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Wed, 08 Apr 2026 21:07:55 -0700 (PDT) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35e3517f2a0sm1658684a91.17.2026.04.08.21.07.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2026 21:07:54 -0700 (PDT) From: Ritesh Harjani (IBM) To: "Huang, Ying" , Donet Tom Cc: 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: <877bqgvs4k.fsf@DESKTOP-5N7EMDA> Date: Thu, 09 Apr 2026 09:12:56 +0530 Message-ID: References: <20260323094849.3903-1-donettom@linux.ibm.com> <87wlyqt52m.fsf@DESKTOP-5N7EMDA> <87o6k1ubg4.fsf@DESKTOP-5N7EMDA> <877bqgvs4k.fsf@DESKTOP-5N7EMDA> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: "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. 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. 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 Thanks for your feedback! -ritesh