mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d()
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>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 86fe697..0e7ded9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -842,20 +842,15 @@
#endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
- pmd_t *pmd)
+ pmd_t *pmd, int flags)
{
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);
}
@@ -884,7 +879,7 @@
return NULL;
if (flags & FOLL_TOUCH)
- touch_pmd(vma, addr, pmd);
+ touch_pmd(vma, addr, pmd, flags);
/*
* device mapped pages can only be returned if the
@@ -995,20 +990,15 @@
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
static void touch_pud(struct vm_area_struct *vma, unsigned long addr,
- pud_t *pud)
+ pud_t *pud, int flags)
{
pud_t _pud;
- /*
- * We should set the dirty bit only for FOLL_WRITE but for now
- * the dirty bit in the pud 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 pud to
- * set the young bit, instead of the current set_pud_at.
- */
- _pud = pud_mkyoung(pud_mkdirty(*pud));
+ _pud = pud_mkyoung(*pud);
+ if (flags & FOLL_WRITE)
+ _pud = pud_mkdirty(_pud);
if (pudp_set_access_flags(vma, addr & HPAGE_PUD_MASK,
- pud, _pud, 1))
+ pud, _pud, flags & FOLL_WRITE))
update_mmu_cache_pud(vma, addr, pud);
}
@@ -1031,7 +1021,7 @@
return NULL;
if (flags & FOLL_TOUCH)
- touch_pud(vma, addr, pud);
+ touch_pud(vma, addr, pud, flags);
/*
* device mapped pages can only be returned if the
@@ -1424,7 +1414,7 @@
page = pmd_page(*pmd);
VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
if (flags & FOLL_TOUCH)
- touch_pmd(vma, addr, pmd);
+ touch_pmd(vma, addr, pmd, flags);
if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
/*
* We don't mlock() pte-mapped THPs. This way we can avoid