Re: [PATCH] mm/sparse: clarify pgdat_to_phys

[Miles Chen <miles.chen@mediatek.com>]

On Fri, 2021-07-02 at 16:11 +0300, Mike Rapoport wrote:
> On Wed, Jun 30, 2021 at 05:23:09PM +0800, Miles Chen wrote:
> > clarify pgdat_to_phys() by wrapping pgdat_to_phys
> > with CONFIG_NUMA. (the same config as contig_page_data)
> > 
> > No functional change intended.
> > 
> > Comment from Mark [1]:
> > "
> > ... and I reckon it'd be clearer and more robust to define
> > pgdat_to_phys() in the same ifdefs as contig_page_data so
> > that these, stay in-sync. e.g. have:
> > 
> > | #ifdef CONFIG_NUMA
> > | #define pgdat_to_phys(x)	virt_to_phys(x)
> > | #else /* CONFIG_NUMA */
> > |
> > | extern struct pglist_data contig_page_data;
> > | ...
> > | #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
> > |
> > | #endif /* CONIFIG_NUMA */
> > "
> > 
> > [1] https://lore.kernel.org/linux-arm-kernel/20210615131902.GB47121@C02TD0UTHF1T.local/
> > 
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> > ---
> >  mm/sparse.c | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 7272f7a1449d..62c21ec28e33 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -344,14 +344,15 @@ size_t mem_section_usage_size(void)
> >  	return sizeof(struct mem_section_usage) + usemap_size();
> >  }
> >  
> > -static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> > -{
> > -#ifndef CONFIG_NUMA
> > -	return __pa_symbol(pgdat);
> > -#else
> > -	return __pa(pgdat);
> > -#endif
> > -}
> > +#ifdef CONFIG_NUMA
> > +#define pgdat_to_phys(pgdat) __pa(pgdat)
> > +#else /* CONFIG_NUMA */
> > +/*
> > + * When !CONFIG_NUMA, we only expect pgdat == &contig_page_data,
> > + * and use __pa_symbol().
> > + */
> > +#define pgdat_to_phys(pgdat) __pa_symbol(pgdat)
> > +#endif /* CONFIG_NUMA */
> 
> I'm not sure a macro is better than a static inline.
> 
> Maybe we'd want to warn if pgdat passed to pgtat_to_phys() is not
> &contig_page_data, e.g something like
> 
> static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
> {
> 	if (!IS_ENABLED(CONFIG_NUMA)) {
> 		if (pgdat == &contig_page_data)
> 			return __pa_symbol(&contig_page_data);
> 		else
> 			pr_warn("Unexpected pglist_data pointer!\n");
> 	}
> 	
> 	return __pa(pgdat);
> }

Sorry for my late response.
Thanks for the guide. It looks better this way.I will submit patch v2.

>   
> >  #ifdef CONFIG_MEMORY_HOTREMOVE
> >  static struct mem_section_usage * __init
> > -- 
> > 2.18.0
> > 
>