> Also, the question of a hard separation between > persistent memory and ephemeral memory, compared to allowing > arbitrary pages to > be persisted. Pkernfs does it via a hard separation defined at boot > time, other > approaches could make the carving out of persistent pages dynamic. Speaking from experience here - in Azure (Boost) we have been using hard-carved out memory areas (DAX devices with ranges configured via DTB) for persisting state across kexec for ~5 years or so. In a nutshell: don't, it's a mistake. It's a constant and consistence source of problems, headaches, issues and workarounds piled upon workarounds, held together with duct tape and prayers. It's just not flexible enough for any modern system. For example, unless _all_ the machines are ridicolously overprovisioned in terms of memory capacity (and guaranteed to remain so, forever), you end up wasting enormous amounts of memory. In Azure we are very much interested in a nice, well-abstracted, first- class replacement for that setup that allows persisting data across kexec, and in systemd userspace we'd very much want to use it as well, but it really, really needs to be dynamic, and avoid the pitfall of hard-configured carved out chunk. -- Kind regards, Luca Boccassi
