From patchwork Tue Feb 11 01:03:39 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Wilcox X-Patchwork-Id: 11374547 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EAE4613A4 for ; Tue, 11 Feb 2020 01:04:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C3FDC20661 for ; Tue, 11 Feb 2020 01:04:30 +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="cXPJFAtg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728066AbgBKBE1 (ORCPT ); Mon, 10 Feb 2020 20:04:27 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:54840 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727979AbgBKBEA (ORCPT ); Mon, 10 Feb 2020 20:04:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description; bh=baDUjVOyCTvDFXzkplCy8sworsJFd3RpUmIL1eLvSj4=; b=cXPJFAtgE5FhnsznCCJJUIeDAg ZnsEKj4WdqobU/sj/rCuxdelkyRIA35K/LvbrL13wwidiAqEUJxEXDmOnZD7XgHEhYkg/iYkPua8F jRKYoZqKmrMpyqmw4GX+ZoQUmkqktL0X+I0DgxtaUeiW2+Y0DPz/cLuSWNHpKfMS4MyY3gKmKMMuQ DBW4YNe35scV1tcNUjCoruGM6iXzhXlpd+N8YViwdMEIuHtPzxgRi7yBeGedYII9n5/ZiFAjUux3Q iNoYMJBV1IfF2WwwMNkg24E5GhRgxlZNvngpcOxy/LT+Hu1Be2Nf4edHVys62te7QkY5vmVctYBpr 6/3pAC9Q==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j1Jxu-0001nt-Da; Tue, 11 Feb 2020 01:03:50 +0000 From: Matthew Wilcox To: linux-fsdevel@vger.kernel.org Cc: "Matthew Wilcox (Oracle)" , 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: [PATCH v5 04/13] mm: Add readahead address space operation Date: Mon, 10 Feb 2020 17:03:39 -0800 Message-Id: <20200211010348.6872-5-willy@infradead.org> X-Mailer: git-send-email 2.21.1 In-Reply-To: <20200211010348.6872-1-willy@infradead.org> References: <20200211010348.6872-1-willy@infradead.org> MIME-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: "Matthew Wilcox (Oracle)" This replaces ->readpages with a saner interface: - Return void instead of an ignored error code. - Pages are already in the page cache when ->readahead is called. - Implementation looks up the pages in the page cache instead of having them passed in a linked list. Signed-off-by: Matthew Wilcox (Oracle) --- Documentation/filesystems/locking.rst | 6 ++- Documentation/filesystems/vfs.rst | 13 +++++++ include/linux/fs.h | 2 + include/linux/pagemap.h | 54 +++++++++++++++++++++++++++ mm/readahead.c | 48 ++++++++++++++---------- 5 files changed, 102 insertions(+), 21 deletions(-) diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 5057e4d9dcd1..0ebc4491025a 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -239,6 +239,7 @@ prototypes:: int (*readpage)(struct file *, struct page *); int (*writepages)(struct address_space *, struct writeback_control *); int (*set_page_dirty)(struct page *page); + void (*readahead)(struct readahead_control *); int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, @@ -271,7 +272,8 @@ writepage: yes, unlocks (see below) readpage: yes, unlocks writepages: set_page_dirty no -readpages: +readahead: yes, unlocks +readpages: no write_begin: locks the page exclusive write_end: yes, unlocks exclusive bmap: @@ -295,6 +297,8 @@ the request handler (/dev/loop). ->readpage() unlocks the page, either synchronously or via I/O completion. +->readahead() unlocks the pages like ->readpage(). + ->readpages() populates the pagecache with the passed pages and starts I/O against them. They come unlocked upon I/O completion. diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index 7d4d09dd5e6d..cabee16b7406 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined: int (*readpage)(struct file *, struct page *); int (*writepages)(struct address_space *, struct writeback_control *); int (*set_page_dirty)(struct page *page); + void (*readahead)(struct readahead_control *); int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, @@ -781,12 +782,24 @@ cache in your filesystem. The following members are defined: If defined, it should set the PageDirty flag, and the PAGECACHE_TAG_DIRTY tag in the radix tree. +``readahead`` + Called by the VM to read pages associated with the address_space + object. The pages are consecutive in the page cache and are + locked. The implementation should decrement the page refcount + after starting I/O on each page. Usually the page will be + unlocked by the I/O completion handler. If the function does + not attempt I/O on some pages, the caller will decrement the page + refcount and unlock the pages for you. Set PageUptodate if the + I/O completes successfully. Setting PageError on any page will + be ignored; simply unlock the page if an I/O error occurs. + ``readpages`` called by the VM to read pages associated with the address_space object. This is essentially just a vector version of readpage. Instead of just one page, several pages are requested. readpages is only used for read-ahead, so read errors are ignored. If anything goes wrong, feel free to give up. + This interface is deprecated; implement readahead instead. ``write_begin`` Called by the generic buffered write code to ask the filesystem diff --git a/include/linux/fs.h b/include/linux/fs.h index 3cd4fe6b845e..d4e2d2964346 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -292,6 +292,7 @@ enum positive_aop_returns { struct page; struct address_space; struct writeback_control; +struct readahead_control; /* * Write life time hint values. @@ -375,6 +376,7 @@ struct address_space_operations { */ int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); + void (*readahead)(struct readahead_control *); int (*write_begin)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, unsigned flags, diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index ccb14b6a16b5..13efafaf7e1f 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -630,6 +630,60 @@ static inline int add_to_page_cache(struct page *page, return error; } +/* + * Readahead is of a block of consecutive pages. + */ +struct readahead_control { + struct file *file; + struct address_space *mapping; +/* private: use the readahead_* accessors instead */ + pgoff_t start; + unsigned int nr_pages; + unsigned int batch_count; +}; + +static inline struct page *readahead_page(struct readahead_control *rac) +{ + struct page *page; + + if (!rac->nr_pages) + return NULL; + + page = xa_load(&rac->mapping->i_pages, rac->start); + VM_BUG_ON_PAGE(!PageLocked(page), page); + rac->batch_count = hpage_nr_pages(page); + rac->start += rac->batch_count; + + return page; +} + +#define readahead_for_each(rac, page) \ + for (; (page = readahead_page(rac)); rac->nr_pages -= rac->batch_count) + +/* The byte offset into the file of this readahead block */ +static inline loff_t readahead_offset(struct readahead_control *rac) +{ + return (loff_t)rac->start * PAGE_SIZE; +} + +/* The number of bytes in this readahead block */ +static inline loff_t readahead_length(struct readahead_control *rac) +{ + return (loff_t)rac->nr_pages * PAGE_SIZE; +} + +/* The index of the first page in this readahead block */ +static inline unsigned int readahead_index(struct readahead_control *rac) +{ + return rac->start; +} + +/* The number of pages in this readahead block */ +static inline unsigned int readahead_count(struct readahead_control *rac) +{ + return rac->nr_pages; +} + static inline unsigned long dir_pages(struct inode *inode) { return (unsigned long)(inode->i_size + PAGE_SIZE - 1) >> diff --git a/mm/readahead.c b/mm/readahead.c index 96c6ca68a174..933b32e0c90a 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -113,25 +113,30 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, EXPORT_SYMBOL(read_cache_pages); -static void read_pages(struct address_space *mapping, struct file *filp, - struct list_head *pages, pgoff_t start, - unsigned int nr_pages) +static void read_pages(struct readahead_control *rac, struct list_head *pages) { + struct page *page; struct blk_plug plug; + const struct address_space_operations *aops = rac->mapping->a_ops; + + if (rac->nr_pages == 0) + return; blk_start_plug(&plug); - if (mapping->a_ops->readpages) { - mapping->a_ops->readpages(filp, mapping, pages, nr_pages); + if (aops->readahead) { + aops->readahead(rac); + readahead_for_each(rac, page) { + unlock_page(page); + put_page(page); + } + } else if (aops->readpages) { + aops->readpages(rac->file, rac->mapping, pages, rac->nr_pages); /* Clean up the remaining pages */ put_pages_list(pages); } else { - struct page *page; - unsigned long index; - - xa_for_each_range(&mapping->i_pages, index, page, start, - start + nr_pages - 1) { - mapping->a_ops->readpage(filp, page); + readahead_for_each(rac, page) { + aops->readpage(rac->file, page); put_page(page); } } @@ -156,10 +161,15 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping, LIST_HEAD(page_pool); int page_idx; pgoff_t page_offset = start; - unsigned long nr_pages = 0; 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, + .start = start, + .nr_pages = 0, + }; if (isize == 0) goto out; @@ -206,15 +216,14 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping, if (page_idx == nr_to_read - lookahead_size) SetPageReadahead(page); - nr_pages++; + rac.nr_pages++; page_offset++; continue; skip: - if (nr_pages) - read_pages(mapping, filp, &page_pool, start, nr_pages); - nr_pages = 0; + read_pages(&rac, &page_pool); + rac.nr_pages = 0; page_offset++; - start = page_offset; + rac.start = page_offset; } /* @@ -222,11 +231,10 @@ unsigned long __do_page_cache_readahead(struct address_space *mapping, * uptodate then the caller will launch readpage again, and * will then handle the error. */ - if (nr_pages) - read_pages(mapping, filp, &page_pool, start, nr_pages); + read_pages(&rac, &page_pool); BUG_ON(!list_empty(&page_pool)); out: - return nr_pages; + return rac.nr_pages; } /*