On Fri, 2 Jun 2006, Adam Litke wrote:

On powerpc, each segment can contain pages of only one size.  When a
hugetlb mapping is requested, a segment is located and marked for use
with huge pages.  This is a uni-directional operation -- hugetlb
segments are never marked for use again with normal pages.  For long
running processes which make use of a combination of normal and hugetlb
mappings, this behavior can unduly constrain the virtual address space.

The following patch introduces a architecture-specific vm_ops.close()
hook.  For all architectures besides powerpc, this is a no-op.  On
powerpc, the low and high segments are scanned to locate empty hugetlb
segments which can be made available for normal mappings.  Comments?

Wouldn't hugetlb_free_pgd_range be a better place to do that kind of
thing, all within arch/powerpc, no need for arch_hugetlb_close_vma etc?

Hugh