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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532eaec185esm43147051cf.3.2026.09.24.07.07.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 07:07:07 -0700 (PDT) Date: Thu, 24 Sep 2026 10:07:05 -0400 From: Gregory Price To: "David Hildenbrand (Arm)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, hannes@cmpxchg.org, shy828301@gmail.com, raghavendra.kt@amd.com, stable@vger.kernel.org Subject: Re: [PATCH v3 2/7] mm: allow shared folios to be promoted to a fast tier Message-ID: References: <20260922182928.2199090-1-gourry@gourry.net> <20260922182928.2199090-3-gourry@gourry.net> Precedence: bulk X-Mailing-List: stable@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 Thu, Sep 24, 2026 at 01:59:15PM +0200, David Hildenbrand (Arm) wrote: > I wonder if a better name would just make the comment above (about memory > tiering) implicit and make more sense of the sysctl_numa_balancing_mode & > NUMA_BALANCING_MEMORY_TIERING) check. > > folio_promotable() > > folio_is_promotable() > > folio_numa_promotable() > > etc. > > because that seems to be what we really test with both things combined. > maybe: folio_numab_promotable() ? > > - if ((vma->vm_flags & VM_EXEC) && folio_maybe_mapped_shared(folio)) > > + if ((vma->vm_flags & VM_EXEC) && > > + folio_maybe_mapped_shared(folio) && > > + (!folio_in_lowtier(folio) || !node_is_toptier(node))) > > return -EACCES; > > > > /* > > Sashiko has some comment about anonymous shared COW folios. I think it has a > point, but didn't look too closely. > its tl;dr: `skipping this check means those folios could end up freely migrating east-west between slow tiers` Which cannot happen (we only migrate to top tier, numab will never migrate *to* a slow tier). basically false-positive ~Gregory