Subject: Re: [PATCH 14/15] x86/numa: remove redundant iteration over memblock.reserved

From: Baoquan He <[email-masked]>
Date: Tue, 28 Jul 2020 19:02:54 +0800

On 07/28/20 at 08:11am, Mike Rapoport wrote:
> From: Mike Rapoport <[email-masked]>
> 
> numa_clear_kernel_node_hotplug() function first traverses numa_meminfo
> regions to set node ID in memblock.reserved and than traverses
> memblock.reserved to update reserved_nodemask to include node IDs that were
> set in the first loop.
> 
> Remove redundant traversal over memblock.reserved and update
> reserved_nodemask while iterating over numa_meminfo.
> 
> Signed-off-by: Mike Rapoport <[email-masked]>
> ---
>  arch/x86/mm/numa.c | 26 ++++++++++----------------
>  1 file changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> index 8ee952038c80..4078abd33938 100644
> --- a/arch/x86/mm/numa.c
> +++ b/arch/x86/mm/numa.c
> @@ -498,31 +498,25 @@ static void __init numa_clear_kernel_node_hotplug(void)
>  	 * and use those ranges to set the nid in memblock.reserved.
>  	 * This will split up the memblock regions along node
>  	 * boundaries and will set the node IDs as well.
> +	 *
> +	 * The nid will also be set in reserved_nodemask which is later
> +	 * used to clear MEMBLOCK_HOTPLUG flag.
> +	 *
> +	 * [ Note, when booting with mem=nn[kMG] or in a kdump kernel,
> +	 *   numa_meminfo might not include all memblock.reserved
> +	 *   memory ranges, because quirks such as trim_snb_memory()
> +	 *   reserve specific pages for Sandy Bridge graphics.
> +	 *   These ranges will remain with nid == MAX_NUMNODES. ]
>  	 */
>  	for (i = 0; i < numa_meminfo.nr_blks; i++) {
>  		struct numa_memblk *mb = numa_meminfo.blk + i;
>  		int ret;
>  
>  		ret = memblock_set_node(mb->start, mb->end - mb->start, &memblock.reserved, mb->nid);
> +		node_set(mb->nid, reserved_nodemask);

Really? This will set all node id into reserved_nodemask. But in the
current code, it's setting nid into memblock reserved region which
interleaves with numa_memoinfo, then get those nid and set it in
reserved_nodemask. This is so different, with my understanding. Please
correct me if I am wrong.

Thanks
Baoquan

>  		WARN_ON_ONCE(ret);
>  	}
>  
> -	/*
> -	 * Now go over all reserved memblock regions, to construct a
> -	 * node mask of all kernel reserved memory areas.
> -	 *
> -	 * [ Note, when booting with mem=nn[kMG] or in a kdump kernel,
> -	 *   numa_meminfo might not include all memblock.reserved
> -	 *   memory ranges, because quirks such as trim_snb_memory()
> -	 *   reserve specific pages for Sandy Bridge graphics. ]
> -	 */
> -	for_each_memblock(reserved, mb_region) {
> -		int nid = memblock_get_region_node(mb_region);
> -
> -		if (nid != MAX_NUMNODES)
> -			node_set(nid, reserved_nodemask);
> -	}
> -
>  	/*
>  	 * Finally, clear the MEMBLOCK_HOTPLUG flag for all memory
>  	 * belonging to the reserved node mask.
> -- 
> 2.26.2
> 
> 

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