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b=A+oM44gqAYtQIxMXkPx3vuoESBuPYWQv90ZRpAAmF/k2fw72YwnvZU9sAwYzrF5ol rkZeB2mLMSbAIHg0MmKlEMev7WicLbHN2AXJ6HnRVnWJRG5s9copv4G1it0PkygtXR sqdevmRv6fDk8KcOXg1ckPYQhxld0P7g85MtBWlb76ldKs6pG7jlrb7SrdQnTl4I2Z EjFWA5oxsTwuJ5bsIBsJR+jQlLup3RVP7CGfqgwF4ieRFcf9zAFPJCMF5RgiO7JBeJ naCFF4fS4WBY4K+8rGVdxnw9btIGppzKqrDIK8rCBFdCSuTMpQj0ssddunds7v1PRj vnqKMlJhVjF+w== Message-ID: <280965b2-c6eb-4f01-a0ac-c4fb7e518f97@kernel.org> Date: Thu, 1 Oct 2026 12:54:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/numa_balancing: allow migrate on protnone reference with MPOL_WEIGHTED_INTERLEAVE policy To: Zi Yan , Gregory Price , Li Zhe , Joshua Hahn Cc: akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260930121154.687586-1-joshua.hahnjy@gmail.com> <2e3f12b7-0dac-428c-b70b-07e1f63de028@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: CE8991C0003 X-Rspam-User: X-Stat-Signature: jw8fgkwwwojkmre6ieq97jk8a97hfihu X-HE-Tag: 1790852070-751562 X-HE-Meta: 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 CgE11e6K 2X8G3RCvPP4slHDEZfPiOpVBYaVhcBzSbhWga+j8b9fdA/cI+nGYnLTz70U23dUiV9Oiei4+qwrjSCYLKfBSB7FeqMKgnxoh7M+Q1PelVBts7WspRFb1stWwOjakfK1gW6esYl3p6DTzWbWqXTGxqqxoKTx/sgVkfaTzOTTJdvHkxlx1wpNmiXKHaaVn0QqV/2Htz0Iu/pWUspFMXLBNap30SvryixgoFuHErd5f//Xy9dvORAgBMneUSrO0NI1quQ/qXmsHJuqg/jqkD3QKVyRt0zvVgtFyrjmx0JUx68fThEtfhJUQgtJExfkxJDaCKkZcTm/rnHjBdr+AV/wBV0MwODB91MNh9Anzj8o8LtUIKTUcCTyfxfj9C5CD+ksxNXu0jIbdpkSsP8vrON/BBdJRkBg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/30/26 17:10, Zi Yan wrote: > On 30 Sep 2026, at 10:50, Gregory Price wrote: > >> On Wed, Sep 30, 2026 at 10:02:23PM +0800, Li Zhe wrote: >>> The use case is closer to the second one, but the main motivation is not >>> only startup-time performance.  The more important point is that each >>> workload has its own DDR/CXL budget assigned by the workload manager. >>> >> >> mempolicy is the wrong interface to do budget policy, you'd be better >> off looking at Joshua's memcg tiered node solutions for that. >> >>> MPOL_WEIGHTED_INTERLEAVE is useful because it lets new allocations >>> follow that per-workload budget from the beginning, instead of placing >>> everything on one tier first and correcting the placement later. This is >>> important for workload orchestration because the workload starts from a >>> placement close to its assigned DDR/CXL ratio. >>> >> >> This however is reasonable to me - you'd prefer to spread out the cost >> of initial faulting placement explicitly, rather than simply take >> fallbacks when the top-tier budget becomes pressured. >> >> i.e. w/o interleave: >> >> [node 0 ] >> ^^^^^^^^^^^^^^ alloc until full >> vvvvvvvvv fallback >> [node 1 ] >> >> in this scenario you end up with considerable hot memory >> on the remote node consolidated in time-space (everything >> allocated after node0 becomes full skews heavily toward >> node1) >> >> Tiering then likely takes many faults to rebalance after >> you've already reached node0 limits. >> >> w/ interleave >> >> [node 0 ] >> ^^^vv^^^vv^^^vv^^^vv^^^vv^^^vv.... >> [node 1 ] >> >> In this scenario you do an initial fill distributed by weight >> and then let tiering figure it out without consolidating all >> of the pressure to the point where node0 has no space left. >> >> That said - this seems like mostly an initial-fill problem, after >> you initially fill your memory, a new allocation largely implies >> the memory is hot - and you probably prefer that to be local. > > If this is a initial-fill problem, can userspace set weighted interleave > initially? The program or harness can observe memory usage of the program > or related NUMA nodes and switch the policy to numa balancing via > set_mempolicy() or mbind() without MPOL_MF_MOVE after certain threshold > is met? You mean: use the weighted policy initially and then switch to a NUMA-balancing one which doesn't involve the weights anymore? That makes more sense to me. Although I struggle to see why an effectively "let's put random memory on slow and others at hot" is a good starting point to later let if be fixed up by actual balancing/tiering. It all sounds a bit hackish. :) -- Cheers, David