Re: [PATCH V2] mm/hugetlb: Avoid soft lockup in set_max_huge_pages()

[Michal Hocko]

On Thu 28-07-16 10:54:02, Jia He wrote:
> In powerpc servers with large memory(32TB), we watched several soft
> lockups for hugepage under stress tests.
> The call trace are as follows:
> 1.
> get_page_from_freelist+0x2d8/0xd50  
> __alloc_pages_nodemask+0x180/0xc20  
> alloc_fresh_huge_page+0xb0/0x190    
> set_max_huge_pages+0x164/0x3b0      
> 
> 2.
> prep_new_huge_page+0x5c/0x100             
> alloc_fresh_huge_page+0xc8/0x190          
> set_max_huge_pages+0x164/0x3b0
> 
> This patch is to fix such soft lockups. It is safe to call cond_resched() 
> there because it is out of spin_lock/unlock section.
> 
> Signed-off-by: Jia He <hejianet@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> 
> ---
> Changes in V2: move cond_resched to a common calling site in set_max_huge_pages
> 
>  mm/hugetlb.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index abc1c5f..9284280 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2216,6 +2216,10 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
>  		 * and reducing the surplus.
>  		 */
>  		spin_unlock(&hugetlb_lock);
> +
> +		/* yield cpu to avoid soft lockup */
> +		cond_resched();
> +
>  		if (hstate_is_gigantic(h))
>  			ret = alloc_fresh_gigantic_page(h, nodes_allowed);
>  		else
> -- 
> 2.5.0
> 
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-- 
Michal Hocko
SUSE Labs