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

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Message-ID: <56DD96F4.1060805@suse.cz>
Date:	Mon, 7 Mar 2016 15:57:56 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>, Nikolay Borisov <kernel@...p.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: remove __GFP_NOFAIL is deprecated comment

On 02/25/2016 02:48 PM, Michal Hocko wrote:
> On Thu 25-02-16 13:36:11, Nikolay Borisov wrote:
> -		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((gfp_flags & __GFP_NOFAIL) && (order > 1));
>   		spin_lock_irqsave(&zone->lock, flags);
>
>   		page = NULL;
>

Hmm, even the reduced text (and the WARN_ON in the first place) sounds 
IMHO discouraging enough to make people think that opencoding a loop 
around such allocations is a good workaround. Yeah, we have a 
better/more thorough explanation around the __GFP_NOFAIL definition, but 
the WARN_ON will point people here.