/*
  * remove user pages in a given range.
  */
 void zap_page_range(struct mm_struct *mm, unsigned long address, unsigned long size)
 {
         mmu_gather_t *tlb;
         pgd_t * dir;
         unsigned long start = address, end = address + size;
         int freed = 0;

         dir = pgd_offset(mm, address);

         /*
          * This is a long-lived spinlock. That's fine.
          * There's no contention, because the page table
          * lock only protects against kswapd anyway, and
          * even if kswapd happened to be looking at this
          * process we _want_ it to get stuck.
          */
         if (address >= end)
                 BUG();
         spin_lock(&mm->page_table_lock);
         flush_cache_range(mm, address, end);
         tlb = tlb_gather_mmu(mm);

         do {
                 freed += zap_pmd_range(tlb, dir, address, end - address);
                 address = (address + PGDIR_SIZE) & PGDIR_MASK;
                 dir++;
         } while (address && (address < end));

         /* this will flush any remaining tlb entries */
         tlb_finish_mmu(tlb, start, end);

         /*
          * Update rss for the mm_struct (not necessarily current->mm)
          * Notice that rss is an unsigned long.
          */
         if (mm->rss > freed)
                 mm->rss -= freed;
         else
                 mm->rss = 0;
         spin_unlock(&mm->page_table_lock);
}