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Tue, 18 Feb 2020 10:11:51 +0000 (UTC) Received: from [10.36.116.190] (ovpn-116-190.ams2.redhat.com [10.36.116.190]) by smtp.corp.redhat.com (Postfix) with ESMTP id EC82460C84; Tue, 18 Feb 2020 10:11:47 +0000 (UTC) Subject: Re: [RFC PATCH] memory_hotplug: disable the functionality for 32b (was: Re: [Bug 206401] kernel panic on Hyper-V after 5 minutes due to) memory hot-add To: Michal Hocko , kkabe@vega.pgw.jp Cc: bhe@redhat.com, osalvador@suse.de, bugzilla-daemon@bugzilla.kernel.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, n-horiguchi@ah.jp.nec.com, linux-mm@kvack.org References: <20200218084700.GD21113@dhcp22.suse.cz> <200218181900.M0115079@vega.pgw.jp> <20200218100532.GA4151@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: <855954eb-9c78-59d6-dffe-d48166b0cb12@redhat.com> Date: Tue, 18 Feb 2020 11:11:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200218100532.GA4151@dhcp22.suse.cz> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: N9nfWx_YOjGMy_ObPnkN1A-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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 18.02.20 11:05, Michal Hocko wrote: > On Tue 18-02-20 18:19:00, kkabe@vega.pgw.jp wrote: >> mhocko@kernel.org sed in <20200218084700.GD21113@dhcp22.suse.cz> >> >>>> On Tue 18-02-20 15:24:48, kkabe@vega.pgw.jp wrote: >>>> [...] >>>>> Tried out the above patch. >>>>> It seems to be working; no panic, total memory has increased and >>>>> the hot-added memory is added as HIGHMEM. >>>> >>>> I was about to post a patch to mark hotplug broken on 32b but it seems >>>> you do care about this setup. Could you describe your usecase please? >> >> My usecase is testing out the kernel on Hyper-V before loading it on >> real i686 machine. Hyper-V machine is faster to skim out other bugs. >> So memory hot-add is not a must requirement for me, >> but having hot-add may be handy to see the application memory requirement. >> (as in the anaconda test revealed) > > OK, thanks for the clarification. I am not sure that this qualifies > as a sufficient reason to maintain the code though. > >> If we're disabling it, we have to announce it somewhere; >> where is appropriate? `modinfo hv_balloon`'s "hot_add" description? > > This should behave the same way as when the CONFIG_MEMORY_HOTPLULG is > not enabled. And from a very cursory look hv_balloon.c already checks > for the config. > > --- > From 562f21abeda508f199c34358e50fbaa518cd5ed8 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Tue, 18 Feb 2020 08:04:13 +0100 > Subject: [PATCH] memory_hotplug: disable the functionality for 32b > > Memory hotlug is broken for 32b systems at least since c6f03e2903c9 > ("mm, memory_hotplug: remove zone restrictions") which has considerably > reworked how can be memory associated with movable/kernel zones. The > same is not really trivial to achieve in 32b where only lowmem is the > kernel zone. While we can tweak this immediate problem around there are > likely other land mines hidden at other places. > > It is also quite dubious that there is a real usecase for the memory > hotplug on 32b in the first place. Low memory is just too small to be > hotplugable (for hot add) and generally unusable for hotremove. Adding > more memory to highmem is also dubious because it would increase the > low mem or vmalloc space pressure for memmaps. > > Restrict the functionality to 64b systems. This will help future > development to focus on usecases that have real life application. We > can remove this restriction in future in presence of a real life usecase > of course but until then make it explicit that hotplug on 32b is broken > and requires a non trivial amount of work to fix. > > Signed-off-by: Michal Hocko > --- > mm/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/Kconfig b/mm/Kconfig > index ab80933be65f..2d5fe9e92969 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -154,6 +154,7 @@ config MEMORY_HOTPLUG > bool "Allow for memory hot-add" > depends on SPARSEMEM || X86_64_ACPI_NUMA > depends on ARCH_ENABLE_MEMORY_HOTPLUG > + depends on 64BIT || BROKEN > > config MEMORY_HOTPLUG_SPARSE > def_bool y > Acked-by: David Hildenbrand -- Thanks, David / dhildenb