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Tue, 12 Jan 2021 14:41:05 +0000 (UTC) Received: from [10.36.115.140] (ovpn-115-140.ams2.redhat.com [10.36.115.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id 202AC5B4B6; Tue, 12 Jan 2021 14:41:02 +0000 (UTC) Subject: Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one To: Michal Hocko Cc: Muchun Song , mike.kravetz@oracle.com, akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi References: <20210110124017.86750-1-songmuchun@bytedance.com> <20210110124017.86750-2-songmuchun@bytedance.com> <1b39d654-0b8c-de3a-55d1-6ab8c2b2e0ba@redhat.com> <20210112112709.GO22493@dhcp22.suse.cz> <20210112121643.GP22493@dhcp22.suse.cz> <20210112142337.GR22493@dhcp22.suse.cz> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <52ec4899-80df-4cbe-41f1-e0a29e838afa@redhat.com> Date: Tue, 12 Jan 2021 15:41:02 +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: <20210112142337.GR22493@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 12.01.21 15:23, Michal Hocko wrote: > On Tue 12-01-21 13:16:45, Michal Hocko wrote: > [...] >> Well, currently pool pages are not migrateable but you are right that >> this is likely something that we will need to look into in the future >> and this optimization would stand in the way. > > After some more thinking I believe I was wrong in my last statement. > This optimization shouldn't have any effect on pages on the pool as > those stay at reference count 0 and they cannot be isolated either > (clear_page_huge_active before it is enqueued). > > That being said, the migration code would still have to learn about > about this pages but that is out of scope of this discussion. > > Sorry about the confusion from my side. > At this point I am fairly confused what's working at what's not :D I think this will require more thought, on how to teach alloc_contig_range() (and eventually in some cases offline_pages()?) to do the right thing. -- Thanks, David / dhildenb