Currently khugepaged does not collapse an anonymous region which does not have a single writable pte. This is wasteful since a region mapped with non-writable ptes, for example, non-writable VMAs mapped by the application, won't benefit from THP collapse. An additional consequence of this constraint is that MADV_COLLAPSE does not perform a collapse on a non-writable VMA, and this restriction is nowhere to be found on the manpage - the restriction itself sounds wrong to me since the user knows the protection of the memory it has mapped, so collapsing read-only memory via madvise() should be a choice of the user which shouldn't be overridden by the kernel. Therefore, remove this restriction by not honouring SCAN_PAGE_RO. Acked-by: David Hildenbrand Acked-by: Zi Yan Reviewed-by: Wei Yang Reviewed-by: Kiryl Shutsemau Reviewed-by: Lorenzo Stoakes Reviewed-by: Baolin Wang Signed-off-by: Dev Jain --- mm/khugepaged.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4ec324a4c1fe..a0f1df2a7ae6 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -676,9 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, writable = true; } - if (unlikely(!writable)) { - result = SCAN_PAGE_RO; - } else if (unlikely(cc->is_khugepaged && !referenced)) { + if (unlikely(cc->is_khugepaged && !referenced)) { result = SCAN_LACK_REFERENCED_PAGE; } else { result = SCAN_SUCCEED; @@ -1421,9 +1419,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, mmu_notifier_test_young(vma->vm_mm, _address))) referenced++; } - if (!writable) { - result = SCAN_PAGE_RO; - } else if (cc->is_khugepaged && + if (cc->is_khugepaged && (!referenced || (unmapped && referenced < HPAGE_PMD_NR / 2))) { result = SCAN_LACK_REFERENCED_PAGE; @@ -2830,7 +2826,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, case SCAN_PMD_NULL: case SCAN_PTE_NON_PRESENT: case SCAN_PTE_UFFD_WP: - case SCAN_PAGE_RO: case SCAN_LACK_REFERENCED_PAGE: case SCAN_PAGE_NULL: case SCAN_PAGE_COUNT: -- 2.30.2