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| -rw-r--r-- | mm/readahead.c | 851 |
1 files changed, 851 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c new file mode 100644 index 000000000..ba4342804 --- /dev/null +++ b/mm/readahead.c @@ -0,0 +1,851 @@ +// 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/blkdev.h> +#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/psi.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; + + if (unlikely(rac->_workingset)) + psi_memstall_enter(&rac->_pflags); + 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); + + folio_get(folio); + rac->ra->size -= nr; + if (rac->ra->async_size >= nr) { + rac->ra->async_size -= nr; + filemap_remove_folio(folio); + } + folio_unlock(folio); + folio_put(folio); + } + } else { + while ((folio = readahead_folio(rac)) != NULL) + aops->read_folio(rac->file, folio); + } + + blk_finish_plug(&plug); + if (unlikely(rac->_workingset)) + psi_memstall_leave(&rac->_pflags); + rac->_workingset = false; + + 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->_workingset |= folio_test_workingset(folio); + ractl->_nr_pages++; + } + + /* + * Now start the IO. We ignore I/O errors - if the folio is not + * uptodate then the caller will launch read_folio 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->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); + return err; + } + + ractl->_nr_pages += 1UL << order; + ractl->_workingset |= folio_test_workingset(folio); + return 0; +} + +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--; + } + + filemap_invalidate_lock_shared(mapping); + 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); + filemap_invalidate_unlock_shared(mapping); + + /* + * 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) && + !S_ISBLK(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); +} + +#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_READAHEAD) +COMPAT_SYSCALL_DEFINE4(readahead, int, fd, compat_arg_u64_dual(offset), size_t, count) +{ + return ksys_readahead(fd, compat_arg_u64_glue(offset), count); +} +#endif + +/** + * 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; + } + if (unlikely(PageWorkingset(page)) && !ractl->_workingset) { + ractl->_workingset = true; + psi_memstall_enter(&ractl->_pflags); + } + ractl->_nr_pages++; + if (ra) { + ra->size++; + ra->async_size++; + } + } +} +EXPORT_SYMBOL(readahead_expand); |