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[2003:cb:c73d:2400:3be1:a856:724c:fd29]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-441c8631256sm40116925e9.20.2025.05.05.01.18.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 05 May 2025 01:18:45 -0700 (PDT) Message-ID: <8180a50d-eebe-4f9b-9ce8-d886654a992d@redhat.com> Date: Mon, 5 May 2025 10:18:43 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] driver/base: Optimize memory block registration to reduce boot time To: Mike Rapoport Cc: Oscar Salvador , Donet Tom , Zi Yan , Greg Kroah-Hartman , Andrew Morton , rafael@kernel.org, Danilo Krummrich , Ritesh Harjani , Jonathan Cameron , Alison Schofield , Yury Norov , Dave Jiang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <188fbfba-afb4-4db7-bbba-7689a96be931@redhat.com> <74c500dd-8d1c-4177-96c7-ddd51ca77306@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05.05.25 09:53, Mike Rapoport wrote: > On Mon, May 05, 2025 at 09:38:43AM +0200, David Hildenbrand wrote: >> On 05.05.25 09:28, Oscar Salvador wrote: >>> On Mon, May 05, 2025 at 09:16:48AM +0200, David Hildenbrand wrote: >>>> memory hotplug code never calls register_one_node(), unless I am missing >>>> something. >>>> >>>> During add_memory_resource(), we call __try_online_node(nid, false), meaning >>>> we skip register_one_node(). >>>> >>>> The only caller of __try_online_node(nid, true) is try_online_node(), called >>>> from CPU hotplug code, and I *guess* that is not required. >>> >>> Well, I guess this is because we need to link the cpus to the node. >>> register_one_node() has two jobs: 1) register cpus belonging to the node >>> and 2) register memory-blocks belonging to the node (if any). >> >> Ah, via __register_one_node() ... >> >> I would assume that an offline node >> >> (1) has no memory >> (2) has no CPUs >> >> When we *hotplug* either memory or CPUs, and we first online the node, there >> is nothing to register. Because if there would be something, the node would >> already be online. >> >> In particular, try_offline_node() will only offline a node if >> >> (A) No present pages: No pages are spanned anymore. This includes >> offline memory blocks. >> (B) No present CPUs. >> >> But maybe there is some case that I am missing ... > > I actually hoped you and Oscar know how that stuff works :) Well, I know how the memory side works, but the CPU side is giving me a hard time :) > > I tried to figure what is going on there and it all looks really convoluted. Jap ... > > So, on boot we have > cpu_up() -> > try_online_node() -> > bails out because all nodes are online (at least on > x86 AFAIU, see 1ca75fa7f19d ("arch/x86/mm/numa: Do > not initialize nodes twice")) > node_dev_init()i -> > register_one_node() -> > this one can use __register_one_node() and loop > over memblock regions. > > And for the hotplug/unplug path, it seems that > register_memory_blocks_under_node(MEMINIT_EARLY) is superfluous, because if > a node had memory it wouldn't get offlined, and if we are hotplugging an > node with memory and cpus, memory hotplug anyway calls > register_memory_blocks_under_node_hotplug(). > > So, IMHO, register_one_node() should not call > register_memory_blocks_under_node() at all, but again, I might have missed > something :) Hm, but someone has to create these links for the memory blocks. It's all very messy :( -- Cheers, David / dhildenb