RE: [External] Re: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp_zone

[Huaisheng HS1 Ye <yehs1@lenovo.com>]

> 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