On Fri, Jun 16, 2017 at 04:19:08PM +0300, Kirill A. Shutemov wrote: > On Fri, Jun 16, 2017 at 12:02:50PM +0900, Minchan Kim wrote: > > Hello, > > > > On Thu, Jun 15, 2017 at 05:52:24PM +0300, Kirill A. Shutemov wrote: > > > This patch uses modifed pmdp_invalidate(), that return previous value of > > > pmd, > > > to transfer dirty and accessed bits. > > > > > > Signed-off-by: Kirill A. Shutemov <[email protected]> > > > --- > > > fs/proc/task_mmu.c | 8 ++++---- > > > mm/huge_memory.c | 29 ++++++++++++----------------- > > > 2 files changed, 16 insertions(+), 21 deletions(-) > > > > > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > > > index f0c8b33d99b1..f2fc1ef5bba2 100644 > > > --- a/fs/proc/task_mmu.c > > > +++ b/fs/proc/task_mmu.c > > > @@ -906,13 +906,13 @@ static inline void clear_soft_dirty(struct > > > vm_area_struct *vma, > > > static inline void clear_soft_dirty_pmd(struct vm_area_struct *vma, > > > unsigned long addr, pmd_t *pmdp) > > > { > > > - pmd_t pmd = *pmdp; > > > + pmd_t old, pmd = *pmdp; > > > > > > /* See comment in change_huge_pmd() */ > > > - pmdp_invalidate(vma, addr, pmdp); > > > - if (pmd_dirty(*pmdp)) > > > + old = pmdp_invalidate(vma, addr, pmdp); > > > + if (pmd_dirty(old)) > > > pmd = pmd_mkdirty(pmd); > > > - if (pmd_young(*pmdp)) > > > + if (pmd_young(old)) > > > pmd = pmd_mkyoung(pmd); > > > > > > pmd = pmd_wrprotect(pmd); > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index a84909cf20d3..0433e73531bf 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -1777,17 +1777,7 @@ int change_huge_pmd(struct vm_area_struct *vma, > > > pmd_t *pmd, > > > * pmdp_invalidate() is required to make sure we don't miss > > > * dirty/young flags set by hardware. > > > */ > > > - entry = *pmd; > > > - pmdp_invalidate(vma, addr, pmd); > > > - > > > - /* > > > - * Recover dirty/young flags. It relies on pmdp_invalidate to not > > > - * corrupt them. > > > - */ > > > - if (pmd_dirty(*pmd)) > > > - entry = pmd_mkdirty(entry); > > > - if (pmd_young(*pmd)) > > > - entry = pmd_mkyoung(entry); > > > + entry = pmdp_invalidate(vma, addr, pmd); > > > > > > entry = pmd_modify(entry, newprot); > > > if (preserve_write) > > > @@ -1927,8 +1917,8 @@ static void __split_huge_pmd_locked(struct > > > vm_area_struct *vma, pmd_t *pmd, > > > struct mm_struct *mm = vma->vm_mm; > > > struct page *page; > > > pgtable_t pgtable; > > > - pmd_t _pmd; > > > - bool young, write, dirty, soft_dirty; > > > + pmd_t old, _pmd; > > > + bool young, write, soft_dirty; > > > unsigned long addr; > > > int i; > > > > > > @@ -1965,7 +1955,6 @@ static void __split_huge_pmd_locked(struct > > > vm_area_struct *vma, pmd_t *pmd, > > > page_ref_add(page, HPAGE_PMD_NR - 1); > > > write = pmd_write(*pmd); > > > young = pmd_young(*pmd); > > > - dirty = pmd_dirty(*pmd); > > > soft_dirty = pmd_soft_dirty(*pmd); > > > > > > pmdp_huge_split_prepare(vma, haddr, pmd); > > > @@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct > > > vm_area_struct *vma, pmd_t *pmd, > > > if (soft_dirty) > > > entry = pte_mksoft_dirty(entry); > > > } > > > - if (dirty) > > > - SetPageDirty(page + i); > > > pte = pte_offset_map(&_pmd, addr); > > > BUG_ON(!pte_none(*pte)); > > > set_pte_at(mm, addr, pte, entry); > > > @@ -2045,7 +2032,15 @@ static void __split_huge_pmd_locked(struct > > > vm_area_struct *vma, pmd_t *pmd, > > > * and finally we write the non-huge version of the pmd entry with > > > * pmd_populate. > > > */ > > > - pmdp_invalidate(vma, haddr, pmd); > > > + old = pmdp_invalidate(vma, haddr, pmd); > > > + > > > + /* > > > + * Transfer dirty bit using value returned by pmd_invalidate() to be > > > + * sure we don't race with CPU that can set the bit under us. > > > + */ > > > + if (pmd_dirty(old)) > > > + SetPageDirty(page); > > > + > > > > When I see this, without this patch, MADV_FREE has been broken because > > it can lose dirty bit by early checking. Right? > > If so, isn't it a candidate for -stable? > > Actually, I don't see how MADV_FREE supposed to work: vmscan splits THP on > reclaim and split_huge_page() would set unconditionally, so MADV_FREE > seems no effect on THP.
split_huge_page set PG_dirty to all subpages unconditionally? If it's true, yes, it doesn't break MADV_FREE. However, I didn't spot that piece of code. What I found one is just __split_huge_page_tail which set PG_dirty to subpage if head page is dirty. IOW, if the head page is not dirty, tail page will be clean, too. Could you point out what routine set PG_dirty to all subpages unconditionally? Thanks.
