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SubjectRE: [External] Re: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp_zone
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> On Fri, May 04, 2018 at 03:35:33PM +0200, Michal Hocko wrote:
> > On Fri 04-05-18 14:52:08, Huaisheng Ye wrote:
> > > Suggest using unsigned int instead of int for bit within gfp_zone.
> > > @@ -401,7 +401,7 @@ static inline bool gfpflags_allow_blocking(const
> gfp_t gfp_flags)
> > > static inline enum zone_type gfp_zone(gfp_t flags)
> > > {
> > > enum zone_type z;
> > > - int bit = (__force int) (flags & GFP_ZONEMASK);
> > > + unsigned int bit = (__force unsigned int) (flags & GFP_ZONEMASK);
> > >
> > > z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
> > > ((1 << GFP_ZONES_SHIFT) - 1);
>
> That reminds me. I wanted to talk about getting rid of GFP_ZONE_TABLE.
> Instead, we should encode the zone number in the bottom three bits of
> the gfp mask, while preserving the rules that ZONE_NORMAL gets encoded
> as zero (so GFP_KERNEL | GFP_HIGHMEM continues to work) and also leaving
> __GFP_MOVABLE in bit 3 so that it can continue to be used as a flag.
>
> So I was thinking ...
>
> -#define ___GFP_DMA 0x01u
> -#define ___GFP_HIGHMEM 0x02u
> -#define ___GFP_DMA32 0x04u
> +#define ___GFP_ZONE_MASK 0x07u
>
> #define __GFP_DMA ((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
> #define __GFP_HIGHMEM ((__force gfp_t)OPT_ZONE_HIGHMEM ^
> ZONE_NORMAL)
> #define __GFP_DMA32 ((__force gfp_t)OPT_ZONE_DMA32 ^
> ZONE_NORMAL)
> #define __GFP_MOVABLE ((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL | \
> ___GFP_MOVABLE)
> #define GFP_ZONEMASK ((__force gfp_t)___GFP_ZONE_MASK |
> ___GFP_MOVABLE)
>
> Then we can delete GFP_ZONE_TABLE and GFP_ZONE_BAD.
> gfp_zone simply becomes:
>
> static inline enum zone_type gfp_zone(gfp_t flags)
> {
> return ((__force int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL;
> }
>
> Huaisheng Ye, would you have time to investigate this idea?

OK, it is a great pleasure for me, let me think about how it works in detail.

Sincerely,
Huaisheng, Ye
OS Team | Lenovo

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