diff options
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 204 |
1 files changed, 55 insertions, 149 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index d3a47546d17d..8e3775829513 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -13,29 +13,29 @@ * * Readahead is used to read content into the page cache before it is * explicitly requested by the application. Readahead only ever - * attempts to read pages that are not yet in the page cache. If a - * page is present but not up-to-date, readahead will not try to read + * 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 ->readpage() will be requested. * * Readahead is triggered when an application read request (whether a - * systemcall or a page fault) finds that the requested page is not in + * 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 - * %PG_readahead flag set. This flag indicates that the page was loaded - * as part of a previous read-ahead request and now that it has been - * accessed, it is time for the next read-ahead. + * 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 - * read-ahead. This is reflected in the struct file_ra_state which - * contains ->size being to total number of pages, and ->async_size - * which is the number of pages in the async section. The first page in - * this async section will have %PG_readahead set as a trigger for a - * subsequent read ahead. Once a series of sequential reads has been + * 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 read ahead request will be fully asynchronous. + * 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, the size of the region, and - * the size of the async tail. + * 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 @@ -45,14 +45,14 @@ * 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. + * 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 %PG_readahead flag, the size of the previous + * 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 @@ -65,52 +65,52 @@ * larger than the current request, and it is not scaled up, unless it * is at the start of file. * - * In general read ahead is accelerated at the start of the file, as + * 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 read ahead size in various special cases and these + * adjustments to the readahead size in various special cases and these * are best discovered by reading the code. * - * The above calculation determines the readahead, to which any requested - * read size may be added. + * 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 - * pages, but may fail to read any or all pages without causing an IO + * folios, but may fail to read any or all folios without causing an I/O * error. The page cache reading code will issue a ->readpage() request - * for any page which ->readahead() does not provided, and only an error + * for any folio which ->readahead() did not read, and only an error * from this will be final. * - * ->readahead() will generally call readahead_page() repeatedly to get - * each page from those prepared for read ahead. It may fail to read a - * page by: + * ->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_page() sufficiently many times, effectively - * ignoring some pages, as might be appropriate if the path to + * * 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 page, + * * 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 page should be unlocked to indicate that - * the read attempt has failed. In the first case the page will be - * unlocked by the caller. + * 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 pages not in the final ``async_size`` of the request should be + * 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. Pages in the final ``async_size`` may be + * 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 delete_from_page_cache() to remove the - * pages from the page cache as is automatically done for pages that - * were not fetched with readahead_page(). This will allow a - * subsequent synchronous read ahead request to try them again. If they + * 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 - * ->readpage(). - * + * ->readpage() which may be less efficient. */ #include <linux/kernel.h> @@ -142,91 +142,14 @@ file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping) } 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; - folio_invalidate(page_folio(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) +static void read_pages(struct readahead_control *rac) { const struct address_space_operations *aops = rac->mapping->a_ops; struct page *page; struct blk_plug plug; if (!readahead_count(rac)) - goto out; + return; blk_start_plug(&plug); @@ -234,7 +157,7 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, aops->readahead(rac); /* * Clean up the remaining pages. The sizes in ->ra - * maybe be used to size next read-ahead, so make sure + * may be used to size the next readahead, so make sure * they accurately reflect what happened. */ while ((page = readahead_page(rac))) { @@ -246,13 +169,6 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, 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); @@ -262,12 +178,7 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, blk_finish_plug(&plug); - BUG_ON(pages && !list_empty(pages)); BUG_ON(readahead_count(rac)); - -out: - if (skip_page) - rac->_index++; } /** @@ -289,7 +200,6 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, { 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; @@ -321,7 +231,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, * have a stable reference to this page, and it's * not worth getting one just for that. */ - read_pages(ractl, &page_pool, true); + read_pages(ractl); + ractl->_index++; i = ractl->_index + ractl->_nr_pages - index - 1; continue; } @@ -329,13 +240,11 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, folio = filemap_alloc_folio(gfp_mask, 0); if (!folio) break; - if (mapping->a_ops->readpages) { - folio->index = index + i; - list_add(&folio->lru, &page_pool); - } else if (filemap_add_folio(mapping, folio, index + i, + if (filemap_add_folio(mapping, folio, index + i, gfp_mask) < 0) { folio_put(folio); - read_pages(ractl, &page_pool, true); + read_pages(ractl); + ractl->_index++; i = ractl->_index + ractl->_nr_pages - index - 1; continue; } @@ -349,7 +258,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, * uptodate then the caller will launch readpage again, and * will then handle the error. */ - read_pages(ractl, &page_pool, false); + read_pages(ractl); filemap_invalidate_unlock_shared(mapping); memalloc_nofs_restore(nofs); } @@ -394,8 +303,7 @@ void force_page_cache_ra(struct readahead_control *ractl, 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)) + if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readahead)) return; /* @@ -512,7 +420,7 @@ static pgoff_t count_history_pages(struct address_space *mapping, } /* - * page cache context based read-ahead + * page cache context based readahead */ static int try_context_readahead(struct address_space *mapping, struct file_ra_state *ra, @@ -624,7 +532,7 @@ void page_cache_ra_order(struct readahead_control *ractl, ra->async_size += index - limit - 1; } - read_pages(ractl, NULL, false); + read_pages(ractl); /* * If there were already pages in the page cache, then we may have @@ -763,9 +671,9 @@ void page_cache_sync_ra(struct readahead_control *ractl, bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM); /* - * Even if read-ahead is disabled, issue this request as read-ahead + * Even if readahead is disabled, issue this request as readahead * 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 + * 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()) { @@ -781,7 +689,6 @@ void page_cache_sync_ra(struct readahead_control *ractl, return; } - /* do read-ahead */ ondemand_readahead(ractl, NULL, req_count); } EXPORT_SYMBOL_GPL(page_cache_sync_ra); @@ -789,7 +696,7 @@ EXPORT_SYMBOL_GPL(page_cache_sync_ra); void page_cache_async_ra(struct readahead_control *ractl, struct folio *folio, unsigned long req_count) { - /* no read-ahead */ + /* no readahead */ if (!ractl->ra->ra_pages) return; @@ -804,7 +711,6 @@ void page_cache_async_ra(struct readahead_control *ractl, if (blk_cgroup_congested()) return; - /* do read-ahead */ ondemand_readahead(ractl, folio, req_count); } EXPORT_SYMBOL_GPL(page_cache_async_ra); |