linux-kernel - Re: [RFC PATCH 1/3] mm/thp: Use pmdp_splitting_flush

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Date:	Thu, 30 Apr 2015 16:30:35 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	akpm@...ux-foundation.org, paulus@...ba.org,
	benh@...nel.crashing.org, kirill.shutemov@...ux.intel.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] mm/thp: Use pmdp_splitting_flush_notify to clear
 pmd on splitting

On Thu, Apr 30, 2015 at 01:55:39PM +0530, Aneesh Kumar K.V wrote:
> Some arch may require an explicit IPI before a THP PMD split. This
> ensures that a local_irq_disable can prevent a parallel THP PMD split.
> So use new function which arch can override
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  include/asm-generic/pgtable.h |  5 +++++
>  mm/huge_memory.c              |  7 ++++---
>  mm/pgtable-generic.c          | 11 +++++++++++
>  3 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index fe617b7e4be6..d091a666f5b1 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -184,6 +184,11 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  #endif
>  
> +#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
> +extern void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
> +					unsigned long address, pmd_t *pmdp);
> +#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..81e9578bf43a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -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);
> diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
> index 2fe699cedd4d..0fc1f5a06979 100644
> --- a/mm/pgtable-generic.c
> +++ b/mm/pgtable-generic.c
> @@ -7,6 +7,7 @@
>   */
>  
>  #include <linux/pagemap.h>
> +#include <linux/mmu_notifier.h>
>  #include <asm/tlb.h>
>  #include <asm-generic/pgtable.h>
>  
> @@ -184,3 +185,13 @@ void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
>  }
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  #endif
> +
> +#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
> +				 unsigned long address, pmd_t *pmdp)
> +{
> +	pmdp_clear_flush_notify(vma, address, pmdp);
> +}
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> +#endif

I think it worth inlining. Let's put it to <asm-generic/pgtable.h>

It probably worth combining with collapse counterpart in the same patch.

-- 
 Kirill A. Shutemov
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