2022-06-18 10:34:36

by Fanjun Kong

Subject: [PATCH] x86/mm: declare static variable inside a function instead of global

Global variables are global capacity variables, unless they are
shadowed, they are available to the entire program.
To reduce the scope of a variable as much as possible is always good
practice.

Signed-off-by: Fanjun Kong <[email protected]>
---
arch/x86/mm/init_64.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 39c5246964a9..582eab896480 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1515,9 +1515,10 @@ static unsigned long probe_memory_block_size(void)
return bz;
}

-static unsigned long memory_block_size_probed;
unsigned long memory_block_size_bytes(void)
{
+ static unsigned long memory_block_size_probed;
+
if (!memory_block_size_probed)
memory_block_size_probed = probe_memory_block_size();

--
2.36.0

2022-06-29 00:04:15

by Andy Lutomirski

Subject: Re: [PATCH] x86/mm: declare static variable inside a function instead of global

On 6/18/22 03:11, Fanjun Kong wrote:
> Global variables are global capacity variables, unless they are
> shadowed, they are available to the entire program.

This is true in general, but:

> -static unsigned long memory_block_size_probed;

^^^^^^

So this isn't actually the case.

> unsigned long memory_block_size_bytes(void)
> {
> + static unsigned long memory_block_size_probed;
> +
> if (!memory_block_size_probed)
> memory_block_size_probed = probe_memory_block_size();
>

I'm sort of okay with the patch, but it's worth noting that, in C++,
initialized function-scope static variables have quite surprising
semantics, so this type of change isn't a pure win in my book. (Yes,
the kernel is C, not C++. But C++ programmers may be nervous anyway.)