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Wed, 28 Oct 2026 23:45:20 -0700 (PDT) Received: from localhost.localdomain ([101.44.96.6]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae6e8401casm2729502a91.11.2026.10.28.23.45.15 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 28 Oct 2026 23:45:20 -0700 (PDT) Sender: Yilei Zheng From: Yilei Zheng To: Muchun Song Cc: Muchun Song , Andrew Morton , Dan Williams , David Hildenbrand , Oscar Salvador , Pankaj Gupta , linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-cxl@vger.kernel.org, Vishal Verma , Dave Jiang , Alison Schofield , Mike Rapoport , Ira Weiny , Jan Kara , Matthew Wilcox , Lorenzo Stoakes , Vlastimil Babka , Michal Hocko , Qi Zheng Subject: Re: [PATCH 3/4] mm: add shared read-only vmemmap support for FS-DAX Date: Thu, 29 Oct 2026 14:45:10 +0800 Message-Id: <20261029064510.17667-1-trilith.zheng@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <2E5C10CF-F3E0-4694-965C-B0E432A1A962@linux.dev> References: <20260903122128.12264-1-songmuchun@bytedance.com> <20260903122128.12264-4-songmuchun@bytedance.com> <20261027065723.66564-1-trilith.zheng@gmail.com> <4c9741cf-ac62-41d4-9c7a-7d5ceea4a8e1@linux.dev> <20261029030511.12004-1-trilith.zheng@gmail.com> <2E5C10CF-F3E0-4694-965C-B0E432A1A962@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > What's the size of the roots image? And I just want to know how much > memory this series could save in your workload. In our setup, the rootfs is an EROFS image exported from the OCI container image, so the pmem device size follows the image size. Most of our workloads are simple today, with images around 1 to 2 GiB, which means 16 to 32 MiB of vmemmap overhead per guest. And we expect the average image size to reach about 5 GiB as we add heavier desktop and agentic RL environments. That would save roughly 80 MiB per guest. At our target density of about 200 sandboxes per node, this adds up to around 16 GiB of guest RAM saved per node. Memory is what caps density here, so this saving helps a lot.