mm, thp: Do not make page table dirty unconditionally in follow_trans_huge_pmd()

Currently, we unconditionally make page table dirty in
follow_trans_huge_pmd(). However, it should be set only in case of
write access.

This is port of upstream commit: a8f97366452ed491d13cf1e44241bc0b5740b1f0

Orabug: 27165913

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>
Signed-off-by: Nitin Gupta <nitin.m.gupta@oracle.com>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b380af5c779b543f0af95f67b0112f08ab415bed..97fade84118bbf4b4d59ac3c9f72713dde59b930 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1335,17 +1335,11 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
        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_POPULATE) && (vma->vm_flags & VM_LOCKED)) {