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Sat, 07 Feb 2026 08:22:22 -0800 (PST) MIME-Version: 1.0 References: <2vxz1pixvk4m.fsf@kernel.org> In-Reply-To: <2vxz1pixvk4m.fsf@kernel.org> From: Pasha Tatashin Date: Sat, 7 Feb 2026 11:21:45 -0500 X-Gm-Features: AZwV_Qht3zZbep386bW-1KaiZcZERZVy19RJjY4UcBBooi6ZQsXGP2uthzMhXJg Message-ID: Subject: Re: [LSF/MM/BPF TOPIC] HugeTLB file preservation across live update To: Pratyush Yadav Cc: linux-mm@kvack.org, lsf-pc@lists.linux-foundation.org, Mike Rapoport , David Rientjes , Muchun Song , Oscar Salvador , David Hildenbrand , Jason Gunthorpe , Alexander Graf , David Matlack Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Queue-Id: C84D1C000D X-Rspamd-Server: rspam07 X-Stat-Signature: d6hgipwxf9qfjg3migk5wif6abn89xky X-HE-Tag: 1770481343-772765 X-HE-Meta: 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 MuzyxT6l 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 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: On Fri, Feb 6, 2026 at 12:48=E2=80=AFPM Pratyush Yadav wrote: > > Hi all, > > I would like to propose the topic of HugeTLB file preservation across +1 > live update for discussion at the upcoming LSF/MM/BPF summit. > > Background > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > 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 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > 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 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > 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. Thank you Pratyush for proposing this topic. A few more thoughts: While the discussion should be about memfd+hugetlb support, the long term goal is to make this work as an enabler for guestmemfd+hugetlb preservation support. Pasha > > Key attendees > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > Live update: > - Alexander Graf > - David Matlack > - Jason Gunthorpe > - Mike Rapoport > - Pasha Tatashin > > HugeTLB: > - David Hildenbrand > - Muchun Song > - Oscar Salvador > > References > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > [0] https://lore.kernel.org/linux-mm/20251125165850.3389713-1-pasha.tatas= hin@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/tr= ee/mm/memfd_luo.c > [4] https://lore.kernel.org/linux-mm/20251206230222.853493-1-pratyush@ker= nel.org/T/#u > [5] https://lpc.events/event/19/contributions/2044/ > > -- > Regards, > Pratyush Yadav