From: Kirill A. Shutemov Date: Mon, 27 Nov 2017 03:21:25 +0000 (+0300) Subject: mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() X-Git-Tag: v4.1.48~14 X-Git-Url: http://git.hungrycats.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=88c251ffb80e140339cbe74f320d6cba38360ab5;p=linux mm, thp: Do not make page table dirty unconditionally in touch_p[mu]d() [ Upstream commit a8f97366452ed491d13cf1e44241bc0b5740b1f0 ] 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 Cc: Michal Hocko Cc: Hugh Dickins Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index bdd6a8dd5797..4aa31c77cbab 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1235,17 +1235,11 @@ 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)) {