Re: [Xen-devel] [PATCH v5 4/8] mm: introduce a helper to get the memory type of a page

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.08.18 at 12:17, <JBeulich@xxxxxxxx> wrote:
>>>> On 14.08.18 at 15:43, <roger.pau@xxxxxxxxxx> wrote:
>> +            switch ( e820.map[i].type )
>> +            {
>> +            case E820_RAM:
>> +                return RAM_TYPE_CONVENTIONAL;
>> +
>> +            case E820_RESERVED:
>> +                return RAM_TYPE_RESERVED;
>> +
>> +            case E820_UNUSABLE:
>> +                return RAM_TYPE_UNUSABLE;
>> +
>> +            case E820_ACPI:
>> +            case E820_NVS:
>> +                return RAM_TYPE_ACPI;
>> +
>> +            default:
>> +                ASSERT_UNREACHABLE();
>> +                return -1;
>> +            }
>> +    }
>> +
>> +    return -1;
>> +}
> 
> One more case to consider: What about a page part of which is
> a given type, and the other part of which is simply missing from
> the E820 table? I'm uncertain whether in that case it might be a
> good idea in general to report it as having the given type; for the
> specific purpose you want the function for, that would imo be
> quite helpful.

Considering RAM_TYPE_* are bit masks - perhaps the function
should OR together all types found for the requested page, and
let the caller go from there? And to account for my earlier remark,
add a separate RAM_TYPE_UNKNOWN (and never have the function
return -1 or some such; its return type then would better be
unsigned int)?

Jan



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