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Thu, 29 Oct 2026 07:31:40 +0000 X-Mizu-Trace-ID: bb58316c57a2d4df X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii X-Archived-By: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.12\)) Subject: Re: [PATCH 3/4] mm: add shared read-only vmemmap support for FS-DAX From: Muchun Song In-Reply-To: <20261029071206.19059-1-trilith.zheng@gmail.com> Date: Thu, 29 Oct 2026 15:31:20 +0800 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 Content-Transfer-Encoding: 7bit Message-Id: 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> <20261029071206.19059-1-trilith.zheng@gmail.com> To: Yilei Zheng X-Mailer: Apple Mail (2.3901.100.1.1.12) X-Rspamd-Queue-Id: 1EA9A20009 X-Stat-Signature: cnru3eewn95h3r5h5btbgskek3ybtq4o X-Rspamd-Server: rspam04 X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793259102-426966 X-HE-Meta: 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 htqUnYg9 SrjXAlVO+/pLtieTGRWr/5ReYNc5Hk9iu7fFI4kChzTNxRmNd8bE0GDmY5r1zIU/61kTws6wgGePKj4xl8RlMkzamOK0nqy42Z8xFdbvRJfdP4q98DLIuviWxhZaJaRT0HdDiKyhium/AiAn4wbo9HpCOhVLi9YGTlsY2/3zexGaAtyPrqLP7vQ2qrPk4JFBW0THOw3CaUZQZjW/qlPmclQTMP/+1n4jMLWorUcpUAJeeqLN7pIyKHRtm0uvibPzjYQBXzDWXyt8+UxZwTN3+fLRYE5Ba3ShPbjDPwZdKe0yWS39SbGTYZXhJ2uLIsouvJGWbgVWuHujZSiajZEEy3Bt2O0Lc7wpt7m3Sw7O/T7MnXrE= 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 > On Oct 29, 2026, at 15:12, Yilei Zheng wrote: > > 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. Thanks for sharing. I think in this scenario it also saves boot time. I'm not sure how significant that is, though, since the number of vmemmap pages isn't large enough to be noticeable. Thanks.