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    Subject[PATCH V2 1/2] mm/thp: Use new functions to clear pmd on splitting and collapse
    Date
    Some arch may require an explicit IPI before a THP PMD split or
    collapse. This enable us to use local_irq_disable to prevent
    a parallel THP PMD split or collapse.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    include/asm-generic/pgtable.h | 32 ++++++++++++++++++++++++++++++++
    mm/huge_memory.c | 9 +++++----
    2 files changed, 37 insertions(+), 4 deletions(-)

    diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
    index fe617b7e4be6..e95c697bef25 100644
    --- a/include/asm-generic/pgtable.h
    +++ b/include/asm-generic/pgtable.h
    @@ -184,6 +184,38 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
    #endif

    +#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
    +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
    +#define pmdp_splitting_flush_notify pmdp_clear_flush_notify
    +#else
    +static inline void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
    + unsigned long address,
    + pmd_t *pmdp)
    +{
    + BUILD_BUG();
    +}
    +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
    +#endif
    +
    +#ifndef __HAVE_ARCH_PMDP_COLLAPSE_FLUSH
    +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
    +static inline pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
    + unsigned long address,
    + pmd_t *pmdp)
    +{
    + return pmdp_clear_flush(vma, address, pmdp);
    +}
    +#else
    +static inline pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
    + unsigned long address,
    + pmd_t *pmdp)
    +{
    + BUILD_BUG();
    + return __pmd(0);
    +}
    +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
    +#endif
    +
    #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
    extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
    pgtable_t pgtable);
    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index cce4604c192f..30c1b46fcf6d 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -2187,7 +2187,7 @@ static void collapse_huge_page(struct mm_struct *mm,
    * huge and small TLB entries for the same virtual address
    * to avoid the risk of CPU bugs in that area.
    */
    - _pmd = pmdp_clear_flush(vma, address, pmd);
    + _pmd = pmdp_collapse_flush(vma, address, pmd);
    spin_unlock(pmd_ptl);
    mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);

    @@ -2606,9 +2606,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,

    write = pmd_write(*pmd);
    young = pmd_young(*pmd);
    -
    - /* leave pmd empty until pte is filled */
    - pmdp_clear_flush_notify(vma, haddr, pmd);
    + /*
    + * leave pmd empty until pte is filled.
    + */
    + pmdp_splitting_flush_notify(vma, haddr, pmd);

    pgtable = pgtable_trans_huge_withdraw(mm, pmd);
    pmd_populate(mm, &_pmd, pgtable);
    --
    2.1.4


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