Re: [PATCH 2/8] Fragmentation Avoidance V17: 002_usemap

[Joel Schopp]

> > > @@ -473,6 +491,15 @@ extern struct pglist_data contig_page_da
> > > #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS
> > > #error Allocator MAX_ORDER exceeds SECTION_SIZE
> > > #endif
> > > +#if ((SECTION_SIZE_BITS - MAX_ORDER) * BITS_PER_RCLM_TYPE) > 64
> > > +#error free_area_usemap is not big enough
> > > +#endif
> >
> > Every time I look at these patches, I see this #if, and I don't remember
> > what that '64' means.  Can it please get a real name?
>
>
> Joel, suggestions?

Oh yeah, blame it on me just because I wrote that bit of code.  How about
#define FREE_AREA_USEMAP_SIZE 64

> > > +/* Usemap initialisation */
> > > +#ifdef CONFIG_SPARSEMEM
> > > +static inline void setup_usemap(struct pglist_data *pgdat,
> > > +				struct zone *zone, unsigned long zonesize) {}
> > > +#endif /* CONFIG_SPARSEMEM */
> > >
> > > struct page;
> > > struct mem_section {
> > > @@ -485,6 +512,7 @@ struct mem_section {
> > > 	 * before using it wrong.
> > > 	 */
> > > 	unsigned long section_mem_map;
> > > +	DECLARE_BITMAP(free_area_usemap,64);
> > > };
> >
> > There's that '64' again!  You need a space after the comma, too.

Ditto.

> > > + * RCLM_SHIFT is the number of bits that a gfp_mask has to be shifted right
> > > + * to have just the __GFP_USER and __GFP_KERNRCLM bits. The static check is
> > > + * made afterwards in case the GFP flags are not updated without updating
> > > + * this number
> > > + */
> > > +#define RCLM_SHIFT 19
> > > +#if (__GFP_USER >> RCLM_SHIFT) != RCLM_USER
> > > +#error __GFP_USER not mapping to RCLM_USER
> > > +#endif
> > > +#if (__GFP_KERNRCLM >> RCLM_SHIFT) != RCLM_KERN
> > > +#error __GFP_KERNRCLM not mapping to RCLM_KERN
> > > +#endif
> >
> > Should this really be in page_alloc.c, or should it be close to the
> > RCLM_* definitions?

I had the same first impression, but concluded this was the best place.  The 
compile time checks should keep things from getting out of sync.
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