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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93ef50287a2sm265747485a.20.2026.10.13.08.49.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 08:49:05 -0700 (PDT) Date: Tue, 13 Oct 2026 11:49:03 -0400 From: Gregory Price To: Yafang Shao Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, akpm@linux-foundation.org, david@kernel.org, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, shakeel.butt@linux.dev, roman.gushchin@linux.dev, yu.c.chen@intel.com, zhao1.liu@intel.com, bpf@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v2 0/3] BPF-based per-cgroup NUMA balancing mode selection Message-ID: References: <20261012120438.52849-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261012120438.52849-1-laoar.shao@gmail.com> On Mon, Oct 12, 2026 at 08:04:35PM +0800, Yafang Shao wrote: > The Problem > =========== > > In our large fleet of Kubernetes-managed servers, NUMA balancing has > been historically disabled globally on each server. With the increasing > deployment of multi-socket AMD EPYC servers, cross-NUMA access has > become a critical performance issue, which made us reconsider. > > Enabling NUMA balancing globally is still not acceptable: it increases > the overall system overhead and can introduce latency spikes for > latency-sensitive workloads. What we need is to choose per workload > whether NUMA balancing runs at all, and which mode it runs in. A > latency-sensitive service may want the scheduler's NUMA statistics > without tiering's promotion machinery, while a batch service wants its > PMEM-resident memory promoted when hot without paying for > scheduler-driven migration. No single global switch serves both. Have you tested with recent fixes? NUMA balancing has been broken for a few years now (starvation issues causing VMAs to never be scanned, east-west filters causing south->north promotions to be skipped, shmem being entirely exempt, others). https://lore.kernel.org/linux-mm/20260629163337.1264881-1-hannes@cmpxchg.org/ https://lore.kernel.org/linux-mm/20260930112206.205083-1-gourry@gourry.net/ I also concur with Tejun that ops seems like overkill for this feature, this seems like something that can already be managed. For example, why not add a new numa balancing mode bit that says "enabled but only for explicitly opted in tasks" and then ignore the global default mempolicy, e.g.: if (numab_mode & NUMA_BALANCING_OPT_IN && mpol != default && mpol.flags & MPOL_F_NUMA_BALANCING) /* do balancing */ ~Gregory