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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C7DC7C43461 for ; Mon, 12 Apr 2021 10:41:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9BB9261278 for ; Mon, 12 Apr 2021 10:41:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239413AbhDLKmE (ORCPT ); Mon, 12 Apr 2021 06:42:04 -0400 Received: from mx2.suse.de ([195.135.220.15]:37350 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237538AbhDLKmD (ORCPT ); Mon, 12 Apr 2021 06:42:03 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 60439AF11; Mon, 12 Apr 2021 10:41:44 +0000 (UTC) Subject: Re: [PATCH 4/9] mm/page_alloc: optimize code layout for __alloc_pages_bulk To: Mel Gorman , Andrew Morton Cc: Chuck Lever , Jesper Dangaard Brouer , Christoph Hellwig , Alexander Duyck , Matthew Wilcox , Ilias Apalodimas , LKML , Linux-Net , Linux-MM , Linux-NFS References: <20210325114228.27719-1-mgorman@techsingularity.net> <20210325114228.27719-5-mgorman@techsingularity.net> From: Vlastimil Babka Message-ID: <71449835-d4da-657e-b4cf-b077e9636ff7@suse.cz> Date: Mon, 12 Apr 2021 12:41:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210325114228.27719-5-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/25/21 12:42 PM, Mel Gorman wrote: > From: Jesper Dangaard Brouer > > Looking at perf-report and ASM-code for __alloc_pages_bulk() it is clear > that the code activated is suboptimal. The compiler guesses wrong and > places unlikely code at the beginning. Due to the use of WARN_ON_ONCE() > macro the UD2 asm instruction is added to the code, which confuse the > I-cache prefetcher in the CPU. Hm that's weird, WARN_ON_ONCE() uses unlikely() too, so the UD2 should end up in the out-of-fast-path part? But anyway. > [mgorman: Minor changes and rebasing] > Signed-off-by: Jesper Dangaard Brouer > Signed-off-by: Mel Gorman Acked-By: Vlastimil Babka > --- > mm/page_alloc.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index be1e33a4df39..1ec18121268b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5001,7 +5001,7 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid, > unsigned int alloc_flags; > int nr_populated = 0; > > - if (WARN_ON_ONCE(nr_pages <= 0)) > + if (unlikely(nr_pages <= 0)) > return 0; > > /* > @@ -5048,7 +5048,7 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid, > * If there are no allowed local zones that meets the watermarks then > * try to allocate a single page and reclaim if necessary. > */ > - if (!zone) > + if (unlikely(!zone)) > goto failed; > > /* Attempt the batch allocation */ > @@ -5066,7 +5066,7 @@ int __alloc_pages_bulk(gfp_t gfp, int preferred_nid, > > page = __rmqueue_pcplist(zone, ac.migratetype, alloc_flags, > pcp, pcp_list); > - if (!page) { > + if (unlikely(!page)) { > /* Try and get at least one page */ > if (!nr_populated) > goto failed_irq; >