Re: [PATCH v2 16/20] mm, hugetlb: move down outside_reserve check

[Aneesh Kumar K.V]

Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> writes:

> Just move down outside_reserve check and don't check
> vma_need_reservation() when outside_resever is true. It is slightly
> optimized implementation.
>
> This makes code more readable.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

I guess this address the comment I had with the previous patch

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>

>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 24de2ca..2372f75 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2499,7 +2499,7 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
>  	struct page *old_page, *new_page;
>  	int outside_reserve = 0;
>  	long chg;
> -	bool use_reserve;
> +	bool use_reserve = false;
>  	unsigned long mmun_start;	/* For mmu_notifiers */
>  	unsigned long mmun_end;		/* For mmu_notifiers */
>
> @@ -2514,6 +2514,11 @@ retry_avoidcopy:
>  		return 0;
>  	}
>
> +	page_cache_get(old_page);
> +
> +	/* Drop page_table_lock as buddy allocator may be called */
> +	spin_unlock(&mm->page_table_lock);
> +
>  	/*
>  	 * If the process that created a MAP_PRIVATE mapping is about to
>  	 * perform a COW due to a shared page count, attempt to satisfy
> @@ -2527,19 +2532,17 @@ retry_avoidcopy:
>  			old_page != pagecache_page)
>  		outside_reserve = 1;
>
> -	page_cache_get(old_page);
> -
> -	/* Drop page_table_lock as buddy allocator may be called */
> -	spin_unlock(&mm->page_table_lock);
> -	chg = vma_needs_reservation(h, vma, address);
> -	if (chg == -ENOMEM) {
> -		page_cache_release(old_page);
> +	if (!outside_reserve) {
> +		chg = vma_needs_reservation(h, vma, address);
> +		if (chg == -ENOMEM) {
> +			page_cache_release(old_page);
>
> -		/* Caller expects lock to be held */
> -		spin_lock(&mm->page_table_lock);
> -		return VM_FAULT_OOM;
> +			/* Caller expects lock to be held */
> +			spin_lock(&mm->page_table_lock);
> +			return VM_FAULT_OOM;
> +		}
> +		use_reserve = !chg;
>  	}
> -	use_reserve = !chg && !outside_reserve;
>
>  	new_page = alloc_huge_page(vma, address, use_reserve);
>
> -- 
> 1.7.9.5

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