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=-2.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, URIBL_DBL_ABUSE_MALW,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 846F0C33CB3 for ; Wed, 29 Jan 2020 00:25:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5A97A22522 for ; Wed, 29 Jan 2020 00:25:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726427AbgA2AZB (ORCPT ); Tue, 28 Jan 2020 19:25:01 -0500 Received: from mail104.syd.optusnet.com.au ([211.29.132.246]:40046 "EHLO mail104.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726293AbgA2AZB (ORCPT ); Tue, 28 Jan 2020 19:25:01 -0500 Received: from dread.disaster.area (pa49-195-111-217.pa.nsw.optusnet.com.au [49.195.111.217]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 32C487E9A77; Wed, 29 Jan 2020 11:24:56 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1iwbA8-0005eI-Bd; Wed, 29 Jan 2020 11:24:56 +1100 Date: Wed, 29 Jan 2020 11:24:56 +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, linux-xfs@vger.kernel.org, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com Subject: Re: [PATCH 04/12] mm: Add readahead address space operation Message-ID: <20200129002456.GH18610@dread.disaster.area> References: <20200125013553.24899-1-willy@infradead.org> <20200125013553.24899-5-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200125013553.24899-5-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=LYdCFQXi c=1 sm=1 tr=0 a=0OveGI8p3fsTA6FL6ss4ZQ==:117 a=0OveGI8p3fsTA6FL6ss4ZQ==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=Jdjhy38mL1oA:10 a=JfrnYn6hAAAA:8 a=7-415B0cAAAA:8 a=bQT49A20HjYUhGx6rhoA:9 a=UEMyszIiLG9v0jT0:21 a=UWfWf6Z2s6wDmKyN:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri, Jan 24, 2020 at 05:35:45PM -0800, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > This replaces ->readpages with a saner interface: > - Return the number of pages not read 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. .... > diff --git a/mm/readahead.c b/mm/readahead.c > index 5a6676640f20..6d65dae6dad0 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -121,7 +121,18 @@ static void read_pages(struct address_space *mapping, struct file *filp, > > blk_start_plug(&plug); > > - if (mapping->a_ops->readpages) { > + if (mapping->a_ops->readahead) { > + unsigned left = mapping->a_ops->readahead(filp, mapping, > + start, nr_pages); > + > + while (left) { > + struct page *page = readahead_page(mapping, > + start + nr_pages - left - 1); Off by one? start = 2, nr_pages = 2, left = 1, this looks up the page at index 2, which is the one we issued IO on, not the one we "left behind" which is at index 3. Cheers, Dave. -- Dave Chinner david@fromorbit.com