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Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0X0hNpcK_1775716754 cluster:ay36) by smtp.aliyun-inc.com; Thu, 09 Apr 2026 14:39:35 +0800 From: "Huang, Ying" To: Ritesh Harjani (IBM) Cc: Donet Tom , David Hildenbrand , Andrew Morton , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang , Ying Huang , Juri Lelli , Mel Gorman Subject: Re: [PATCH v2] memory tiering: Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled In-Reply-To: (Ritesh Harjani's message of "Thu, 09 Apr 2026 09:12:56 +0530") References: <20260323094849.3903-1-donettom@linux.ibm.com> <87wlyqt52m.fsf@DESKTOP-5N7EMDA> <87o6k1ubg4.fsf@DESKTOP-5N7EMDA> <877bqgvs4k.fsf@DESKTOP-5N7EMDA> Date: Thu, 09 Apr 2026 14:39:12 +0800 Message-ID: <87fr54y6wf.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 05C8E80010 X-Stat-Signature: j9343dud9rp3oj1pyfez9jbms5pitf9h X-Rspam-User: X-HE-Tag: 1775716781-616871 X-HE-Meta: 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 RMnL2f4R VE4Z0nxgXQp9CFgEnHWFMZxA0n+8XQWQsupRPI9r0GFXDOOp+7z5CLs7vlfRKpsi67+qksuCH/k9ojA9y1B1wCLNW3GkW05Px6xHvX4fJ+zv0kRiD1R7uSkzJ73TVbrrnWgD8a7fQ9WwiTau81r89k7Ky2xSFdhB/k1N5Q3dXWchOdPki+PqroIUFvBES5fljoTCAesWv/G6plLt3OOspqf9yG1sRHbnw6PNepMYqckAOAXU5OjZezWKx6dnUjDCUrsivt95bnX+9PnLczsgIRpYFZjES7zJejVuv6B9K6r4EVHO/dbgBgKiXDviWkUAef4315bhpZKTJG4Xz9YQ1cDnqn8ORMilOpObofahmGyupMj50rmc/HDql2986OrKSGIIa0DHMR1myBXUuKVbsCiPLeBSSPfAwu1CyGaNMKvwRXC8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Ritesh Harjani (IBM) writes: > "Huang, Ying" writes: > >>>>>> Donet Tom writes: >>> >>> >>> Thanks for the clarification. I was running some experiments where I >>> only required migration, not promotion. However, I observed that >>> promotion was still occurring even when NUMA_BALANCING_MEMORY_TIERING >>> was disabled, which led me to believe it might be a bug, so I reported >>> it. >>> >>> As I understand it, enabling both NUMA_BALANCING_MEMORY_TIERING and >>> NUMA_BALANCING_NORMAL results in both promotion and migration. Given >>> this, do you see any concerns with modifying the behavior of >>> NUMA_BALANCING_NORMAL? >>> >>> With this patch, we would have better control over enabling and >>> disabling promotion independently. I would appreciate your thoughts on >>> this. >> >> IIUC, we change the existing user visible behavior only with strong >> enough practical reason. > > So what I understood from this discussion so far is, we don't have any > mechanism to do auto-numa base page migration between DRAM -to- DRAM w/o > triggering promotions too from a lower tiers to higher tiers. > > ... This to me sounds more like a broken interface. > >> If so, making something conceptually better isn't enough for that. >> > > I think Donet's approach was more towards fixing the problem, then > making it conceptually better. To fix a theoretical problem instead of a practical problem? > So, as of now most of us may not see this > as a problem, since not many systems have different memory tiers > attached. But with more widespread CXL adoption and more memory tiers in > the system, we might require more finer control over auto-numa based > page migration. By design, normal NUMA balancing (not memory tiering) should migrate pages between tiers too. Because it migrates pages to the node near a CPU regardless of the memory tiers to optimize NUMA locality. > But hey, I just wanted to voice out my opinion here. If we think > changing user visible behavior is going to break existing applications > and we don't want that - then in that case the reasoning sounds ok to > me. --- Best Regards, Huang, Ying