| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * mm/readahead.c - address_space-level file readahead. |
| * |
| * Copyright (C) 2002, Linus Torvalds |
| * |
| * 09Apr2002 Andrew Morton |
| * Initial version. |
| */ |
| |
| /** |
| * DOC: Readahead Overview |
| * |
| * Readahead is used to read content into the page cache before it is |
| * explicitly requested by the application. Readahead only ever |
| * attempts to read folios that are not yet in the page cache. If a |
| * folio is present but not up-to-date, readahead will not try to read |
| * it. In that case a simple ->read_folio() will be requested. |
| * |
| * Readahead is triggered when an application read request (whether a |
| * system call or a page fault) finds that the requested folio is not in |
| * the page cache, or that it is in the page cache and has the |
| * readahead flag set. This flag indicates that the folio was read |
| * as part of a previous readahead request and now that it has been |
| * accessed, it is time for the next readahead. |
| * |
| * Each readahead request is partly synchronous read, and partly async |
| * readahead. This is reflected in the struct file_ra_state which |
| * contains ->size being the total number of pages, and ->async_size |
| * which is the number of pages in the async section. The readahead |
| * flag will be set on the first folio in this async section to trigger |
| * a subsequent readahead. Once a series of sequential reads has been |
| * established, there should be no need for a synchronous component and |
| * all readahead request will be fully asynchronous. |
| * |
| * When either of the triggers causes a readahead, three numbers need |
| * to be determined: the start of the region to read, the size of the |
| * region, and the size of the async tail. |
| * |
| * The start of the region is simply the first page address at or after |
| * the accessed address, which is not currently populated in the page |
| * cache. This is found with a simple search in the page cache. |
| * |
| * The size of the async tail is determined by subtracting the size that |
| * was explicitly requested from the determined request size, unless |
| * this would be less than zero - then zero is used. NOTE THIS |
| * CALCULATION IS WRONG WHEN THE START OF THE REGION IS NOT THE ACCESSED |
| * PAGE. ALSO THIS CALCULATION IS NOT USED CONSISTENTLY. |
| * |
| * The size of the region is normally determined from the size of the |
| * previous readahead which loaded the preceding pages. This may be |
| * discovered from the struct file_ra_state for simple sequential reads, |
| * or from examining the state of the page cache when multiple |
| * sequential reads are interleaved. Specifically: where the readahead |
| * was triggered by the readahead flag, the size of the previous |
| * readahead is assumed to be the number of pages from the triggering |
| * page to the start of the new readahead. In these cases, the size of |
| * the previous readahead is scaled, often doubled, for the new |
| * readahead, though see get_next_ra_size() for details. |
| * |
| * If the size of the previous read cannot be determined, the number of |
| * preceding pages in the page cache is used to estimate the size of |
| * a previous read. This estimate could easily be misled by random |
| * reads being coincidentally adjacent, so it is ignored unless it is |
| * larger than the current request, and it is not scaled up, unless it |
| * is at the start of file. |
| * |
| * In general readahead is accelerated at the start of the file, as |
| * reads from there are often sequential. There are other minor |
| * adjustments to the readahead size in various special cases and these |
| * are best discovered by reading the code. |
| * |
| * The above calculation, based on the previous readahead size, |
| * determines the size of the readahead, to which any requested read |
| * size may be added. |
| * |
| * Readahead requests are sent to the filesystem using the ->readahead() |
| * address space operation, for which mpage_readahead() is a canonical |
| * implementation. ->readahead() should normally initiate reads on all |
| * folios, but may fail to read any or all folios without causing an I/O |
| * error. The page cache reading code will issue a ->read_folio() request |
| * for any folio which ->readahead() did not read, and only an error |
| * from this will be final. |
| * |
| * ->readahead() will generally call readahead_folio() repeatedly to get |
| * each folio from those prepared for readahead. It may fail to read a |
| * folio by: |
| * |
| * * not calling readahead_folio() sufficiently many times, effectively |
| * ignoring some folios, as might be appropriate if the path to |
| * storage is congested. |
| * |
| * * failing to actually submit a read request for a given folio, |
| * possibly due to insufficient resources, or |
| * |
| * * getting an error during subsequent processing of a request. |
| * |
| * In the last two cases, the folio should be unlocked by the filesystem |
| * to indicate that the read attempt has failed. In the first case the |
| * folio will be unlocked by the VFS. |
| * |
| * Those folios not in the final ``async_size`` of the request should be |
| * considered to be important and ->readahead() should not fail them due |
| * to congestion or temporary resource unavailability, but should wait |
| * for necessary resources (e.g. memory or indexing information) to |
| * become available. Folios in the final ``async_size`` may be |
| * considered less urgent and failure to read them is more acceptable. |
| * In this case it is best to use filemap_remove_folio() to remove the |
| * folios from the page cache as is automatically done for folios that |
| * were not fetched with readahead_folio(). This will allow a |
| * subsequent synchronous readahead request to try them again. If they |
| * are left in the page cache, then they will be read individually using |
| * ->read_folio() which may be less efficient. |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/dax.h> |
| #include <linux/gfp.h> |
| #include <linux/export.h> |
| #include <linux/backing-dev.h> |
| #include <linux/task_io_accounting_ops.h> |
| #include <linux/pagevec.h> |
| #include <linux/pagemap.h> |
| #include <linux/syscalls.h> |
| #include <linux/file.h> |
| #include <linux/mm_inline.h> |
| #include <linux/blk-cgroup.h> |
| #include <linux/fadvise.h> |
| #include <linux/sched/mm.h> |
| |
| #include "internal.h" |
| |
| /* |
| * Initialise a struct file's readahead state. Assumes that the caller has |
| * memset *ra to zero. |
| */ |
| void |
| file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) |
| { |
| ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages; |
| ra->prev_pos = -1; |
| } |
| EXPORT_SYMBOL_GPL(file_ra_state_init); |
| |
| static void read_pages(struct readahead_control *rac) |
| { |
| const struct address_space_operations *aops = rac->mapping->a_ops; |
| struct folio *folio; |
| struct blk_plug plug; |
| |
| if (!readahead_count(rac)) |
| return; |
| |
| blk_start_plug(&plug); |
| |
| if (aops->readahead) { |
| aops->readahead(rac); |
| /* |
| * Clean up the remaining folios. The sizes in ->ra |
| * may be used to size the next readahead, so make sure |
| * they accurately reflect what happened. |
| */ |
| while ((folio = readahead_folio(rac)) != NULL) { |
| unsigned long nr = folio_nr_pages(folio); |
| |
| rac->ra->size -= nr; |
| if (rac->ra->async_size >= nr) { |
| rac->ra->async_size -= nr; |
| filemap_remove_folio(folio); |
| } |
| folio_unlock(folio); |
| } |
| } else if (aops->read_folio) { |
| while ((folio = readahead_folio(rac)) != NULL) |
| aops->read_folio(rac->file, folio); |
| } else { |
| while ((folio = readahead_folio(rac)) != NULL) |
| aops->readpage(rac->file, &folio->page); |
| } |
| |
| blk_finish_plug(&plug); |
| |
| BUG_ON(readahead_count(rac)); |
| } |
| |
| /** |
| * page_cache_ra_unbounded - Start unchecked readahead. |
| * @ractl: Readahead control. |
| * @nr_to_read: The number of pages to read. |
| * @lookahead_size: Where to start the next readahead. |
| * |
| * This function is for filesystems to call when they want to start |
| * readahead beyond a file's stated i_size. This is almost certainly |
| * not the function you want to call. Use page_cache_async_readahead() |
| * or page_cache_sync_readahead() instead. |
| * |
| * Context: File is referenced by caller. Mutexes may be held by caller. |
| * May sleep, but will not reenter filesystem to reclaim memory. |
| */ |
| void page_cache_ra_unbounded(struct readahead_control *ractl, |
| unsigned long nr_to_read, unsigned long lookahead_size) |
| { |
| struct address_space *mapping = ractl->mapping; |
| unsigned long index = readahead_index(ractl); |
| gfp_t gfp_mask = readahead_gfp_mask(mapping); |
| unsigned long i; |
| |
| /* |
| * Partway through the readahead operation, we will have added |
| * locked pages to the page cache, but will not yet have submitted |
| * them for I/O. Adding another page may need to allocate memory, |
| * which can trigger memory reclaim. Telling the VM we're in |
| * the middle of a filesystem operation will cause it to not |
| * touch file-backed pages, preventing a deadlock. Most (all?) |
| * filesystems already specify __GFP_NOFS in their mapping's |
| * gfp_mask, but let's be explicit here. |
| */ |
| unsigned int nofs = memalloc_nofs_save(); |
| |
| filemap_invalidate_lock_shared(mapping); |
| /* |
| * Preallocate as many pages as we will need. |
| */ |
| for (i = 0; i < nr_to_read; i++) { |
| struct folio *folio = xa_load(&mapping->i_pages, index + i); |
| |
| if (folio && !xa_is_value(folio)) { |
| /* |
| * Page already present? Kick off the current batch |
| * of contiguous pages before continuing with the |
| * next batch. This page may be the one we would |
| * have intended to mark as Readahead, but we don't |
| * have a stable reference to this page, and it's |
| * not worth getting one just for that. |
| */ |
| read_pages(ractl); |
| ractl->_index++; |
| i = ractl->_index + ractl->_nr_pages - index - 1; |
| continue; |
| } |
| |
| folio = filemap_alloc_folio(gfp_mask, 0); |
| if (!folio) |
| break; |
| if (filemap_add_folio(mapping, folio, index + i, |
| gfp_mask) < 0) { |
| folio_put(folio); |
| read_pages(ractl); |
| ractl->_index++; |
| i = ractl->_index + ractl->_nr_pages - index - 1; |
| continue; |
| } |
| if (i == nr_to_read - lookahead_size) |
| folio_set_readahead(folio); |
| ractl->_nr_pages++; |
| } |
| |
| /* |
| * Now start the IO. We ignore I/O errors - if the page is not |
| * uptodate then the caller will launch readpage again, and |
| * will then handle the error. |
| */ |
| read_pages(ractl); |
| filemap_invalidate_unlock_shared(mapping); |
| memalloc_nofs_restore(nofs); |
| } |
| EXPORT_SYMBOL_GPL(page_cache_ra_unbounded); |
| |
| /* |
| * do_page_cache_ra() actually reads a chunk of disk. It allocates |
| * the pages first, then submits them for I/O. This avoids the very bad |
| * behaviour which would occur if page allocations are causing VM writeback. |
| * We really don't want to intermingle reads and writes like that. |
| */ |
| static void do_page_cache_ra(struct readahead_control *ractl, |
| unsigned long nr_to_read, unsigned long lookahead_size) |
| { |
| struct inode *inode = ractl->mapping->host; |
| unsigned long index = readahead_index(ractl); |
| loff_t isize = i_size_read(inode); |
| pgoff_t end_index; /* The last page we want to read */ |
| |
| if (isize == 0) |
| return; |
| |
| end_index = (isize - 1) >> PAGE_SHIFT; |
| if (index > end_index) |
| return; |
| /* Don't read past the page containing the last byte of the file */ |
| if (nr_to_read > end_index - index) |
| nr_to_read = end_index - index + 1; |
| |
| page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size); |
| } |
| |
| /* |
| * Chunk the readahead into 2 megabyte units, so that we don't pin too much |
| * memory at once. |
| */ |
| void force_page_cache_ra(struct readahead_control *ractl, |
| unsigned long nr_to_read) |
| { |
| struct address_space *mapping = ractl->mapping; |
| struct file_ra_state *ra = ractl->ra; |
| struct backing_dev_info *bdi = inode_to_bdi(mapping->host); |
| unsigned long max_pages, index; |
| |
| if (unlikely(!mapping->a_ops->read_folio && |
| !mapping->a_ops->readpage && !mapping->a_ops->readahead)) |
| return; |
| |
| /* |
| * If the request exceeds the readahead window, allow the read to |
| * be up to the optimal hardware IO size |
| */ |
| index = readahead_index(ractl); |
| max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages); |
| nr_to_read = min_t(unsigned long, nr_to_read, max_pages); |
| while (nr_to_read) { |
| unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_SIZE; |
| |
| if (this_chunk > nr_to_read) |
| this_chunk = nr_to_read; |
| ractl->_index = index; |
| do_page_cache_ra(ractl, this_chunk, 0); |
| |
| index += this_chunk; |
| nr_to_read -= this_chunk; |
| } |
| } |
| |
| /* |
| * Set the initial window size, round to next power of 2 and square |
| * for small size, x 4 for medium, and x 2 for large |
| * for 128k (32 page) max ra |
| * 1-2 page = 16k, 3-4 page 32k, 5-8 page = 64k, > 8 page = 128k initial |
| */ |
| static unsigned long get_init_ra_size(unsigned long size, unsigned long max) |
| { |
| unsigned long newsize = roundup_pow_of_two(size); |
| |
| if (newsize <= max / 32) |
| newsize = newsize * 4; |
| else if (newsize <= max / 4) |
| newsize = newsize * 2; |
| else |
| newsize = max; |
| |
| return newsize; |
| } |
| |
| /* |
| * Get the previous window size, ramp it up, and |
| * return it as the new window size. |
| */ |
| static unsigned long get_next_ra_size(struct file_ra_state *ra, |
| unsigned long max) |
| { |
| unsigned long cur = ra->size; |
| |
| if (cur < max / 16) |
| return 4 * cur; |
| if (cur <= max / 2) |
| return 2 * cur; |
| return max; |
| } |
| |
| /* |
| * On-demand readahead design. |
| * |
| * The fields in struct file_ra_state represent the most-recently-executed |
| * readahead attempt: |
| * |
| * |<----- async_size ---------| |
| * |------------------- size -------------------->| |
| * |==================#===========================| |
| * ^start ^page marked with PG_readahead |
| * |
| * To overlap application thinking time and disk I/O time, we do |
| * `readahead pipelining': Do not wait until the application consumed all |
| * readahead pages and stalled on the missing page at readahead_index; |
| * Instead, submit an asynchronous readahead I/O as soon as there are |
| * only async_size pages left in the readahead window. Normally async_size |
| * will be equal to size, for maximum pipelining. |
| * |
| * In interleaved sequential reads, concurrent streams on the same fd can |
| * be invalidating each other's readahead state. So we flag the new readahead |
| * page at (start+size-async_size) with PG_readahead, and use it as readahead |
| * indicator. The flag won't be set on already cached pages, to avoid the |
| * readahead-for-nothing fuss, saving pointless page cache lookups. |
| * |
| * prev_pos tracks the last visited byte in the _previous_ read request. |
| * It should be maintained by the caller, and will be used for detecting |
| * small random reads. Note that the readahead algorithm checks loosely |
| * for sequential patterns. Hence interleaved reads might be served as |
| * sequential ones. |
| * |
| * There is a special-case: if the first page which the application tries to |
| * read happens to be the first page of the file, it is assumed that a linear |
| * read is about to happen and the window is immediately set to the initial size |
| * based on I/O request size and the max_readahead. |
| * |
| * The code ramps up the readahead size aggressively at first, but slow down as |
| * it approaches max_readhead. |
| */ |
| |
| /* |
| * Count contiguously cached pages from @index-1 to @index-@max, |
| * this count is a conservative estimation of |
| * - length of the sequential read sequence, or |
| * - thrashing threshold in memory tight systems |
| */ |
| static pgoff_t count_history_pages(struct address_space *mapping, |
| pgoff_t index, unsigned long max) |
| { |
| pgoff_t head; |
| |
| rcu_read_lock(); |
| head = page_cache_prev_miss(mapping, index - 1, max); |
| rcu_read_unlock(); |
| |
| return index - 1 - head; |
| } |
| |
| /* |
| * page cache context based readahead |
| */ |
| static int try_context_readahead(struct address_space *mapping, |
| struct file_ra_state *ra, |
| pgoff_t index, |
| unsigned long req_size, |
| unsigned long max) |
| { |
| pgoff_t size; |
| |
| size = count_history_pages(mapping, index, max); |
| |
| /* |
| * not enough history pages: |
| * it could be a random read |
| */ |
| if (size <= req_size) |
| return 0; |
| |
| /* |
| * starts from beginning of file: |
| * it is a strong indication of long-run stream (or whole-file-read) |
| */ |
| if (size >= index) |
| size *= 2; |
| |
| ra->start = index; |
| ra->size = min(size + req_size, max); |
| ra->async_size = 1; |
| |
| return 1; |
| } |
| |
| /* |
| * There are some parts of the kernel which assume that PMD entries |
| * are exactly HPAGE_PMD_ORDER. Those should be fixed, but until then, |
| * limit the maximum allocation order to PMD size. I'm not aware of any |
| * assumptions about maximum order if THP are disabled, but 8 seems like |
| * a good order (that's 1MB if you're using 4kB pages) |
| */ |
| #ifdef CONFIG_TRANSPARENT_HUGEPAGE |
| #define MAX_PAGECACHE_ORDER HPAGE_PMD_ORDER |
| #else |
| #define MAX_PAGECACHE_ORDER 8 |
| #endif |
| |
| static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index, |
| pgoff_t mark, unsigned int order, gfp_t gfp) |
| { |
| int err; |
| struct folio *folio = filemap_alloc_folio(gfp, order); |
| |
| if (!folio) |
| return -ENOMEM; |
| mark = round_up(mark, 1UL << order); |
| if (index == mark) |
| folio_set_readahead(folio); |
| err = filemap_add_folio(ractl->mapping, folio, index, gfp); |
| if (err) |
| folio_put(folio); |
| else |
| ractl->_nr_pages += 1UL << order; |
| return err; |
| } |
| |
| void page_cache_ra_order(struct readahead_control *ractl, |
| struct file_ra_state *ra, unsigned int new_order) |
| { |
| struct address_space *mapping = ractl->mapping; |
| pgoff_t index = readahead_index(ractl); |
| pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT; |
| pgoff_t mark = index + ra->size - ra->async_size; |
| int err = 0; |
| gfp_t gfp = readahead_gfp_mask(mapping); |
| |
| if (!mapping_large_folio_support(mapping) || ra->size < 4) |
| goto fallback; |
| |
| limit = min(limit, index + ra->size - 1); |
| |
| if (new_order < MAX_PAGECACHE_ORDER) { |
| new_order += 2; |
| if (new_order > MAX_PAGECACHE_ORDER) |
| new_order = MAX_PAGECACHE_ORDER; |
| while ((1 << new_order) > ra->size) |
| new_order--; |
| } |
| |
| while (index <= limit) { |
| unsigned int order = new_order; |
| |
| /* Align with smaller pages if needed */ |
| if (index & ((1UL << order) - 1)) { |
| order = __ffs(index); |
| if (order == 1) |
| order = 0; |
| } |
| /* Don't allocate pages past EOF */ |
| while (index + (1UL << order) - 1 > limit) { |
| if (--order == 1) |
| order = 0; |
| } |
| err = ra_alloc_folio(ractl, index, mark, order, gfp); |
| if (err) |
| break; |
| index += 1UL << order; |
| } |
| |
| if (index > limit) { |
| ra->size += index - limit - 1; |
| ra->async_size += index - limit - 1; |
| } |
| |
| read_pages(ractl); |
| |
| /* |
| * If there were already pages in the page cache, then we may have |
| * left some gaps. Let the regular readahead code take care of this |
| * situation. |
| */ |
| if (!err) |
| return; |
| fallback: |
| do_page_cache_ra(ractl, ra->size, ra->async_size); |
| } |
| |
| /* |
| * A minimal readahead algorithm for trivial sequential/random reads. |
| */ |
| static void ondemand_readahead(struct readahead_control *ractl, |
| struct folio *folio, unsigned long req_size) |
| { |
| struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host); |
| struct file_ra_state *ra = ractl->ra; |
| unsigned long max_pages = ra->ra_pages; |
| unsigned long add_pages; |
| pgoff_t index = readahead_index(ractl); |
| pgoff_t expected, prev_index; |
| unsigned int order = folio ? folio_order(folio) : 0; |
| |
| /* |
| * If the request exceeds the readahead window, allow the read to |
| * be up to the optimal hardware IO size |
| */ |
| if (req_size > max_pages && bdi->io_pages > max_pages) |
| max_pages = min(req_size, bdi->io_pages); |
| |
| /* |
| * start of file |
| */ |
| if (!index) |
| goto initial_readahead; |
| |
| /* |
| * It's the expected callback index, assume sequential access. |
| * Ramp up sizes, and push forward the readahead window. |
| */ |
| expected = round_up(ra->start + ra->size - ra->async_size, |
| 1UL << order); |
| if (index == expected || index == (ra->start + ra->size)) { |
| ra->start += ra->size; |
| ra->size = get_next_ra_size(ra, max_pages); |
| ra->async_size = ra->size; |
| goto readit; |
| } |
| |
| /* |
| * Hit a marked folio without valid readahead state. |
| * E.g. interleaved reads. |
| * Query the pagecache for async_size, which normally equals to |
| * readahead size. Ramp it up and use it as the new readahead size. |
| */ |
| if (folio) { |
| pgoff_t start; |
| |
| rcu_read_lock(); |
| start = page_cache_next_miss(ractl->mapping, index + 1, |
| max_pages); |
| rcu_read_unlock(); |
| |
| if (!start || start - index > max_pages) |
| return; |
| |
| ra->start = start; |
| ra->size = start - index; /* old async_size */ |
| ra->size += req_size; |
| ra->size = get_next_ra_size(ra, max_pages); |
| ra->async_size = ra->size; |
| goto readit; |
| } |
| |
| /* |
| * oversize read |
| */ |
| if (req_size > max_pages) |
| goto initial_readahead; |
| |
| /* |
| * sequential cache miss |
| * trivial case: (index - prev_index) == 1 |
| * unaligned reads: (index - prev_index) == 0 |
| */ |
| prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT; |
| if (index - prev_index <= 1UL) |
| goto initial_readahead; |
| |
| /* |
| * Query the page cache and look for the traces(cached history pages) |
| * that a sequential stream would leave behind. |
| */ |
| if (try_context_readahead(ractl->mapping, ra, index, req_size, |
| max_pages)) |
| goto readit; |
| |
| /* |
| * standalone, small random read |
| * Read as is, and do not pollute the readahead state. |
| */ |
| do_page_cache_ra(ractl, req_size, 0); |
| return; |
| |
| initial_readahead: |
| ra->start = index; |
| ra->size = get_init_ra_size(req_size, max_pages); |
| ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; |
| |
| readit: |
| /* |
| * Will this read hit the readahead marker made by itself? |
| * If so, trigger the readahead marker hit now, and merge |
| * the resulted next readahead window into the current one. |
| * Take care of maximum IO pages as above. |
| */ |
| if (index == ra->start && ra->size == ra->async_size) { |
| add_pages = get_next_ra_size(ra, max_pages); |
| if (ra->size + add_pages <= max_pages) { |
| ra->async_size = add_pages; |
| ra->size += add_pages; |
| } else { |
| ra->size = max_pages; |
| ra->async_size = max_pages >> 1; |
| } |
| } |
| |
| ractl->_index = ra->start; |
| page_cache_ra_order(ractl, ra, order); |
| } |
| |
| void page_cache_sync_ra(struct readahead_control *ractl, |
| unsigned long req_count) |
| { |
| bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM); |
| |
| /* |
| * Even if readahead is disabled, issue this request as readahead |
| * as we'll need it to satisfy the requested range. The forced |
| * readahead will do the right thing and limit the read to just the |
| * requested range, which we'll set to 1 page for this case. |
| */ |
| if (!ractl->ra->ra_pages || blk_cgroup_congested()) { |
| if (!ractl->file) |
| return; |
| req_count = 1; |
| do_forced_ra = true; |
| } |
| |
| /* be dumb */ |
| if (do_forced_ra) { |
| force_page_cache_ra(ractl, req_count); |
| return; |
| } |
| |
| ondemand_readahead(ractl, NULL, req_count); |
| } |
| EXPORT_SYMBOL_GPL(page_cache_sync_ra); |
| |
| void page_cache_async_ra(struct readahead_control *ractl, |
| struct folio *folio, unsigned long req_count) |
| { |
| /* no readahead */ |
| if (!ractl->ra->ra_pages) |
| return; |
| |
| /* |
| * Same bit is used for PG_readahead and PG_reclaim. |
| */ |
| if (folio_test_writeback(folio)) |
| return; |
| |
| folio_clear_readahead(folio); |
| |
| if (blk_cgroup_congested()) |
| return; |
| |
| ondemand_readahead(ractl, folio, req_count); |
| } |
| EXPORT_SYMBOL_GPL(page_cache_async_ra); |
| |
| ssize_t ksys_readahead(int fd, loff_t offset, size_t count) |
| { |
| ssize_t ret; |
| struct fd f; |
| |
| ret = -EBADF; |
| f = fdget(fd); |
| if (!f.file || !(f.file->f_mode & FMODE_READ)) |
| goto out; |
| |
| /* |
| * The readahead() syscall is intended to run only on files |
| * that can execute readahead. If readahead is not possible |
| * on this file, then we must return -EINVAL. |
| */ |
| ret = -EINVAL; |
| if (!f.file->f_mapping || !f.file->f_mapping->a_ops || |
| !S_ISREG(file_inode(f.file)->i_mode)) |
| goto out; |
| |
| ret = vfs_fadvise(f.file, offset, count, POSIX_FADV_WILLNEED); |
| out: |
| fdput(f); |
| return ret; |
| } |
| |
| SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count) |
| { |
| return ksys_readahead(fd, offset, count); |
| } |
| |
| /** |
| * readahead_expand - Expand a readahead request |
| * @ractl: The request to be expanded |
| * @new_start: The revised start |
| * @new_len: The revised size of the request |
| * |
| * Attempt to expand a readahead request outwards from the current size to the |
| * specified size by inserting locked pages before and after the current window |
| * to increase the size to the new window. This may involve the insertion of |
| * THPs, in which case the window may get expanded even beyond what was |
| * requested. |
| * |
| * The algorithm will stop if it encounters a conflicting page already in the |
| * pagecache and leave a smaller expansion than requested. |
| * |
| * The caller must check for this by examining the revised @ractl object for a |
| * different expansion than was requested. |
| */ |
| void readahead_expand(struct readahead_control *ractl, |
| loff_t new_start, size_t new_len) |
| { |
| struct address_space *mapping = ractl->mapping; |
| struct file_ra_state *ra = ractl->ra; |
| pgoff_t new_index, new_nr_pages; |
| gfp_t gfp_mask = readahead_gfp_mask(mapping); |
| |
| new_index = new_start / PAGE_SIZE; |
| |
| /* Expand the leading edge downwards */ |
| while (ractl->_index > new_index) { |
| unsigned long index = ractl->_index - 1; |
| struct page *page = xa_load(&mapping->i_pages, index); |
| |
| if (page && !xa_is_value(page)) |
| return; /* Page apparently present */ |
| |
| page = __page_cache_alloc(gfp_mask); |
| if (!page) |
| return; |
| if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) { |
| put_page(page); |
| return; |
| } |
| |
| ractl->_nr_pages++; |
| ractl->_index = page->index; |
| } |
| |
| new_len += new_start - readahead_pos(ractl); |
| new_nr_pages = DIV_ROUND_UP(new_len, PAGE_SIZE); |
| |
| /* Expand the trailing edge upwards */ |
| while (ractl->_nr_pages < new_nr_pages) { |
| unsigned long index = ractl->_index + ractl->_nr_pages; |
| struct page *page = xa_load(&mapping->i_pages, index); |
| |
| if (page && !xa_is_value(page)) |
| return; /* Page apparently present */ |
| |
| page = __page_cache_alloc(gfp_mask); |
| if (!page) |
| return; |
| if (add_to_page_cache_lru(page, mapping, index, gfp_mask) < 0) { |
| put_page(page); |
| return; |
| } |
| ractl->_nr_pages++; |
| if (ra) { |
| ra->size++; |
| ra->async_size++; |
| } |
| } |
| } |
| EXPORT_SYMBOL(readahead_expand); |