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(p200300cbc71e06009fbbf0bfd9585c70.dip0.t-ipconnect.de. [2003:cb:c71e:600:9fbb:f0bf:d958:5c70]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d4b79f69dsm12226388f8f.81.2024.10.14.12.47.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Oct 2024 12:47:14 -0700 (PDT) Message-ID: <177ca9d5-9fc7-4f43-83fb-ea5105621cc8@redhat.com> Date: Mon, 14 Oct 2024 21:47:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 7/7] s390/sparsemem: reduce section size to 128 MiB To: Heiko Carstens Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, virtualization@lists.linux.dev, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Huth , Cornelia Huck , Janosch Frank , Claudio Imbrenda , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Morton , Jonathan Corbet , Mario Casquero References: <20241014144622.876731-1-david@redhat.com> <20241014144622.876731-8-david@redhat.com> <20241014175335.10447-B-hca@linux.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20241014175335.10447-B-hca@linux.ibm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: rpio6dzo8bpti49faen1bxko59i5i4to X-Rspamd-Queue-Id: DB8EDC0010 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1728935233-8934 X-HE-Meta: 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 LFLQrLw4 hfuP+Tak3a88QMkTp+LmmTX1epyDfTeCgB1T7n7IKe2/eV7S9obcNl6gzFLa68UZsBFpt36PZfp6f/oBg8ncVuJdw8xg+Zcc6bQutyTdk4e7wb7of7TJAX6a+p4flxevuQUpLyR9jB9j8al4gkEIjO1WKLFG3/P+q0adfwpnwjgbmiNK8mn9c4tqI/A14QFYm56Z/I3p5YLAaatefbdSMBNaAkW4PqANYZo6qy9fm2LSI/QsuV/WlNt9sZYFPmHR2CcNUK4javZFhmoTMtY8icZpgbqmyyp0IffvIajmUXDQAJynfGxE7sAVsRDh5sl9ImTb3aLYailsaAiBZz9wqXg/SPzQygpTKezN7wcdKkaOn026ACAA6plSMd4EtOf3mLppHeN6ExB3MkbcyoQ+WQgxySYr8wiSK4/TrFbHVhEcykgk= 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: List-Subscribe: List-Unsubscribe: On 14.10.24 19:53, Heiko Carstens wrote: > On Mon, Oct 14, 2024 at 04:46:19PM +0200, David Hildenbrand wrote: >> Ever since commit 421c175c4d609 ("[S390] Add support for memory hot-add.") >> we've been using a section size of 256 MiB on s390 and 32 MiB on s390. >> Before that, we were using a section size of 32 MiB on both >> architectures. >> >> Likely the reason was that we'd expect a storage increment size of >> 256 MiB under z/VM back then. As we didn't support memory blocks spanning >> multiple memory sections, we would have had to handle having multiple >> memory blocks for a single storage increment, which complicates things. >> Although that issue reappeared with even bigger storage increment sizes >> later, nowadays we have memory blocks that can span multiple memory >> sections and we avoid any such issue completely. > > I doubt that z/VM had support for memory hotplug back then already; and the > sclp memory hotplug code was always written in a way that it could handle > increment sizes smaller, larger or equal to section sizes. > > If I remember correctly the section size was also be used to represent each > piece of memory in sysfs (aka memory block). So the different sizes were > chosen to avoid an excessive number of sysfs entries on 64 bit. > > This problem went away later with the introduction of memory_block_size. > > Even further back in time I think there were static arrays which had > 2^(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS) elements. Interesting. I'll drop the "Likely ..." paragraph then! > > I just gave it a try and, as nowadays expected, bloat-o-meter doesn't > indicate anything like that anymore. > >> 128 MiB has been used by x86-64 since the very beginning. arm64 with 4k >> base pages switched to 128 MiB as well: it's just big enough on these >> architectures to allows for using a huge page (2 MiB) in the vmemmap in >> sane setups with sizeof(struct page) == 64 bytes and a huge page mapping >> in the direct mapping, while still allowing for small hot(un)plug >> granularity. >> >> For s390, we could even switch to a 64 MiB section size, as our huge page >> size is 1 MiB: but the smaller the section size, the more sections we'll >> have to manage especially on bigger machines. Making it consistent with >> x86-64 and arm64 feels like te right thing for now. > > That's fine with me. > > Acked-by: Heiko Carstens > Thanks! -- Cheers, David / dhildenb