Re: [PATCH v5 06/11] thp: change split_huge_page_pmd() interface

Kirill A. Shutemov
2012-11-15T08:51:17Z

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On Wed, Nov 14, 2012 at 03:22:03PM -0800, David Rientjes wrote:
> On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:
>
> > diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
> > index f734bb2..677a599 100644
> > --- a/Documentation/vm/transhuge.txt
> > +++ b/Documentation/vm/transhuge.txt
> > @@ -276,7 +276,7 @@ unaffected. libhugetlbfs will also work fine as usual.
> > == Graceful fallback ==
> >
> > Code walking pagetables but unware about huge pmds can simply call
> > -split_huge_page_pmd(mm, pmd) where the pmd is the one returned by
> > +split_huge_page_pmd(vma, pmd, addr) where the pmd is the one returned by
> > pmd_offset. It's trivial to make the code transparent hugepage aware
> > by just grepping for "pmd_offset" and adding split_huge_page_pmd where
> > missing after pmd_offset returns the pmd. Thanks to the graceful
> > @@ -299,7 +299,7 @@ diff --git a/mm/mremap.c b/mm/mremap.c
> > return NULL;
> >
> > pmd = pmd_offset(pud, addr);
> > -+ split_huge_page_pmd(mm, pmd);
> > ++ split_huge_page_pmd(vma, pmd, addr);
> > if (pmd_none_or_clear_bad(pmd))
> > return NULL;
> >
> > diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
> > index 5c9687b..1dfe69c 100644
> > --- a/arch/x86/kernel/vm86_32.c
> > +++ b/arch/x86/kernel/vm86_32.c
> > @@ -182,7 +182,7 @@ static void mark_screen_rdonly(struct mm_struct *mm)
> > if (pud_none_or_clear_bad(pud))
> > goto out;
> > pmd = pmd_offset(pud, 0xA0000);
> > - split_huge_page_pmd(mm, pmd);
> > + split_huge_page_pmd_mm(mm, 0xA0000, pmd);
> > if (pmd_none_or_clear_bad(pmd))
> > goto out;
> > pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl);
>
> Why not be consistent and make this split_huge_page_pmd_mm(mm, pmd, addr)?
>
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 90c63f9..291a0d1 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -643,7 +643,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> > spinlock_t *ptl;
> > struct page *page;
> >
> > - split_huge_page_pmd(walk->mm, pmd);
> > + split_huge_page_pmd(vma, addr, pmd);
>
> Ah, it's because the change to the documentation is wrong: the format is
> actually split_huge_page_pmd(vma, addr, pmd).

Thanks, will fix.

> > if (pmd_trans_unstable(pmd))
> > return 0;
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index b31cb7d..856f080 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -91,12 +91,14 @@ extern int handle_pte_fault(struct mm_struct *mm,
> > struct vm_area_struct *vma, unsigned long address,
> > pte_t *pte, pmd_t *pmd, unsigned int flags);
> > extern int split_huge_page(struct page *page);
> > -extern void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd);
> > -#define split_huge_page_pmd(__mm, __pmd) \
> > +extern void __split_huge_page_pmd(struct vm_area_struct *vma,
> > + unsigned long address, pmd_t *pmd);
> > +#define split_huge_page_pmd(__vma, __address, __pmd) \
> > do { \
> > pmd_t *____pmd = (__pmd); \
> > if (unlikely(pmd_trans_huge(*____pmd))) \
> > - __split_huge_page_pmd(__mm, ____pmd); \
> > + __split_huge_page_pmd(__vma, __address, \
> > + ____pmd); \
> > } while (0)
> > #define wait_split_huge_page(__anon_vma, __pmd) \
> > do { \
> > @@ -106,6 +108,8 @@ extern void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd);
> > BUG_ON(pmd_trans_splitting(*____pmd) || \
> > pmd_trans_huge(*____pmd)); \
> > } while (0)
> > +extern void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
> > + pmd_t *pmd);
> > #if HPAGE_PMD_ORDER > MAX_ORDER
> > #error "hugepages can't be allocated by the buddy allocator"
> > #endif
> > @@ -173,10 +177,12 @@ static inline int split_huge_page(struct page *page)
> > {
> > return 0;
> > }
> > -#define split_huge_page_pmd(__mm, __pmd) \
> > +#define split_huge_page_pmd(__vma, __address, __pmd) \
> > do { } while (0)
> > #define wait_split_huge_page(__anon_vma, __pmd) \
> > do { } while (0)
> > +#define split_huge_page_pmd_mm(__mm, __address, __pmd) \
> > + do { } while (0)
> > #define compound_trans_head(page) compound_head(page)
> > static inline int hugepage_madvise(struct vm_area_struct *vma,
> > unsigned long *vm_flags, int advice)
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 05490b3..90e651c 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2509,19 +2509,23 @@ static int khugepaged(void *none)
> > return 0;
> > }
> >
> > -void __split_huge_page_pmd(struct mm_struct *mm, pmd_t *pmd)
> > +void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
> > + pmd_t *pmd)
> > {
> > struct page *page;
> > + unsigned long haddr = address & HPAGE_PMD_MASK;
> >
>
> Just do
>
> struct mm_struct *mm = vma->vm_mm;
>
> here and it makes everything else simpler.

Okay.

> > - spin_lock(&mm->page_table_lock);
> > + BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
> > +
> > + spin_lock(&vma->vm_mm->page_table_lock);
> > if (unlikely(!pmd_trans_huge(*pmd))) {
> > - spin_unlock(&mm->page_table_lock);
> > + spin_unlock(&vma->vm_mm->page_table_lock);
> > return;
> > }
> > page = pmd_page(*pmd);
> > VM_BUG_ON(!page_count(page));
> > get_page(page);
> > - spin_unlock(&mm->page_table_lock);
> > + spin_unlock(&vma->vm_mm->page_table_lock);
> >
> > split_huge_page(page);
> >

--
Kirill A. Shutemov

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