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Date:   Wed, 22 Mar 2023 15:49:24 +0100
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Subject: Re: [PATCH v2 04/14] mm: handle hashdist initialization in
 mm/mm_init.c
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To:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Doug Berger <opendmb@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        linux-mm@kvack.org
References: <20230321170513.2401534-1-rppt@kernel.org>
 <20230321170513.2401534-5-rppt@kernel.org>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20230321170513.2401534-5-rppt@kernel.org>
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On 3/21/23 18:05, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@kernel.org>
> 
> The hashdist variable must be initialized before the first call to
> alloc_large_system_hash() and free_area_init() looks like a better place
> for it than page_alloc_init().
> 
> Move hashdist handling to mm/mm_init.c
> 
> Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
> Acked-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Looks like this will move the fixup_hashdist() call earlier, but can't
result in seeing less N_MEMORY nodes than before, right?
I wonder if the whole thing lacks hotplug support anyway, what if system
boots with one node and more are added later? Hmm.

> ---
>  mm/mm_init.c    | 22 ++++++++++++++++++++++
>  mm/page_alloc.c | 18 ------------------
>  2 files changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 68d0187c7886..2e60c7186132 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -607,6 +607,25 @@ int __meminit early_pfn_to_nid(unsigned long pfn)
>  
>  	return nid;
>  }
> +
> +int hashdist = HASHDIST_DEFAULT;
> +
> +static int __init set_hashdist(char *str)
> +{
> +	if (!str)
> +		return 0;
> +	hashdist = simple_strtoul(str, &str, 0);
> +	return 1;
> +}
> +__setup("hashdist=", set_hashdist);
> +
> +static inline void fixup_hashdist(void)
> +{
> +	if (num_node_state(N_MEMORY) == 1)
> +		hashdist = 0;
> +}
> +#else
> +static inline void fixup_hashdist(void) {}
>  #endif /* CONFIG_NUMA */
>  
>  #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> @@ -1855,6 +1874,9 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>  	}
>  
>  	memmap_init();
> +
> +	/* disable hash distribution for systems with a single node */
> +	fixup_hashdist();
>  }
>  
>  /**
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c56c147bdf27..ff6a2fff2880 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6383,28 +6383,10 @@ static int page_alloc_cpu_online(unsigned int cpu)
>  	return 0;
>  }
>  
> -#ifdef CONFIG_NUMA
> -int hashdist = HASHDIST_DEFAULT;
> -
> -static int __init set_hashdist(char *str)
> -{
> -	if (!str)
> -		return 0;
> -	hashdist = simple_strtoul(str, &str, 0);
> -	return 1;
> -}
> -__setup("hashdist=", set_hashdist);
> -#endif
> -
>  void __init page_alloc_init(void)
>  {
>  	int ret;
>  
> -#ifdef CONFIG_NUMA
> -	if (num_node_state(N_MEMORY) == 1)
> -		hashdist = 0;
> -#endif
> -
>  	ret = cpuhp_setup_state_nocalls(CPUHP_PAGE_ALLOC,
>  					"mm/page_alloc:pcp",
>  					page_alloc_cpu_online,