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=-2.3 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 EBC42C34035 for ; Tue, 18 Feb 2020 05:08:34 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A807D24658 for ; Tue, 18 Feb 2020 05:08:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A807D24658 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48M85C6P5fzDqTP for ; Tue, 18 Feb 2020 16:08:31 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.helo=mail104.syd.optusnet.com.au (client-ip=211.29.132.246; helo=mail104.syd.optusnet.com.au; envelope-from=david@fromorbit.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=fromorbit.com Received: from mail104.syd.optusnet.com.au (mail104.syd.optusnet.com.au [211.29.132.246]) by lists.ozlabs.org (Postfix) with ESMTP id 48M8566tFWzDqLl for ; Tue, 18 Feb 2020 16:08:26 +1100 (AEDT) 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 415077E9CE8; Tue, 18 Feb 2020 16:08:26 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1j3v7Q-0005sF-Jw; Tue, 18 Feb 2020 16:08:24 +1100 Date: Tue, 18 Feb 2020 16:08:24 +1100 From: Dave Chinner To: Matthew Wilcox Subject: Re: [PATCH v6 04/19] mm: Rearrange readahead loop Message-ID: <20200218050824.GJ10776@dread.disaster.area> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-5-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200217184613.19668-5-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=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=xb1gzgCgqvQNCHvA9YAA:9 a=NFtlFkhSHy5C-G_b:21 a=QFM0elaIi_6nPVwS:21 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=biEYGPWJfzWAr4FL6Ov7:22 X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-mm@kvack.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" 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. > @@ -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... -- Dave Chinner david@fromorbit.com