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b=ibP2GdyfxqfzpgDDjiQSdyNd5Dus9LZ2QzgfsM5+KBbDn1k/H+xUX08CbdlkRuTkI UM4Dp25y438hTEwXk8mUPC55PILi1MMYXraHzZQRrC2m9T6RJG6qHpM/+RUL2mQvUr 9oprQifE4HVzBVOPNRQ2wmQ41CNrChMuQdKlzf9RquQmqAXu/Z4k6C+d7VkqcYDuBw xjKw9Obr8qb8JCVVlttb69I4fLwtPlxtwtxvWBUTyrGs/+N8jt+ksaz1MTZmOevNnS 1SxVnccfZcXxzpk5fJ2LhwNH1q48swPQCjgEC06SG8H8wZGzYjqhALP5EanDaB1bjm B5xXDl/AJyTmw== From: Pratyush Yadav To: linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org Cc: Mike Rapoport , Pasha Tatashin , David Rientjes , Muchun Song , Oscar Salvador , David Hildenbrand , Jason Gunthorpe , Alexander Graf , David Matlack , Pratyush Yadav Subject: [LSF/MM/BPF TOPIC] HugeTLB file preservation across live update Date: Fri, 06 Feb 2026 18:48:09 +0100 Message-ID: <2vxz1pixvk4m.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Server: rspam12 X-Stat-Signature: eka6xhdch9cw71gura1mmq7su6q8us11 X-Rspamd-Queue-Id: 57F0240018 X-Rspam-User: X-HE-Tag: 1770400094-736461 X-HE-Meta: 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 oIo6H+57 UzeQPfxsq3wBB84kgfWNyrGqId5CeKwE54ysVPXjWtNYAe80Aml89D227tpIDWaC+x1+xfWbJ2dsQpwU5BkHhHgY0Tkc1cYSPxHiZETLjuvactVCLTpJzQ3QrOGuWfeZW20sFaI9hOEpVdwP/ksDJX6m7HU7NGVfURDflc94FnACmkwNg45MbqzzxeP5YVjPI9A4iQxaLRI+UMoIxkM5NekbKbbhP0mJXrqPiQdjHmcuTf+D+KFEnBA5Xv9QnBI5Wyo/7v9AGKPV6Yik9pzubEwV35ult5w9OjV91o6r9nGLgh/S1ZlV44bqR50m//JMV7AH6LFOdO9/1AM5dF96ikcoD4N1WwBbAQO5JT5K/ls7WflQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi all, I would like to propose the topic of HugeTLB file preservation across live update for discussion at the upcoming LSF/MM/BPF summit. Background ========== Support for performing a live update was recently added to the kernel via the Live Update Orchestrator (LUO) subsystem [0]. Live update allows a full kernel update over kexec without terminating running workloads. The main target is live updating the hypervisor without terminating VMs. For more information on live update and LUO, see its kernel documentation [1], the LUO patchset [0], or this LPC 2025 presentation [2]. MEMFD preservation ================== MEMFD is the first file type that added support for live update. This support was merged with the LUO series. The memfd preservation code can be found in mm/memfd_luo.c [3]. MEMFD can use pages backed by shmem or HugeTLB. The live update support in mainline currently only works with shmem-backed MEMFDs. HugeTLB preservation ==================== While shmem support for live update is useful for many things, using it for VM memory (and other memory-intensive workloads) is inefficient. The next step for MEMFD support for live update is to allow preserving HugeTLB-backed files. Note that we do not attempt to preserve the whole HugeTLB file system. We only preserve the memory pages for the files specified by userspace. The HugeTLB file is re-created fresh on the next kernel and the pages are inserted back in. This lets us keep the maintenance footprint smaller. Current status -------------- This support was sent out on the list as an RFC [4] in December 2025, and was also presented at LPC 2025 [5] in the Live Update microconference. While the patchset has got some initial reviews from live update maintainers, it has not yet had any review from HugeTLB developers or maintainers. Goals of the discussion ----------------------- This session will aim to present the topic, explain why it is needed, show how the support works, and most importantly, collect feedback on how to proceed with this work. PS: if any HugeTLB developers or maintainers are reading this, it would be great to have your initial thoughts on the RFC [4] so I can present a more polished patchset at the conference and make the most of the discussion. Key attendees ============= Live update: - Alexander Graf - David Matlack - Jason Gunthorpe - Mike Rapoport - Pasha Tatashin HugeTLB: - David Hildenbrand - Muchun Song - Oscar Salvador References ========== [0] https://lore.kernel.org/linux-mm/20251125165850.3389713-1-pasha.tatashin@soleen.com/T/#u [1] https://docs.kernel.org/core-api/liveupdate.html [2] https://lpc.events/event/19/contributions/2052/ [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/memfd_luo.c [4] https://lore.kernel.org/linux-mm/20251206230222.853493-1-pratyush@kernel.org/T/#u [5] https://lpc.events/event/19/contributions/2044/ -- Regards, Pratyush Yadav