From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4B007402B87; Mon, 11 May 2026 15:56:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778514987; cv=none; b=KoY6A5jwu4s5haU0bCze8wdUAVFd4U7fxApaJIUT4xl2oGxWunHdENsgQxArpG5QM6StoYiP+5+FPEhqLgErMP8I2mviRgpMc93+O1/cKYo/SwB0LejTnADfa1zZmuJ/uWZ6c45/7dWxGC0EyIUIgFfo4UfB8hpWQlsmH7p9/2Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778514987; c=relaxed/simple; bh=wHF3j54IopBAPswmwUy+Go6x+2HXg2Z8f8E+TCPm3PQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ijZCqYZgWmbJGOMbRsh29/BxiwzJ7YjxE879UyRaRDiYFDMSJkRa7WkXgZaZsbMHsCtxhlXzSqr+JcZVy0YH2jtfa8Z8yqw4da55mTXx0uZIbBIbnguQWSh/XHbG+Q8iddIVeeJVAEWczMvS5JW+xi3IhEYmtWJQJllQud6PffE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=iWY1agl2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="iWY1agl2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11D17C2BCB0; Mon, 11 May 2026 15:56:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778514986; bh=wHF3j54IopBAPswmwUy+Go6x+2HXg2Z8f8E+TCPm3PQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=iWY1agl25YwFg/1AFNy9/VKJjHwRcbFqhG2jvhJjHofiGhZENmc49UsWAL8ItB0VX LuQiFxMk08urZ4n1sV0aCAEm3T36Nn6DRFSMyjCl9IvcVUFcciMK5IGGCfzTkvVgkZ FJkI4LfP4jrPSYkLwkSjXILCi/XOOV99yUNeMjgim97fCybsUeuHgCqfCBK4sKgyYU jh3Sk0psLkcXDXKeBLWUrQBvwYJ2hc7secFOqxsYYu2cGoR9z8dO91DNCV9bevvz+V L66WRhCxH76G0hDBACkxMGxDegrnu7E0dLI9mWZNrXaoFHTugvb8+sXLBrc9iu0Ae4 PU8UnQrRVFCBw== Message-ID: <3ff8b23a-479d-46e8-b820-a23697587f01@kernel.org> Date: Mon, 11 May 2026 17:56:19 +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: [RFC PATCH 0/9 v2] mm/memcontrol: Make memory cgroup limits tier-aware To: Joshua Hahn , linux-mm@kvack.org Cc: Tejun Heo , Johannes Weiner , Michal Koutny , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton , Chris Li , Kairui Song , Muchun Song , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , Qi Zheng , Axel Rasmussen , Yuanchu Xie , Wei Xu , Kaiyang Zhao , David Rientjes , Yiannis Nikolakopoulos , "Rao, Bharata Bhasker" , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260423203445.2914963-1-joshua.hahnjy@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20260423203445.2914963-1-joshua.hahnjy@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/23/26 22:34, Joshua Hahn wrote: > INTRODUCTION > ============ > Memory cgroups provide an interface that allow multiple works on a host to > co-exist via weak and strong memory isolation guarantees. This works, because > for the most part, all memory has equal utility. Isolating a cgroup’s memory > footprint restricts how much it can hurt other workloads competing for memory, > or protects it from other cgroups looking for more memory. > > However, on systems with tiered memory (e.g. CXL), memory utility is no longer > homogeneous; toptier and lowtier memory provide different performance > characteristics and have different scarcity, meaning memory footprint no longer > serves as an accurate representation of a cgroup’s consumption of the system’s > limited resources. As an extreme example, a cgroup with 10G of toptier > (e.g. DRAM) memory and a cgroup with 10G of lowtier (e.g. CXL) memory both > appear to be consuming the same amount of system resources from memcg’s > perspective, despite the performance asymmetry between the two workloads. > > Therefore on tiered systems, memory isolation cannot currently happen, as > workloads that are well-behaved within their memcg limits may still hurt the > performance of other well-behaving workloads by hogging more than its > “fair share” of toptier memory. > > Introduce tier-aware memcg limits, which establish independent toptier limits > that scale with the memory limits and the ratio of toptier:total memory > available on the system. > > INTERFACE > ========= > This series introduces only one adjustable knob to userspace; a new cgroup mount > option “memory_tiered_limits” which toggles whether the cgroup mount will scale > toptier limits. It also introduces 4 new read-only sysfs entries per-cgroup: > memory.toptier_{min, low, high, max}. > > The new toptier memory limits are scaled according to the amount of toptier > memory and total memory available on the system as such: > > memory.toptier_high = (toptier_mem / total_mem) * memory.high > > For instance, on a host with 100GB memory, with 75G toptier and 25G CXL, the > “toptier ratio” would be 75 / 100 = 0.75. A cgroup with the following memcg > limits {min: 8G, low: 12G, high: 20G, max: 24G} might see toptier limits scaled > at {min: 6G, low: 9G, high: 15G, max: 18G}. Assume you have a bigger hierarchy (HBP, DRAM, CXL), or assume you have multiple NUMA nodes with a hierarchy each. Your proposal doesn't really seem to be very versatile, or am I wrong? -- Cheers, David