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

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Message-ID: <966F5E5885D4F1D5+ZiX6aJqbscCJBrwU@centos8>
Date: Mon, 22 Apr 2024 13:49:28 +0800
From: Dawei Li <dawei.li@...ngroup.cn>
To: Sam Ravnborg <sam@...nborg.org>
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

Hi Sam,

Thanks for review.

On Sat, Apr 20, 2024 at 10:28:05AM +0200, Sam Ravnborg wrote:
> 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.

Acked. I will remove __initdata annotation.

Thanks,

    Dawei

> 
> 	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
>