Xen devel - Jul 2006 - difference between alloc_vm_area() and balloon_alloc_empty_page_range()

When I read the blkfront.c and blkback.c, I noticed that in some places (e.g,
map_frontend_page()) it uses alloc_vm_area() to allocate memory for foreign
page mapping.  However, in some other places,
it used balloon_alloc_empty_page_range() to allocate memory for mapping.
What''s the difference between these two functions? Why not just use one
function like alloc_vm_area() or balloon_alloc_empty_page_range()?

More important, I noticed that with alloc_vm_area(), it requires
lock_vm_area() to lock down the vm area. Why do we need this? Why don''t
we
need some locking mechanisms on memory allocated with
balloon_alloc_empty_page_range()?

thanks in advance for your kind help!

lily


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