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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c041eb7f89sm167312585a.110.2025.02.07.01.54.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 Feb 2025 01:54:12 -0800 (PST) Date: Fri, 7 Feb 2025 04:54:10 -0500 From: Gregory Price To: Honggyu Kim Cc: Byungchul Park , kernel_team@skhynix.com, Matthew Wilcox , Hyeonggon Yoo <42.hyeyoo@gmail.com>, lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org 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 06:34:43PM +0900, Honggyu Kim wrote: > On 2/7/2025 5:57 PM, Gregory Price wrote: > > > The default kernel stack size is like 16kb. You'd need like 100,000 > > threads to eat up 1.5GB, and 2048 threads only eats like 32MB. > > > > It's not an interesting amount of memory if you have a 20TB system. > > The amount might be small, but having those data in slow tier can > make performance degradation if it is heavily accessed. > > The number of accesses isn't linearly corelated to the size of the > memory region. > Right, I started by saying: [CXL is] "generally not fit for kernel use" I have the opinion that CXL memory should be defaulted to ZONE_MOVABLE, but I understand the pressure on ZONE_NORMAL means this may not be possible for large capacities. I don't think the solution is to make kernel memory migratable and allow kernel allocations on CXL. There's a reason most kernel allocations are not swappable. > Thanks, > Honggyu