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Tue, 08 Sep 2020 05:15:02 -0400 X-MC-Unique: ALN8d0JLOa2GjrMmfOyngg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 595811084D72; Tue, 8 Sep 2020 09:15:01 +0000 (UTC) Received: from [10.36.115.46] (ovpn-115-46.ams2.redhat.com [10.36.115.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6B2457ED90; Tue, 8 Sep 2020 09:14:59 +0000 (UTC) Subject: Re: [PATCH v2 02/10] mm/memory_hotplug: enforce section granularity when onlining/offlining To: Wei Yang , Oscar Salvador Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Andrew Morton , Baoquan He , Pankaj Gupta References: <20200819175957.28465-1-david@redhat.com> <20200819175957.28465-3-david@redhat.com> <20200824103917.GB6315@linux> <20200825021129.GA78808@L-31X9LVDL-1304.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200825021129.GA78808@L-31X9LVDL-1304.local> 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-Rspamd-Queue-Id: DE8CF18140B67 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 25.08.20 04:11, Wei Yang wrote: > On Mon, Aug 24, 2020 at 12:39:18PM +0200, Oscar Salvador wrote: >> On Wed, Aug 19, 2020 at 07:59:49PM +0200, David Hildenbrand wrote: >>> Already two people (including me) tried to offline subsections, because >>> the function looks like it can deal with it. But we really can only >>> online/offline full sections that are properly aligned (e.g., we can only >>> mark full sections online/offline via SECTION_IS_ONLINE). >>> >>> Add a simple safety net to document the restriction now. Current users >>> (core and powernv/memtrace) respect these restrictions. >> >> It's been a while since I looked at sub-section handling stuff so sorry to ask >> this, but was it true that we can hot-{remove,add} sub-section granularity, while >> we can only online /offline on section granularity? >> Yes, we can hot-{remove,add} sub-section granularity ZONE_DEVICE memory, but not memory to be managed by the buddy. Examples are - Memory block devices span 1..X sections and can either be online/offline - We can only mark full sections to be online/offline in sparsemem - Besides section handling, current onlining/offlining code could only work in MAX_ORDER - 1 granularity, not necessarily sub-section granularity. Thanks for having a look. > > Seems you are right. -- Thanks, David / dhildenb