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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 2C8F6C433DB for ; Wed, 10 Feb 2021 14:17:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0070564E6F for ; Wed, 10 Feb 2021 14:17:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231634AbhBJORQ (ORCPT ); Wed, 10 Feb 2021 09:17:16 -0500 Received: from mx2.suse.de ([195.135.220.15]:59092 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232110AbhBJOPL (ORCPT ); Wed, 10 Feb 2021 09:15:11 -0500 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 7E9F1AC43; Wed, 10 Feb 2021 14:14:27 +0000 (UTC) Date: Wed, 10 Feb 2021 15:14:25 +0100 From: Oscar Salvador To: David Hildenbrand Cc: Mike Kravetz , Muchun Song , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/2] mm,page_alloc: Make alloc_contig_range handle in-use hugetlb pages Message-ID: <20210210141425.GB3636@localhost.localdomain> References: <20210208103812.32056-1-osalvador@suse.de> <20210208103812.32056-2-osalvador@suse.de> <6aa21eb3-7bee-acff-8f3c-7c13737066ba@redhat.com> <20210210140941.GA3636@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 10, 2021 at 03:11:05PM +0100, David Hildenbrand wrote: > On 10.02.21 15:09, Oscar Salvador wrote: > > On Wed, Feb 10, 2021 at 09:56:37AM +0100, David Hildenbrand wrote: > > > On 08.02.21 11:38, Oscar Salvador wrote: > > > > alloc_contig_range is not prepared to handle hugetlb pages and will > > > > fail if it ever sees one, but since they can be migrated as any other > > > > page (LRU and Movable), it makes sense to also handle them. > > > > > > > > For now, do it only when coming from alloc_contig_range. > > > > > > > > Signed-off-by: Oscar Salvador > > > > --- > > > > mm/compaction.c | 17 +++++++++++++++++ > > > > mm/vmscan.c | 5 +++-- > > > > 2 files changed, 20 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/mm/compaction.c b/mm/compaction.c > > > > index e5acb9714436..89cd2e60da29 100644 > > > > --- a/mm/compaction.c > > > > +++ b/mm/compaction.c > > > > @@ -940,6 +940,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > > > > goto isolate_fail; > > > > } > > > > + /* > > > > + * Handle hugetlb pages only when coming from alloc_contig > > > > + */ > > > > + if (PageHuge(page) && cc->alloc_contig) { > > > > + if (page_count(page)) { > > > > > > I wonder if we should care about races here. What if someone concurrently > > > allocates/frees? > > > > > > Note that PageHuge() succeeds on tail pages, isolate_huge_page() not, i > > > assume we'll have to handle that as well. > > > > > > I wonder if it would make sense to move some of the magic to hugetlb code > > > and handle it there with less chances for races (isolate if used, > > > alloc-and-dissolve if not). > > > > Yes, it makes sense to keep the magic in hugetlb code. > > Note, though, that removing all races might be tricky. > > > > isolate_huge_page() checks for PageHuge under hugetlb_lock, > > so there is a race between a call to PageHuge(x) and a subsequent > > call to isolate_huge_page(). > > But we should be fine as isolate_huge_page will fail in case the page is > > no longer HugeTLB. > > > > Also, since isolate_migratepages_block() gets called with ranges > > pageblock aligned, we should never be handling tail pages in the core > > of the function. E.g: the same way we handle THP: > > Gigantic pages? (spoiler: see my comments to next patch :) ) Oh, yeah, that sucks. We had the same problem in scan_movable_pages/has_unmovable_pages with such pages. Uhm, I will try to be more careful :-) -- Oscar Salvador SUSE L3