Re: [PATCH 22/37] xen/arm: use NR_MEM_BANKS to override default NR_NODE_MEMBLKS

[Stefano Stabellini <sstabellini@kernel.org>]

On Thu, 23 Sep 2021, Wei Chen wrote:
> As a memory range described in device tree cannot be split across
> multiple nodes. So we define NR_NODE_MEMBLKS as NR_MEM_BANKS in
> arch header.

This statement is true but what is the goal of this patch? Is it to
reduce code size and memory consumption?

I am asking because NR_MEM_BANKS is 128 and
NR_NODE_MEMBLKS=2*MAX_NUMNODES which is 64 by default so again
NR_NODE_MEMBLKS is 128 before this patch.

In other words, this patch alone doesn't make any difference; at least
doesn't make any difference unless CONFIG_NR_NUMA_NODES is increased.

So, is the goal to reduce memory usage when CONFIG_NR_NUMA_NODES is
higher than 64?


> And keep default NR_NODE_MEMBLKS in common header
> for those architectures NUMA is disabled.

This last sentence is not accurate: on x86 NUMA is enabled and
NR_NODE_MEMBLKS is still defined in xen/include/xen/numa.h (there is no
x86 definition of it)


> Signed-off-by: Wei Chen <wei.chen@arm.com>
> ---
>  xen/include/asm-arm/numa.h | 8 +++++++-
>  xen/include/xen/numa.h     | 2 ++
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/include/asm-arm/numa.h b/xen/include/asm-arm/numa.h
> index 8f1c67e3eb..21569e634b 100644
> --- a/xen/include/asm-arm/numa.h
> +++ b/xen/include/asm-arm/numa.h
> @@ -3,9 +3,15 @@
>  
>  #include <xen/mm.h>
>  
> +#include <asm/setup.h>
> +
>  typedef u8 nodeid_t;
>  
> -#ifndef CONFIG_NUMA
> +#ifdef CONFIG_NUMA
> +
> +#define NR_NODE_MEMBLKS NR_MEM_BANKS
> +
> +#else
>  
>  /* Fake one node for now. See also node_online_map. */
>  #define cpu_to_node(cpu) 0
> diff --git a/xen/include/xen/numa.h b/xen/include/xen/numa.h
> index 1978e2be1b..1731e1cc6b 100644
> --- a/xen/include/xen/numa.h
> +++ b/xen/include/xen/numa.h
> @@ -12,7 +12,9 @@
>  #define MAX_NUMNODES    1
>  #endif
>  
> +#ifndef NR_NODE_MEMBLKS
>  #define NR_NODE_MEMBLKS (MAX_NUMNODES*2)
> +#endif
>  
>  #define vcpu_to_node(v) (cpu_to_node((v)->processor))
>  
> -- 
> 2.25.1
>