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 DD5C8C4361A for ; Thu, 3 Dec 2020 15:49:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4B4B5207A4 for ; Thu, 3 Dec 2020 15:49:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4B4B5207A4 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 7E6446B006C; Thu, 3 Dec 2020 10:49:28 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 76EB06B006E; Thu, 3 Dec 2020 10:49:28 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 65E398D0001; Thu, 3 Dec 2020 10:49:28 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0139.hostedemail.com [216.40.44.139]) by kanga.kvack.org (Postfix) with ESMTP id 4B9CB6B006C for ; Thu, 3 Dec 2020 10:49:28 -0500 (EST) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 0F5A5180AD807 for ; Thu, 3 Dec 2020 15:49:28 +0000 (UTC) X-FDA: 77552405616.06.aunt45_420d7a2273bd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id DFC70100404D6 for ; Thu, 3 Dec 2020 15:49:27 +0000 (UTC) X-HE-Tag: aunt45_420d7a2273bd X-Filterd-Recvd-Size: 3165 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Dec 2020 15:49:27 +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 EF434AD89; Thu, 3 Dec 2020 15:49:25 +0000 (UTC) Subject: Re: [External] Re: [PATCH] mm/page_isolation: do not isolate the max order page To: Muchun Song Cc: Andrew Morton , Linux Memory Management List , LKML , Joonsoo Kim References: <20201202122114.75316-1-songmuchun@bytedance.com> <1505b548-968b-2053-fd17-0cc4ae240a2f@suse.cz> From: Vlastimil Babka Message-ID: <35f00013-c161-b651-197b-bbe079170fa4@suse.cz> Date: Thu, 3 Dec 2020 16:49:24 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 12/3/20 3:43 AM, Muchun Song wrote: > On Thu, Dec 3, 2020 at 8:03 AM Vlastimil Babka wrote: >> >> 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. >> > >> > Signed-off-by: Muchun Song >> >> Acked-by: Vlastimil Babka >> >> > --- >> > mm/page_isolation.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > 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 *page, unsigned migratetype) >> > */ >> > if (PageBuddy(page)) { >> > order = buddy_order(page); >> > - if (order >= pageblock_order) { >> > + if (order >= pageblock_order && order < MAX_ORDER - 1) { >> > pfn = page_to_pfn(page); >> > buddy_pfn = __find_buddy_pfn(pfn, order); >> > buddy = page + (buddy_pfn - pfn); >> >> Hm I wonder if order == MAX_ORDER - 1, then the buddy can actually be a >> !pfn_valid() in some corner case? pfn_valid_within(buddy_pfn) that follows would >> only catch it on archs with holes in zone. Then is_migrate_isolate_page(buddy) >> might access an invalid buddy. So this might be actually a bug fix and not just >> optimization, just the bug hasn't been observed in practice. > > Agree. Should we add a Fixes tag in the commit log? Thanks. Right. Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock") The criteria for CC stable is not met though as it's theoretical. >> >> > >> > >