Re: [Qemu-devel] memory: Why subpage is introduced?

[Zhi Yong Wu]

On Wed, Dec 21, 2011 at 9:30 PM, Avi Kivity <address@hidden> wrote:
> On 12/21/2011 02:09 PM, Zhi Yong Wu wrote:
>> HI,
>>
>> For memory management, i have several questions as below:
>>
>> 1.) Why is subpage introduced? what is its goal?
>
> A TLB entry spans one page; a subpage is a way of dispatching accesses
> through that tlb entry to various memory regions.
thanks.
>
>> 2.) How to render MemoryRegion into one disjoint flatrange list? That
>> rendering function is a bit difficult to understand. Can anyone simply
>> explain it?
>
> What exactly don't you understand?
1.) e.g. some fields such as offset_in_region, terminates, offset in
MemoryRegion struct. What are separately their meanings?
2.)  render_memory_region(), how does it render one MemoryRegion into
the global view flatview? Can you simply explain this function's
algorithm logic?

>
>>
>> 3.) What are separately the meanings of these flags? such as
>> IO_MEM_RAM, IO_MEM_ROM, IO_MEM_UNASSIGNED, IO_MEM_*, IO_MEM_ROMD, and
>> IO_MEM_SUBPAGE.
>
> RAM = RAM
> ROM = ROM
> UNASSIGNED = nothing handles this range
> ROMD = ROM when read, device (i.e. callbacks) when written
> SUBPAGE = dispatch using the lower address bits to obtain final I/O handler.
thanks.

By the way, if you are available, can you simply explain what is the
relationship among them and how they work together? such as
MemoryRegion, RamBlock, PhysPageDesc, and MemorySlot.

>
> --
> error compiling committee.c: too many arguments to function
>



-- 
Regards,

Zhi Yong Wu