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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261012120438.52849-1-laoar.shao@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 04CABC0007 X-Stat-Signature: 6kcxph9m8i1sqmzwzywtr96jbmp3s51x X-HE-Tag: 1791906546-613517 X-HE-Meta: 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 pq6fyjj6 XUcPEfOUuS/H2DBy8G+bkKd3ukSGrjnW8VzP7IecjSE5qfF/9tA9dMaUelXN0UdqXjVIXKCw8bAEreufDjwy+kyowoxSaF0X7VsR4n7pbPZXvaELZEmSjALS54fDJ68HDyL9Vq3fgUtXlEuyAXmhFWqO/u2B/9HDQRkMbmNMn/MFocHA/1o/EjuAlhNlDLLem6AHdlkuRnkFzUaLlWugbzRJgr3QAZFjWKhq+aqoYcingLTvLkdUkfDZ/wtNFedWu9d+K/YuPU6UhvlR+p0sskpDDZSCPrrsL6la09hwohfS6j85b4lFCKsUKJhWQ7xJezDmd6C1QBKgNMjJ27kpE2Rz79Cn9gMRQTMW1KcZJq6Vv4auOYK1QYJKYnSGXBgRfGfu/vSxX2ATDrAwBhCTArnQrmeBHEXDMm+J7+jVMYsnm6hmH7N4GSPCpF3RQMQ7alIZq+2KZU7nJeIZSZVfKfDjVvZvUspParxbxB4IzpKIN6qOE9DxeincIdZ2xK8bMGT5/9MSxmfUfZi5gAJ5Sc3x/KRn/xxr0BwLF Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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