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SubjectRe: [PATCH 2/3] include/linux/gfp.h: use unsigned int in gfp_zone
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?

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