linux-kernel - Re: [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE

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Message-ID: <20180510163023.GB30442@bombadil.infradead.org>
Date:   Thu, 10 May 2018 09:30:23 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Huaisheng Ye <yehs1@...ovo.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org, mhocko@...e.com,
        vbabka@...e.cz, mgorman@...hsingularity.net,
        alexander.levin@...izon.com, colyli@...e.de, chengnt@...ovo.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE_TABLE/BAD

On Fri, May 11, 2018 at 12:10:25AM +0800, Huaisheng Ye wrote:
> -#define __GFP_DMA	((__force gfp_t)___GFP_DMA)
> -#define __GFP_HIGHMEM	((__force gfp_t)___GFP_HIGHMEM)
> -#define __GFP_DMA32	((__force gfp_t)___GFP_DMA32)
> +#define __GFP_DMA	((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
> +#define __GFP_HIGHMEM	((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL)
> +#define __GFP_DMA32	((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL)

No, you've made gfp_zone even more complex than it already is.
If you can't use OPT_ZONE_HIGHMEM here, then this is a waste of time.

>  static inline enum zone_type gfp_zone(gfp_t flags)
>  {
>  	enum zone_type z;
> -	int bit = (__force int) (flags & GFP_ZONEMASK);
> +	z = ((__force unsigned int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL;
> +
> +	if (z > OPT_ZONE_HIGHMEM)
> +		z = OPT_ZONE_HIGHMEM +
> +			!!((__force unsigned int)flags & ___GFP_MOVABLE);
>  
> -	z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
> -					 ((1 << GFP_ZONES_SHIFT) - 1);
> -	VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> +	VM_BUG_ON(z > ZONE_MOVABLE);
>  	return z;
>  }