On 7/22/26 4:16 AM, Gregory Price wrote: > On Tue, Jul 21, 2026 at 01:46:01PM +1000, Balbir Singh wrote: >> On 7/21/26 5:33 AM, Gregory Price wrote: >>> >>> Patch Layout >>> ============ >>> The series is broken into two sections: >>> >>> 1) N_MEMORY_PRIVATE Introduction. >>> Introduce the node state. >>> Opt those nodes out of mm/ services. >>> >>> 2) NODE_PRIVATE_CAP_* features >>> A set of mm/ service opt-in flags that augment private >>> nodes to make them more useful (i.e. reclaim = overcommit). >>> >>> NODE_PRIVATE_CAP_LTPIN for private node folio pinning >>> NODE_PRIVATE_CAP_NUMA_BALANCING for private-node NUMA balancing >>> NODE_PRIVATE_CAP_DEMOTION for private-node tiering demotion >>> NODE_PRIVATE_CAP_HOTUNPLUG for opted-in private nodes >>> NODE_PRIVATE_CAP_USER_NUMA for userland numa controls >>> NODE_PRIVATE_CAP_RECLAIM for opted-in private node reclaim >>> >> >> Looks reasonable, I wonder why USER_NUMA/HOTUNPUG is an opt-in? >> > > Ideologically: Private nodes default to fully isolated, why should any > given feature be special? > > Concretely: > > User-numa > > Some devices don't want the user to have control over placement. > I have been working on compressed memory, for example, which only > ever wants to be used as a reclaim-demotion target. > > (The reasoning for this is another thread, i plan on publishing > my research on this this year) >
I don't fully understand, how do we allocate memory on these devices then? Is the driver expected to allocate and map via vm_insert_page()? > Hot-unplug: > > Some devices can't necessarily handle unexpected migration, and > hot-unplug is fundamentally a migration. So the HOTUNPLUG cap > actually means "hot-unplug can execute migrations". > > If the entire device has pre-drained the memory (all memory is free) > then unplug works - it's just not very hot (no migrations) :] > > Maybe a naming issue? > Yes, I would prefer MIGRATION in the name, HOTUNPLUG made me wonder how these devices come online and because it is a device, it can go offline while the system is still online > ~Gregory > Balbir
