From: Lance Yang As pointed out by Dev, the PTE checks for disjoint conditions in the scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn), and pte_uffd_wp are mutually exclusive. This patch refactors the loops in both __collapse_huge_page_isolate() and hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain instead of separate if blocks. While at it, the redundant pte_present() check before is_zero_pfn() is also removed. Also, this is a preparatory step to make it easier to merge the almost-duplicated scanning logic in these two functions, as suggested by David. Reviewed-by: Wei Yang Reviewed-by: Dev Jain Reviewed-by: Zi Yan Suggested-by: Dev Jain Suggested-by: David Hildenbrand Signed-off-by: Lance Yang --- mm/khugepaged.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f4f57ba69d72..808523f92c7b 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -548,8 +548,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++, addr += PAGE_SIZE) { pte_t pteval = ptep_get(_pte); - if (pte_none(pteval) || (pte_present(pteval) && - is_zero_pfn(pte_pfn(pteval)))) { + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { ++none_or_zero; if (!userfaultfd_armed(vma) && (!cc->is_khugepaged || @@ -560,12 +559,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, count_vm_event(THP_SCAN_EXCEED_NONE_PTE); goto out; } - } - if (!pte_present(pteval)) { + } else if (!pte_present(pteval)) { result = SCAN_PTE_NON_PRESENT; goto out; - } - if (pte_uffd_wp(pteval)) { + } else if (pte_uffd_wp(pteval)) { result = SCAN_PTE_UFFD_WP; goto out; } @@ -1316,8 +1313,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); goto out_unmap; } - } - if (pte_uffd_wp(pteval)) { + } else if (pte_uffd_wp(pteval)) { /* * Don't collapse the page if any of the small * PTEs are armed with uffd write protection. -- 2.49.0