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[209.132.183.28]) by mx.google.com with ESMTPS id i53si278759qvi.108.2019.04.17.06.48.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Apr 2019 06:48:21 -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-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 06C95308404C; Wed, 17 Apr 2019 13:48:20 +0000 (UTC) Received: from [10.36.116.187] (ovpn-116-187.ams2.redhat.com [10.36.116.187]) by smtp.corp.redhat.com (Postfix) with ESMTP id 034DD5D6A6; Wed, 17 Apr 2019 13:48:17 +0000 (UTC) Subject: Re: [PATCH v1 1/4] mm/memory_hotplug: Release memory resource after arch_remove_memory() To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Oscar Salvador , Pavel Tatashin , Wei Yang , Qian Cai , Arun KS , Mathieu Malaterre References: <20190409100148.24703-1-david@redhat.com> <20190409100148.24703-2-david@redhat.com> <20190417131258.GI5878@dhcp22.suse.cz> <20190417133131.GK5878@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/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190417133131.GK5878@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 17 Apr 2019 13:48:21 +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 17.04.19 15:31, Michal Hocko wrote: > On Wed 17-04-19 15:24:47, David Hildenbrand wrote: >> On 17.04.19 15:12, Michal Hocko wrote: >>> On Tue 09-04-19 12:01:45, David Hildenbrand wrote: >>>> __add_pages() doesn't add the memory resource, so __remove_pages() >>>> shouldn't remove it. Let's factor it out. Especially as it is a special >>>> case for memory used as system memory, added via add_memory() and >>>> friends. >>>> >>>> We now remove the resource after removing the sections instead of doing >>>> it the other way around. I don't think this change is problematic. >>>> >>>> add_memory() >>>> register memory resource >>>> arch_add_memory() >>>> >>>> remove_memory >>>> arch_remove_memory() >>>> release memory resource >>>> >>>> While at it, explain why we ignore errors and that it only happeny if >>>> we remove memory in a different granularity as we added it. >>> >>> OK, I agree that the symmetry is good in general and it certainly makes >>> sense here as well. But does it make sense to pick up this particular >>> part without larger considerations of add vs. remove apis? I have a >>> strong feeling this wouldn't be the only thing to care about. In other >>> words does this help future changes or it is more likely to cause more >>> code conflicts with other features being developed right now? >> >> I am planning to >> >> 1. factor out memory block device handling, so features like sub-section >> add/remove are easier to add internally. Move it to the user that wants >> it. Clean up all the mess we have right now due to supporting memory >> block devices that span several sections. >> >> 2. Make sure that any arch_add_pages() and friends clean up properly if >> they fail instead of indicating failure but leaving some partially added >> memory lying around. >> >> 3. Clean up node handling regarding to memory hotplug/unplug. Especially >> don't allow to offline/remove memory spanning several nodes etc. > > Yes, this all sounds sane to me. > >> IOW, in order to properly clean up memory block device handling and >> prepare for more changes people are interested in (e.g. sub-section add >> of device memory), this is the right thing to do. The other parts are >> bigger changes. > > This would be really valuable to have in the cover. Beause there is so > much to clean up in this mess but making random small cleanups without a > larger plan tends to step on others toes more than being useful. I agree, let's discuss the bigger plan I have in mind 1. arch_add_memory()/arch_remove_memory() don't deal with memory block devices. add_memory()/remove_memory()/online_pages()/offline_pages() do. 2. add_memory()/remove_memory()/online_pages()/offline_pages() - Only work on memory block device alignment/granularity - Only work on single nodes. - Only work on single zones. 3. mem->nid correctly indicates if - Memory block devices belongs to single node / no node / multiple nodes - Fast and reliable way to detect remove_memory()/online_pages()/offline_pages() being called with multiple nodes. 4. arch_remove_memory() and friends never fail. Removing of memory always succeeds. This allows better error handling when adding of memory fails. We will move some parts from CONFIG_MEMORY_HOTREMOVE to CONFIG_MEMORY_HOTPLUG, so we can use them to clean up if adding of memory fails. 5. Remove all accesses to struct_page from memory removal path. Pages might never have been initialized, they should not be touched. All other features I see on the horizon (vmemmap on added memory, sub-section hot-add) would mainly be centered around arch_add_memory()/arch_remove_memory(), which would not have to deal with any special cases around memory block device memory. Do you agree, do you have any other points/things in mind you consider important? -- Thanks, David / dhildenb