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Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 861 |
1 files changed, 861 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c new file mode 100644 index 000000000..6e5563290 --- /dev/null +++ b/mm/readahead.c @@ -0,0 +1,861 @@ +// 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/blk_plug.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/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> + +#define CREATE_TRACE_POINTS +#include <trace/events/readahead.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); + +/** + * read_pages() - Start IO for a contiguous range of allocated folios in the + * page cache. + * @rac: Readahead control. + * + * When read_pages() returns, it is guaranteed that all of the folios will have + * been processed or removed so that ``readahead_count(rac) == 0``. However, + * that does not imply that ``readahead_index(rac)`` will be updated to point + * to the end of the originally requested range because, for example, the + * filesystem may expand the range upwards. + */ +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. */ + while ((folio = readahead_folio(rac)) != NULL) { + folio_get(folio); + 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)); +} + +static struct folio *ractl_alloc_folio(struct readahead_control *ractl, + gfp_t gfp_mask, unsigned int order) +{ + struct folio *folio; + + folio = filemap_alloc_folio(gfp_mask, order, NULL); + if (folio && ractl->dropbehind) + __folio_set_dropbehind(folio); + + return folio; +} + +/** + * 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, and ractl->mapping->invalidate_lock + * must be held by the caller at least in shared mode. 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 mark = ULONG_MAX, i = 0; + unsigned int min_nrpages = mapping_min_folio_nrpages(mapping); + + /* + * 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(); + + lockdep_assert_held(&mapping->invalidate_lock); + + trace_page_cache_ra_unbounded(mapping->host, index, nr_to_read, + lookahead_size); + index = mapping_align_index(mapping, index); + + /* + * As iterator `i` is aligned to min_nrpages, round_up the + * difference between nr_to_read and lookahead_size to mark the + * index that only has lookahead or "async_region" to set the + * readahead flag. + */ + if (lookahead_size <= nr_to_read) { + unsigned long ra_folio_index; + + ra_folio_index = round_up(readahead_index(ractl) + + nr_to_read - lookahead_size, + min_nrpages); + mark = ra_folio_index - index; + } + nr_to_read += readahead_index(ractl) - index; + ractl->_index = index; + + /* + * Preallocate as many pages as we will need. + */ + while (i < nr_to_read) { + struct folio *folio = xa_load(&mapping->i_pages, index + i); + int ret; + + 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 += min_nrpages; + i = ractl->_index - index; + continue; + } + + folio = ractl_alloc_folio(ractl, gfp_mask, + mapping_min_folio_order(mapping)); + if (!folio) + break; + + ret = filemap_add_folio(mapping, folio, index + i, gfp_mask); + if (ret < 0) { + folio_put(folio); + if (ret == -ENOMEM) + break; + read_pages(ractl); + ractl->_index += min_nrpages; + i = ractl->_index - index; + continue; + } + if (i == mark) + folio_set_readahead(folio); + ractl->_workingset |= folio_test_workingset(folio); + ractl->_nr_pages += min_nrpages; + i += min_nrpages; + } + + /* + * 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); + 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 address_space *mapping = ractl->mapping; + unsigned long index = readahead_index(ractl); + loff_t isize = i_size_read(mapping->host); + 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; + /* We've reached the end, so don't set a readahead marker. */ + lookahead_size = 0; + } + + filemap_invalidate_lock_shared(mapping); + page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size); + filemap_invalidate_unlock_shared(mapping); +} + +/* + * 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; + + 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 + */ + 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; + do_page_cache_ra(ractl, this_chunk, 0); + + 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_readahead. + */ + +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 = ractl_alloc_folio(ractl, gfp, order); + + if (!folio) + return -ENOMEM; + mark = round_down(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) +{ + struct address_space *mapping = ractl->mapping; + pgoff_t start = readahead_index(ractl); + pgoff_t index = start; + unsigned int min_order = mapping_min_folio_order(mapping); + pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT; + pgoff_t mark; + unsigned int nofs; + int err = 0; + gfp_t gfp = readahead_gfp_mask(mapping); + unsigned int new_order = ra->order; + + trace_page_cache_ra_order(mapping->host, start, ra); + if (!mapping_large_folio_support(mapping)) { + ra->order = 0; + goto fallback; + } + + if (limit > index + ra->size - 1) { + limit = index + ra->size - 1; + mark = index + ra->size - ra->async_size; + } else { + /* We've reached the end, so don't set a readahead marker. */ + mark = ULONG_MAX; + } + + new_order = min(mapping_max_folio_order(mapping), new_order); + new_order = min_t(unsigned int, new_order, ilog2(ra->size)); + new_order = max(new_order, min_order); + + ra->order = new_order; + + /* See comment in page_cache_ra_unbounded() */ + nofs = memalloc_nofs_save(); + filemap_invalidate_lock_shared(mapping); + /* + * If the new_order is greater than min_order and index is + * already aligned to new_order, then this will be noop as index + * aligned to new_order should also be aligned to min_order. + */ + ractl->_index = mapping_align_index(mapping, index); + index = readahead_index(ractl); + + while (index <= limit) { + unsigned int order = new_order; + + /* Align with smaller pages if needed */ + if (index & ((1UL << order) - 1)) + order = __ffs(index); + /* Don't allocate pages past EOF */ + while (order > min_order && index + (1UL << order) - 1 > limit) + order--; + err = ra_alloc_folio(ractl, index, mark, order, gfp); + if (err) + break; + index += 1UL << order; + } + + read_pages(ractl); + filemap_invalidate_unlock_shared(mapping); + memalloc_nofs_restore(nofs); + + /* + * 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 below. + */ + if (!err) + return; +fallback: + /* + * ->readahead() may have updated readahead window size so we have to + * check there's still something to read. + */ + if (ra->size > index - start) + do_page_cache_ra(ractl, ra->size - (index - start), + ra->async_size); +} + +static unsigned long ractl_max_pages(struct readahead_control *ractl, + unsigned long req_size) +{ + struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host); + unsigned long max_pages = ractl->ra->ra_pages; + + /* + * 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); + return max_pages; +} + +void page_cache_sync_ra(struct readahead_control *ractl, + unsigned long req_count) +{ + pgoff_t index = readahead_index(ractl); + bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM); + struct file_ra_state *ra = ractl->ra; + unsigned long max_pages, contig_count; + pgoff_t prev_index, miss; + + trace_page_cache_sync_ra(ractl->mapping->host, index, ra, req_count); + /* + * 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 (!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; + } + + max_pages = ractl_max_pages(ractl, req_count); + prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT; + /* + * A start of file, oversized read, or sequential cache miss: + * trivial case: (index - prev_index) == 1 + * unaligned reads: (index - prev_index) == 0 + */ + if (!index || req_count > max_pages || index - prev_index <= 1UL) { + ra->start = index; + ra->size = get_init_ra_size(req_count, max_pages); + ra->async_size = ra->size > req_count ? ra->size - req_count : + ra->size >> 1; + goto readit; + } + + /* + * Query the page cache and look for the traces(cached history pages) + * that a sequential stream would leave behind. + */ + rcu_read_lock(); + miss = page_cache_prev_miss(ractl->mapping, index - 1, max_pages); + rcu_read_unlock(); + contig_count = index - miss - 1; + /* + * Standalone, small random read. Read as is, and do not pollute the + * readahead state. + */ + if (contig_count <= req_count) { + do_page_cache_ra(ractl, req_count, 0); + return; + } + /* + * File cached from the beginning: + * it is a strong indication of long-run stream (or whole-file-read) + */ + if (miss == ULONG_MAX) + contig_count *= 2; + ra->start = index; + ra->size = min(contig_count + req_count, max_pages); + ra->async_size = 1; +readit: + ra->order = 0; + ractl->_index = ra->start; + page_cache_ra_order(ractl, ra); +} +EXPORT_SYMBOL_GPL(page_cache_sync_ra); + +void page_cache_async_ra(struct readahead_control *ractl, + struct folio *folio, unsigned long req_count) +{ + unsigned long max_pages; + struct file_ra_state *ra = ractl->ra; + pgoff_t index = readahead_index(ractl); + pgoff_t expected, start, end, aligned_end, align; + + /* no readahead */ + if (!ra->ra_pages) + return; + + /* + * Same bit is used for PG_readahead and PG_reclaim. + */ + if (folio_test_writeback(folio)) + return; + + trace_page_cache_async_ra(ractl->mapping->host, index, ra, req_count); + folio_clear_readahead(folio); + + if (blk_cgroup_congested()) + return; + + max_pages = ractl_max_pages(ractl, req_count); + /* + * It's the expected callback index, assume sequential access. + * Ramp up sizes, and push forward the readahead window. + */ + expected = round_down(ra->start + ra->size - ra->async_size, + folio_nr_pages(folio)); + if (index == expected) { + ra->start += ra->size; + /* + * In the case of MADV_HUGEPAGE, the actual size might exceed + * the readahead window. + */ + ra->size = max(ra->size, get_next_ra_size(ra, max_pages)); + 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. + */ + 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_count; + ra->size = get_next_ra_size(ra, max_pages); +readit: + ra->order += 2; + align = 1UL << min(ra->order, ffs(max_pages) - 1); + end = ra->start + ra->size; + aligned_end = round_down(end, align); + if (aligned_end > ra->start) + ra->size -= end - aligned_end; + ra->async_size = ra->size; + ractl->_index = ra->start; + page_cache_ra_order(ractl, ra); +} +EXPORT_SYMBOL_GPL(page_cache_async_ra); + +ssize_t ksys_readahead(int fd, loff_t offset, size_t count) +{ + struct file *file; + const struct inode *inode; + + CLASS(fd, f)(fd); + if (fd_empty(f)) + return -EBADF; + + file = fd_file(f); + if (!(file->f_mode & FMODE_READ)) + return -EBADF; + + /* + * 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. + */ + if (!file->f_mapping) + return -EINVAL; + if (!file->f_mapping->a_ops) + return -EINVAL; + + inode = file_inode(file); + if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode)) + return -EINVAL; + if (IS_ANON_FILE(inode)) + return -EINVAL; + + return vfs_fadvise(fd_file(f), offset, count, POSIX_FADV_WILLNEED); +} + +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); + unsigned long min_nrpages = mapping_min_folio_nrpages(mapping); + unsigned int min_order = mapping_min_folio_order(mapping); + + new_index = new_start / PAGE_SIZE; + /* + * Readahead code should have aligned the ractl->_index to + * min_nrpages before calling readahead aops. + */ + VM_BUG_ON(!IS_ALIGNED(ractl->_index, min_nrpages)); + + /* Expand the leading edge downwards */ + while (ractl->_index > new_index) { + unsigned long index = ractl->_index - 1; + struct folio *folio = xa_load(&mapping->i_pages, index); + + if (folio && !xa_is_value(folio)) + return; /* Folio apparently present */ + + folio = ractl_alloc_folio(ractl, gfp_mask, min_order); + if (!folio) + return; + + index = mapping_align_index(mapping, index); + if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) { + folio_put(folio); + return; + } + if (unlikely(folio_test_workingset(folio)) && + !ractl->_workingset) { + ractl->_workingset = true; + psi_memstall_enter(&ractl->_pflags); + } + ractl->_nr_pages += min_nrpages; + ractl->_index = folio->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 folio *folio = xa_load(&mapping->i_pages, index); + + if (folio && !xa_is_value(folio)) + return; /* Folio apparently present */ + + folio = ractl_alloc_folio(ractl, gfp_mask, min_order); + if (!folio) + return; + + index = mapping_align_index(mapping, index); + if (filemap_add_folio(mapping, folio, index, gfp_mask) < 0) { + folio_put(folio); + return; + } + if (unlikely(folio_test_workingset(folio)) && + !ractl->_workingset) { + ractl->_workingset = true; + psi_memstall_enter(&ractl->_pflags); + } + ractl->_nr_pages += min_nrpages; + if (ra) { + ra->size += min_nrpages; + ra->async_size += min_nrpages; + } + } +} +EXPORT_SYMBOL(readahead_expand); |