linux-kernel - Re: [PATCH] mm: remove __GFP_NOFAIL is deprecated comment

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Message-ID: <56CEE72B.5040009@kyup.com>
Date:	Thu, 25 Feb 2016 13:36:11 +0200
From:	Nikolay Borisov <kernel@...p.com>
To:	Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm: remove __GFP_NOFAIL is deprecated comment



On 02/25/2016 12:43 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> 647757197cd3 ("mm: clarify __GFP_NOFAIL deprecation status") was
> incomplete and didn't remove the comment about __GFP_NOFAIL being
> deprecated in buffered_rmqueue. Let's get rid of this leftover
> but keep the WARN_ON_ONCE for order > 1 because we should really
> discourage from using __GFP_NOFAIL with higher order allocations
> because those are just too subtle.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
> Hi,
> this popped out when discussing another patch http://lkml.kernel.org/r/56CEC568.6080809@kyup.com
> so I think it is worth removing the comment.
> 
>  mm/page_alloc.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1993894b4219..109d975a7172 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2347,19 +2347,11 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>  		list_del(&page->lru);
>  		pcp->count--;
>  	} else {
> -		if (unlikely(gfp_flags & __GFP_NOFAIL)) {
> -			/*
> -			 * __GFP_NOFAIL is not to be used in new code.
> -			 *
> -			 * All __GFP_NOFAIL callers should be fixed so that they
> -			 * properly detect and handle allocation failures.
> -			 *
> -			 * We most definitely don't want callers attempting to
> -			 * allocate greater than order-1 page units with
> -			 * __GFP_NOFAIL.
> -			 */
> -			WARN_ON_ONCE(order > 1);
> -		}
> +		/*
> +		 * We most definitely don't want callers attempting to
> +		 * allocate greater than order-1 page units with __GFP_NOFAIL.
> +		 */
> +		WARN_ON_ONCE(unlikely(gfp_flags & __GFP_NOFAIL) && (order > 1));

WARN_ON_ONCE already includes an unlikely in its definition:
http://lxr.free-electrons.com/source/include/asm-generic/bug.h#L109

>  		spin_lock_irqsave(&zone->lock, flags);
>  
>  		page = NULL;
> 


Reviewed-by: Nikolay Borisov <kernel@...p.com>