linux-kernel - Re: [PATCH v3 1/3] mm/memblock: introduce a new helper memblock_estimated_nr

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Message-ID: <Zoe4XN-gKJnjJtzi@kernel.org>
Date: Fri, 5 Jul 2024 12:09:48 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, oleg@...hat.com,
	mjguzik@...il.com, tandersen@...flix.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, david@...hat.com
Subject: Re: [PATCH v3 1/3] mm/memblock: introduce a new helper
 memblock_estimated_nr_pages()

On Wed, Jul 03, 2024 at 12:51:49AM +0000, Wei Yang wrote:
> Instead of using raw memblock api, we wrap a new helper for user.

The changelog should be more elaborate and explain why this function is
needed.
 
> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
> ---
>  include/linux/memblock.h |  1 +
>  mm/memblock.c            | 19 +++++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index 40c62aca36ec..7d1c32b3dc12 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_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..c1f1aac0459f 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1729,6 +1729,25 @@ phys_addr_t __init_memblock memblock_reserved_size(void)
>  	return memblock.reserved.total_size;
>  }
>  
> +/**
> + * memblock_estimated_nr_pages - return number of pages from memblock point of
> + * view

This function returns the estimate for free pages, not the number of pages
in RAM.

How about memblock_estimated_nr_free_pages()?

> + * some calculation before all pages are freed to buddy system, especially
> + * when CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.

I'm failing to parse this sentence. The return value here won't depend on
CONFIG_DEFERRED_STRUCT_PAGE_INIT.

> + *
> + * At this point, we can get this information from memblock. Since the system
> + * state is not settle down and address alignment, the value is an estimation.
> + *
> + * Return:
> + * An estimated number of pages from memblock point of view.

                            ^ free

> + */
> +unsigned long __init memblock_estimated_nr_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.