linux-kernel - Re: [PATCH v2 5/7] sparc: Remove on-stack cpumask var

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Date: Sat, 20 Apr 2024 10:28:05 +0200
From: Sam Ravnborg <sam@...nborg.org>
To: Dawei Li <dawei.li@...ngroup.cn>
Cc: davem@...emloft.net, andreas@...sler.com, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] sparc: Remove on-stack cpumask var

On Sat, Apr 20, 2024 at 01:15:45PM +0800, Dawei Li wrote:
> In general it's preferable to avoid placing cpumasks on the stack, as
> for large values of NR_CPUS these can consume significant amounts of
> stack space and make stack overflows more likely.
> 
> Since the cpumask var resides in __init function, which means it's free
> of any concurrenct access, it can be safely marked with static to get
> rid of allocation on stack.
> 
> while at it, mark it with __initdata to keep it from persistently
> consumed memory.

I do not see the need for this - it does not fix a bug and it
complicates things.
If the size is a real concern the normal pattern is to allocate
and not declare it __initdata.

Yes - __initdata is used in some place.
I suggest to leave it as is unless we are fixing a real bug here.

	Sam

> 
> Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>
> ---
>  arch/sparc/mm/init_64.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> index 1ca9054d9b97..088d9c103dcc 100644
> --- a/arch/sparc/mm/init_64.c
> +++ b/arch/sparc/mm/init_64.c
> @@ -1438,7 +1438,7 @@ static int __init numa_attach_mlgroup(struct mdesc_handle *md, u64 grp,
>  static int __init numa_parse_mdesc_group(struct mdesc_handle *md, u64 grp,
>  					 int index)
>  {
> -	cpumask_t mask;
> +	static cpumask_t mask __initdata;
>  	int cpu;
>  
>  	numa_parse_mdesc_group_cpus(md, grp, &mask);
> -- 
> 2.27.0