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Wed, 10 Feb 2021 14:11:08 +0000 (UTC) Received: from [10.36.113.218] (ovpn-113-218.ams2.redhat.com [10.36.113.218]) by smtp.corp.redhat.com (Postfix) with ESMTP id BCEF95C1BD; Wed, 10 Feb 2021 14:11:06 +0000 (UTC) Subject: Re: [RFC PATCH 1/2] mm,page_alloc: Make alloc_contig_range handle in-use hugetlb pages To: Oscar Salvador Cc: Mike Kravetz , Muchun Song , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210208103812.32056-1-osalvador@suse.de> <20210208103812.32056-2-osalvador@suse.de> <6aa21eb3-7bee-acff-8f3c-7c13737066ba@redhat.com> <20210210140941.GA3636@localhost.localdomain> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Wed, 10 Feb 2021 15:11:05 +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: <20210210140941.GA3636@localhost.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Stat-Signature: 6npu74b6zsqrxd1jb6mt1qggg7sie89z X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 29D9DC0001E6 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf03; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=63.128.21.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612966272-598052 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 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 :) ) -- Thanks, David / dhildenb