On Fri, Jun 20 2025, Pasha Tatashin wrote: > On Fri, Jun 20, 2025 at 11:28 AM Pratyush Yadav <pratyush@xxxxxxxxxx> wrote: >> On Thu, Jun 19 2025, Pasha Tatashin wrote: [...] >> Outside of hypervisor live update, I have a very clear use case in mind: >> userspace memory handover (on guest side). Say a guest running an >> in-memory cache like memcached with many gigabytes of cache wants to >> reboot. It can just shove the cache into a memfd, give it to LUO, and >> restore it after reboot. Some services that suffer from long reboots are >> looking into using this to reduce downtime. Since it pretty much >> overlaps with the hypervisor work for now, I haven't been talking about >> it as much. >> >> Would you also call this use case "live update"? Does it also fit with >> your vision of where LUO should go? > > Yes, absolutely. The use case you described (preserving a memcached > instance via memfd) is a perfect fit for LUO's vision. > > While the primary use case driving this work is supporting the > preservation of virtual machines on a hypervisor, the framework itself > is not restricted to that scenario. We define "live update" as the > process of updating the kernel from one version to another while > preserving FD-based resources and keeping selected devices > operational. The machine itself can be running storage, database, > networking, containers, or anything else. > > A good parallel is Kernel Live Patching: we don't distinguish what > workload is running on a machine when applying a security patch; we > simply patch the running kernel. In the same way, Live Update is > designed to be workload-agnostic. Whether the system is running an > in-memory database, containers, or VMs, its primary goal is to enable > a full kernel update while preserving the userspace-requested state. Okay, then we are on the same page and I can live with whatever name we go with :-) BTW, I think it would be useful to make this clarification on the LUO docs as well so the intended use case/audience of the API is clear. Currently the doc string in luo_core.c only talks about hypervisors and VMs. -- Regards, Pratyush Yadav
