>On Fri, Mar 31, 2023 at 08:37:15PM +0900, Kyungsan Kim wrote: >> >> We resolved the issue using ZONE_EXMEM by allowing seletively choice of the two usecases. >> > >> >This sounds dangerously confused. Do you want the EXMEM to be removable >> >or not? If you do, then allocations from it have to be movable. If >> >you don't, why go to all this trouble? >> >> I'm sorry to make you confused. We will try more to clearly explain our thought. >> We think the CXL DRAM device should be removable along with HW pluggable nature. >> For MM point of view, we think a page of CXL DRAM can be both movable and unmovable. >> An user or kernel context should be able to determine it. Thus, we think dedication on the ZONE_NORMAL or the ZONE_MOVABLE is not enough. > >No, this is not the right approach. If CXL is to be hot-pluggable, >then all CXL allocations must be movable. If even one allocation on a >device is not movable, then the device cannot be removed. ZONE_EXMEM >feels like a solution in search of a problem We know the situation. When a CXL DRAM channel is located under ZONE_NORMAL, a random allocation of a kernel object by calling kmalloc() siblings makes the entire CXL DRAM unremovable. Also, not all kernel objects can be allocated from ZONE_MOVABLE. ZONE_EXMEM does not confine a movability attribute(movable or unmovable), rather it allows a calling context can decide it. In that aspect, it is the same with ZONE_NORMAL but ZONE_EXMEM works for extended memory device. It does not mean ZONE_EXMEM support both movability and kernel object allocation at the same time. In case multiple CXL DRAM channels are connected, we think a memory consumer possibly dedicate a channel for movable or unmovable purpose.
