Commit a8f97366 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4fbd8d19

mm/huge_memory.c

+13 −23
Original line number Diff line number Diff line
@@ -842,20 +842,15 @@ EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud); 
#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 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr, 
		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 @@ out: 


#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 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr, 
		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 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, 
	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

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