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 98AF9C3404C for ; Tue, 18 Feb 2020 22:48:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7A5E322B48 for ; Tue, 18 Feb 2020 22:48:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726851AbgBRWsd (ORCPT ); Tue, 18 Feb 2020 17:48:33 -0500 Received: from mail104.syd.optusnet.com.au ([211.29.132.246]:57094 "EHLO mail104.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726556AbgBRWsc (ORCPT ); Tue, 18 Feb 2020 17:48:32 -0500 Received: from dread.disaster.area (pa49-179-138-28.pa.nsw.optusnet.com.au [49.179.138.28]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id D144F7E9387; Wed, 19 Feb 2020 09:48:29 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j4BfJ-0003lA-7e; Wed, 19 Feb 2020 09:48:29 +1100 Date: Wed, 19 Feb 2020 09:48:29 +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 04/19] mm: Rearrange readahead loop Message-ID: <20200218224829.GU10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-5-willy@infradead.org> <20200218050824.GJ10776@dread.disaster.area> <20200218135736.GP7778@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218135736.GP7778@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=X6os11be 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=alOI8opFAFPe2SRtgw8A:9 a=xQkswpi2j_EUEYvS:21 a=GSRXKHwoUNCfdhKr: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 Tue, Feb 18, 2020 at 05:57:36AM -0800, Matthew Wilcox wrote: > On Tue, Feb 18, 2020 at 04:08:24PM +1100, Dave Chinner wrote: > > On Mon, Feb 17, 2020 at 10:45:45AM -0800, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" > > > > > > Move the declaration of 'page' to inside the loop and move the 'kick > > > off a fresh batch' code to the end of the function for easier use in > > > subsequent patches. > > > > Stale? the "kick off" code is moved to the tail of the loop, not the > > end of the function. > > Braino; I meant to write end of the loop. > > > > @@ -183,14 +183,14 @@ void __do_page_cache_readahead(struct address_space *mapping, > > > page = xa_load(&mapping->i_pages, page_offset); > > > if (page && !xa_is_value(page)) { > > > /* > > > - * Page already present? Kick off the current batch of > > > - * contiguous pages before continuing with the next > > > - * batch. > > > + * Page already present? Kick off the current batch > > > + * of contiguous pages before continuing with the > > > + * next batch. This page may be the one we would > > > + * have intended to mark as Readahead, but we don't > > > + * have a stable reference to this page, and it's > > > + * not worth getting one just for that. > > > */ > > > - if (readahead_count(&rac)) > > > - read_pages(&rac, &page_pool, gfp_mask); > > > - rac._nr_pages = 0; > > > - continue; > > > + goto read; > > > } > > > > > > page = __page_cache_alloc(gfp_mask); > > > @@ -201,6 +201,11 @@ void __do_page_cache_readahead(struct address_space *mapping, > > > if (page_idx == nr_to_read - lookahead_size) > > > SetPageReadahead(page); > > > rac._nr_pages++; > > > + continue; > > > +read: > > > + if (readahead_count(&rac)) > > > + read_pages(&rac, &page_pool, gfp_mask); > > > + rac._nr_pages = 0; > > > } > > > > Also, why? This adds a goto from branched code that continues, then > > adds a continue so the unbranched code doesn't execute the code the > > goto jumps to. In absence of any explanation, this isn't an > > improvement and doesn't make any sense... > > I thought I was explaining it ... "for easier use in subsequent patches". Sorry, my braino there. :) I commented on the problem with the first part of the sentence, then the rest of the sentence completely failed to sink in. -Dave. -- Dave Chinner david@fromorbit.com