linux-kernel - Re: [PATCH v2 3/3] slab: use logical instead of bitwise operation in kmalloc

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Message-Id: <20181109105314.c6a6acfa9badba6733c3f72e@linux-foundation.org>
Date:   Fri, 9 Nov 2018 10:53:14 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-kernel@...r.kernel.org,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH v2 3/3] slab: use logical instead of bitwise operation
 in kmalloc_type()

On Fri,  9 Nov 2018 10:35:34 +0100 Johannes Berg <johannes@...solutions.net> wrote:

> The operation here really is more logical than bitwise, even if
> due to the setup the bitwise operation works fine. However, this
> causes a complaint from sparse that the operation doesn't really
> make sense due to the not.
> 
> Use a logical and instead of bitwise.
> 
> In my (somewhat unscientific) test this caused no differences in
> the generated code.
> 
> ...
>
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -329,7 +329,7 @@ static __always_inline enum kmalloc_cache_type kmalloc_type(gfp_t flags)
>  	 * If an allocation is both __GFP_DMA and __GFP_RECLAIMABLE, return
>  	 * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
>  	 */
> -	return type_dma + (is_reclaimable & !is_dma) * KMALLOC_RECLAIM;
> +	return type_dma + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM;
>  }
>  
>  /*

Thanks.  There's presently a bit of head-scratching going on over this.
http://lkml.kernel.org/r/20181105204000.129023-1-bvanassche@acm.org -
please feel free to weigh in ;)