Subject: Re: [PATCH 06/17] x86/numa: simplify numa_distance allocation

From: Jonathan Cameron <[email-masked]>
Date: Fri, 19 Jul 2024 17:28:49 +0100

On Tue, 16 Jul 2024 14:13:35 +0300
Mike Rapoport <[email-masked]> wrote:

> From: "Mike Rapoport (Microsoft)" <[email-masked]>
> 
> Allocation of numa_distance uses memblock_phys_alloc_range() to limit
> allocation to be below the last mapped page.
> 
> But NUMA initializaition runs after the direct map is populated and

initialization (one too many 'i's)

> there is also code in setup_arch() that adjusts memblock limit to
> reflect how much memory is already mapped in the direct map.
> 
> Simplify the allocation of numa_distance and use plain memblock_alloc().
> This makes the code clearer and ensures that when numa_distance is not
> allocated it is always NULL.
Doesn't this break the comment in numa_set_distance() kernel-doc?
"
 * If such table cannot be allocated, a warning is printed and further
 * calls are ignored until the distance table is reset with
 * numa_reset_distance().
"

Superficially that looks to be to avoid repeatedly hitting the
singleton bit at the top of numa_set_distance() as SRAT or similar
parsing occurs.

> 
> Signed-off-by: Mike Rapoport (Microsoft) <[email-masked]>
> ---
>  arch/x86/mm/numa.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index 5e1dde26674b..ab2d4ecef786 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -319,8 +319,7 @@ void __init numa_reset_distance(void)
>  {
>  	size_t size = numa_distance_cnt * numa_distance_cnt * sizeof(numa_distance[0]);
>  
> -	/* numa_distance could be 1LU marking allocation failure, test cnt */
> -	if (numa_distance_cnt)
> +	if (numa_distance)
>  		memblock_free(numa_distance, size);
>  	numa_distance_cnt = 0;
>  	numa_distance = NULL;	/* enable table creation */
> @@ -331,7 +330,6 @@ static int __init numa_alloc_distance(void)
>  	nodemask_t nodes_parsed;
>  	size_t size;
>  	int i, j, cnt = 0;
> -	u64 phys;
>  
>  	/* size the new table and allocate it */
>  	nodes_parsed = numa_nodes_parsed;
> @@ -342,16 +340,12 @@ static int __init numa_alloc_distance(void)
>  	cnt++;
>  	size = cnt * cnt * sizeof(numa_distance[0]);
>  
> -	phys = memblock_phys_alloc_range(size, PAGE_SIZE, 0,
> -					 PFN_PHYS(max_pfn_mapped));
> -	if (!phys) {
> +	numa_distance = memblock_alloc(size, PAGE_SIZE);
> +	if (!numa_distance) {
>  		pr_warn("Warning: can't allocate distance table!\n");
> -		/* don't retry until explicitly reset */
> -		numa_distance = (void *)1LU;
>  		return -ENOMEM;
>  	}
>  
> -	numa_distance = __va(phys);
>  	numa_distance_cnt = cnt;
>  
>  	/* fill with the default distances */