For most non-anonymous vmas, we do not copy page tables at fork time, but rather lazily populate the tables after fork via faults. The routine vma_needs_copy() is used to make this decision. For VM_HUGETLB vmas, it always returns true. Anyone know/remember why? The code was added more than 15 years ago and my search for why hugetlb vmas were excluded came up empty. I do not see a reason why VM_HUGETLB is in this list. Initial testing did not reveal any problems when I removed the VM_HUGETLB check. FYI - I am looking at the performance of fork and exec (unmap) of processes with very large hugetlb mappings. Skipping the copy at fork time would certainly speed things up. Of course, there could some users who would notice if hugetlb page tables are not copied at fork time. However, this is the behavior for 'normal' mappings. I am inclined to make hugetlb be 'more normal'. -- Mike Kravetz
