On 21.08.20 20:27, Dan Williams wrote: > On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >> >>>> >>>> 1. On x86-64, e820 indicates "soft-reserved" memory. This memory is not >>>> automatically used in the buddy during boot, but remains untouched >>>> (similar to pmem). But as it involves ACPI as well, it could also be >>>> used on arm64 (-e820), correct? >>> >>> Correct, arm64 also gets the EFI support for enumerating memory this >>> way. However, I would clarify that whether soft-reserved is given to >>> the buddy allocator by default or not is the kernel's policy choice, >>> "buddy-by-default" is ok and is what will happen anyways with older >>> kernels on platforms that enumerate a memory range this way. >> >> Is "soft-reserved" then the right terminology for that? It sounds very >> x86-64/e820 specific. Maybe a compressed for of "performance >> differentiated memory" might be a better fit to expose to user space, no? > > No. The EFI "Specific Purpose" bit is an attribute independent of > e820, it's x86-Linux that entangles those together. There is no > requirement for platform firmware to use that designation even for > drastic performance differentiation between ranges, and conversely > there is no requirement that memory *with* that designation has any > performance difference compared to the default memory pool. So it > really is a reservation policy about a memory range to keep out of the > buddy allocator by default. Okay, still "soft-reserved" is x86-64 specific, no? (AFAIK, "soft-reserved" will be visible in /proc/iomem, or am I confusing stuff?) IOW, it "performance differentiated" is not universally applicable, maybe "specific purpose memory" is ? -- Thanks, David / dhildenb
