linux-kernel - Re: [PATCH 1/3] mm: sparse: pass section_nr to section_mark

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Date:   Fri, 2 Jul 2021 19:54:52 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Ohhoon Kwon <ohoono.kwon@...sung.com>, akpm@...ux-foundation.org,
        mhocko@...e.com
Cc:     bhe@...hat.com, rppt@...ux.ibm.com, ohkwon1043@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm: sparse: pass section_nr to section_mark_present

On 02.07.21 11:41, Ohhoon Kwon wrote:
> With CONFIG_SPARSEMEM_EXTREME enabled, __section_nr() which converts
> mem_section to section_nr could be costly since it iterates all
> section roots to check if the given mem_section is in its range.
> 
> On the other hand, __nr_to_section() which converts section_nr to
> mem_section can be done in O(1).
> 
> Let's pass section_nr instead of mem_section ptr to
> section_mark_present() in order to reduce needless iterations.
> 
> Signed-off-by: Ohhoon Kwon <ohoono.kwon@...sung.com>
> ---
>   mm/sparse.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 55c18aff3e42..4a2700e9a65f 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -186,13 +186,14 @@ void __meminit mminit_validate_memmodel_limits(unsigned long *start_pfn,
>    * those loops early.
>    */
>   unsigned long __highest_present_section_nr;
> -static void section_mark_present(struct mem_section *ms)
> +static void section_mark_present(unsigned long section_nr)
>   {
> -	unsigned long section_nr = __section_nr(ms);
> +	struct mem_section *ms;
>   
>   	if (section_nr > __highest_present_section_nr)
>   		__highest_present_section_nr = section_nr;
>   
> +	ms = __nr_to_section(section_nr);
>   	ms->section_mem_map |= SECTION_MARKED_PRESENT;
>   }
>   
> @@ -279,7 +280,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
>   		if (!ms->section_mem_map) {
>   			ms->section_mem_map = sparse_encode_early_nid(nid) |
>   							SECTION_IS_ONLINE;
> -			section_mark_present(ms);
> +			section_mark_present(section);
>   		}
>   	}
>   }
> @@ -933,7 +934,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>   
>   	ms = __nr_to_section(section_nr);
>   	set_section_nid(section_nr, nid);
> -	section_mark_present(ms);
> +	section_mark_present(section_nr);
>   
>   	/* Align memmap to section boundary in the subsection case */
>   	if (section_nr_to_pfn(section_nr) != start_pfn)
> 

Fine for me either like this, or as Michal suggested. It's an internal 
helper either way.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb