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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c041dedba2sm166192085a.16.2025.02.07.01.27.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Feb 2025 01:27:37 -0800 (PST) Date: Fri, 7 Feb 2025 04:27:35 -0500 From: Gregory Price To: Byungchul Park Cc: Matthew Wilcox , Hyeonggon Yoo <42.hyeyoo@gmail.com>, lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, Honggyu Kim , kernel_team@skhynix.com Subject: Re: [LSF/MM/BPF TOPIC] Restricting or migrating unmovable kernel allocations from slow tier Message-ID: References: <20250207072024.GA48419@system.software.com> Precedence: bulk X-Mailing-List: linux-cxl@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 Fri, Feb 07, 2025 at 03:57:45AM -0500, Gregory Price wrote: > On Fri, Feb 07, 2025 at 04:20:24PM +0900, Byungchul Park wrote: > > My thoughts here are that memory tiering is the wrong tool for the > problem you are trying to solve. > > Maybe there's a world in which we propose a ZONE_MEMDESC which is > exclusively used for `struct page` for a node. > > At least then you could design CXL capacities *around* that. > Dumb question time Is this maybe not an entirely horrible idea? Even at 16-byte page structs we use 4GB-per-1TB of capacity. Maybe a memory device providing additional capacity SHOULD be made (given the option?) to service its own struct pages - but maintain some control over hot-plug-ability? At least it could tear down all the ZONE_MOVABLE regions and finally release the MEMDESC region when finished. Seems too obvious to have not been proposed already. :shrug: ~Gregory