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[34.125.132.248]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a3e3cd2ac2sm115208825ad.90.2026.01.09.15.46.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Jan 2026 15:46:02 -0800 (PST) Date: Fri, 9 Jan 2026 23:45:57 +0000 From: Bing Jiao To: Donet Tom Cc: linux-mm@kvack.org, Andrew Morton , Johannes Weiner , David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Axel Rasmussen , Yuanchu Xie , Wei Xu , linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 1/2] mm/vmscan: balance demotion allocation in alloc_demote_folio() Message-ID: References: <20260107072814.2324646-1-bingjiao@google.com> <20260107072814.2324646-2-bingjiao@google.com> <761533a9-b188-43b1-a24a-1893622ce18c@linux.ibm.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: <761533a9-b188-43b1-a24a-1893622ce18c@linux.ibm.com> On Thu, Jan 08, 2026 at 06:14:02PM +0530, Donet Tom wrote: > > On 1/7/26 12:58 PM, Bing Jiao wrote: > > + /* Randomly select a node from fallback nodes for balanced allocation */ > > + if (allowed_mask) { > > + mtc->nid = node_random(allowed_mask); > > > This random selection can cause allocations to fall back to distant memory > even when the nearer demotion target has sufficient free memory, correct? > Could this also lead to increased promotion latency? Hi Donet, Thanks for your questions. Yes, the random selection could select a distant node and lead to incresed promotion latency. I just realized that the the fallback allocation should not weighted by a single metric, such as node distance, capacity, free space. We need a thoroughly study before changing alloc_demote_folio(). Best, Bing