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Wed, 30 Sep 2026 05:03:54 -0700 (PDT) Date: Wed, 30 Sep 2026 08:03:52 -0400 From: Gregory Price To: "David Hildenbrand (Arm)" Cc: Li Zhe , akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/numa_balancing: allow migrate on protnone reference with MPOL_WEIGHTED_INTERLEAVE policy Message-ID: References: <20260930072617.64665-1-lizhe.67@bytedance.com> Precedence: bulk X-Mailing-List: linux-doc@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: On Wed, Sep 30, 2026 at 01:26:17PM +0200, David Hildenbrand (Arm) wrote: > > > > Initial placement is only a starting point. Pages initially allocated on > > fast memory are not necessarily the long-term hot pages, and pages > > initially allocated on slower memory may become hot as the workload's hot > > set changes. The policy therefore needs to be able to combine weighted > > initial placement with memory tiering's NUMA fault based hot-page > > promotion. > > Ok, so memory allocation will respect the weights but balancing will ignore > them? That really sounds rather odd to me. > > And I assume that was the reason why we might have disallowed the combination: > it turns a weighted mechanism into an unweighted mechanism. > > So are we really sure these semantics that you would essentially set in stone > here are the semantics we want? (ignoring weights) > Right, but you're requesting this configuration. If you didn't set F_NUMA_BALANCING then you get the existing semantics. In the existing semantics, if we're INTERLEAVE and WEIGHTED_INTERLEAVE we just always say "no tiering for you". But as an opt-in option? I don't quite see the argument for saying interleaved regions (or tasks) to be opted-out if the user asks for it - that just seems like an arbitrary limitation. ~Gregory