Re: [PATCH 2/2] mm: add the "struct mm_struct *mm" local into

[Hugh Dickins]

On Tue, 29 Sep 2015, Oleg Nesterov wrote:

> Cosmetic, but expand_upwards() and expand_downwards() overuse
> vma->vm_mm, a local variable makes sense imho.
> 
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>

> ---
>  mm/mmap.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 4efdc37..7edf9ed 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2148,6 +2148,7 @@ static int acct_stack_growth(struct vm_area_struct *vma, unsigned long size, uns
>   */
>  int expand_upwards(struct vm_area_struct *vma, unsigned long address)
>  {
> +	struct mm_struct *mm = vma->vm_mm;
>  	int error;
>  
>  	if (!(vma->vm_flags & VM_GROWSUP))
> @@ -2197,10 +2198,10 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
>  				 * So, we reuse mm->page_table_lock to guard
>  				 * against concurrent vma expansions.
>  				 */
> -				spin_lock(&vma->vm_mm->page_table_lock);
> +				spin_lock(&mm->page_table_lock);
>  				if (vma->vm_flags & VM_LOCKED)
> -					vma->vm_mm->locked_vm += grow;
> -				vm_stat_account(vma->vm_mm, vma->vm_flags,
> +					mm->locked_vm += grow;
> +				vm_stat_account(mm, vma->vm_flags,
>  						vma->vm_file, grow);
>  				anon_vma_interval_tree_pre_update_vma(vma);
>  				vma->vm_end = address;
> @@ -2208,8 +2209,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
>  				if (vma->vm_next)
>  					vma_gap_update(vma->vm_next);
>  				else
> -					vma->vm_mm->highest_vm_end = address;
> -				spin_unlock(&vma->vm_mm->page_table_lock);
> +					mm->highest_vm_end = address;
> +				spin_unlock(&mm->page_table_lock);
>  
>  				perf_event_mmap(vma);
>  			}
> @@ -2217,7 +2218,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
>  	}
>  	vma_unlock_anon_vma(vma);
>  	khugepaged_enter_vma_merge(vma, vma->vm_flags);
> -	validate_mm(vma->vm_mm);
> +	validate_mm(mm);
>  	return error;
>  }
>  #endif /* CONFIG_STACK_GROWSUP || CONFIG_IA64 */
> @@ -2228,6 +2229,7 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
>  int expand_downwards(struct vm_area_struct *vma,
>  				   unsigned long address)
>  {
> +	struct mm_struct *mm = vma->vm_mm;
>  	int error;
>  
>  	/*
> @@ -2272,17 +2274,17 @@ int expand_downwards(struct vm_area_struct *vma,
>  				 * So, we reuse mm->page_table_lock to guard
>  				 * against concurrent vma expansions.
>  				 */
> -				spin_lock(&vma->vm_mm->page_table_lock);
> +				spin_lock(&mm->page_table_lock);
>  				if (vma->vm_flags & VM_LOCKED)
> -					vma->vm_mm->locked_vm += grow;
> -				vm_stat_account(vma->vm_mm, vma->vm_flags,
> +					mm->locked_vm += grow;
> +				vm_stat_account(mm, vma->vm_flags,
>  						vma->vm_file, grow);
>  				anon_vma_interval_tree_pre_update_vma(vma);
>  				vma->vm_start = address;
>  				vma->vm_pgoff -= grow;
>  				anon_vma_interval_tree_post_update_vma(vma);
>  				vma_gap_update(vma);
> -				spin_unlock(&vma->vm_mm->page_table_lock);
> +				spin_unlock(&mm->page_table_lock);
>  
>  				perf_event_mmap(vma);
>  			}
> @@ -2290,7 +2292,7 @@ int expand_downwards(struct vm_area_struct *vma,
>  	}
>  	vma_unlock_anon_vma(vma);
>  	khugepaged_enter_vma_merge(vma, vma->vm_flags);
> -	validate_mm(vma->vm_mm);
> +	validate_mm(mm);
>  	return error;
>  }
>  
> -- 
> 2.4.3
> 
> 
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