| /* |
| * mm/readahead.c - address_space-level file readahead. |
| * |
| * Copyright (C) 2002, Linus Torvalds |
| * |
| * 09Apr2002 Andrew Morton |
| * Initial version. |
| */ |
| |
| #include <linux/kernel.h> |
| #include <linux/fs.h> |
| #include <linux/gfp.h> |
| #include <linux/mm.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> |
| |
| /* |
| * 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 = mapping->backing_dev_info->ra_pages; |
| ra->prev_pos = -1; |
| } |
| EXPORT_SYMBOL_GPL(file_ra_state_init); |
| |
| #define list_to_page(head) (list_entry((head)->prev, struct page, lru)) |
| |
| /* |
| * 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->mapping = NULL; |
| unlock_page(page); |
| } |
| page_cache_release(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 = list_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. |
| */ |
| 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 = list_to_page(pages); |
| list_del(&page->lru); |
| if (add_to_page_cache_lru(page, mapping, |
| page->index, GFP_KERNEL)) { |
| read_cache_pages_invalidate_page(mapping, page); |
| continue; |
| } |
| page_cache_release(page); |
| |
| ret = filler(data, page); |
| if (unlikely(ret)) { |
| read_cache_pages_invalidate_pages(mapping, pages); |
| break; |
| } |
| task_io_account_read(PAGE_CACHE_SIZE); |
| } |
| return ret; |
| } |
| |
| EXPORT_SYMBOL(read_cache_pages); |
| |
| static int read_pages(struct address_space *mapping, struct file *filp, |
| struct list_head *pages, unsigned nr_pages) |
| { |
| struct blk_plug plug; |
| unsigned page_idx; |
| int ret; |
| |
| blk_start_plug(&plug); |
| |
| if (mapping->a_ops->readpages) { |
| ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages); |
| /* Clean up the remaining pages */ |
| put_pages_list(pages); |
| goto out; |
| } |
| |
| for (page_idx = 0; page_idx < nr_pages; page_idx++) { |
| struct page *page = list_to_page(pages); |
| list_del(&page->lru); |
| if (!add_to_page_cache_lru(page, mapping, |
| page->index, GFP_KERNEL)) { |
| mapping->a_ops->readpage(filp, page); |
| } |
| page_cache_release(page); |
| } |
| ret = 0; |
| |
| out: |
| blk_finish_plug(&plug); |
| |
| return ret; |
| } |
| |
| /* |
| * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all |
| * the pages first, then submits them all 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. |
| * |
| * Returns the number of pages requested, or the maximum amount of I/O allowed. |
| */ |
| static int |
| __do_page_cache_readahead(struct address_space *mapping, struct file *filp, |
| pgoff_t offset, unsigned long nr_to_read, |
| unsigned long lookahead_size) |
| { |
| struct inode *inode = mapping->host; |
| struct page *page; |
| unsigned long end_index; /* The last page we want to read */ |
| LIST_HEAD(page_pool); |
| int page_idx; |
| int ret = 0; |
| loff_t isize = i_size_read(inode); |
| |
| if (isize == 0) |
| goto out; |
| |
| end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); |
| |
| /* |
| * Preallocate as many pages as we will need. |
| */ |
| for (page_idx = 0; page_idx < nr_to_read; page_idx++) { |
| pgoff_t page_offset = offset + page_idx; |
| |
| if (page_offset > end_index) |
| break; |
| |
| rcu_read_lock(); |
| page = radix_tree_lookup(&mapping->page_tree, page_offset); |
| rcu_read_unlock(); |
| if (page) |
| continue; |
| |
| page = page_cache_alloc_readahead(mapping); |
| if (!page) |
| break; |
| page->index = page_offset; |
| list_add(&page->lru, &page_pool); |
| if (page_idx == nr_to_read - lookahead_size) |
| SetPageReadahead(page); |
| ret++; |
| } |
| |
| /* |
| * 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. |
| */ |
| if (ret) |
| read_pages(mapping, filp, &page_pool, ret); |
| BUG_ON(!list_empty(&page_pool)); |
| out: |
| return ret; |
| } |
| |
| /* |
| * Chunk the readahead into 2 megabyte units, so that we don't pin too much |
| * memory at once. |
| */ |
| int force_page_cache_readahead(struct address_space *mapping, struct file *filp, |
| pgoff_t offset, unsigned long nr_to_read) |
| { |
| int ret = 0; |
| |
| if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) |
| return -EINVAL; |
| |
| nr_to_read = max_sane_readahead(nr_to_read); |
| while (nr_to_read) { |
| int err; |
| |
| unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE; |
| |
| if (this_chunk > nr_to_read) |
| this_chunk = nr_to_read; |
| err = __do_page_cache_readahead(mapping, filp, |
| offset, this_chunk, 0); |
| if (err < 0) { |
| ret = err; |
| break; |
| } |
| ret += err; |
| offset += this_chunk; |
| nr_to_read -= this_chunk; |
| } |
| return ret; |
| } |
| |
| /* |
| * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a |
| * sensible upper limit. |
| */ |
| unsigned long max_sane_readahead(unsigned long nr) |
| { |
| return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE) |
| + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2); |
| } |
| |
| /* |
| * Submit IO for the read-ahead request in file_ra_state. |
| */ |
| unsigned long ra_submit(struct file_ra_state *ra, |
| struct address_space *mapping, struct file *filp) |
| { |
| int actual; |
| |
| actual = __do_page_cache_readahead(mapping, filp, |
| ra->start, ra->size, ra->async_size); |
| |
| return actual; |
| } |
| |
| /* |
| * Set the initial window size, round to next power of 2 and square |
| * Small size is not dependant on max value - only a one-page read is regarded |
| * as small. |
| * 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 <= 1) |
| 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; |
| unsigned long newsize; |
| |
| if (cur < max / 16) |
| newsize = 4 * cur; |
| else |
| newsize = 2 * cur; |
| |
| return min(newsize, 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 @offset-1 to @offset-@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, |
| struct file_ra_state *ra, |
| pgoff_t offset, unsigned long max) |
| { |
| pgoff_t head; |
| |
| rcu_read_lock(); |
| head = radix_tree_prev_hole(&mapping->page_tree, offset - 1, max); |
| rcu_read_unlock(); |
| |
| return offset - 1 - head; |
| } |
| |
| /* |
| * page cache context based read-ahead |
| */ |
| static int try_context_readahead(struct address_space *mapping, |
| struct file_ra_state *ra, |
| pgoff_t offset, |
| unsigned long req_size, |
| unsigned long max) |
| { |
| pgoff_t size; |
| |
| size = count_history_pages(mapping, ra, offset, max); |
| |
| /* |
| * no history pages: |
| * it could be a random read |
| */ |
| if (!size) |
| return 0; |
| |
| /* |
| * starts from beginning of file: |
| * it is a strong indication of long-run stream (or whole-file-read) |
| */ |
| if (size >= offset) |
| size *= 2; |
| |
| ra->start = offset; |
| ra->size = get_init_ra_size(size + req_size, max); |
| ra->async_size = ra->size; |
| |
| return 1; |
| } |
| |
| /* |
| * A minimal readahead algorithm for trivial sequential/random reads. |
| */ |
| static unsigned long |
| ondemand_readahead(struct address_space *mapping, |
| struct file_ra_state *ra, struct file *filp, |
| bool hit_readahead_marker, pgoff_t offset, |
| unsigned long req_size) |
| { |
| unsigned long max = max_sane_readahead(ra->ra_pages); |
| |
| /* |
| * start of file |
| */ |
| if (!offset) |
| goto initial_readahead; |
| |
| /* |
| * It's the expected callback offset, assume sequential access. |
| * Ramp up sizes, and push forward the readahead window. |
| */ |
| if ((offset == (ra->start + ra->size - ra->async_size) || |
| offset == (ra->start + ra->size))) { |
| ra->start += ra->size; |
| ra->size = get_next_ra_size(ra, max); |
| 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 = radix_tree_next_hole(&mapping->page_tree, offset+1,max); |
| rcu_read_unlock(); |
| |
| if (!start || start - offset > max) |
| return 0; |
| |
| ra->start = start; |
| ra->size = start - offset; /* old async_size */ |
| ra->size += req_size; |
| ra->size = get_next_ra_size(ra, max); |
| ra->async_size = ra->size; |
| goto readit; |
| } |
| |
| /* |
| * oversize read |
| */ |
| if (req_size > max) |
| goto initial_readahead; |
| |
| /* |
| * sequential cache miss |
| */ |
| if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 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(mapping, ra, offset, req_size, max)) |
| goto readit; |
| |
| /* |
| * standalone, small random read |
| * Read as is, and do not pollute the readahead state. |
| */ |
| return __do_page_cache_readahead(mapping, filp, offset, req_size, 0); |
| |
| initial_readahead: |
| ra->start = offset; |
| ra->size = get_init_ra_size(req_size, max); |
| 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. |
| */ |
| if (offset == ra->start && ra->size == ra->async_size) { |
| ra->async_size = get_next_ra_size(ra, max); |
| ra->size += ra->async_size; |
| } |
| |
| return ra_submit(ra, mapping, filp); |
| } |
| |
| /** |
| * page_cache_sync_readahead - generic file readahead |
| * @mapping: address_space which holds the pagecache and I/O vectors |
| * @ra: file_ra_state which holds the readahead state |
| * @filp: passed on to ->readpage() and ->readpages() |
| * @offset: start offset into @mapping, in pagecache page-sized units |
| * @req_size: hint: total size of the read which the caller is performing in |
| * pagecache pages |
| * |
| * page_cache_sync_readahead() should be called when a cache miss happened: |
| * it will submit the read. The readahead logic may decide to piggyback more |
| * pages onto the read request if access patterns suggest it will improve |
| * performance. |
| */ |
| void page_cache_sync_readahead(struct address_space *mapping, |
| struct file_ra_state *ra, struct file *filp, |
| pgoff_t offset, unsigned long req_size) |
| { |
| /* no read-ahead */ |
| if (!ra->ra_pages) |
| return; |
| |
| /* be dumb */ |
| if (filp && (filp->f_mode & FMODE_RANDOM)) { |
| force_page_cache_readahead(mapping, filp, offset, req_size); |
| return; |
| } |
| |
| /* do read-ahead */ |
| ondemand_readahead(mapping, ra, filp, false, offset, req_size); |
| } |
| EXPORT_SYMBOL_GPL(page_cache_sync_readahead); |
| |
| /** |
| * page_cache_async_readahead - file readahead for marked pages |
| * @mapping: address_space which holds the pagecache and I/O vectors |
| * @ra: file_ra_state which holds the readahead state |
| * @filp: passed on to ->readpage() and ->readpages() |
| * @page: the page at @offset which has the PG_readahead flag set |
| * @offset: start offset into @mapping, in pagecache page-sized units |
| * @req_size: hint: total size of the read which the caller is performing in |
| * pagecache pages |
| * |
| * page_cache_async_readahead() should be called when a page is used which |
| * has the PG_readahead flag; this is a marker to suggest that the application |
| * has used up enough of the readahead window that we should start pulling in |
| * more pages. |
| */ |
| void |
| page_cache_async_readahead(struct address_space *mapping, |
| struct file_ra_state *ra, struct file *filp, |
| struct page *page, pgoff_t offset, |
| unsigned long req_size) |
| { |
| /* 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 (bdi_read_congested(mapping->backing_dev_info)) |
| return; |
| |
| /* do read-ahead */ |
| ondemand_readahead(mapping, ra, filp, true, offset, req_size); |
| } |
| EXPORT_SYMBOL_GPL(page_cache_async_readahead); |