linux-kernel - Re: [PATCH v4 1/3] mm/memblock: introduce a new helper memblock_estimated_nr_free

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Message-ID: <e84fcec1-31bc-4397-851a-da70dd754b19@redhat.com>
Date: Mon, 8 Jul 2024 09:56:21 +0200
From: David Hildenbrand <david@...hat.com>
To: Wei Yang <richard.weiyang@...il.com>, rppt@...nel.org,
 akpm@...ux-foundation.org, brauner@...nel.org, oleg@...hat.com,
 mjguzik@...il.com, tandersen@...flix.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mm/memblock: introduce a new helper
 memblock_estimated_nr_free_pages()

On 08.07.24 03:00, 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@...il.com>
> CC: David Hildenbrand <david@...hat.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> 
> ---
> v4: adjust comment per david's suggestion
> ---
>   include/linux/memblock.h |  1 +
>   mm/memblock.c            | 20 ++++++++++++++++++++
>   2 files changed, 21 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);

^ stale name

>   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..26162902789f 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1729,6 +1729,26 @@ 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.
> + *
> + * While we can get the estimated number of free pages from memblock, which is
> + * good enough for estimation.

I'd drop that sentence.


Apart form that LGTM

-- 
Cheers,

David / dhildenb