On 20.12.24 16:17, Gregory Price wrote:
On Fri, Dec 20, 2024 at 03:59:58PM +0100, David Hildenbrand wrote:
On 20.12.24 15:45, Gregory Price wrote:
When memory hotplug auto-online is enabled, hotplug memory blocks are
onlined into ZONE_NORMAL by default. The `memhp_default_state` boot
param allows runtime configuration, but no build-time config exists.
+ you can configure it at runtime.
Add a build-time configuration option to change default hotplug zone.
build config:
MEMHP_DEFAULT_TYPE
Selections:
MEMHP_DEFAULT_TYPE_NORMAL => mhp_default_online_type = "online"
MEMHP_DEFAULT_TYPE_MOVABLE => mhp_default_online_type = "online_movable"
When MEMORY_HOTPLUG_DEFAULT_ONLINE is disabled, MEMHP_DEFAULT_TYPE is
set to "offline" to match the current system behavior.
ZONE_NORMAL still remains the default, because for systems with a large
amount of hotplug memory, defaulting it to ZONE_MOVABLE may result in
portions failing to online if sufficient ZONE_NORMAL memory does not
exist to describe it.
What's the use case?
I'm hoping that we can move away from the compile-time option and let user
space, who better knows what to do (especially with different kinds of
memory having different requirements) configure auto-onlining or online
manually (e.g., devdax).
At Meta we have a fairly complex boot process that goes through multiple
kernels before we get to a target kernel to run workloads. Each of those> kernels may have health-checks that want to see the memory is online.
Fancy, I'd love to learn some more about that if there is public
information available somewhere.
The build switch makes this particular feature consistent for us across
all those kernels without having to carry the boot parameter. Eventually
we'd like to move to udev, but it's not feasible for us right now due
to the state of CXL BIOS/Platform/Drivers - driver-management does not
work reliable for all platforms and all devices.
I see.
This gets us where we're going while the rest catch up.
Understood, let me review the patch briefly.
--
Cheers,
David / dhildenb
