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 5F699C433FE for ; Thu, 3 Dec 2020 17:15:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 886EF206B6 for ; Thu, 3 Dec 2020 17:15:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 886EF206B6 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 B83608D0001; Thu, 3 Dec 2020 12:15:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B346F6B0070; Thu, 3 Dec 2020 12:15:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A4AA98D0001; Thu, 3 Dec 2020 12:15:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0087.hostedemail.com [216.40.44.87]) by kanga.kvack.org (Postfix) with ESMTP id 8E9FC6B006E for ; Thu, 3 Dec 2020 12:15:46 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id A2896180AD811 for ; Thu, 3 Dec 2020 17:15:45 +0000 (UTC) X-FDA: 77552623050.12.year37_4b11ac2273bd Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 202511801B85B for ; Thu, 3 Dec 2020 17:15:41 +0000 (UTC) X-HE-Tag: year37_4b11ac2273bd X-Filterd-Recvd-Size: 3614 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Dec 2020 17:15:39 +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 EFBA6AC2E; Thu, 3 Dec 2020 17:15:37 +0000 (UTC) To: David Hildenbrand , 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> <1505b548-968b-2053-fd17-0cc4ae240a2f@suse.cz> <29022300-6d8e-0532-7abc-6d11ab1db04a@redhat.com> From: Vlastimil Babka Subject: Re: [PATCH] mm/page_isolation: do not isolate the max order page Message-ID: <92e54bf2-adc5-d51b-3b78-b881567335dc@suse.cz> Date: Thu, 3 Dec 2020 18:15:34 +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: <29022300-6d8e-0532-7abc-6d11ab1db04a@redhat.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 12/3/20 5:26 PM, David Hildenbrand wrote: > On 03.12.20 01:03, 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 >>=20 >> Acked-by: Vlastimil Babka >>=20 >>> --- >>> 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 =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); >>=20 >> 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 fol= lows would >> only catch it on archs with holes in zone. Then is_migrate_isolate_pag= e(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. >=20 > I think we have no users that isolate/unisolate close to holes. >=20 > CMA regions are properly aligned (to max of page_order / > max_order_nr_pages) and don't contain holes. The problem as I see it, is that buddy_order(page) might be already MAX_O= RDER - 1 (e.g. two pageblocks on x86), and then finding buddy of that one is bey= ond the guaranteed alignment (if they merged, which they can't, it would be four pageblocks). Might not be just a hole within zone, but also across zone b= oundary? While being isolated and used pages migrated away, the freed pages should= n't merge to MAX_ORDER-1, but if the MAX_ORDER-1 free page was already there = before the isolation? > virtio-mem does not apply as it knows its range has no holes. >=20 > gigantic pages are aligned naturally and we check that there are no > holes upfront. >=20 > There are no other users. >=20 >=20 > I don't see a need for stable/fixes. >=20