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[2003:d8:2f19:6500:e1c1:8216:4c25:efe4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447eee9d8desm241148415e9.0.2025.05.26.03.49.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 May 2025 03:49:20 -0700 (PDT) Message-ID: Date: Mon, 26 May 2025 12:49:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 0/5] mm, bpf: BPF based THP adjustment To: Yafang Shao Cc: akpm@linux-foundation.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@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> 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: LjoVpfWHVzEVLfvM68Qk00-VHf63IezXOClAlf-2u-U_1748256562 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 14B8C16000A X-Stat-Signature: wu78e4es56oy7gab9ienoa3mk5rusqcp X-Rspam-User: X-HE-Tag: 1748256564-30979 X-HE-Meta: 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 3FDIE/FY 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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 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. >> >> The could be added on top of the current proposals that are flying >> around, and could be done e.g., per-process. > > How about introducing a dedicated "process" mode? This would allow > each process to use different THP modes—some in "always," others in > "madvise," and the rest in "never." Future THP modes could also be > added to this framework. We have to be really careful about not creating even more mess with more modes. How would that design look like in detail (how would we set it per process etc?)? -- Cheers, David / dhildenb