On 21.08.20 23:33, David Hildenbrand wrote: > > >> Am 21.08.2020 um 23:17 schrieb Dan Williams <dan.j.williams@xxxxxxxxx>: >> >> On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >>> >>>> 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? >> >> There's nothing preventing other EFI archs, or a similar designation >> in another firmware spec, picking up this policy. >> >>> (AFAIK, >>> "soft-reserved" will be visible in /proc/iomem, or am I confusing >>> stuff?) >> >> No, you're correct. >> >>> IOW, it "performance differentiated" is not universally >>> applicable, maybe "specific purpose memory" is ? >> >> Those bikeshed colors don't seem an improvement to me. >> >> "Soft-reserved" actually tells you something about the kernel policy >> for the memory. The criticism of "specific purpose" that led to >> calling it "soft-reserved" in Linux is the fact that "specific" is >> undefined as far as the firmware knows, and "specific" may have >> different applications based on the platform user. "Soft-reserved" >> like "Reserved" tells you that a driver policy might be in play for >> that memory. >> >> Also note that the current color of the bikeshed has already shipped since v5.5: >> >> 262b45ae3ab4 x86/efi: EFI soft reservation to E820 enumeration >> > > I was asking because I was struggling to even understand what „soft-reserved“ is and I could bet most people have no clue what that is supposed to be. > > In contrast „persistent memory“ or „special purpose memory“ in /proc/iomem is something normal (Linux using) human beings can understand. s/normal/most/ , shouldn't be writing emails from my smartphone. Cheers! -- Thanks, David / dhildenb
