RE: hugepage: Fix hugepage logic in free_pgtables()

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Hugh Dickins wrote on Thursday, March 02, 2006 12:27 PM
> But the first part, || instead of && in is_hugepage_only_range, looks
> insufficient: the start and end of the range might each fall in a
> non-huge region, but the range still cross a huge region.
> 
> Ah, does RGN_HPAGE nestle up against the TASK_SIZE roof, so any range
> already tested against TASK_SIZE (as get_unmapped_area has) cannot
> cross RGN_HPAGE?  If so, perhaps it deserves a comment there.  And
> if that is so, and can be relied upon, is_hugepage_only_range need
> only be testing REGION_NUMBER(addr+len-1) - but it does seem fragile.

There are many address range check before we hit get_unmapped area.
ia64 can never have a vma range that crosses region boundary.  David
pointed out earlier that shmat and mremap can still slip through the
crack and he has a patch that fixed it. But yes, this patch is making
that assumption (or relying on checks being done properly beforehand).

- Ken