On Wed, Jan 14, 2026 at 11:55:21AM +0100, David Hildenbrand (Red Hat) wrote: > On 1/14/26 09:51, Gregory Price wrote: > > The dax kmem driver currently onlines memory automatically during > > probe using the system's default online policy but provides no way > > to control or query the memory state at runtime. Users cannot change > > the online type after probe, and there's no atomic way to offline and > > remove memory blocks together. > > > > Add a new 'hotplug' sysfs attribute that allows userspace to control > > and query the memory state. The interface supports the following states: > > > > - "offline": memory is added but not online > > - "online": memory is online as normal system RAM > > - "online_movable": memory is online in ZONE_MOVABLE > > - "unplug": memory is offlined and removed > > > > The initial state after probe uses MMOP_SYSTEM_DEFAULT to preserve > > backwards compatibility - existing systems with auto-online policies > > will continue to work as before. > > > > The state machine enforces valid transitions: > > - From offline: can transition to online, online_movable, or unplug > > - From online/online_movable: can transition to offline or unplug > > - Cannot switch directly between online and online_movable > > Do we have to support these transitions right from the start? > > What are the use cases for adding memory as offline and then onlining it, > and why do we have to support that through this interface? >
After a re-read of the feedback - are you suggested to basically kill the entire offline state of blocks entirely? (e.g. if a driver calls to offline a block, instead fully unplug it) I took a look at the acpi and ppc code you suggested, and I think they also have "expect offline then online" as a default expectation. I can't speak to those users requirements. This would definitely break things like daxctl/ndctl, but maybe that's preferable? I pointed out that patch 8 does this anyway - and I'd like input from ndctl folks as to whether that should end in a NACK. ~Gregory
