Il 14/10/2014 14:48, Peter Maydell ha scritto: > Why don't we just do that automatically for all RAM regions > the machine creates? We're already splitting up a contiguous > chunk of RAM to parcel out to RAM regions, that's what the > indirection through ramaddrs is all about.
I can think of one reason to not do this. If we just mmap-ed RAM regions consecutively from a file, the offset in the file should be aligned to the huge page size for "main" RAM region(s). For example, assume gigabyte-sized huge pages; the offset for main RAM must be gigabyte aligned. If the board creates 16MiB of VRAM first, and 2 GiB of main RAM second, you will end up wasting 1024-16 MiB of RAM for VRAM. This same waste happened before the introduction of memory_region_allocate_system_memory, in fact. Of course this could in principle be fixed by having boards create main RAM first, but it would be an even more complicated change. You could come up with a way of reserving ram_addr_t ranges, which would also help hotplug; however, I am not sure if all architectures require the maximum hotplugged memory size to be specified upfront. Ultimately, if a RAM region other than main RAM has benefits from huge pages, the device that creates it probably should have a memdev property. This is not the case for any current device, except perhaps ivshmem. Paolo
