Re: [Xen-devel] Difference between alloc_domheap_pages vs. alloc_xenheap_pages?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-06-26 at 15:41 -0700, Xinxin Jin wrote:


> I noticed the only difference between the two is to add PGC_xen_heap
> flag in allocated xenheap pages. So does it matter to exchange these
> two functions when allocating a heap page?

xenheap pages are always mapped, domheap pages are only mapped on demand
with (un)map_domain_page. The big clue is that alloc_xenheap_pages
returns a void* while alloc_domheap_pages returns a struct page_info*.

On some architectures with a large virtual address space (i.e. 64-bit
ones) the two can be combined and the distinction becomes a bit moot,
but it remains for the benefit of common code and also because even on
64-bit architectures when you have large amounts of RAM you may still
end up with RAM which is not permanently mapped -- e.g. on x86_64 if you
have >5TB of RAM then you end up with a split again.

Ian.



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