From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7FE653FF1A9; Thu, 1 Oct 2026 10:54:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790852072; cv=none; b=qX5g7q7Rc9f9ViNhCv7haV+lei+3E3fv37ZcKoPG6QAc7oIybrpjLdbtTNF37oK96zsFyR9AwQT5/sLKTpMMFamiCNPS6iHSxCTScwi3YiW+FMUFnxw8ODNKby+oVp71tiijcK80mzbncE2MNtJjVJOy02XW4jNaVvMhwWVaCFg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790852072; c=relaxed/simple; bh=bh6K6HDciC6POiG/no12b5OcCPyjonPt6pds/xyzlZY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EbLKTnm+qN2MrDWLajLUy5Momw29kbeZ+opUgLGjVZz5cnYqcHUaK07S6CUmBtH+LqhYfKSlM8daB02OFUegFMDIFTIY+IJCIh6OWzeOAF1lJ7mlumdcuK9vOZev6IRPbM8eQlJLUW0dVvkfPOZaXFxSZMd985WFhl+qCcfRsno= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A+oM44gq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A+oM44gq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54F131F000FF; Thu, 1 Oct 2026 10:54:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790852070; bh=aA5+KUvXhlWCHJtSM04hRod0BwqPg5dVCGPChHmxQ64=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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