On 21.08.20 23:33, David Hildenbrand wrote:
> Am 21.08.2020 um 23:17 schrieb Dan Williams <dan.j.williams(a)intel.com>:
> On Fri, Aug 21, 2020 at 11:30 AM David Hildenbrand <david(a)redhat.com> wrote:
>>> On 21.08.20 20:27, Dan Williams wrote:
>>> On Fri, Aug 21, 2020 at 3:15 AM David Hildenbrand <david(a)redhat.com>
>>>>>> 1. On x86-64, e820 indicates "soft-reserved" memory.
This memory is not
>>>>>> automatically used in the buddy during boot, but remains
>>>>>> (similar to pmem). But as it involves ACPI as well, it could also
>>>>>> 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
>>>>> "buddy-by-default" is ok and is what will happen anyways
>>>>> kernels on platforms that enumerate a memory range this way.
>>>> Is "soft-reserved" then the right terminology for that? It
>>>> x86-64/e820 specific. Maybe a compressed for of "performance
>>>> differentiated memory" might be a better fit to expose to user
>>> 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.
>> "soft-reserved" will be visible in /proc/iomem, or am I confusing
> 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"
> 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!
David / dhildenb