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[209.132.183.28]) by mx.google.com with ESMTPS id m50si4676068qtm.179.2019.04.05.01.05.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Apr 2019 01:05:15 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8A91E81E19; Fri, 5 Apr 2019 08:05:14 +0000 (UTC) Received: from [10.36.117.86] (ovpn-117-86.ams2.redhat.com [10.36.117.86]) by smtp.corp.redhat.com (Postfix) with ESMTP id BEE511001E8A; Fri, 5 Apr 2019 08:05:10 +0000 (UTC) Subject: Re: [PATCH 2/2] mm, memory_hotplug: provide a more generic restrictions for memory hotplug To: Michal Hocko Cc: Oscar Salvador , akpm@linux-foundation.org, dan.j.williams@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20190404125916.10215-1-osalvador@suse.de> <20190404125916.10215-3-osalvador@suse.de> <880c5d09-7d4e-2a97-e826-a8a6572216b2@redhat.com> <20190404180144.lgpf6qgnp67ib5s7@d104.suse.de> <5f735328-3451-ebd7-048e-e83e74e2c622@redhat.com> <20190405071418.GN12864@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190405071418.GN12864@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 05 Apr 2019 08:05:14 +0000 (UTC) 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 05.04.19 09:14, Michal Hocko wrote: > On Thu 04-04-19 20:27:41, David Hildenbrand wrote: >> On 04.04.19 20:01, Oscar Salvador wrote: > [...] >>> But I am not really convinced by MHP_SYSTEM_RAM name, and I think we should stick >>> with MHP_MEMBLOCK_API because it represents __what__ is that flag about and its >>> function, e.g: create memory block devices. > > Exactly Fine with me for keeping what Oscar has. > >> This nicely aligns with the sub-section memory add support discussion. >> >> MHP_MEMBLOCK_API immediately implies that >> >> - memory is used as system ram. Memory can be onlined/offlined. Markers >> at sections indicate if the section is online/offline. > > No there is no implication like that. It means only that the onlined > memory has a sysfs interface. Nothing more, nothing less As soon as there is a online/offline interface, you *can* (and user space usually *will*) online that memory. Onlining/offlining is only defined for memory to be added to the buddy - memory to be used as "system ram". Doing it for random device memory will not work / result in undefined behavior. Not adding memory block devices for system ram will not allow user space to online/offline it and break kdump reload for hot-added memory. But memory can be onlined/offlined using internal APIs of course - if that's what you were referring to. > > This is an internal API so we are not carving anything into the stone. That is true. > So can we simply start with what we have and go from there? Sure, what Oscar does here is just a simple refactoring of the interface and I was just wondering if the interface needs a general overhaul. >I am getting > felling that this discussion just makes the whole thing more muddy. I think this discussion is helpful to understand how the whole thing is supposed to work :) At least on my side. Meanwhile, I will have a look if memory block devices cannot simply be created by the caller of arch_add_memory(). At least it feels like creating memory bock devices could be factored out - I remember that it was not that easy. -- Thanks, David / dhildenb