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Thu, 09 Apr 2026 18:14:50 -0700 (PDT) Received: from pve-server ([49.205.216.49]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35e3515b404sm4611574a91.15.2026.04.09.18.14.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Apr 2026 18:14:49 -0700 (PDT) From: Ritesh Harjani (IBM) To: Gregory Price Cc: "Huang, Ying" , 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: Date: Fri, 10 Apr 2026 06:37:08 +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: Gregory Price writes: > On Thu, Apr 09, 2026 at 09:12:56AM +0530, Ritesh Harjani wrote: >> "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. >> > > It only seems that way because the naming suggests tiering did not exist > prior to _TIERING - instead _NORMAL just operates in a suboptimal manner > when multiple tiers exist. > > _NORMAL migrates a page when it detects the node it's on is not the > local node of the task doing the work. > > _TIERING takes into account the liveliness of the pages with a > timestamp. > Sure Gregory and Ying, got the point. Thanks for your comments and feedback. Appreciate it! For now let's live with that, in case if we come across a real world usecase where we would want, only-migration w/o tiering behavior, then will share it. -ritesh