Faults on the huge zero page are pointless and there is a BUG_ON to catch them during fault time. This patch reintroduces a check that avoids marking the zero page PAGE_NONE. Signed-off-by: Mel Gorman <mgorman@xxxxxxx> --- include/linux/huge_mm.h | 3 ++- mm/huge_memory.c | 13 ++++++++++++- mm/memory.c | 1 - mm/mprotect.c | 15 ++++++++++++++- 4 files changed, 28 insertions(+), 4 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 554bbe3..ad9051b 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -31,7 +31,8 @@ extern int move_huge_pmd(struct vm_area_struct *vma, unsigned long new_addr, unsigned long old_end, pmd_t *old_pmd, pmd_t *new_pmd); extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long addr, pgprot_t newprot); + unsigned long addr, pgprot_t newprot, + int prot_numa); enum transparent_hugepage_flag { TRANSPARENT_HUGEPAGE_FLAG, diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 668f1a3..3013eb8 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1502,7 +1502,7 @@ out: * - HPAGE_PMD_NR is protections changed and TLB flush necessary */ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long addr, pgprot_t newprot) + unsigned long addr, pgprot_t newprot, int prot_numa) { struct mm_struct *mm = vma->vm_mm; spinlock_t *ptl; @@ -1510,6 +1510,17 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) { pmd_t entry; + + /* + * Avoid trapping faults against the zero page. The read-only + * data is likely to be read-cached on the local CPU and + * local/remote hits to the zero page are not interesting. + */ + if (prot_numa && is_huge_zero_pmd(*pmd)) { + spin_unlock(ptl); + return 0; + } + ret = 1; entry = pmdp_get_and_clear(mm, addr, pmd); entry = pmd_modify(entry, newprot); diff --git a/mm/memory.c b/mm/memory.c index 900127b..a725c08 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3142,7 +3142,6 @@ static int do_numa_page(struct mm_struct *mm, struct vm_area_struct *vma, pte_unmap_unlock(ptep, ptl); return 0; } - BUG_ON(is_zero_pfn(page_to_pfn(page))); /* * Avoid grouping on DSO/COW pages in specific and RO pages diff --git a/mm/mprotect.c b/mm/mprotect.c index dc65c0f..33dfafb 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -75,6 +75,19 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, oldpte = *pte; if (pte_present(oldpte)) { pte_t ptent; + + /* + * Avoid trapping faults against the zero or KSM + * pages. See similar comment in change_huge_pmd. + */ + if (prot_numa) { + struct page *page; + + page = vm_normal_page(vma, addr, oldpte); + if (!page || PageKsm(page)) + continue; + } + ptent = ptep_modify_prot_start(mm, addr, pte); ptent = pte_modify(ptent, newprot); @@ -141,7 +154,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, split_huge_page_pmd(vma, addr, pmd); else { int nr_ptes = change_huge_pmd(vma, pmd, addr, - newprot); + newprot, prot_numa); if (nr_ptes) { if (nr_ptes == HPAGE_PMD_NR) { -- 2.1.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>