On Wed, 31 Aug 2016 08:55:49 +0530 Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx> wrote:
> zone_names[] is used to identify any zone given it's index which
> can be used in many other places. So moving the definition into
> include/linux/mmzone.h for broader access.
>
> ...
>
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -341,6 +341,23 @@ enum zone_type {
>
> };
>
> +static char * const zone_names[__MAX_NR_ZONES] = {
> +#ifdef CONFIG_ZONE_DMA
> + "DMA",
> +#endif
> +#ifdef CONFIG_ZONE_DMA32
> + "DMA32",
> +#endif
> + "Normal",
> +#ifdef CONFIG_HIGHMEM
> + "HighMem",
> +#endif
> + "Movable",
> +#ifdef CONFIG_ZONE_DEVICE
> + "Device",
> +#endif
> +};
> +
> #ifndef __GENERATING_BOUNDS_H
>
> struct zone {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3fbe73a..8e2261c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -207,23 +207,6 @@ int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = {
>
> EXPORT_SYMBOL(totalram_pages);
>
> -static char * const zone_names[MAX_NR_ZONES] = {
> -#ifdef CONFIG_ZONE_DMA
> - "DMA",
> -#endif
> -#ifdef CONFIG_ZONE_DMA32
> - "DMA32",
> -#endif
> - "Normal",
> -#ifdef CONFIG_HIGHMEM
> - "HighMem",
> -#endif
> - "Movable",
> -#ifdef CONFIG_ZONE_DEVICE
> - "Device",
> -#endif
> -};
> -
> char * const migratetype_names[MIGRATE_TYPES] = {
> "Unmovable",
> "Movable",
This is worrisome. On some (ancient) compilers, this will produce a
copy of that array into each compilation unit which includes mmzone.h.
On smarter compilers, it will produce a copy of the array in each
compilation unit which *uses* zone_names[].
On even smarter compilers (and linkers!), only one copy of zone_names[]
will exist in vmlinux.
I don't know if gcc is an "even smarter compiler" and I didn't check,
and I didn't check which gcc versions are even smarter. I'd rather not
have to ;) It is risky.
So, let's just make it non-static and add a declaration into mmzone.h,
please.
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