On Fri, 2 Jun 2006, Adam Litke wrote:

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?

IA64 has similar issues and uses the hook suggested by Hugh. However, we 
have a permanently reserved memory area. I am a bit surprised about the 
need to make address space available for normal mappings. Is this for 32 
bit powerpc support?

void hugetlb_free_pgd_range(struct mmu_gather **tlb,
                        unsigned long addr, unsigned long end,
                        unsigned long floor, unsigned long ceiling)
{
        /*
         * This is called to free hugetlb page tables.
         *
         * The offset of these addresses from the base of the hugetlb
         * region must be scaled down by HPAGE_SIZE/PAGE_SIZE so that
         * the standard free_pgd_range will free the right page tables.
         *
         * If floor and ceiling are also in the hugetlb region, they
         * must likewise be scaled down; but if outside, left unchanged.
         */

        addr = htlbpage_to_page(addr);
        end  = htlbpage_to_page(end);
        if (REGION_NUMBER(floor) == RGN_HPAGE)
                floor = htlbpage_to_page(floor);
        if (REGION_NUMBER(ceiling) == RGN_HPAGE)
                ceiling = htlbpage_to_page(ceiling);

        free_pgd_range(tlb, addr, end, floor, ceiling);
}