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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f3ce483bsm257682615e9.33.2025.05.27.00.57.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 May 2025 00:57:59 -0700 (PDT) Message-ID: Date: Tue, 27 May 2025 09:57:58 +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: fJQu-8eMGlH_XqcbmVQ5nursJ-CYas2nApvc_1GLVTM_1748332681 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: rspam03 X-Rspamd-Queue-Id: 4DD3C18000E X-Stat-Signature: d86d8kenumgjb41s4c6x4bwkrucutgeg X-Rspam-User: X-HE-Tag: 1748332684-457282 X-HE-Meta: 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 7Li5qmAH 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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 27.05.25 07:46, Yafang Shao wrote: > On Mon, May 26, 2025 at 6:49 PM David Hildenbrand wrote: >> >> 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?)? > > I have a preliminary idea to implement this using BPF. I don't think we want to add such a mechanism (new mode) where the primary configuration mechanism is through bpf. Maybe bpf could be used as an alternative, but we should look into a reasonable alternative first, like the discussed mctrl()/.../ raised in the process_madvise() series. No "bpf" mode in disguise, please :) > We could define > the API as follows: > > struct bpf_thp_ops { > /** > * @task_thp_mode: Get the THP mode for a specific task > * > * Return: > * - TASK_THP_ALWAYS: "always" mode > * - TASK_THP_MADVISE: "madvise" mode > * - TASK_THP_NEVER: "never" mode > * Future modes can also be added. > */ > int (*task_thp_mode)(struct task_struct *p); > }; > > For observability, we could add a "THP mode" field to > /proc/[pid]/status. For example: > > $ grep "THP mode" /proc/123/status > always > $ grep "THP mode" /proc/456/status > madvise > $ grep "THP mode" /proc/789/status > never > > The THP mode for each task would be determined by the attached BPF > program based on the task's attributes. We would place the BPF hook in > appropriate kernel functions. Note that this setting wouldn't be > inherited during fork/exec - the BPF program would make the decision > dynamically for each task. What would be the mode (default) when the bpf program would not be active? > This approach also enables runtime adjustments to THP modes based on > system-wide conditions, such as memory fragmentation or other > performance overheads. The BPF program could adapt policies > dynamically, optimizing THP behavior in response to changing > workloads. I am not sure that is the proper way to handle these scenarios: I never heard that people would be adjusting the system-wide policy dynamically in that way either. Whatever we do, we have to make sure that what we add won't over-complicate things in the future. Having tooling dynamically adjust the THP policy of processes that coarsely sounds ... very wrong long-term. > > As Liam pointed out in another thread, naming is challenging here - > "process" might not be the most accurate term for this context. No, it's not even a per-process thing. It is per MM, and a MM might be used by multiple processes ... -- Cheers, David / dhildenb