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Commit 7031ae2a authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Greg Kroah-Hartman
Browse files

mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() 



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: 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>
[Salvatore Bonaccorso: backport for 4.9:
 - 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: default avatarBen Hutchings <ben@decadent.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 29bd7003

mm/huge_memory.c

+7 −12
Original line number Diff line number Diff line
@@ -745,20 +745,15 @@ int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, 
EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);



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);

}
@@ -787,7 +782,7 @@ 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
@@ -1158,7 +1153,7 @@ 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