Re: [PATCH 2/2] mm/mm_init.c: count nr_initialised only for last zone

[Mike Rapoport <rppt@kernel.org>]

On Wed, May 22, 2024 at 07:29:59AM +0000, Wei Yang wrote:
> Since we always populate low zones, it is not necessary to count
> nr_initialised for them. Let's move the last zone check ahead to skip
> the nr_initialised reset.

We also don't need to count initialized pfns after first_deferred_pfn is
detected, so the reset of nr_initialised can be moved even lower.

> Assume low zones counts for 4G, this change may reduce 1M times
> comparison of prev_end_pfn and end_pfn.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
>  mm/mm_init.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 2dfb87841fdb..4cc627b4ebfe 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -676,6 +676,11 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>  
>  	if (early_page_ext_enabled())
>  		return false;
> +
> +	/* Always populate low zones for address-constrained allocations */
> +	if (end_pfn < pgdat_end_pfn(NODE_DATA(nid)))
> +		return false;
> +
>  	/*
>  	 * prev_end_pfn static that contains the end of previous zone
>  	 * No need to protect because called very early in boot before smp_init.
> @@ -685,10 +690,6 @@ defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>  		nr_initialised = 0;
>  	}
>  
> -	/* Always populate low zones for address-constrained allocations */
> -	if (end_pfn < pgdat_end_pfn(NODE_DATA(nid)))
> -		return false;
> -
>  	if (NODE_DATA(nid)->first_deferred_pfn != ULONG_MAX)
>  		return true;
>  	/*
> -- 
> 2.34.1
> 

-- 
Sincerely yours,
Mike.