David Hildenbrand <david@xxxxxxxxxx> writes: > On 16.06.23 00:00, Vishal Verma wrote: >> The dax/kmem driver can potentially hot-add large amounts of memory >> originating from CXL memory expanders, or NVDIMMs, or other 'device >> memories'. There is a chance there isn't enough regular system memory >> available to fit ythe memmap for this new memory. It's therefore >> desirable, if all other conditions are met, for the kmem managed memory >> to place its memmap on the newly added memory itself. >> >> Arrange for this by first allowing for a module parameter override for >> the mhp_supports_memmap_on_memory() test using a flag, adjusting the >> only other caller of this interface in dirvers/acpi/acpi_memoryhotplug.c, >> exporting the symbol so it can be called by kmem.c, and finally changing >> the kmem driver to add_memory() in chunks of memory_block_size_bytes(). > > 1) Why is the override a requirement here? Just let the admin > configure it then then add conditional support for kmem. > > 2) I recall that there are cases where we don't want the memmap to > land on slow memory (which online_movable would achieve). Just imagine > the slow PMEM case. So this might need another configuration knob on > the kmem side. >From my memory, the case where you don't want the memmap to land on *persistent memory* is when the device is small (such as NVDIMM-N), and you want to reserve as much space as possible for the application data. This has nothing to do with the speed of access. -Jeff
