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Biederman" Cc: James Morse , kexec@lists.infradead.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Dave Young , Baoquan He References: <20200501165701.24587-1-james.morse@arm.com> <40b07632-b044-d1cd-96a2-81eec3da93e7@redhat.com> <8736892l92.fsf@x220.int.ebiederm.org> <87h7wmtna1.fsf@x220.int.ebiederm.org> 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: <4d5f69b6-fdfd-a461-0ac9-6d05636508f1@redhat.com> Date: Tue, 12 May 2020 09:45:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <87h7wmtna1.fsf@x220.int.ebiederm.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 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: >>> Phrasing it that way is non-sense. What is important is memory >>> available in the system. A memory map is just a reflection upon that= , >>> a memory map is not the definition of truth. >>> >>> So if this notifier reflects when memory is coming and going on the >>> system this is a reasonable approach. =20 >>> >>> Do these notifiers might fire for special kinds of memory that should >>> only be used for very special purposes? >>> >>> This change with the addition of some filters say to limit taking act= ion >>> to MEM_ONLINE and MEM_OFFLINE looks reasonable to me. Probably also >>> filtering out special kinds of memory that is not gernally useful. >> >> There are cases, where this notifier will not get called (e.g., hotplu= g >> a DIMM and don't online it) or will get called, although nothing chang= ed >> (offline+re-online to a different zone triggered by user space). AFAIK= , >> nothing in kexec (*besides kdump) cares about online vs. offline memor= y. >> This is why this feels wrong. >=20 > So what precisely does offline and online of memory mean in this contex= t? > Is it turning the memory on and off? (which is the obvious meaning) > Or is offline and online letting the ordinary kernel use a chunk > of memory and not use a chunk of memory and the memory remains running > the entire time? >=20 A DIMM is partitioned into fixed-size memory blocks. Each memory block is represented in /sys/device/system/memory/memoryX/. There, it can be onlined of offlined. onlining/offlining a memory block simply defines - if the memory will be used by the buddy - how the memory will be used by the buddy (e.g., ZONE_NORMAL vs. ZONE_MOVABLE) nothing else (esp. no hardware is switched on/off). e.g., echo "online_movable" > /sys/devices/system/memory/memory9/state echo "offline" > /sys/devices/system/memory/memory9/state echo "online_kernel" > /sys/devices/system/memory/memory9/state When hotplugging memory, all memory blocks are either onlined directly from the kernel, or userspace has to do it manually via e.g., udev rules. The latter is common is distributions. Before hotunplugging memory, all memory blocks have to be offline. This means - memory was never onlined - memory was offlined by user space manually - memory will be offlined automatically when unplugging the dimm Of course, offlining of some memory blocks might fail (esp. in case of ZONE_NORMAL when they contain unmovable allocations). Then, the memory cannot get hotunplugged. The representation in /proc/iomem and /sys/firmware/memmap is independent of the state (online/offline) of a memory block. >=20 >> add_memory()/try_remove_memory() is the place where: >> - Memblocks are created/deleted (if the memblock allocator is still >> alive) >> - Memory resources are created/deleted (e.g., reflected in /proc/iomem= ) >> - Firmware memmap entries are created/deleted (/sys/firmware/memmap) >> >> My idea would be to add something like >> kexec_map_add()/kexec_map_remove() where we have >> firmware_map_add_hotplug()/firmware_map_remove(). From there, we can >> unload the kexec image like done in this patch. >=20 > I don't see the connection with a firmware_map. Maybe that is how it i= s > thought about in the code but in principle the firmware can not exist > or completely ignore memory hotplug. The firmware_map callbacks simply update /sys/firmware/memmap in case that interface is configured into the kernel (mostly x86 only), nothing else. We just want similar callbacks to update kexec' representation. >=20 >> And these callbacks might come in handy for fixing up the kexec initia= l >> memmap in case of kexec_file_load(). AFAIKS on x86_64: >=20 > Maybe we have enough information to fixup the loaded kexec image > in the kexec_file_load case, we certainly don't in the ordinary > kexec_load case. Yes, that's also what I mentioned in my reply to Baoquan. >=20 > For now I want to stick to the simplest thing we can do which is either > blocking the memory hotplug operation (if that is possible) or > dropping the loaded kexec image. Yes, the latter is the best for now. It's simple. I am suggesting to add explicit callbacks to add_memory()/remove_memory(), and calling the invalidation from there - because I see various issues with the memory notifier approach (racy, false positives, never called if memory is not onlined). --=20 Thanks, David / dhildenb