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[2003:d8:2f30:ec00:8f7e:58a4:ebf0:6a36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4eac8a9aasm2439145f8f.51.2025.05.28.13.32.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 May 2025 13:32:44 -0700 (PDT) Message-ID: <4e0e2874-1dfb-428f-9bff-0a6e174399b7@redhat.com> Date: Wed, 28 May 2025 22:32:39 +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> <5f0aadb1-28a8-4be0-bad9-16b738840e57@redhat.com> <5d48d0c3-89a3-44da-bc1a-9a4601f146a4@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3F7361A0010 X-Stat-Signature: xuuydsyyanc59k9yrzfrpws7wronrh3d X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1748464368-866299 X-HE-Meta: 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 QY5R2BFU Pas55UP8LVbjl234SIz2oNh0hzjuwe2ItJx4AAgG4McF+jSXKXGkL2FpsVsU5x0z2/evUqXnjB7SUWtBzJc7g/SMvUMfseQYOtEKvpO4vsGwcCN4aN4JYkDEPp0bVmoblU9/hTtRVLwkwi4r7vmUM8or6zP/TkZXqT/SJ7p9Xuh2fxQ6JWbIEeMlkOHnMxeKAaMO8AOnieVR5SVrp/X1Um0VKF13ev1j+197sKZ8+xAOZZzO4X0rHkl5eZCU+BDdayWKuIq0xCNEM61o+MJiucnJWQ/RhtrVKTy1JIgu7AoodTIEsVfRT1+e4Cp5cDbium/QJK0EqOPtBw6BQe5ZEp3d31ad61Nbf8hL7VZ6KVYMB1GLXxRmp3MpXhX2YSOO5z9Px5qFmgDzgKq/3vRZwcc931wnWc2fny2csR1NOwt/6/KaSPWLoWCVs+J3symbK+wEBqnIyrXsj9cgsa/msOOo2p5KfbZNt3Plh 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: >> >> I mean, with THPs, there are no guarantees, ever :( >> >>> If that's the case, we should revisit RFC v1 [0], >>> where we proposed rejecting THP allocations in certain scenarios for >>> specific tasks. >> >> Hooking into actual page allocation during page faults (e.g., THP size, >> khugepaged collapse decisions) is IMHO a much better application of ebpf >> than setting a THP mode per process (or MM ... ) using epbf. >> >> So yes, you could drive the system in "always" mode and decide to not >> allocate THPs during page faults / khugepaged for specific processes. >> >> IMHO that also does not contradict the VM_HUGEPAGE / VM_NOHUGEPAGE >> default setting proposal: VM_HUGEPAGE could feed into the epbf program >> as yet another parameter to make a decision. > > That seems like a viable solution. Thank you for your help. Good! And the required ebpf hooks would probably come in handy to write more advanced policies / allocation logic than just "give it THPs" vs. "don't give it THPs". -- Cheers, David / dhildenb