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[80.187.83.189]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fc78559c8sm29186175e9.4.2025.10.13.05.41.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Oct 2025 05:42:02 -0700 (PDT) Message-ID: <7176597b-006f-40ad-9421-860d80d7e696@redhat.com> Date: Mon, 13 Oct 2025 14:41:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 mm-new 03/11] mm: thp: add support for BPF based THP order selection To: Yafang Shao , Tejun Heo , Michal Hocko , Roman Gushchin Cc: Zi Yan , Alexei Starovoitov , Johannes Weiner , Andrew Morton , baolin.wang@linux.alibaba.com, Lorenzo Stoakes , Liam Howlett , npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, Matthew Wilcox , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Amery Hung , David Rientjes , Jonathan Corbet , 21cnbao@gmail.com, Shakeel Butt , lance.yang@linux.dev, Randy Dunlap , bpf , linux-mm , "open list:DOCUMENTATION" , LKML References: <20250930055826.9810-1-laoar.shao@gmail.com> <20250930055826.9810-4-laoar.shao@gmail.com> <27e002e3-b39f-40f9-b095-52da0fbd0fc7@redhat.com> <7723a2c7-3750-44f7-9eb5-4ef64b64fbb8@redhat.com> <96AE1C18-3833-4EB8-9145-202517331DF5@nvidia.com> <129379f6-18c7-4d10-8241-8c6c5596d6d5@redhat.com> <3577f7fd-429a-49c5-973b-38174a67be15@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: amm9c5idufudni7fs3hryqeyxk8kak56 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2FDF220009 X-HE-Tag: 1760359328-539974 X-HE-Meta: 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 RmMihCWa 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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: >> I came to the same conclusion. At least it's a valid start. >> >> Maybe we would later want a global fallback BPF-THP prog if none was >> enabled for a specific MM. > > good idea. We can fallback to the global model when attaching pid 1. > >> >> But I would expect to start with a per MM way of doing it, it gives you >> way more flexibility in the long run. > > THP, such as shmem and file-backed THP, are shareable across multiple > processes and cgroups. If we allow different BPF-THP policies to be > applied to these shared resources, it could lead to policy > inconsistencies. Sure, but nothing new about that (e.g., VM_HUGEPAGE, VM_NOHUGEPAGE, PR_GET_THP_DISABLE). I'd expect that we focus on anon THP as the first step either way. Skimming over this series, anon memory seems to be the main focus. > This would ultimately recreate a long-standing issue > in memcg, which still lacks a robust solution for this problem [0]. > > This suggests that applying SCOPED policies to SHAREABLE memory may be > fundamentally flawed ;-) Yeah, shared memory is usually more tricky: see mempolicy handling for shmem. There, the policy is much rather glued to a file than to a process. -- Cheers David / dhildenb