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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> 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> X-Rspam-User: X-Stat-Signature: hnbufb3m45sdeur4efgjhd4au4xuwjau X-Rspamd-Queue-Id: E5F3B4000B X-Rspamd-Server: rspam04 X-HE-Tag: 1768002364-729348 X-HE-Meta: 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 4F09agnj UZ0NHXg9sqU3bY+HfHwi6IgWRpetfNnTG1YNCjSJeea3H+QVdqWRnqPJ6q8cdbOHiafJbw5b2KqREOqMgA5M4m9VqRPzDBPgSyq/58scL3Wj4JvdNz0M4XMtkxBVPFNf5SaMaCcMEGbCwthlGR5zpvhMU3xzUcX4T4f5B/5B2L9iuBshYTeN7L9NLRuXUOliXSehtAh30q+Rz09o3D4738vJp5t+psmCJrgAqY35cZX1NymnP5B9Z/+/DXFW3Fn7QYSCZfCYxWRZep3ZQEl96CBLIwO8GQc182kKW3H9ydEDQbixyylX+DclXez0u3Kv2pGf83ZNIGo4LKKOhJ4lqtIZ/WHuyI1T+Myp5P62pTxAshl588ZrgUr5oonvtkEjQ+qxzqmOgEzOW7aqjjMDXY1A5/A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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