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Thu, 29 Oct 2026 00:12:16 -0700 (PDT) Received: from localhost.localdomain ([101.44.96.6]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae6f01e8a5sm1180018a91.0.2026.10.29.00.12.11 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 29 Oct 2026 00:12:16 -0700 (PDT) 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 15:12:06 +0800 Message-Id: <20261029071206.19059-1-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-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 350EE140004 X-Stat-Signature: j9h5rnw9r7ibwigezk6kag4wajxs1455 X-Rspam-User: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_ADSP_CUSTOM_MED, DKIM_INVALID,DKIM_SIGNED,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1793257938-169919 X-HE-Meta: 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 uZukw7ep qpg2mt6KwlY2Pvs/pnaclaSk/joQEW7QbMfCAiQfbG4GqLtr/t1pDjin+5zawDf3EFjI8243safgUvauG2W/1B2YFDTD5otj6xkQDmlikApsgNraxl/BJnWtlMvUwk9tcLRAPtWiFRzh0JvJGi9ndbYOFB2YtrPQPPVuIypQ/kxcH2LNWj1iIMoNhg4IbJUgb2XFM+Ylf4TwWXE5oJpggJ/pFProdAltH9UGp6VHiaqNiZxQHcWgNJyScaYIC83m9bLzRTDxFJ/qjYWwk2mjfOyf/PBU1vj3ZrbpR2uuPOBU2RYzqf2hwjLV48E4xNFNEgjMv364GhyBmgVUre8xcxa+a4p8VDh4fAoPZXvc/mx7LWoHD/c6zmFn/udw2uMI9J+hU28pUrtlUlriClkugrZ2A9YYBA2MOFQC6+NJUK6m+R/8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 I forgot to mention the tool execution case in my last mail. Those microVMs start, run a small task, and exit. DAX is there to save memory, but the vmemmap is allocated for the whole image. A 2 GiB image pays 32 MiB of vmemmap even if a microVM only reads a few MB, so for those microVMs the DAX setup can use more memory than the same image on virtio-blk. That is also a case this series fixes for us.