 * |==================#===========================|
295 * ^start ^page marked with PG_readahead
296 *
297 * To overlap application thinking time and disk I/O time, we do
298 * `readahead pipelining': Do not wait until the application consumed all
299 * readahead pages and stalled on the missing page at readahead_index;
300 * Instead, submit an asynchronous readahead I/O as soon as there are
301 * only async_size pages left in the readahead window. Normally async_size
302 * will be equal to size, for maximum pipelining.
303 *
304 * In interleaved sequential reads, concurrent streams on the same fd can
305 * be invalidating each other's readahead state. So we flag the new readahead
306 * page at (start+size-async_size) with PG_readahead, and use it as readahead
307 * indicator. The flag won't be set on already cached pages, to avoid the
308 * readahead-for-nothing fuss, saving pointless page cache lookups.
309 *
310 * prev_pos tracks the last visited byte in the _previous_ read request.
311 * It should be maintained by the caller, and will be used for detecting
312 * small random reads. Note that the readahead algorithm checks loosely
313 * for sequential patterns. Hence interleaved reads might be served as
314 * sequential ones.
315 *
316 * There is a special-case: if the first page which the application tries to
317 * read happens to be the first page of the file, it is assumed that a linear
318 * read is about to happen and the window is immediately set to the initial size
319 * based on I/O request size and the max_readahead.
320 *
321 * The code ramps up the readahead size aggressively at first, but slow down as
322 * it approaches max_readhead.
323 */
324
325/*
326 * Count contiguously cached pages from @offset-1 to @offset-@max,
327 * this count is a conservative estimation of
328 * - length of the sequential read sequence, or
329 * - thrashing threshold in memory tight systems
330 */
331static pgoff_t count_history_pages(struct address_space *mapping,
332 pgoff_t offset, unsigned long max)
333{
334 pgoff_t head;
335
336 rcu_read_lock();
337 head = page_cache_prev_hole(mapping, offset - 1, max);
338 rcu_read_unlock();
339
340 return offset - 1 - head;
341}
342
343/*
344 * page cache context based read-ahead
345 */
346static int try_context_readahead(struct address_space *mapping,
347 struct file_ra_state *ra,
348 pgoff_t offset,
349 unsigned long req_size,
350 unsigned long max)
351{
352 pgoff_t size;
353
354 size = count_history_pages(mapping, offset, max);
355
356 /*
357 * not enough history pages:
358 * it could be a random read
359 */
360 if (size <= req_size)
361 return 0;
362
363 /*
364 * starts from beginning of file:
365 * it is a strong indication of long-run stream (or whole-file-read)
366 */
367 if (size >= offset)
368 size *= 2;
369
370 ra->start = offset;
371 ra->size = min(size + req_size, max);
372 ra->async_size = 1;
373
374 return 1;
375}
376
377/*
378 * A minimal readahead algorithm for trivial sequential/random reads.
379 */
380static unsigned long
381ondemand_readahead(struct address_space *mapping,
382 struct file_ra_state *ra, struct file *filp,
383 bool hit_readahead_marker, pgoff_t offset,
384 unsigned long req_size)
385{
386 struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
387 unsigned long max_pages = ra->ra_pages;
388 unsigned long add_pages;
389 pgoff_t prev_offset;
390
391 /*
392 * If the request exceeds the readahead window, allow the read to
393 * be up to the optimal hardware IO size
394 */
395 if (req_size > max_pages && bdi->io_pages > max_pages)
396 max_pages = min(req_size, bdi->io_pages);
397
398 /*
399 * start of file
400 */
401 if (!offset)
402 goto initial_readahead;
403
404 /*
405 * It's the expected callback offset, assume sequential access.
406 * Ramp up sizes, and push forward the readahead window.
407 */
408 if ((offset == (ra->start + ra->size - ra->async_size) ||
409 offset == (ra->start + ra->size))) {
410 ra->start += ra->size;
411 ra->size = get_next_ra_size(ra, max_pages);
412 ra->async_size = ra->size;
413 goto readit;
414 }
415
416 /*
417 * Hit a marked page without valid readahead state.
418 * E.g. interleaved reads.
419 * Query the pagecache for async_size, which normally equals to
420 * readahead size. Ramp it up and use it as the new readahead size.
421 */
422 if (hit_readahead_marker) {
423 pgoff_t start;
424
425 rcu_read_lock();
426 start = page_cache_next_hole(mapping, offset + 1, max_pages);
427 rcu_read_unlock();
428
429 if (!start || start - offset > max_pages)
430 return 0;
431
432 ra->start = start;
433 ra->size = start - offset; /* old async_size */
434 ra->size += req_size;
435 ra->size = get_next_ra_size(ra, max_pages);
436 ra->async_size = ra->size;
437 goto readit;
438 }
439
440 /*
441 * oversize read
442 */
443 if (req_size > max_pages)
444 goto initial_readahead;
445
446 /*
447 * sequential cache miss
448 * trivial case: (offset - prev_offset) == 1
449 * unaligned reads: (offset - prev_offset) == 0
450 */
451 prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
452 if (offset - prev_offset <= 1UL)
453 goto initial_readahead;
454
455 /*
456 * Query the page cache and look for the traces(cached history pages)
457 * that a sequential stream would leave behind.
458 */
459 if (try_context_readahead(mapping, ra, offset, req_size, max_pages))
460 goto readit;
461
462 /*
463 * standalone, small random read
464 * Read as is, and do not pollute the readahead state.
465 */
466 return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
467
468initial_readahead:
469 ra->start = offset;
470 ra->size = get_init_ra_size(req_size, max_pages);
471 ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
472
473readit:
474 /*
475 * Will this read hit the readahead marker made by itself?
476 * If so, trigger the readahead marker hit now, and merge
477 * the resulted next readahead window into the current one.
478 * Take care of maximum IO pages as above.
479 */
480 if (offset == ra->start && ra->size == ra->async_size) {
481 add_pages = get_next_ra_size(ra, max_pages);
482 if (ra->size + add_pages <= max_pages) {
483 ra->async_size = add_pages;
484 ra->size += add_pages;
485 } else {
486 ra->size = max_pages;
487 ra->async_size = max_pages >> 1;
488 }
489 }
490
491 return ra_submit(ra, mapping, filp);
492}
493
494/**
495 * page_cache_sync_readahead - generic file readahead
496 * @mapping: address_space which holds the pagecache and I/O vectors
497 * @ra: file_ra_state which holds the readahead state
498 * @filp: passed on to ->readpage() and ->readpages()
499 * @offset: start offset into @mapping, in pagecache page-sized units
500 * @req_size: hint: total size of the read which the caller is performing in
501 * pagecache pages
502 *
503 * page_cache_sync_readahead() should be called when a cache miss happened:
504 * it will submit the read. The readahead logic may decide to piggyback more
505 * pages onto the read request if access patterns suggest it will improve
506 * performance.
507 */
508void page_cache_sync_readahead(struct address_space *mapping,
509 struct file_ra_state *ra, struct file *filp,
510 pgoff_t offset, unsigned long req_size)
511{
512 /* no read-ahead */
513 if (!ra->ra_pages)
514 return;
515
516 /* be dumb */
517 if (filp && (filp->f_mode & FMODE_RANDOM)) {
518 force_page_cache_readahead(mapping, filp, offset, req_size);
519 return;
520 }
521
522 /* do read-ahead */
523 ondemand_readahead(mapping, ra, filp, false, offset, req_size);
524}
525EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
526
527/**
528 * page_cache_async_readahead - file readahead for marked pages
529 * @mapping: address_space which holds the pagecache and I/O vectors
530 * @ra: file_ra_state which holds the readahead state
531 * @filp: passed on to ->readpage() and ->readpages()
532 * @page: the page at @offset which has the PG_readahead flag set
533 * @offset: start offset into @mapping, in pagecache page-sized units
534 * @req_size: hint: total size of the read which the caller is performing in
535 * pagecache pages
536 *
537 * page_cache_async_readahead() should be called when a page is used which
538 * has the PG_readahead flag; this is a marker to suggest that the application
539 * has used up enough of the readahead window that we should start pulling in
540 * more pages.
541 */
542void
543page_cache_async_readahead(struct address_space *mapping,
544 struct file_ra_state *ra, struct file *filp,
545 struct page *page, pgoff_t offset,
546 unsigned long req_size)
547{
548 /* no read-ahead */
549 if (!ra->ra_pages)
550 return;
551
552 /*
553 * Same bit is used for PG_readahead and PG_reclaim.
554 */
555 if (PageWriteback(page))
556 return;
557
558 ClearPageReadahead(page);
559
560 /*
561 * Defer asynchronous read-ahead on IO congestion.
562 */
563 if (inode_read_congested(mapping->host))
564 return;
565
566 /* do read-ahead */
567 ondemand_readahead(mapping, ra, filp, true, offset, req_size);
568}
569EXPORT_SYMBOL_GPL(page_cache_async_readahead);
570
571static ssize_t
572do_readahead(struct address_space *mapping, struct file *filp,
573 pgoff_t index, unsigned long nr)
574{
575 if (!mapping || !mapping->a_ops)
576 return -EINVAL;
577
578 /*
579 * Readahead doesn't make sense for DAX inodes, but we don't want it
580 * to report a failure either. Instead, we just return success and
581 * don't do any work.
582 */
583 if (dax_mapping(mapping))
584 return 0;
585
586 return force_page_cache_readahead(mapping, filp, index, nr);
587}
588
589SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
590{
591 ssize_t ret;
592 struct fd f;
593
594 ret = -EBADF;
595 f = fdget(fd);
596 if (f.file) {
597 if (f.file->f_mode & FMODE_READ) {
598 struct address_space *mapping = f.file->f_mapping;
599 pgoff_t start = offset >> PAGE_SHIFT;
600 pgoff_t end = (offset + count - 1) >> PAGE_SHIFT;
601 unsigned long len = end - start + 1;
602 ret = do_readahead(mapping, f.file, start, len);
603 }
604 fdput(f);
605 }
606 return ret;
607}
608
generated by cgit at 2024-05-18 15:51:21 (GMT)