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Howlett" , Yafang Shao , akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, hannes@cmpxchg.org, usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, willy@infradead.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org References: <20250520060504.20251-1-laoar.shao@gmail.com> <7d8a9a5c-e0ef-4e36-9e1d-1ef8e853aed4@redhat.com> <3b792576-6189-4f53-b47f-95875181a656@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-MFC-PROC-ID: s7hzwUJDIxfSgZzGVwNmGG9dbkGEwTPjOGL8ek-CpSo_1748279539 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: upq88h1jdkeapasbhskfi8mansesgbou X-Rspamd-Queue-Id: DEB18A000D X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1748279543-550188 X-HE-Meta: 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 u+LunEac 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 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 26.05.25 19:07, Liam R. Howlett wrote: > * David Hildenbrand [250526 12:51]: >> On 26.05.25 17:54, Liam R. Howlett wrote: >>> * Liam R. Howlett [250526 10:54]: >>>> * David Hildenbrand [250526 06:49]: >>>>> On 26.05.25 11:37, Yafang Shao wrote: >>>>>> On Mon, May 26, 2025 at 4:14 PM David Hildenbrand wrote: >>>>>>> >>>>>>>> Hi all, >>>>>>>> >>>>>>>> Let’s summarize the current state of the discussion and identify how >>>>>>>> to move forward. >>>>>>>> >>>>>>>> - Global-Only Control is Not Viable >>>>>>>> We all seem to agree that a global-only control for THP is unwise. In >>>>>>>> practice, some workloads benefit from THP while others do not, so a >>>>>>>> one-size-fits-all approach doesn’t work. >>>>>>>> >>>>>>>> - Should We Use "Always" or "Madvise"? >>>>>>>> I suspect no one would choose 'always' in its current state. ;) >>>>>>> >>>>>>> IIRC, RHEL9 has the default set to "always" for a long time. >>>>>> >>>>>> good to know. >>>>>> >>>>>>> >>>>>>> I guess it really depends on how different the workloads are that you >>>>>>> are running on the same machine. >>>>>> >>>>>> Correct. If we want to enable THP for specific workloads without >>>>>> modifying the kernel, we must isolate them on dedicated servers. >>>>>> However, this approach wastes resources and is not an acceptable >>>>>> solution. >>>>>> >>>>>>> >>>>>>> > Both Lorenzo and David propose relying on the madvise mode. However,> >>>>>>> since madvise is an unprivileged userspace mechanism, any user can >>>>>>>> freely adjust their THP policy. This makes fine-grained control >>>>>>>> impossible without breaking userspace compatibility—an undesirable >>>>>>>> tradeoff. >>>>>>> >>>>>>> If required, we could look into a "sealing" mechanism, that would >>>>>>> essentially lock modification attempts performed by the process (i.e., >>>>>>> MADV_HUGEPAGE). >>>>>> >>>>>> If we don’t introduce a new THP mode and instead rely solely on >>>>>> madvise, the "sealing" mechanism could either violate the intended >>>>>> semantics of madvise(), or simply break madvise() entirely, right? >>>>> >>>>> We would have to be a bit careful, yes. >>>>> >>>>> Errors from MADV_HUGEPAGE/MADV_NOHUGEPAGE are often ignored, because these >>>>> options also fail with -EINVAL on kernels without THP support. >>>>> >>>>> Ignoring MADV_NOHUGEPAGE can be problematic with userfaultfd. >>>>> >>>>> What you likely really want to do is seal when you configured >>>>> MADV_NOHUGEPAGE to be the default, and fail MADV_HUGEPAGE later. >>> >>> I am also not entirely sure how sealing a non-existing vma would work. >>> We'd have to seal the default flags, but sealing is one way and this >>> surely shouldn't be one way? >> >> You probably have mseal() in mind. Just like we wouldn't be using >> madvise(), we also wouldn't be using mseal(). > > yes, I do - but mostly in terms of the language used and not the code as > that can't be used here. > > Do we use the term seal somewhere that allows undoing the sealed thing? > I'm _really_ hoping we don't, but am almost sure you're going to say > we do. The other place that comes to mind is memfd_create() with MFD_ALLOW_SEALING and fcntl() with F_ADD_SEALS. And yes, there is no "F_DEL_SEALS" :) -- Cheers, David / dhildenb