On Thu, 2022-07-21 at 13:52 +1200, Kai Huang wrote: > Also, if I understand correctly above, your suggestion is we want to prevent any > CMR memory going offline so it won't be hot-removed (assuming we can get CMRs > during boot). This looks contradicts to the requirement of being able to allow > moving memory from core-mm to driver. When we offline the memory, we cannot > know whether the memory will be used by driver, or later hot-removed. Hi Dave, The high level flow of device hot-removal is: acpi_scan_hot_remove() -> acpi_scan_try_to_offline() -> acpi_bus_offline() -> device_offline() -> memory_subsys_offline() -> acpi_bus_trim() -> acpi_memory_device_remove() And memory_subsys_offline() can also be triggered via /sysfs: echo 0 > /sys/devices/system/memory/memory30/online After the memory block is offline, my understanding is kernel can theoretically move it to, i.e. ZONE_DEVICE via memremap_pages(). As you can see memory_subsys_offline() is the entry point of memory device offline (before it the code is generic for all ACPI device), and it cannot distinguish whether the removal is from ACPI event, or from /sysfs, so it seems we are unable to refuse to offline memory in memory_subsys_offline() when it is called from ACPI event. Any comments? -- Thanks, -Kai
