From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 681D9C34047 for ; Tue, 18 Feb 2020 19:54:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 22C3F21D56 for ; Tue, 18 Feb 2020 19:54:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="O1En3UG2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726528AbgBRTyF (ORCPT ); Tue, 18 Feb 2020 14:54:05 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:60854 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726283AbgBRTyF (ORCPT ); Tue, 18 Feb 2020 14:54:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=0fbPHabH5rtRjpop0nvOgXSZPwl/5hzmmLwctoYuLtg=; b=O1En3UG2/SWLTrMtnpJrjjgjSj eDzVzRDQGtNtvubDjDkjRGIJMAo2/GoMR9u4cwrm8+0raSMb0Dy9hL/V3FpFf/NmyWWubRiI9r+hm MvOlhqGPP2nSWK8OHRdeyCeOjeD1HWTFC623D5HCt0pjipMPDmuypyH+NFt9zlecrKxRdrer+o3u3 pi3Enpw1YLfghmY62DGTbp2PLvGeLps7dpV1mZuLhZpmvdT2mfnn1muQ0TCMLV4/avuAAjtPVLxIY Zyl5nqtrsKk/bKNP/w3WTu5SkxFkRP5G2N41SHaU+CoUG3Z05IW3gfMCxRt4E82CyQ0E1TCT81pxh cxgZHRXg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j48wW-0003Wd-Ia; Tue, 18 Feb 2020 19:54:04 +0000 Date: Tue, 18 Feb 2020 11:54:04 -0800 From: Matthew Wilcox To: Dave Chinner Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org Subject: Re: [PATCH v6 09/19] mm: Add page_cache_readahead_limit Message-ID: <20200218195404.GD24185@bombadil.infradead.org> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-16-willy@infradead.org> <20200218063110.GO10776@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218063110.GO10776@dread.disaster.area> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Feb 18, 2020 at 05:31:10PM +1100, Dave Chinner wrote: > On Mon, Feb 17, 2020 at 10:45:56AM -0800, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" > > > > ext4 and f2fs have duplicated the guts of the readahead code so > > they can read past i_size. Instead, separate out the guts of the > > readahead code so they can call it directly. > > Gross and nasty (hosting non-stale data beyond EOF in the page > cache, that is). I thought you meant sneaking changes into the VFS (that were rejected) by copying VFS code and modifying it ... > > +/** > > + * page_cache_readahead_limit - Start readahead beyond a file's i_size. > > + * @mapping: File address space. > > + * @file: This instance of the open file; used for authentication. > > + * @offset: First page index to read. > > + * @end_index: The maximum page index to read. > > + * @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 potentially beyond a file's stated i_size. If you want > > + * to start readahead on a normal file, you probably want to call > > + * 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 __do_page_cache_readahead(struct address_space *mapping, > > - struct file *filp, pgoff_t offset, unsigned long nr_to_read, > > - unsigned long lookahead_size) > > +void page_cache_readahead_limit(struct address_space *mapping, > > ... I don't think the function name conveys it's purpose. It's > really a ranged readahead that ignores where i_size lies. i.e > > page_cache_readahead_range(mapping, start, end, nr_to_read) > > seems like a better API to me, and then you can drop the "start > readahead beyond i_size" comments and replace it with "Range is not > limited by the inode's i_size and hence can be used to read data > stored beyond EOF into the page cache." I'm concerned that calling it 'range' implies "I want to read between start and end" rather than "I want to read nr_to_read at start, oh but don't go past end". Maybe the right way to do this is have the three callers cap nr_to_read. Well, the one caller ... after all, f2fs and ext4 have no desire to cap the length. Then we can call it page_cache_readahead_exceed() or page_cache_readahead_dangerous() or something else like that to make it clear that you shouldn't be calling it. > Also: "This is almost certainly not the function you want to call. > Use page_cache_async_readahead or page_cache_sync_readahead() > instead." +1 to that ;-) Here's what I currently have: >From d202dda7a92566496fe9e233ee7855fb560324ce Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Mon, 10 Feb 2020 18:31:15 -0500 Subject: [PATCH] mm: Add page_cache_readahead_exceed ext4 and f2fs have duplicated the guts of the readahead code so they can read past i_size. Instead, separate out the guts of the readahead code so they can call it directly. Signed-off-by: Matthew Wilcox (Oracle) --- fs/ext4/verity.c | 35 ++-------------------- fs/f2fs/verity.c | 35 ++-------------------- include/linux/pagemap.h | 3 ++ mm/readahead.c | 66 ++++++++++++++++++++++++++++------------- 4 files changed, 52 insertions(+), 87 deletions(-) diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c index dc5ec724d889..172ebf860014 100644 --- a/fs/ext4/verity.c +++ b/fs/ext4/verity.c @@ -342,37 +342,6 @@ static int ext4_get_verity_descriptor(struct inode *inode, void *buf, return desc_size; } -/* - * Prefetch some pages from the file's Merkle tree. - * - * This is basically a stripped-down version of __do_page_cache_readahead() - * which works on pages past i_size. - */ -static void ext4_merkle_tree_readahead(struct address_space *mapping, - pgoff_t start_index, unsigned long count) -{ - LIST_HEAD(pages); - unsigned int nr_pages = 0; - struct page *page; - pgoff_t index; - struct blk_plug plug; - - for (index = start_index; index < start_index + count; index++) { - page = xa_load(&mapping->i_pages, index); - if (!page || xa_is_value(page)) { - page = __page_cache_alloc(readahead_gfp_mask(mapping)); - if (!page) - break; - page->index = index; - list_add(&page->lru, &pages); - nr_pages++; - } - } - blk_start_plug(&plug); - ext4_mpage_readpages(mapping, &pages, NULL, nr_pages, true); - blk_finish_plug(&plug); -} - static struct page *ext4_read_merkle_tree_page(struct inode *inode, pgoff_t index, unsigned long num_ra_pages) @@ -386,8 +355,8 @@ static struct page *ext4_read_merkle_tree_page(struct inode *inode, if (page) put_page(page); else if (num_ra_pages > 1) - ext4_merkle_tree_readahead(inode->i_mapping, index, - num_ra_pages); + page_cache_readahead_exceed(inode->i_mapping, NULL, + index, num_ra_pages, 0); page = read_mapping_page(inode->i_mapping, index, NULL); } return page; diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c index d7d430a6f130..f240ad087162 100644 --- a/fs/f2fs/verity.c +++ b/fs/f2fs/verity.c @@ -222,37 +222,6 @@ static int f2fs_get_verity_descriptor(struct inode *inode, void *buf, return size; } -/* - * Prefetch some pages from the file's Merkle tree. - * - * This is basically a stripped-down version of __do_page_cache_readahead() - * which works on pages past i_size. - */ -static void f2fs_merkle_tree_readahead(struct address_space *mapping, - pgoff_t start_index, unsigned long count) -{ - LIST_HEAD(pages); - unsigned int nr_pages = 0; - struct page *page; - pgoff_t index; - struct blk_plug plug; - - for (index = start_index; index < start_index + count; index++) { - page = xa_load(&mapping->i_pages, index); - if (!page || xa_is_value(page)) { - page = __page_cache_alloc(readahead_gfp_mask(mapping)); - if (!page) - break; - page->index = index; - list_add(&page->lru, &pages); - nr_pages++; - } - } - blk_start_plug(&plug); - f2fs_mpage_readpages(mapping, &pages, NULL, nr_pages, true); - blk_finish_plug(&plug); -} - static struct page *f2fs_read_merkle_tree_page(struct inode *inode, pgoff_t index, unsigned long num_ra_pages) @@ -266,8 +235,8 @@ static struct page *f2fs_read_merkle_tree_page(struct inode *inode, if (page) put_page(page); else if (num_ra_pages > 1) - f2fs_merkle_tree_readahead(inode->i_mapping, index, - num_ra_pages); + page_cache_readahead_exceed(inode->i_mapping, NULL, + index, num_ra_pages, 0); page = read_mapping_page(inode->i_mapping, index, NULL); } return page; diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 48c3bca57df6..1f7964d2b8ca 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -623,6 +623,9 @@ void page_cache_sync_readahead(struct address_space *, struct file_ra_state *, void page_cache_async_readahead(struct address_space *, struct file_ra_state *, struct file *, struct page *, pgoff_t index, unsigned long req_count); +void page_cache_readahead_exceed(struct address_space *, struct file *, + pgoff_t index, unsigned long nr_to_read, + unsigned long lookahead_count); /* * Like add_to_page_cache_locked, but used to add newly allocated pages: diff --git a/mm/readahead.c b/mm/readahead.c index 9dd431fa16c9..cad26287ad8b 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -142,45 +142,43 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages) blk_finish_plug(&plug); } -/* - * __do_page_cache_readahead() 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. +/** + * page_cache_readahead_exceed - Start unchecked readahead. + * @mapping: File address space. + * @file: This instance of the open file; used for authentication. + * @index: First page index to read. + * @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 __do_page_cache_readahead(struct address_space *mapping, - struct file *filp, pgoff_t index, unsigned long nr_to_read, +void page_cache_readahead_exceed(struct address_space *mapping, + struct file *file, pgoff_t index, unsigned long nr_to_read, unsigned long lookahead_size) { - struct inode *inode = mapping->host; - unsigned long end_index; /* The last page we want to read */ LIST_HEAD(page_pool); unsigned long i; - loff_t isize = i_size_read(inode); gfp_t gfp_mask = readahead_gfp_mask(mapping); bool use_list = mapping->a_ops->readpages; struct readahead_control rac = { .mapping = mapping, - .file = filp, + .file = file, ._start = index, ._nr_pages = 0, }; - if (isize == 0) - return; - - end_index = ((isize - 1) >> PAGE_SHIFT); - /* * Preallocate as many pages as we will need. */ for (i = 0; i < nr_to_read; i++) { - struct page *page; - - if (index > end_index) - break; + struct page *page = xa_load(&mapping->i_pages, index); - page = xa_load(&mapping->i_pages, index); if (page && !xa_is_value(page)) { /* * Page already present? Kick off the current batch @@ -225,6 +223,32 @@ void __do_page_cache_readahead(struct address_space *mapping, read_pages(&rac, &page_pool); BUG_ON(!list_empty(&page_pool)); } +EXPORT_SYMBOL_GPL(page_cache_readahead_exceed); + +/* + * __do_page_cache_readahead() 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_readahead(struct address_space *mapping, + struct file *file, pgoff_t index, unsigned long nr_to_read, + unsigned long lookahead_size) +{ + struct inode *inode = mapping->host; + loff_t isize = i_size_read(inode); + pgoff_t end_index; + + if (isize == 0) + return; + + end_index = (isize - 1) >> PAGE_SHIFT; + if (end_index < index + nr_to_read) + nr_to_read = end_index - index; + + page_cache_readahead_exceed(mapping, file, index, nr_to_read, + lookahead_size); +} /* * Chunk the readahead into 2 megabyte units, so that we don't pin too much -- 2.25.0