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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> X-Rspamd-Queue-Id: 50D41160006 X-Stat-Signature: 7z4yoky341udbyuciygqtuyk3fb7yius X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775707676-1765 X-HE-Meta: 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 THSO+U8b 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.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