linux-kernel - Re: ***UNCHECKED*** [PATCH v3 1/1] mm: sparse: pass section_nr to section_mark

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Date:   Wed, 7 Jul 2021 16:32:05 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Ohhoon Kwon <ohoono.kwon@...sung.com>
Cc:     david@...hat.com, akpm@...ux-foundation.org, bhe@...hat.com,
        rppt@...ux.ibm.com, ohkwon1043@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: ***UNCHECKED*** [PATCH v3 1/1] mm: sparse: pass section_nr to
 section_mark_present

On Wed 07-07-21 22:14:43, 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.
> 
> Since both callers of section_mark_present already know section_nr,
> let's also pass section_nr as well as mem_section in order to reduce
> costly translation.
> 
> Signed-off-by: Ohhoon Kwon <ohoono.kwon@...sung.com>
> Acked-by: Mike Rapoport <rppt@...ux.ibm.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>

I would simply fold that into the first patch but a separate patch is
also OK.

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks

> ---
>  mm/sparse.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 6326cdf36c4f..8018ee7fcda5 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -187,10 +187,9 @@ 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(struct mem_section *ms,
> +		unsigned long section_nr)
>  {
> -	unsigned long section_nr = __section_nr(ms);
> -
>  	if (section_nr > __highest_present_section_nr)
>  		__highest_present_section_nr = section_nr;
>  
> @@ -280,7 +279,7 @@ 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(ms, section);
>  		}
>  	}
>  }
> @@ -934,7 +933,7 @@ 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(ms, section_nr);
>  
>  	/* Align memmap to section boundary in the subsection case */
>  	if (section_nr_to_pfn(section_nr) != start_pfn)
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs