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Tue, 21 Apr 2020 13:06:22 +0000 (UTC) Received: from [10.36.113.245] (ovpn-113-245.ams2.redhat.com [10.36.113.245]) by smtp.corp.redhat.com (Postfix) with ESMTP id 329153A0; Tue, 21 Apr 2020 13:06:21 +0000 (UTC) Subject: Re: [PATCH RFC 1/2] mm/memory_hotplug: no need to init new pgdat with node_start_pfn To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Baoquan He , Oscar Salvador , Pankaj Gupta References: <20200416104707.20219-1-david@redhat.com> <20200416104707.20219-2-david@redhat.com> <20200421123011.GE27314@dhcp22.suse.cz> <20200421125250.GG27314@dhcp22.suse.cz> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Tue, 21 Apr 2020 15:06:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200421125250.GG27314@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Content-Transfer-Encoding: quoted-printable 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 21.04.20 14:52, Michal Hocko wrote: > On Tue 21-04-20 14:35:12, David Hildenbrand wrote: >> On 21.04.20 14:30, Michal Hocko wrote: >>> Sorry for the late reply >>> >>> On Thu 16-04-20 12:47:06, David Hildenbrand wrote: >>>> A hotadded node/pgdat will span no pages at all, until memory is mov= ed to >>>> the zone/node via move_pfn_range_to_zone() -> resize_pgdat_range - e= .g., >>>> when onlining memory blocks. We don't have to initialize the >>>> node_start_pfn to the memory we are adding. >>> >>> You are right that the node is empty at this phase but that is alread= y >>> reflected by zero present pages (hmm, I do not see spanned pages to b= e >>> set 0 though). What I am missing here is why this is an improvement. = The >>> new node is already visible here and I do not see why we hide the >>> information we already know. >> >> "information we already know" - no, not before we online the memory. >=20 > Is this really the case? All add_memory_resource users operate on a > physical memory range. Having the first add_memory() to magically set node_start_pfn of a hotplu= gged node isn't dangerous, I think we agree on that. It's just completely unnecessary here and at least left me confused why this is needed at all- because the node start/end pfn is only really touched when onlining/offlining memory (when resizing the zone and the pgdat). >=20 >> Before onlining, it's just setting node_start_pfn to *some value* to b= e >> overwritten in move_pfn_range_to_zone()->resize_pgdat_range(). >=20 > Yes the value is overwritten but I am not sure this is actually correct > thing to do. I cannot remember why I've chosen to do that. It doesn't > really seem unlikely to online node in a higher physical address. >=20 Well, we decided to glue the node span to onlining/offlining of memory. So, the value really has no meaning without any of that memory being online/the node span being 0. > Btw. one thing that I have in my notes, I was never able to actually > test the no numa node case. Because I have always been testing with nod= e > being allocated during the boot. Do you have any way to trigger this > path? Sure, here is my test case #! /bin/bash sudo qemu-system-x86_64 \ --enable-kvm \ -m 4G,maxmem=3D20G,slots=3D2 \ -smp sockets=3D2,cores=3D2 \ -numa node,nodeid=3D0,cpus=3D0-1,mem=3D4G -numa node,nodeid=3D1,mem=3D= 0G \ -kernel /home/dhildenb/git/linux/arch/x86_64/boot/bzImage \ -append "console=3DttyS0 rd.shell rd.luks=3D0 rd.lvm=3D0 rd.md=3D0 rd= .dm=3D0 page_owner=3Don" \ -initrd /boot/initramfs-5.4.7-200.fc31.x86_64.img \ -machine pc \ -nographic \ -nodefaults \ -chardev stdio,id=3Dserial \ -device isa-serial,chardev=3Dserial \ -chardev socket,id=3Dmonitor,path=3D/var/tmp/monitor,server,nowait \ -mon chardev=3Dmonitor,mode=3Dreadline \ -device virtio-balloon \ -object memory-backend-ram,id=3Dmem0,size=3D512M \ -object memory-backend-ram,id=3Dmem1,size=3D512M \ -device pc-dimm,id=3Ddimm0,memdev=3Dmem0,node=3D1 \ -device pc-dimm,id=3Ddimm1,memdev=3Dmem1,node=3D1 Instead of coldplugging the DIMMs to node 1, you could also hotplug them = later (let me know if you need information on how to do that). I use this test = to verify that the node is properly onlined/offlined once I unplug/replug th= e two DIMMs (e.g., after onlining/offlining the memory blocks). --=20 Thanks, David / dhildenb