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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 EB2C6C34033 for ; Tue, 18 Feb 2020 06:31:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CE07B20836 for ; Tue, 18 Feb 2020 06:31:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726289AbgBRGbR (ORCPT ); Tue, 18 Feb 2020 01:31:17 -0500 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:53608 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726065AbgBRGbQ (ORCPT ); Tue, 18 Feb 2020 01:31:16 -0500 Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id 5BBFE3A2633; Tue, 18 Feb 2020 17:31:12 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j3wPX-0006P4-0T; Tue, 18 Feb 2020 17:31:11 +1100 Date: Tue, 18 Feb 2020 17:31:10 +1100 From: Dave Chinner To: Matthew Wilcox 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: <20200218063110.GO10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-16-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200217184613.19668-16-willy@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=zAxSp4fFY/GQY8/esVNjqw==:117 a=zAxSp4fFY/GQY8/esVNjqw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=l697ptgUJYAA:10 a=JfrnYn6hAAAA:8 a=7-415B0cAAAA:8 a=ven5Kus8yXOb1GZ9o24A:9 a=H2SKM-hdKVZ4IyYU:21 a=MGgw-NAvouSNSaNI:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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). Code is pretty simple, but... > } > > -/* > - * __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_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." Also: "This is almost certainly not the function you want to call. Use page_cache_async_readahead or page_cache_sync_readahead() instead." Cheers, Dave. -- Dave Chinner david@fromorbit.com