On 03/07/2017 07:57 PM, Matthew Wilcox wrote: > On Tue, Mar 07, 2017 at 10:28:41AM -0800, Matthew Wilcox wrote: >> On Tue, Mar 07, 2017 at 03:10:20PM +0100, Michal Hocko wrote: >>> This patch simply uses __GFP_HIGHMEM implicitly when allocating pages to >>> be mapped to the vmalloc space. Current users which add __GFP_HIGHMEM >>> are simplified and drop the flag. > > btw, I had another idea for GFP_HIGHMEM -- remove it when CONFIG_HIGHMEM > isn't enabled. Saves 26 bytes of .text and 64 bytes of .data on my > laptop's kernel build. What do you think? > > Also, I suspect the layout of bits is suboptimal from an assembly > language perspective. I still mostly care about x86 which doesn't > benefit, so I'm not inclined to do the work, but certainly ARM, PA-RISC, > SPARC and Itanium would all benefit from having frequently-used bits > (ie those used in GFP_KERNEL and GFP_ATOMIC) placed in the low 8 bits. > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index 0fe0b6295ab5..d88cb532d7c8 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -16,7 +16,11 @@ struct vm_area_struct; > > /* Plain integer GFP bitmasks. Do not use this directly. */ > #define ___GFP_DMA 0x01u > +#ifdef CONFIG_HIGHMEM > #define ___GFP_HIGHMEM 0x02u > +#else > +#define ___GFP_HIGHMEM 0x0u
Make sure you don't break the users of __def_gfpflag_names e.g. format_flags(). IIRC zero is a terminator in the table. But the savings don't seem to be worth the trouble. > +#endif > #define ___GFP_DMA32 0x04u > #define ___GFP_MOVABLE 0x08u > #define ___GFP_RECLAIMABLE 0x10u >
