On Tue, Nov 14, 2023 at 07:27:35PM +0100, David Hildenbrand wrote: > On 14.11.23 19:02, Sumanth Korikkar wrote: > > Add new memory notifiers to mimic the dynamic ACPI event triggered logic > > for memory hotplug on platforms that do not generate such events. This > > will be used to implement "memmap on memory" feature for s390 in a later > > patch. > > > > Platforms such as x86 can support physical memory hotplug via ACPI. When > > there is physical memory hotplug, ACPI event leads to the memory > > addition with the following callchain: > > acpi_memory_device_add() > > -> acpi_memory_enable_device() > > -> __add_memory() > > > > After this, the hotplugged memory is physically accessible, and altmap > > support prepared, before the "memmap on memory" initialization in > > memory_block_online() is called. > > > > On s390, memory hotplug works in a different way. The available hotplug > > memory has to be defined upfront in the hypervisor, but it is made > > physically accessible only when the user sets it online via sysfs, > > currently in the MEM_GOING_ONLINE notifier. This requires calling > > add_memory() during early memory detection, in order to get the sysfs > > representation, but we cannot use "memmap on memory" altmap support at > > this stage, w/o having it physically accessible. > > > > Since no ACPI or similar events are generated, there is no way to set up > > altmap support, or even make the memory physically accessible at all, > > before the "memmap on memory" initialization in memory_block_online(). > > > > The new MEM_PHYS_ONLINE notifier allows to work around this, by > > providing a hook to make the memory physically accessible, and also call > > __add_pages() with altmap support, early in memory_block_online(). > > Similarly, the MEM_PHYS_OFFLINE notifier allows to make the memory > > inaccessible and call __remove_pages(), at the end of > > memory_block_offline(). > > > > Calling __add/remove_pages() requires mem_hotplug_lock, so move > > mem_hotplug_begin/done() to include the new notifiers. > > > > All architectures ignore unknown memory notifiers, so this patch should > > not introduce any functional changes. > > Sorry to say, no. No hacks please, and this is a hack for memory that has > already been added to the system. > > If you want memory without an altmap to suddenly not have an altmap anymore, > then look into removing and readding that memory, or some way to convert > offline memory. Sorry, I couldnt get the context. Could you please give me more details? Thanks
