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 CBED9443312; Fri, 2 Oct 2026 07:56:44 +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=1790927807; cv=none; b=KSCdN8ONXjsGQ5KVRO3Gy7gLNvuqDBlGen1zHpCqdcC7YbLNO/nzqZ+ButJAno2tOwJkhdrHQxzBkjYhk5FvIuVYNDzaR3GZRfqvRXGKzo5Uy+GmfxaN64qPXzGJGQZUv2GBbOnDkkmyKrxsOF0UP6lZIa5PDn71YjUVIM7DVfE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790927807; c=relaxed/simple; bh=6JChq8W0DHpZXMJrJ0FL635durNAwbGay8TZ4eHl8mU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PqFYE7M0AFABjru3kg2EDDNqYxFrhT/qE985BkPve/VKRJFOTSNcif3BoVAItzDKifLW8D751dO51HOTI8Up04hQLCulUEcqykA/75yqX3kms8go7/I8BYWoyePjz5OoDS9l/iPNSePwi+VszSOlfQ9BnIZBAtZbCrP2VfAXMuY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EQ91VK2+; 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="EQ91VK2+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09FD91F000FF; Fri, 2 Oct 2026 07:56:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790927804; bh=CEkWEbF0eWef2VJO7bWrlTNl1U8dJ/sz3+7inKUMUkw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EQ91VK2+BapVfmlNmGOB3cBrGS0uYiybL6rZ+zR2N7XSMIyvRWsYaK1X6j1d0ksJJ WzFtg42cKFOm6Iz0X5D44fWVtsaCvVaBxDfnKwKRcNHhx9mhcA6UWOsEsQOeKqUpOp xiQm/EshPiBxqnjjYipQ31j+o0YJjTdAoJAc0ic+SsTk5LRCBmrqsLgJ+TM2bMgixC 37Wx9BliiaJhDNUYuLoAStPxjVINOzmLHXTi0vNoPpZEC7J8Ch6W5Yf5oNaVXeWXQm aryC884o39Ko8E6iAhQBiKJZKgvPaqvf5uDewF0RqF4lA1LLcE5VMaXZlv+rI1cEeG smlxu332w9sMA== Message-ID: <44d15437-6aae-4d7c-bfd4-296276583826@kernel.org> Date: Fri, 2 Oct 2026 09:56:36 +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: Gregory Price Cc: Zi Yan , Li Zhe , Joshua Hahn , 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> <280965b2-c6eb-4f01-a0ac-c4fb7e518f97@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/1/26 15:26, Gregory Price wrote: > On Thu, Oct 01, 2026 at 12:54:22PM +0200, David Hildenbrand (Arm) wrote: >>> 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. :) >> > > It is a bit of a non-combo (Nonbo). You're using weighted interleave > with the intent of spreading out the bandwidth utilization (and maybe to > offset some reclaim behavior? *shrug*) but then undo all the placement > with tiering. I can understand the "random initial placement will help if you cross your fingers" argument from Zi. But then the question really is whether the app should then change the policy after the initial placement was done and the weighted stuff no longer makes a lot of sense. > > But, in defense of the hackery - I have seen strategies like this work > to optimize startup times and then let tiering optimize runtime. Phased > execution gets funky like that. No doubt about that. -- Cheers, David