On Tue, Jul 09, 2024 at 02:36:07AM +0000, Wei Yang wrote:
> During bootup, system may need the number of free pages in the whole system
> to do some calculation before all pages are freed to buddy system. Usually
> this number is get from totalram_pages(). Since we plan to move the free
> pages accounting in __free_pages_core(), this value may not represent
> total free pages at the early stage, especially when
> CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
>
> Instead of using raw memblock api, let's introduce a new helper for user
> to get the estimated number of free pages from memblock point of view.
>
> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> CC: David Hildenbrand <david@xxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxx>
>
> ---
> v5: cleanup the stale name
> v4: adjust comment per david's suggestion
> ---
> include/linux/memblock.h | 1 +
> mm/memblock.c | 17 +++++++++++++++++
> 2 files changed, 18 insertions(+)
>
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index 40c62aca36ec..aba7ed9f2531 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -486,6 +486,7 @@ static inline __init_memblock bool memblock_bottom_up(void)
>
> phys_addr_t memblock_phys_mem_size(void);
> phys_addr_t memblock_reserved_size(void);
> +unsigned long memblock_estimated_nr_free_pages(void);
> phys_addr_t memblock_start_of_DRAM(void);
> phys_addr_t memblock_end_of_DRAM(void);
> void memblock_enforce_memory_limit(phys_addr_t memory_limit);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index e81fb68f7f88..ae8e58fc4e7f 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1729,6 +1729,23 @@ phys_addr_t __init_memblock memblock_reserved_size(void)
> return memblock.reserved.total_size;
> }
>
> +/**
> + * memblock_estimated_nr_free_pages - return estimated number of free pages
> + * from memblock point of view
> + *
> + * During bootup, subsystems might need a rough estimate of the number of free
> + * pages in the whole system, before precise numbers are available from the
> + * buddy. Especially with CONFIG_DEFERRED_STRUCT_PAGE_INIT, the numbers
> + * obtained from the buddy might be very imprecise during bootup.
> + *
> + * Return:
> + * An estimated number of free pages from memblock point of view.
> + */
> +unsigned long __init memblock_estimated_nr_free_pages(void)
> +{
> + return PHYS_PFN(memblock_phys_mem_size() - memblock_reserved_size());
> +}
> +
> /* lowest address */
> phys_addr_t __init_memblock memblock_start_of_DRAM(void)
> {
> --
> 2.34.1
>
--
Sincerely yours,
Mike.
