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=ham 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 33DA8C4361A for ; Thu, 3 Dec 2020 17:37:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 886CC206EC for ; Thu, 3 Dec 2020 17:37:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 886CC206EC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BB19B8D0006; Thu, 3 Dec 2020 12:37:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B628D8D0005; Thu, 3 Dec 2020 12:37:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A79DE8D0006; Thu, 3 Dec 2020 12:37:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0148.hostedemail.com [216.40.44.148]) by kanga.kvack.org (Postfix) with ESMTP id 918488D0005 for ; Thu, 3 Dec 2020 12:37:03 -0500 (EST) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 1FACD180AD807 for ; Thu, 3 Dec 2020 17:37:03 +0000 (UTC) X-FDA: 77552676726.02.lead14_2b0cd9d273bd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin02.hostedemail.com (Postfix) with ESMTP id 034B310097AA1 for ; Thu, 3 Dec 2020 17:37:02 +0000 (UTC) X-HE-Tag: lead14_2b0cd9d273bd X-Filterd-Recvd-Size: 3089 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf13.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Dec 2020 17:37:02 +0000 (UTC) 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 5A47CAD2D; Thu, 3 Dec 2020 17:37:01 +0000 (UTC) To: Muchun Song , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201202121838.75218-1-songmuchun@bytedance.com> From: Vlastimil Babka Subject: Re: [PATCH] mm/page_alloc: speeding up the iteration of max_order Message-ID: <320c8522-4ed5-809f-e6fc-8a185587519c@suse.cz> Date: Thu, 3 Dec 2020 18:37:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201202121838.75218-1-songmuchun@bytedance.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/2/20 1:18 PM, Muchun Song wrote: > When we free a page whose order is very close to MAX_ORDER and greater > than pageblock_order, it wastes some CPU cycles to increase max_order > to MAX_ORDER one by one and check the pageblock migratetype of that pag= e But we have to do that. It's not the same page, it's the merged page and = the new buddy is a different pageblock and we need to check if they have compatib= le migratetypes and can merge, or we have to bail out. So the patch is wrong= . > repeatedly especially when MAX_ORDER is much larger than pageblock_orde= r. Do we have such architectures/configurations anyway? > Signed-off-by: Muchun Song > --- > mm/page_alloc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) >=20 > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 141f12e5142c..959541234e1d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1041,7 +1041,7 @@ static inline void __free_one_page(struct page *p= age, > pfn =3D combined_pfn; > order++; > } > - if (max_order < MAX_ORDER) { > + if (max_order < MAX_ORDER && order < MAX_ORDER - 1) { > /* If we are here, it means order is >=3D pageblock_order. > * We want to prevent merge between freepages on isolate > * pageblock and normal pageblock. Without this, pageblock > @@ -1062,6 +1062,8 @@ static inline void __free_one_page(struct page *p= age, > is_migrate_isolate(buddy_mt))) > goto done_merging; > } > + if (unlikely(order !=3D max_order - 1)) > + max_order =3D order + 1; Or maybe I just don't understand what this is doing. When is the new 'if'= even true? We just bailed out of "while (order < max_order - 1)" after the las= t "order++", which means it should hold that "order =3D=3D max_order - 1")? Your description sounds like you want to increase max_order to MAX_ORDER = in one step, which as I explained would be wrong. But the implementation looks a= ctually like a no-op. > max_order++; > goto continue_merging; > } >=20