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Sat, 28 Mar 2026 18:03:33 -0700 (PDT) Received: from [2a00:79e0:2eb0:8:a947:3e4f:679c:4c03] ([2a00:79e0:2eb0:8:a947:3e4f:679c:4c03]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82ca843d8e5sm3682786b3a.5.2026.03.28.18.03.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 28 Mar 2026 18:03:32 -0700 (PDT) Date: Sat, 28 Mar 2026 18:03:31 -0700 (PDT) From: David Rientjes To: Alexander Graf , "Andersen, Tycho" , Anthony Yznaga , Baolu Lu , David Hildenbrand , David Matlack , James Gowans , Jason Gunthorpe , Mike Rapoport , Pankaj Gupta , Pasha Tatashin , Pratyush Yadav , Praveen Kumar , Vipin Sharma , Vishal Annapurve , "Woodhouse, David" cc: linux-mm@kvack.org, kexec@lists.infradead.org Subject: [Hypervisor Live Update] Notes from March 23, 2026 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: C9B5E1C000F X-Stat-Signature: 4res39wpakmo6k8e7ghum9yfjh86x4ad X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774746215-719389 X-HE-Meta: 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 ucr+jjdQ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi everybody, Here are the notes from the last Hypervisor Live Update call that happened on Monday, March 23. Thanks to everybody who was involved! These notes are intended to bring people up to speed who could not attend the call as well as keep the conversation going in between meetings. ----->o----- Pasha updated on the status of luod and a good conversation with Luca who is interested in integration. Luca had proposed to do it in phases with the first phase being support for systemd logging during shutdown when devices are unmounted. Luod will require preserving the logs and passing them to the next kernel and next systemd. He was also interested in the next LPC discussion on the topic. Pasha also updated that there are new tabs added to the design doc[1], this will be expanded for systemd and its communication channel. The plan is to have 100% integration into systemd. Jork Loeser noted in his discussions that systemd was very adamant about supporting fd store and asked to what extent we need multiple sessions per service. This would include the LUO client interface as well. Pasha noted there were discussions on how many files per session we can save, for example, and added a limits tab to the design doc. Right now, it's about 128 files and a thousand sessions. In the future, the file and session count limits should be removed entirely. Jork was asking about whether systemd should expose an interface to the clients where the yget explicitly tied and create multiple sessions, or whether the interface was just fd store. Pasha said the plan was that systemd would expose the sessions interface so clients can create new sessions. Pasha said next steps include getting the design ready and then the first implementation for systemd logging. The latter would be implemented before the next LPC. ----->o----- We chatted about deferred struct page initialization. The patches are not yet ready to be merged so we would follow up next time. Pasha noted that Pratyush and Jork had discussed scalability of memblock reservations. Jork said a couple approaches were discussed one of which is to move the quadratic initialization or setup of the memblock list to be linear. This would allow us to interate over the struct pages as well as the KHO tree to avoid restoring the memblock list. There was also an idea to side-step the memblock entirely and to use the buddy allocator. Pasha asked about the proposed changes to the radix tree: if we move the order then the bit in the bitmap at the leaf levels would not represent the order size but rather represent the page size. So the memory overhead could be much larger. Pasha suggested allowing the scratch areas to grow when needed by finding the biggest hole in the radix tree, this could help to solve some scalability problems. ----->o----- David Matlack updated on VFIO v3 which is pretty much done and is going through final testing for posting this week. v4 should include a roadmap for what comes next. Starting at v4, the series may get split into two: PCI patches are growing so it may make sense to split PCI and VFIO patches. Most of the code is behind config options that should help with merging as well as the new documentation that should also move this along. ----->o----- Samiullah updated on IOMMU persistence: his series is getting reviews upstream. He's preparing for the next verison of the series. There was no update on the hitless replacement, this would be worked on next. There was a comment that we should standardize on naming in the tree between LU shorthand and using liveupdate as a single word. ----->o----- Ackerley updated on the UAPI for guest_memfd HugeTLB enligthenment, he is still working on the conversion support. That work is pushing out into April. ----->o----- Next meeting will be on Monday, April 6 at 8am PDT (UTC-7), everybody is welcome: https://meet.google.com/rjn-dmzu-hgq Topics for the next meeting: - luod design feedback and intersection with systemd; implementation and next steps - KHO optimizations for boot time performance including initialization of memblock list and deferred struct page initialization - HugeTLB preservation support including selftests + debrief discussion from Linux MM Alignment Session - VFIO v3 patch series posting to the list and roadmap for v4 - phase 1 of IOMMU persistence patch series, then phase 2 status and updates - hitless replacement for iommu domains and patches from Intel - guest_memfd HugeTLB enlightenment: conversion support, HugeTLB support without restructuring, and HugeTLB support with restructuring - later: versioning support for luod to negotiate - later: ordering issues when disabling interrupts based on feedback from Nvidia - later: update on PCI preservation series and next steps - later: KHO enlightenment for ASI Please let me know if you'd like to propose additional topics for discussion, thank you! [1] https://tinyurl.com/luoddesign