On Mon, May 16, 2022 at 06:22:07PM +0800, Muchun Song wrote:
> We are almost running out of free slots, only one bit is available in the
I would be more precise about what are we running out of. Free slots of
what?
> worst case (powerpc with 256k pages). However, there are still some free
> slots on other architectures (e.g. x86_64 has 10 bits available, arm64
> has 8 bits available with worst case of 64K pages). We have hard coded
> those numbers in code, it is inconvenient to use those bits on other
> architectures except powerpc. So transfer those section flags to
> enumeration to make it easy to add new section flags in the future. Also,
> move SECTION_TAINT_ZONE_DEVICE into the scope of CONFIG_ZONE_DEVICE
> to save a bit on non-zone-device case.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
...
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1418,16 +1418,37 @@ extern size_t mem_section_usage_size(void);
> * (equal SECTION_SIZE_BITS - PAGE_SHIFT), and the
> * worst combination is powerpc with 256k pages,
> * which results in PFN_SECTION_SHIFT equal 6.
> - * To sum it up, at least 6 bits are available.
> + * To sum it up, at least 6 bits are available on all architectures.
> + * However, we can exceed 6 bits on some other architectures except
> + * powerpc (e.g. 15 bits are available on x86_64, 13 bits are available
> + * with the worst case of 64K pages on arm64) if we make sure the
> + * exceeded bit is not applicable to powerpc.
> */
> -#define SECTION_MARKED_PRESENT (1UL<<0)
> -#define SECTION_HAS_MEM_MAP (1UL<<1)
> -#define SECTION_IS_ONLINE (1UL<<2)
> -#define SECTION_IS_EARLY (1UL<<3)
> -#define SECTION_TAINT_ZONE_DEVICE (1UL<<4)
> -#define SECTION_MAP_LAST_BIT (1UL<<5)
> +#define ENUM_SECTION_FLAG(MAPPER) \
> + MAPPER(MARKED_PRESENT) \
> + MAPPER(HAS_MEM_MAP) \
> + MAPPER(IS_ONLINE) \
> + MAPPER(IS_EARLY) \
> + MAPPER(TAINT_ZONE_DEVICE, CONFIG_ZONE_DEVICE) \
> + MAPPER(MAP_LAST_BIT)
> +
> +#define __SECTION_SHIFT_FLAG_MAPPER_0(x)
> +#define __SECTION_SHIFT_FLAG_MAPPER_1(x) SECTION_##x##_SHIFT,
> +#define __SECTION_SHIFT_FLAG_MAPPER(x, ...) \
> + __PASTE(__SECTION_SHIFT_FLAG_MAPPER_, IS_ENABLED(__VA_ARGS__))(x)
> +
> +#define __SECTION_FLAG_MAPPER_0(x)
> +#define __SECTION_FLAG_MAPPER_1(x) SECTION_##x = BIT(SECTION_##x##_SHIFT),
> +#define __SECTION_FLAG_MAPPER(x, ...) \
> + __PASTE(__SECTION_FLAG_MAPPER_, IS_ENABLED(__VA_ARGS__))(x)
> +
> +enum {
> + ENUM_SECTION_FLAG(__SECTION_SHIFT_FLAG_MAPPER)
> + ENUM_SECTION_FLAG(__SECTION_FLAG_MAPPER)
> +};
> +
> #define SECTION_MAP_MASK (~(SECTION_MAP_LAST_BIT-1))
> -#define SECTION_NID_SHIFT 6
> +#define SECTION_NID_SHIFT SECTION_MAP_LAST_BIT_SHIFT
Is this really worth the extra code? And it might be me that I am not
familiar with all this magic, but it looks overcomplicated.
Maybe some comments here and there help clarifying what it is going on
here.
> static inline struct page *__section_mem_map_addr(struct mem_section *section)
> {
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 111684878fd9..aef3f041dec7 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -655,12 +655,18 @@ static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned lon
>
> }
>
> +#ifdef CONFIG_ZONE_DEVICE
> static void section_taint_zone_device(unsigned long pfn)
> {
> struct mem_section *ms = __pfn_to_section(pfn);
>
> ms->section_mem_map |= SECTION_TAINT_ZONE_DEVICE;
> }
> +#else
> +static inline void section_taint_zone_device(unsigned long pfn)
> +{
> +}
> +#endif
>
> /*
> * Associate the pfn range with the given zone, initializing the memmaps
> --
> 2.11.0
>
>
--
Oscar Salvador
SUSE Labs
