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

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Message-ID: <20240709005618.a4uvufvnledd4vb5@master>
Date: Tue, 9 Jul 2024 00:56:18 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: 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, 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 Mon, Jul 08, 2024 at 09:56:21AM +0200, David Hildenbrand wrote:
>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

My bad.

>
>>   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.
>

Will update it.

>
>Apart form that LGTM
>
>-- 
>Cheers,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me