| From a8f97366452ed491d13cf1e44241bc0b5740b1f0 Mon Sep 17 00:00:00 2001 |
| From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> |
| Date: Mon, 27 Nov 2017 06:21:25 +0300 |
| Subject: mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() |
| |
| From: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> |
| |
| commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 upstream. |
| |
| Currently, we unconditionally make page table dirty in touch_pmd(). |
| It may result in false-positive can_follow_write_pmd(). |
| |
| We may avoid the situation, if we would only make the page table entry |
| dirty if caller asks for write access -- FOLL_WRITE. |
| |
| The patch also changes touch_pud() in the same way. |
| |
| Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> |
| Cc: Michal Hocko <mhocko@suse.com> |
| Cc: Hugh Dickins <hughd@google.com> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| [Salvatore Bonaccorso: backport for 3.16: |
| - Adjust context |
| - Drop specific part for PUD-sized transparent hugepages. Support |
| for PUD-sized transparent hugepages was added in v4.11-rc1 |
| ] |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| mm/huge_memory.c | 14 ++++---------- |
| 1 file changed, 4 insertions(+), 10 deletions(-) |
| |
| --- a/mm/huge_memory.c |
| +++ b/mm/huge_memory.c |
| @@ -1304,17 +1304,11 @@ struct page *follow_trans_huge_pmd(struc |
| VM_BUG_ON_PAGE(!PageHead(page), page); |
| if (flags & FOLL_TOUCH) { |
| pmd_t _pmd; |
| - /* |
| - * We should set the dirty bit only for FOLL_WRITE but |
| - * for now the dirty bit in the pmd is meaningless. |
| - * And if the dirty bit will become meaningful and |
| - * we'll only set it with FOLL_WRITE, an atomic |
| - * set_bit will be required on the pmd to set the |
| - * young bit, instead of the current set_pmd_at. |
| - */ |
| - _pmd = pmd_mkyoung(pmd_mkdirty(*pmd)); |
| + _pmd = pmd_mkyoung(*pmd); |
| + if (flags & FOLL_WRITE) |
| + _pmd = pmd_mkdirty(_pmd); |
| if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK, |
| - pmd, _pmd, 1)) |
| + pmd, _pmd, flags & FOLL_WRITE)) |
| update_mmu_cache_pmd(vma, addr, pmd); |
| } |
| if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { |
