Excerpts from Christoph Hellwig's message of April 14, 2020 11:02 pm:

On Tue, Apr 14, 2020 at 10:13:44PM +1000, Nicholas Piggin wrote:

quoted

Which case? Usually the answer would be because you don't want to use
contiguous physical memory and/or you don't want to use the linear 
mapping.

But with huge pages you do by definition already use large contiguous
areas.  So you want allocations larger than "small" huge pages but not
using gigantic pages using vmalloc?

Yes.

Thanks,
Nick