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[195.135.220.15]) by mx.google.com with ESMTPS id e14si3061553ejs.265.2019.04.03.01.12.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Apr 2019 01:12:40 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id CB885B010; Wed, 3 Apr 2019 08:12:38 +0000 (UTC) Date: Wed, 3 Apr 2019 10:12:32 +0200 From: Michal Hocko To: Oscar Salvador Cc: David Hildenbrand , akpm@linux-foundation.org, dan.j.williams@intel.com, Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded memory Message-ID: <20190403081232.GB15605@dhcp22.suse.cz> References: <20190328134320.13232-1-osalvador@suse.de> <20190329084547.5k37xjwvkgffwajo@d104.suse.de> <20190329134243.GA30026@dhcp22.suse.cz> <20190401075936.bjt2qsrhw77rib77@d104.suse.de> <20190401115306.GF28293@dhcp22.suse.cz> <20190402082812.fefamf7qlzulb7t2@d104.suse.de> <20190402124845.GD28293@dhcp22.suse.cz> <20190403080113.adj2m3szhhnvzu56@d104.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190403080113.adj2m3szhhnvzu56@d104.suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Wed 03-04-19 10:01:16, Oscar Salvador wrote: > On Tue, Apr 02, 2019 at 02:48:45PM +0200, Michal Hocko wrote: > > So what is going to happen when you hotadd two memblocks. The first one > > holds memmaps and then you want to hotremove (not just offline) it? > > If you hot-add two memblocks, this means that either: > > a) you hot-add a 256MB-memory-device (128MB per memblock) > b) you hot-add two 128MB-memory-device > > Either way, hot-removing only works for memory-device as a whole, so > there is no problem. > > Vmemmaps are created per hot-added operations, this means that > vmemmaps will be created for the hot-added range. > And since hot-add/hot-remove operations works with the same granularity, > there is no problem. What does prevent calling somebody arch_add_memory for a range spanning multiple memblocks from a driver directly. In other words aren't you making assumptions about a future usage based on the qemu usecase? -- Michal Hocko SUSE Labs