Re: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB

H. Peter Anvin
2008-03-05T17:32:26Z

Jeremy Fitzhardinge wrote:
>>
>> I am aware that it would take more work to tell all kernel code that it
>> shouldn't look for BIOS data on this region when running as a domU guest,
>> but it seems that it would be a better solution.
>
> For the moment that's true, but we should be able to release those
> pages. On the other hand, there's been talk of making Xen hand out
> memory in physically contigious 2M chunks, which means trying to unmap
> 300k won't be possible or worthwhile. I suspect real hardware will just
> waste this memory too (it won't remap that 320k of ram to somewhere
> else; it will just be shadowed) - which is nothing compared to chipsets
> which will just throw away 1G to make space for PCI...
>

Not that 384K is all that much to worry about, but you could just map
memory from 2 MB upward, and set the kernel load address to 2 MB (which
is good for performance anyway.)

There has been talk of making the default kernel load address 16 MB, to
keep the DMA zone free.

-hpa