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=-15.2 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,URIBL_BLOCKED, 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 4E9F1C64E7C for ; Thu, 3 Dec 2020 00:03:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 8A681221EB for ; Thu, 3 Dec 2020 00:03:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8A681221EB 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 F23036B005D; Wed, 2 Dec 2020 19:03:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id ED4026B0068; Wed, 2 Dec 2020 19:03:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE73A6B006C; Wed, 2 Dec 2020 19:03:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0028.hostedemail.com [216.40.44.28]) by kanga.kvack.org (Postfix) with ESMTP id C23FB6B005D for ; Wed, 2 Dec 2020 19:03:53 -0500 (EST) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 934C1180AD80F for ; Thu, 3 Dec 2020 00:03:53 +0000 (UTC) X-FDA: 77550022746.10.drum40_1f0ddd5273b7 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin10.hostedemail.com (Postfix) with ESMTP id 749E716A4B0 for ; Thu, 3 Dec 2020 00:03:53 +0000 (UTC) X-HE-Tag: drum40_1f0ddd5273b7 X-Filterd-Recvd-Size: 2393 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf24.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Dec 2020 00:03:52 +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 84A7EAB63; Thu, 3 Dec 2020 00:03:51 +0000 (UTC) To: Muchun Song , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim References: <20201202122114.75316-1-songmuchun@bytedance.com> From: Vlastimil Babka Subject: Re: [PATCH] mm/page_isolation: do not isolate the max order page Message-ID: <1505b548-968b-2053-fd17-0cc4ae240a2f@suse.cz> Date: Thu, 3 Dec 2020 01:03:47 +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: <20201202122114.75316-1-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 1:21 PM, Muchun Song wrote: > The max order page has no buddy page and never merge to other order. > So isolating and then freeing it is pointless. >=20 > Signed-off-by: Muchun Song Acked-by: Vlastimil Babka > --- > mm/page_isolation.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) >=20 > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index a254e1f370a3..bddf788f45bf 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -88,7 +88,7 @@ static void unset_migratetype_isolate(struct page *pa= ge, unsigned migratetype) > */ > if (PageBuddy(page)) { > order =3D buddy_order(page); > - if (order >=3D pageblock_order) { > + if (order >=3D pageblock_order && order < MAX_ORDER - 1) { > pfn =3D page_to_pfn(page); > buddy_pfn =3D __find_buddy_pfn(pfn, order); > buddy =3D page + (buddy_pfn - pfn); Hm I wonder if order =3D=3D MAX_ORDER - 1, then the buddy can actually be= a !pfn_valid() in some corner case? pfn_valid_within(buddy_pfn) that follow= s would only catch it on archs with holes in zone. Then is_migrate_isolate_page(b= uddy) might access an invalid buddy. So this might be actually a bug fix and no= t just optimization, just the bug hasn't been observed in practice. >=20