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[79.242.59.99]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37ecf066707sm2652823f8f.36.2024.10.18.12.27.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 18 Oct 2024 12:27:06 -0700 (PDT) Message-ID: <3f096ba0-b6f0-4db7-9d65-ba0550eb98b1@redhat.com> Date: Fri, 18 Oct 2024 21:27:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [External] : Re: [RFC PATCH v1 00/57] Boot-time page size selection for arm64 To: Joseph Salisbury , Ryan Roberts , Andrew Morton , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , Greg Marsden , Ivan Ivanov , Kalesh Singh , Marc Zyngier , Mark Rutland , Matthias Brugger , Miroslav Benes , Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20241014105514.3206191-1-ryan.roberts@arm.com> <915e2f0c-f603-4617-8429-da4dacc862c4@redhat.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: 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: 8bit X-Stat-Signature: 136ots61kd8p3qc57muyikjssshbwj1u X-Rspamd-Queue-Id: 989EC80008 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1729279609-643194 X-HE-Meta: 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 uRWxBl/H lBT234usjuc7zp3/RUpWofcnng5mYCdn82kYhmeNZGmf3oIZa0KxLyr0J/Nze2Y5fPeEQ5dwmy0yXqNnrrG87l5eiWWQKQJ/+XT2NpvnpQMMcmcSde4Ei+RwSE8ZlBJ0KJG67kH/DVH7W+IMNbZOGPdz+Ks5BZ9pShH9/6WuZFooAgFEdfOFWhPSxdJuvOV7uK0VzKqVlkoiCFK8KjqipmubZilOOEZnipUncPFSfREu9fB4wgUMvUfB965aHS4cy2++46Q6krm5RZWUx2bKrQArqjB6Aj+p6D635zxAGymm7M57MSiGrvYZyUPLFTMjBIcm6Ka5qA/yc3cBCUI69HMgICI7/B1cx60uz9NEQIr9DieAzt1Zl4fs5Dh7CxiDPzyUeDlKMJzVGd2c581NH4MPzgtdnOEgLvOYvu7/JWBe6I/aN+C3qIFKVPvGlCaeQRlke 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: >>> Hi Ryan, >>> >>> First off, this is excellent work!  Your cover page was very detailed >>> and made the patch set easier to understand. >>> >>> Some questions/comments: >>> >>> Once a kernel is booted with a certain page size, could there be issues >>> if it is booted later with a different page size?  How about if this is >>> done frequently? >> >> I think that is the reason why you are only given the option in RHEL >> to select the kernel (4K vs. 64K) to use at install time. >> >> Software can easily use a different data format for persistance based >> on the base page size. I would suspect DBs might be the usual suspects. >> >> One example is swap space I think, where the base page size used when >> formatting the device is used, and it cannot be used with a different >> page size unless reformatting it. >> >> So ... one has to be a bit careful ... >> > Yes, that is what I was thinking.  Once a userspace process does an I/O > and if it is based on PAGE_SIZE things can go south.  I think this is > not an issue with THP, so maybe it's possible with boot-time page selection? THP is a different beast and has different semantics: the base page size doesn't change: the result of getpagesize() is unmodified ("transparent"). One would have to emulate for a given user space process a different page size ... and Ryan can likely tell some stories about that. Not that I consider it reasonable to have dynamic page sizes in the kernel and then try emulating a different one for all user space. -- Cheers, David / dhildenb