khugepaged_scan_pmd

static int khugepaged_scan_pmd(struct mm_struct *mm,
                               struct vm_area_struct *vma,
                               unsigned long address,
                               struct page **hpage)
{
        pmd_t *pmd;
        pte_t *pte, *_pte;
        int ret = 0, referenced = 0, none = 0, ro = 0;
        struct page *page;
        unsigned long _address;
        spinlock_t *ptl;
        int node = NUMA_NO_NODE;

        VM_BUG_ON(address & ~HPAGE_PMD_MASK);

        pmd = mm_find_pmd(mm, address);
        if (!pmd)
                goto out;

        memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
        pte = pte_offset_map_lock(mm, pmd, address, &ptl);
        for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
             _pte++, _address += PAGE_SIZE) {
                pte_t pteval = *_pte;
                if (pte_none(pteval)) {
                        if (++none <= khugepaged_max_ptes_none)
                                continue;
                        else
                                goto out_unmap;
                }
                if (!pte_present(pteval))
                        pr_info("unpresent\n");
                        goto out_unmap;
                if (!pte_write(pteval)) {
                        pr_info("read-only\n");
                        if (++ro > khugepaged_max_ptes_none)
                                goto out;
                }
                page = vm_normal_page(vma, _address, pteval);
                if (unlikely(!page))
                        goto out_unmap;
                /*
                 * Record which node the original page is from and save this
                 * information to khugepaged_node_load[].
                 * Khupaged will allocate hugepage from the node has the max
                 * hit record.
                 */
                node = page_to_nid(page);
                if (khugepaged_scan_abort(node))
                        goto out_unmap;
                khugepaged_node_load[node]++;
                VM_BUG_ON_PAGE(PageCompound(page), page);
                if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
                        goto out_unmap;
                /* cannot use mapcount: can't collapse if there's a gup pin */
                if (page_count(page) != 1 + !!PageSwapCache(page))
                        pr_info("page_count error, scan_pmd\n");
                        goto out_unmap;
                if (pte_young(pteval) || PageReferenced(page) ||
                    mmu_notifier_test_young(vma->vm_mm, address)) {
                        pr_info("set 1\n");
                        referenced = 1;
                }
        }
        if (referenced)
                ret = 1;
out_unmap:
        pte_unmap_unlock(pte, ptl);
        if (ret) {
                node = khugepaged_find_target_node();
                /* collapse_huge_page will return with the mmap_sem released */
                collapse_huge_page(mm, address, hpage, vma, node);
        }
out:
        return ret;
}