[Xen-devel] difference between alloc_vm_area() and balloon_alloc_empty_page_range()

["Lily Huang" <ushuanglily@xxxxxxxxx>]

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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