LCOV - code coverage report
Current view: top level - mm - readahead.c (source / functions) Hit Total Coverage
Test: combined.info Lines: 121 209 57.9 %
Date: 2022-04-01 14:17:54 Functions: 8 15 53.3 %
Branches: 61 266 22.9 %

           Branch data     Line data    Source code
       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                 :            : 
      26                 :            : #include "internal.h"
      27                 :            : 
      28                 :            : /*
      29                 :            :  * Initialise a struct file's readahead state.  Assumes that the caller has
      30                 :            :  * memset *ra to zero.
      31                 :            :  */
      32                 :            : void
      33                 :     179562 : file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
      34                 :            : {
      35                 :     179562 :         ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
      36                 :     179562 :         ra->prev_pos = -1;
      37                 :     179562 : }
      38                 :            : EXPORT_SYMBOL_GPL(file_ra_state_init);
      39                 :            : 
      40                 :            : /*
      41                 :            :  * see if a page needs releasing upon read_cache_pages() failure
      42                 :            :  * - the caller of read_cache_pages() may have set PG_private or PG_fscache
      43                 :            :  *   before calling, such as the NFS fs marking pages that are cached locally
      44                 :            :  *   on disk, thus we need to give the fs a chance to clean up in the event of
      45                 :            :  *   an error
      46                 :            :  */
      47                 :          0 : static void read_cache_pages_invalidate_page(struct address_space *mapping,
      48                 :            :                                              struct page *page)
      49                 :            : {
      50         [ #  # ]:          0 :         if (page_has_private(page)) {
      51   [ #  #  #  # ]:          0 :                 if (!trylock_page(page))
      52                 :          0 :                         BUG();
      53                 :          0 :                 page->mapping = mapping;
      54                 :          0 :                 do_invalidatepage(page, 0, PAGE_SIZE);
      55                 :          0 :                 page->mapping = NULL;
      56                 :          0 :                 unlock_page(page);
      57                 :            :         }
      58                 :          0 :         put_page(page);
      59                 :          0 : }
      60                 :            : 
      61                 :            : /*
      62                 :            :  * release a list of pages, invalidating them first if need be
      63                 :            :  */
      64                 :          0 : static void read_cache_pages_invalidate_pages(struct address_space *mapping,
      65                 :            :                                               struct list_head *pages)
      66                 :            : {
      67                 :          0 :         struct page *victim;
      68                 :            : 
      69         [ #  # ]:          0 :         while (!list_empty(pages)) {
      70                 :          0 :                 victim = lru_to_page(pages);
      71                 :          0 :                 list_del(&victim->lru);
      72                 :          0 :                 read_cache_pages_invalidate_page(mapping, victim);
      73                 :            :         }
      74                 :          0 : }
      75                 :            : 
      76                 :            : /**
      77                 :            :  * read_cache_pages - populate an address space with some pages & start reads against them
      78                 :            :  * @mapping: the address_space
      79                 :            :  * @pages: The address of a list_head which contains the target pages.  These
      80                 :            :  *   pages have their ->index populated and are otherwise uninitialised.
      81                 :            :  * @filler: callback routine for filling a single page.
      82                 :            :  * @data: private data for the callback routine.
      83                 :            :  *
      84                 :            :  * Hides the details of the LRU cache etc from the filesystems.
      85                 :            :  *
      86                 :            :  * Returns: %0 on success, error return by @filler otherwise
      87                 :            :  */
      88                 :          0 : int read_cache_pages(struct address_space *mapping, struct list_head *pages,
      89                 :            :                         int (*filler)(void *, struct page *), void *data)
      90                 :            : {
      91                 :          0 :         struct page *page;
      92                 :          0 :         int ret = 0;
      93                 :            : 
      94         [ #  # ]:          0 :         while (!list_empty(pages)) {
      95                 :          0 :                 page = lru_to_page(pages);
      96                 :          0 :                 list_del(&page->lru);
      97         [ #  # ]:          0 :                 if (add_to_page_cache_lru(page, mapping, page->index,
      98                 :            :                                 readahead_gfp_mask(mapping))) {
      99                 :          0 :                         read_cache_pages_invalidate_page(mapping, page);
     100                 :          0 :                         continue;
     101                 :            :                 }
     102                 :          0 :                 put_page(page);
     103                 :            : 
     104                 :          0 :                 ret = filler(data, page);
     105         [ #  # ]:          0 :                 if (unlikely(ret)) {
     106                 :          0 :                         read_cache_pages_invalidate_pages(mapping, pages);
     107                 :          0 :                         break;
     108                 :            :                 }
     109                 :          0 :                 task_io_account_read(PAGE_SIZE);
     110                 :            :         }
     111                 :          0 :         return ret;
     112                 :            : }
     113                 :            : 
     114                 :            : EXPORT_SYMBOL(read_cache_pages);
     115                 :            : 
     116                 :       8680 : static int read_pages(struct address_space *mapping, struct file *filp,
     117                 :            :                 struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
     118                 :            : {
     119                 :       8680 :         struct blk_plug plug;
     120                 :       8680 :         unsigned page_idx;
     121                 :       8680 :         int ret;
     122                 :            : 
     123                 :       8680 :         blk_start_plug(&plug);
     124                 :            : 
     125         [ -  + ]:       8680 :         if (mapping->a_ops->readpages) {
     126                 :       8680 :                 ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
     127                 :            :                 /* Clean up the remaining pages */
     128                 :       8680 :                 put_pages_list(pages);
     129                 :       8680 :                 goto out;
     130                 :            :         }
     131                 :            : 
     132         [ #  # ]:          0 :         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
     133                 :          0 :                 struct page *page = lru_to_page(pages);
     134                 :          0 :                 list_del(&page->lru);
     135         [ #  # ]:          0 :                 if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
     136                 :          0 :                         mapping->a_ops->readpage(filp, page);
     137                 :          0 :                 put_page(page);
     138                 :            :         }
     139                 :            :         ret = 0;
     140                 :            : 
     141                 :       8680 : out:
     142                 :       8680 :         blk_finish_plug(&plug);
     143                 :            : 
     144                 :       8680 :         return ret;
     145                 :            : }
     146                 :            : 
     147                 :            : /*
     148                 :            :  * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates
     149                 :            :  * the pages first, then submits them for I/O. This avoids the very bad
     150                 :            :  * behaviour which would occur if page allocations are causing VM writeback.
     151                 :            :  * We really don't want to intermingle reads and writes like that.
     152                 :            :  *
     153                 :            :  * Returns the number of pages requested, or the maximum amount of I/O allowed.
     154                 :            :  */
     155                 :       9539 : unsigned int __do_page_cache_readahead(struct address_space *mapping,
     156                 :            :                 struct file *filp, pgoff_t offset, unsigned long nr_to_read,
     157                 :            :                 unsigned long lookahead_size)
     158                 :            : {
     159                 :       9539 :         struct inode *inode = mapping->host;
     160                 :       9539 :         struct page *page;
     161                 :       9539 :         unsigned long end_index;        /* The last page we want to read */
     162                 :       9539 :         LIST_HEAD(page_pool);
     163                 :       9539 :         int page_idx;
     164                 :       9539 :         unsigned int nr_pages = 0;
     165         [ +  + ]:       9539 :         loff_t isize = i_size_read(inode);
     166         [ +  + ]:       9539 :         gfp_t gfp_mask = readahead_gfp_mask(mapping);
     167                 :            : 
     168         [ +  + ]:       9539 :         if (isize == 0)
     169                 :         22 :                 goto out;
     170                 :            : 
     171                 :       9517 :         end_index = ((isize - 1) >> PAGE_SHIFT);
     172                 :            : 
     173                 :            :         /*
     174                 :            :          * Preallocate as many pages as we will need.
     175                 :            :          */
     176         [ +  + ]:     146824 :         for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
     177                 :     141831 :                 pgoff_t page_offset = offset + page_idx;
     178                 :            : 
     179         [ +  + ]:     141831 :                 if (page_offset > end_index)
     180                 :            :                         break;
     181                 :            : 
     182                 :     137307 :                 page = xa_load(&mapping->i_pages, page_offset);
     183   [ +  +  +  - ]:     137307 :                 if (page && !xa_is_value(page)) {
     184                 :            :                         /*
     185                 :            :                          * Page already present?  Kick off the current batch of
     186                 :            :                          * contiguous pages before continuing with the next
     187                 :            :                          * batch.
     188                 :            :                          */
     189         [ +  + ]:      32935 :                         if (nr_pages)
     190                 :       1483 :                                 read_pages(mapping, filp, &page_pool, nr_pages,
     191                 :            :                                                 gfp_mask);
     192                 :      32935 :                         nr_pages = 0;
     193                 :      32935 :                         continue;
     194                 :            :                 }
     195                 :            : 
     196                 :     104372 :                 page = __page_cache_alloc(gfp_mask);
     197         [ +  - ]:     104372 :                 if (!page)
     198                 :            :                         break;
     199                 :     104372 :                 page->index = page_offset;
     200         [ +  + ]:     104372 :                 list_add(&page->lru, &page_pool);
     201         [ +  + ]:     104372 :                 if (page_idx == nr_to_read - lookahead_size)
     202                 :       3343 :                         SetPageReadahead(page);
     203                 :     104372 :                 nr_pages++;
     204                 :            :         }
     205                 :            : 
     206                 :            :         /*
     207                 :            :          * Now start the IO.  We ignore I/O errors - if the page is not
     208                 :            :          * uptodate then the caller will launch readpage again, and
     209                 :            :          * will then handle the error.
     210                 :            :          */
     211         [ +  + ]:       9517 :         if (nr_pages)
     212                 :       7197 :                 read_pages(mapping, filp, &page_pool, nr_pages, gfp_mask);
     213         [ -  + ]:       9517 :         BUG_ON(!list_empty(&page_pool));
     214                 :       9517 : out:
     215                 :       9539 :         return nr_pages;
     216                 :            : }
     217                 :            : 
     218                 :            : /*
     219                 :            :  * Chunk the readahead into 2 megabyte units, so that we don't pin too much
     220                 :            :  * memory at once.
     221                 :            :  */
     222                 :       1056 : int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
     223                 :            :                                pgoff_t offset, unsigned long nr_to_read)
     224                 :            : {
     225                 :       1056 :         struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
     226                 :       1056 :         struct file_ra_state *ra = &filp->f_ra;
     227                 :       1056 :         unsigned long max_pages;
     228                 :            : 
     229   [ -  +  -  - ]:       1056 :         if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
     230                 :            :                 return -EINVAL;
     231                 :            : 
     232                 :            :         /*
     233                 :            :          * If the request exceeds the readahead window, allow the read to
     234                 :            :          * be up to the optimal hardware IO size
     235                 :            :          */
     236                 :       1056 :         max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
     237                 :       1056 :         nr_to_read = min(nr_to_read, max_pages);
     238         [ +  + ]:       2112 :         while (nr_to_read) {
     239                 :       1056 :                 unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE;
     240                 :            : 
     241         [ +  - ]:       1056 :                 if (this_chunk > nr_to_read)
     242                 :       1056 :                         this_chunk = nr_to_read;
     243                 :       1056 :                 __do_page_cache_readahead(mapping, filp, offset, this_chunk, 0);
     244                 :            : 
     245                 :       1056 :                 offset += this_chunk;
     246                 :       1056 :                 nr_to_read -= this_chunk;
     247                 :            :         }
     248                 :            :         return 0;
     249                 :            : }
     250                 :            : 
     251                 :            : /*
     252                 :            :  * Set the initial window size, round to next power of 2 and square
     253                 :            :  * for small size, x 4 for medium, and x 2 for large
     254                 :            :  * for 128k (32 page) max ra
     255                 :            :  * 1-8 page = 32k initial, > 8 page = 128k initial
     256                 :            :  */
     257                 :       3289 : static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
     258                 :            : {
     259   [ -  +  -  -  :       3289 :         unsigned long newsize = roundup_pow_of_two(size);
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     260                 :            : 
     261         [ +  - ]:       3289 :         if (newsize <= max / 32)
     262                 :       3289 :                 newsize = newsize * 4;
     263         [ #  # ]:          0 :         else if (newsize <= max / 4)
     264                 :          0 :                 newsize = newsize * 2;
     265                 :            :         else
     266                 :            :                 newsize = max;
     267                 :            : 
     268                 :       3289 :         return newsize;
     269                 :            : }
     270                 :            : 
     271                 :            : /*
     272                 :            :  *  Get the previous window size, ramp it up, and
     273                 :            :  *  return it as the new window size.
     274                 :            :  */
     275                 :       2321 : static unsigned long get_next_ra_size(struct file_ra_state *ra,
     276                 :            :                                       unsigned long max)
     277                 :            : {
     278                 :       2321 :         unsigned long cur = ra->size;
     279                 :            : 
     280                 :       2321 :         if (cur < max / 16)
     281                 :         22 :                 return 4 * cur;
     282   [ +  +  +  +  :       2299 :         if (cur <= max / 2)
                   -  - ]
     283                 :        251 :                 return 2 * cur;
     284                 :            :         return max;
     285                 :            : }
     286                 :            : 
     287                 :            : /*
     288                 :            :  * On-demand readahead design.
     289                 :            :  *
     290                 :            :  * The fields in struct file_ra_state represent the most-recently-executed
     291                 :            :  * readahead attempt:
     292                 :            :  *
     293                 :            :  *                        |<----- async_size ---------|
     294                 :            :  *     |------------------- size -------------------->|
     295                 :            :  *     |==================#===========================|
     296                 :            :  *     ^start             ^page marked with PG_readahead
     297                 :            :  *
     298                 :            :  * To overlap application thinking time and disk I/O time, we do
     299                 :            :  * `readahead pipelining': Do not wait until the application consumed all
     300                 :            :  * readahead pages and stalled on the missing page at readahead_index;
     301                 :            :  * Instead, submit an asynchronous readahead I/O as soon as there are
     302                 :            :  * only async_size pages left in the readahead window. Normally async_size
     303                 :            :  * will be equal to size, for maximum pipelining.
     304                 :            :  *
     305                 :            :  * In interleaved sequential reads, concurrent streams on the same fd can
     306                 :            :  * be invalidating each other's readahead state. So we flag the new readahead
     307                 :            :  * page at (start+size-async_size) with PG_readahead, and use it as readahead
     308                 :            :  * indicator. The flag won't be set on already cached pages, to avoid the
     309                 :            :  * readahead-for-nothing fuss, saving pointless page cache lookups.
     310                 :            :  *
     311                 :            :  * prev_pos tracks the last visited byte in the _previous_ read request.
     312                 :            :  * It should be maintained by the caller, and will be used for detecting
     313                 :            :  * small random reads. Note that the readahead algorithm checks loosely
     314                 :            :  * for sequential patterns. Hence interleaved reads might be served as
     315                 :            :  * sequential ones.
     316                 :            :  *
     317                 :            :  * There is a special-case: if the first page which the application tries to
     318                 :            :  * read happens to be the first page of the file, it is assumed that a linear
     319                 :            :  * read is about to happen and the window is immediately set to the initial size
     320                 :            :  * based on I/O request size and the max_readahead.
     321                 :            :  *
     322                 :            :  * The code ramps up the readahead size aggressively at first, but slow down as
     323                 :            :  * it approaches max_readhead.
     324                 :            :  */
     325                 :            : 
     326                 :            : /*
     327                 :            :  * Count contiguously cached pages from @offset-1 to @offset-@max,
     328                 :            :  * this count is a conservative estimation of
     329                 :            :  *      - length of the sequential read sequence, or
     330                 :            :  *      - thrashing threshold in memory tight systems
     331                 :            :  */
     332                 :          0 : static pgoff_t count_history_pages(struct address_space *mapping,
     333                 :            :                                    pgoff_t offset, unsigned long max)
     334                 :            : {
     335                 :          0 :         pgoff_t head;
     336                 :            : 
     337                 :          0 :         rcu_read_lock();
     338                 :          0 :         head = page_cache_prev_miss(mapping, offset - 1, max);
     339                 :          0 :         rcu_read_unlock();
     340                 :            : 
     341                 :          0 :         return offset - 1 - head;
     342                 :            : }
     343                 :            : 
     344                 :            : /*
     345                 :            :  * page cache context based read-ahead
     346                 :            :  */
     347                 :          0 : static int try_context_readahead(struct address_space *mapping,
     348                 :            :                                  struct file_ra_state *ra,
     349                 :            :                                  pgoff_t offset,
     350                 :            :                                  unsigned long req_size,
     351                 :            :                                  unsigned long max)
     352                 :            : {
     353                 :          0 :         pgoff_t size;
     354                 :            : 
     355                 :          0 :         size = count_history_pages(mapping, offset, max);
     356                 :            : 
     357                 :            :         /*
     358                 :            :          * not enough history pages:
     359                 :            :          * it could be a random read
     360                 :            :          */
     361         [ #  # ]:          0 :         if (size <= req_size)
     362                 :            :                 return 0;
     363                 :            : 
     364                 :            :         /*
     365                 :            :          * starts from beginning of file:
     366                 :            :          * it is a strong indication of long-run stream (or whole-file-read)
     367                 :            :          */
     368         [ #  # ]:          0 :         if (size >= offset)
     369                 :          0 :                 size *= 2;
     370                 :            : 
     371                 :          0 :         ra->start = offset;
     372                 :          0 :         ra->size = min(size + req_size, max);
     373                 :          0 :         ra->async_size = 1;
     374                 :            : 
     375                 :          0 :         return 1;
     376                 :            : }
     377                 :            : 
     378                 :            : /*
     379                 :            :  * A minimal readahead algorithm for trivial sequential/random reads.
     380                 :            :  */
     381                 :            : static unsigned long
     382                 :       5610 : ondemand_readahead(struct address_space *mapping,
     383                 :            :                    struct file_ra_state *ra, struct file *filp,
     384                 :            :                    bool hit_readahead_marker, pgoff_t offset,
     385                 :            :                    unsigned long req_size)
     386                 :            : {
     387                 :       5610 :         struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
     388                 :       5610 :         unsigned long max_pages = ra->ra_pages;
     389                 :       5610 :         unsigned long add_pages;
     390                 :       5610 :         pgoff_t prev_offset;
     391                 :            : 
     392                 :            :         /*
     393                 :            :          * If the request exceeds the readahead window, allow the read to
     394                 :            :          * be up to the optimal hardware IO size
     395                 :            :          */
     396   [ +  +  +  - ]:       5610 :         if (req_size > max_pages && bdi->io_pages > max_pages)
     397                 :         88 :                 max_pages = min(req_size, bdi->io_pages);
     398                 :            : 
     399                 :            :         /*
     400                 :            :          * start of file
     401                 :            :          */
     402         [ +  + ]:       5610 :         if (!offset)
     403                 :       3289 :                 goto initial_readahead;
     404                 :            : 
     405                 :            :         /*
     406                 :            :          * It's the expected callback offset, assume sequential access.
     407                 :            :          * Ramp up sizes, and push forward the readahead window.
     408                 :            :          */
     409   [ +  +  -  + ]:       2321 :         if ((offset == (ra->start + ra->size - ra->async_size) ||
     410                 :            :              offset == (ra->start + ra->size))) {
     411                 :        625 :                 ra->start += ra->size;
     412         [ +  + ]:        625 :                 ra->size = get_next_ra_size(ra, max_pages);
     413                 :        625 :                 ra->async_size = ra->size;
     414                 :        625 :                 goto readit;
     415                 :            :         }
     416                 :            : 
     417                 :            :         /*
     418                 :            :          * Hit a marked page without valid readahead state.
     419                 :            :          * E.g. interleaved reads.
     420                 :            :          * Query the pagecache for async_size, which normally equals to
     421                 :            :          * readahead size. Ramp it up and use it as the new readahead size.
     422                 :            :          */
     423         [ +  - ]:       1696 :         if (hit_readahead_marker) {
     424                 :       1696 :                 pgoff_t start;
     425                 :            : 
     426                 :       1696 :                 rcu_read_lock();
     427                 :       1696 :                 start = page_cache_next_miss(mapping, offset + 1, max_pages);
     428                 :       1696 :                 rcu_read_unlock();
     429                 :            : 
     430   [ +  -  +  - ]:       1696 :                 if (!start || start - offset > max_pages)
     431                 :            :                         return 0;
     432                 :            : 
     433                 :       1696 :                 ra->start = start;
     434                 :       1696 :                 ra->size = start - offset;   /* old async_size */
     435                 :       1696 :                 ra->size += req_size;
     436         [ -  + ]:       1696 :                 ra->size = get_next_ra_size(ra, max_pages);
     437                 :       1696 :                 ra->async_size = ra->size;
     438                 :       1696 :                 goto readit;
     439                 :            :         }
     440                 :            : 
     441                 :            :         /*
     442                 :            :          * oversize read
     443                 :            :          */
     444         [ #  # ]:          0 :         if (req_size > max_pages)
     445                 :          0 :                 goto initial_readahead;
     446                 :            : 
     447                 :            :         /*
     448                 :            :          * sequential cache miss
     449                 :            :          * trivial case: (offset - prev_offset) == 1
     450                 :            :          * unaligned reads: (offset - prev_offset) == 0
     451                 :            :          */
     452                 :          0 :         prev_offset = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
     453         [ #  # ]:          0 :         if (offset - prev_offset <= 1UL)
     454                 :          0 :                 goto initial_readahead;
     455                 :            : 
     456                 :            :         /*
     457                 :            :          * Query the page cache and look for the traces(cached history pages)
     458                 :            :          * that a sequential stream would leave behind.
     459                 :            :          */
     460         [ #  # ]:          0 :         if (try_context_readahead(mapping, ra, offset, req_size, max_pages))
     461                 :          0 :                 goto readit;
     462                 :            : 
     463                 :            :         /*
     464                 :            :          * standalone, small random read
     465                 :            :          * Read as is, and do not pollute the readahead state.
     466                 :            :          */
     467                 :          0 :         return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
     468                 :            : 
     469                 :       3289 : initial_readahead:
     470                 :       3289 :         ra->start = offset;
     471                 :       3289 :         ra->size = get_init_ra_size(req_size, max_pages);
     472         [ +  - ]:       3289 :         ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
     473                 :            : 
     474                 :       5610 : readit:
     475                 :            :         /*
     476                 :            :          * Will this read hit the readahead marker made by itself?
     477                 :            :          * If so, trigger the readahead marker hit now, and merge
     478                 :            :          * the resulted next readahead window into the current one.
     479                 :            :          * Take care of maximum IO pages as above.
     480                 :            :          */
     481   [ +  +  -  + ]:       5610 :         if (offset == ra->start && ra->size == ra->async_size) {
     482         [ #  # ]:          0 :                 add_pages = get_next_ra_size(ra, max_pages);
     483         [ #  # ]:          0 :                 if (ra->size + add_pages <= max_pages) {
     484                 :          0 :                         ra->async_size = add_pages;
     485                 :          0 :                         ra->size += add_pages;
     486                 :            :                 } else {
     487                 :          0 :                         ra->size = max_pages;
     488                 :          0 :                         ra->async_size = max_pages >> 1;
     489                 :            :                 }
     490                 :            :         }
     491                 :            : 
     492                 :       5610 :         return ra_submit(ra, mapping, filp);
     493                 :            : }
     494                 :            : 
     495                 :            : /**
     496                 :            :  * page_cache_sync_readahead - generic file readahead
     497                 :            :  * @mapping: address_space which holds the pagecache and I/O vectors
     498                 :            :  * @ra: file_ra_state which holds the readahead state
     499                 :            :  * @filp: passed on to ->readpage() and ->readpages()
     500                 :            :  * @offset: start offset into @mapping, in pagecache page-sized units
     501                 :            :  * @req_size: hint: total size of the read which the caller is performing in
     502                 :            :  *            pagecache pages
     503                 :            :  *
     504                 :            :  * page_cache_sync_readahead() should be called when a cache miss happened:
     505                 :            :  * it will submit the read.  The readahead logic may decide to piggyback more
     506                 :            :  * pages onto the read request if access patterns suggest it will improve
     507                 :            :  * performance.
     508                 :            :  */
     509                 :       4345 : void page_cache_sync_readahead(struct address_space *mapping,
     510                 :            :                                struct file_ra_state *ra, struct file *filp,
     511                 :            :                                pgoff_t offset, unsigned long req_size)
     512                 :            : {
     513                 :            :         /* no read-ahead */
     514         [ +  - ]:       4345 :         if (!ra->ra_pages)
     515                 :            :                 return;
     516                 :            : 
     517         [ +  - ]:       4345 :         if (blk_cgroup_congested())
     518                 :            :                 return;
     519                 :            : 
     520                 :            :         /* be dumb */
     521   [ +  -  +  + ]:       4345 :         if (filp && (filp->f_mode & FMODE_RANDOM)) {
     522                 :       1056 :                 force_page_cache_readahead(mapping, filp, offset, req_size);
     523                 :       1056 :                 return;
     524                 :            :         }
     525                 :            : 
     526                 :            :         /* do read-ahead */
     527                 :       3289 :         ondemand_readahead(mapping, ra, filp, false, offset, req_size);
     528                 :            : }
     529                 :            : EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
     530                 :            : 
     531                 :            : /**
     532                 :            :  * page_cache_async_readahead - file readahead for marked pages
     533                 :            :  * @mapping: address_space which holds the pagecache and I/O vectors
     534                 :            :  * @ra: file_ra_state which holds the readahead state
     535                 :            :  * @filp: passed on to ->readpage() and ->readpages()
     536                 :            :  * @page: the page at @offset which has the PG_readahead flag set
     537                 :            :  * @offset: start offset into @mapping, in pagecache page-sized units
     538                 :            :  * @req_size: hint: total size of the read which the caller is performing in
     539                 :            :  *            pagecache pages
     540                 :            :  *
     541                 :            :  * page_cache_async_readahead() should be called when a page is used which
     542                 :            :  * has the PG_readahead flag; this is a marker to suggest that the application
     543                 :            :  * has used up enough of the readahead window that we should start pulling in
     544                 :            :  * more pages.
     545                 :            :  */
     546                 :            : void
     547                 :       2321 : page_cache_async_readahead(struct address_space *mapping,
     548                 :            :                            struct file_ra_state *ra, struct file *filp,
     549                 :            :                            struct page *page, pgoff_t offset,
     550                 :            :                            unsigned long req_size)
     551                 :            : {
     552                 :            :         /* no read-ahead */
     553         [ +  - ]:       2321 :         if (!ra->ra_pages)
     554                 :            :                 return;
     555                 :            : 
     556                 :            :         /*
     557                 :            :          * Same bit is used for PG_readahead and PG_reclaim.
     558                 :            :          */
     559   [ -  +  +  - ]:       4642 :         if (PageWriteback(page))
     560                 :            :                 return;
     561                 :            : 
     562                 :       2321 :         ClearPageReadahead(page);
     563                 :            : 
     564                 :            :         /*
     565                 :            :          * Defer asynchronous read-ahead on IO congestion.
     566                 :            :          */
     567         [ +  - ]:       2321 :         if (inode_read_congested(mapping->host))
     568                 :            :                 return;
     569                 :            : 
     570                 :       2321 :         if (blk_cgroup_congested())
     571                 :            :                 return;
     572                 :            : 
     573                 :            :         /* do read-ahead */
     574                 :       2321 :         ondemand_readahead(mapping, ra, filp, true, offset, req_size);
     575                 :            : }
     576                 :            : EXPORT_SYMBOL_GPL(page_cache_async_readahead);
     577                 :            : 
     578                 :          0 : ssize_t ksys_readahead(int fd, loff_t offset, size_t count)
     579                 :            : {
     580                 :          0 :         ssize_t ret;
     581                 :          0 :         struct fd f;
     582                 :            : 
     583                 :          0 :         ret = -EBADF;
     584                 :          0 :         f = fdget(fd);
     585   [ #  #  #  # ]:          0 :         if (!f.file || !(f.file->f_mode & FMODE_READ))
     586                 :          0 :                 goto out;
     587                 :            : 
     588                 :            :         /*
     589                 :            :          * The readahead() syscall is intended to run only on files
     590                 :            :          * that can execute readahead. If readahead is not possible
     591                 :            :          * on this file, then we must return -EINVAL.
     592                 :            :          */
     593                 :          0 :         ret = -EINVAL;
     594   [ #  #  #  #  :          0 :         if (!f.file->f_mapping || !f.file->f_mapping->a_ops ||
                   #  # ]
     595         [ #  # ]:          0 :             !S_ISREG(file_inode(f.file)->i_mode))
     596                 :          0 :                 goto out;
     597                 :            : 
     598                 :          0 :         ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED);
     599                 :          0 : out:
     600         [ #  # ]:          0 :         fdput(f);
     601                 :          0 :         return ret;
     602                 :            : }
     603                 :            : 
     604                 :          0 : SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
     605                 :            : {
     606                 :          0 :         return ksys_readahead(fd, offset, count);
     607                 :            : }

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