diff options
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 641 |
1 files changed, 641 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c new file mode 100644 index 000000000..d30bcf4bc --- /dev/null +++ b/mm/readahead.c @@ -0,0 +1,641 @@ +// 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. + */ + +#include <linux/kernel.h> +#include <linux/dax.h> +#include <linux/gfp.h> +#include <linux/export.h> +#include <linux/blkdev.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); + +/* + * see if a page needs releasing upon read_cache_pages() failure + * - the caller of read_cache_pages() may have set PG_private or PG_fscache + * before calling, such as the NFS fs marking pages that are cached locally + * on disk, thus we need to give the fs a chance to clean up in the event of + * an error + */ +static void read_cache_pages_invalidate_page(struct address_space *mapping, + struct page *page) +{ + if (page_has_private(page)) { + if (!trylock_page(page)) + BUG(); + page->mapping = mapping; + do_invalidatepage(page, 0, PAGE_SIZE); + page->mapping = NULL; + unlock_page(page); + } + put_page(page); +} + +/* + * release a list of pages, invalidating them first if need be + */ +static void read_cache_pages_invalidate_pages(struct address_space *mapping, + struct list_head *pages) +{ + struct page *victim; + + while (!list_empty(pages)) { + victim = lru_to_page(pages); + list_del(&victim->lru); + read_cache_pages_invalidate_page(mapping, victim); + } +} + +/** + * read_cache_pages - populate an address space with some pages & start reads against them + * @mapping: the address_space + * @pages: The address of a list_head which contains the target pages. These + * pages have their ->index populated and are otherwise uninitialised. + * @filler: callback routine for filling a single page. + * @data: private data for the callback routine. + * + * Hides the details of the LRU cache etc from the filesystems. + * + * Returns: %0 on success, error return by @filler otherwise + */ +int read_cache_pages(struct address_space *mapping, struct list_head *pages, + int (*filler)(void *, struct page *), void *data) +{ + struct page *page; + int ret = 0; + + while (!list_empty(pages)) { + page = lru_to_page(pages); + list_del(&page->lru); + if (add_to_page_cache_lru(page, mapping, page->index, + readahead_gfp_mask(mapping))) { + read_cache_pages_invalidate_page(mapping, page); + continue; + } + put_page(page); + + ret = filler(data, page); + if (unlikely(ret)) { + read_cache_pages_invalidate_pages(mapping, pages); + break; + } + task_io_account_read(PAGE_SIZE); + } + return ret; +} + +EXPORT_SYMBOL(read_cache_pages); + +static void read_pages(struct readahead_control *rac, struct list_head *pages, + bool skip_page) +{ + const struct address_space_operations *aops = rac->mapping->a_ops; + struct page *page; + struct blk_plug plug; + + if (!readahead_count(rac)) + goto out; + + blk_start_plug(&plug); + + if (aops->readahead) { + aops->readahead(rac); + /* Clean up the remaining pages */ + while ((page = readahead_page(rac))) { + unlock_page(page); + put_page(page); + } + } else if (aops->readpages) { + aops->readpages(rac->file, rac->mapping, pages, + readahead_count(rac)); + /* Clean up the remaining pages */ + put_pages_list(pages); + rac->_index += rac->_nr_pages; + rac->_nr_pages = 0; + } else { + while ((page = readahead_page(rac))) { + aops->readpage(rac->file, page); + put_page(page); + } + } + + blk_finish_plug(&plug); + + BUG_ON(!list_empty(pages)); + BUG_ON(readahead_count(rac)); + +out: + if (skip_page) + rac->_index++; +} + +/** + * 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); + LIST_HEAD(page_pool); + 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(); + + /* + * Preallocate as many pages as we will need. + */ + for (i = 0; i < nr_to_read; i++) { + struct page *page = xa_load(&mapping->i_pages, index + i); + + BUG_ON(index + i != ractl->_index + ractl->_nr_pages); + + if (page && !xa_is_value(page)) { + /* + * 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, &page_pool, true); + continue; + } + + page = __page_cache_alloc(gfp_mask); + if (!page) + break; + if (mapping->a_ops->readpages) { + page->index = index + i; + list_add(&page->lru, &page_pool); + } else if (add_to_page_cache_lru(page, mapping, index + i, + gfp_mask) < 0) { + put_page(page); + read_pages(ractl, &page_pool, true); + continue; + } + if (i == nr_to_read - lookahead_size) + SetPageReadahead(page); + 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, &page_pool, false); + 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. + */ +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, + struct file_ra_state *ra, unsigned long nr_to_read) +{ + struct address_space *mapping = ractl->mapping; + struct backing_dev_info *bdi = inode_to_bdi(mapping->host); + unsigned long max_pages, index; + + if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages && + !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 + * 1-8 page = 32k initial, > 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 read-ahead + */ +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; +} + +/* + * A minimal readahead algorithm for trivial sequential/random reads. + */ +static void ondemand_readahead(struct readahead_control *ractl, + struct file_ra_state *ra, bool hit_readahead_marker, + unsigned long req_size) +{ + struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host); + unsigned long max_pages = ra->ra_pages; + unsigned long add_pages; + unsigned long index = readahead_index(ractl); + pgoff_t prev_index; + + /* + * 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. + */ + if ((index == (ra->start + ra->size - ra->async_size) || + 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 page 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 (hit_readahead_marker) { + 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; + do_page_cache_ra(ractl, ra->size, ra->async_size); +} + +void page_cache_sync_ra(struct readahead_control *ractl, + struct file_ra_state *ra, unsigned long req_count) +{ + bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM); + + /* + * Even if read-ahead is disabled, issue this request as read-ahead + * as we'll need it to satisfy the requested range. The forced + * read-ahead 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, ra, req_count); + return; + } + + /* do read-ahead */ + ondemand_readahead(ractl, ra, false, req_count); +} +EXPORT_SYMBOL_GPL(page_cache_sync_ra); + +void page_cache_async_ra(struct readahead_control *ractl, + struct file_ra_state *ra, struct page *page, + unsigned long req_count) +{ + /* no read-ahead */ + if (!ra->ra_pages) + return; + + /* + * Same bit is used for PG_readahead and PG_reclaim. + */ + if (PageWriteback(page)) + return; + + ClearPageReadahead(page); + + /* + * Defer asynchronous read-ahead on IO congestion. + */ + if (inode_read_congested(ractl->mapping->host)) + return; + + if (blk_cgroup_congested()) + return; + + /* do read-ahead */ + ondemand_readahead(ractl, ra, true, 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); +} |