Re: [PATCH] consolidate WARN_...ONCE() static variables

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 22 Dec 2011 15:53:49 +0000
"Jan Beulich" <JBeulich@suse.com> wrote:

> Due to the alignment of following variables, these typically consume
> more than just the single byte that 'bool' requires, and as there are
> a few hundred instances, the cache pollution (not so much the waste of
> memory) sums op. Put these variables into their own section, outside
> of half way frequently used memory range.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> ---
>  include/asm-generic/bug.h         |    6 +++---
>  include/asm-generic/vmlinux.lds.h |    1 +
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> --- 3.2-rc6/include/asm-generic/bug.h
> +++ 3.2-rc6-warn-once-flag-cold/include/asm-generic/bug.h
> @@ -134,7 +134,7 @@ extern void warn_slowpath_null(const cha
>  #endif
>  
>  #define WARN_ON_ONCE(condition)	({				\
> -	static bool __warned;					\
> +	static bool __section(.data.unlikely) __warned;		\
>  	int __ret_warn_once = !!(condition);			\
>  								\
>  	if (unlikely(__ret_warn_once))				\
> @@ -144,7 +144,7 @@ extern void warn_slowpath_null(const cha
>  })
>  
>  #define WARN_ONCE(condition, format...)	({			\
> -	static bool __warned;					\
> +	static bool __section(.data.unlikely) __warned;		\
>  	int __ret_warn_once = !!(condition);			\
>  								\
>  	if (unlikely(__ret_warn_once))				\
> @@ -154,7 +154,7 @@ extern void warn_slowpath_null(const cha
>  })
>  
>  #define WARN_TAINT_ONCE(condition, taint, format...)	({	\
> -	static bool __warned;					\
> +	static bool __section(.data.unlikely) __warned;		\
>  	int __ret_warn_once = !!(condition);			\
>  								\
>  	if (unlikely(__ret_warn_once))				\
> --- 3.2-rc6/include/asm-generic/vmlinux.lds.h
> +++ 3.2-rc6-warn-once-flag-cold/include/asm-generic/vmlinux.lds.h
> @@ -167,6 +167,7 @@
>  	CPU_KEEP(exit.data)						\
>  	MEM_KEEP(init.data)						\
>  	MEM_KEEP(exit.data)						\
> +	*(.data.unlikely)						\
>  	STRUCT_ALIGN();							\
>  	*(__tracepoints)						\
>  	/* implement dynamic printk debug */				\

The patch seems reasonable.

printk_once() should also be converted.  And ata_print_version_once(),
if it insists on continuing to exist.  Also rcu_lockdep_assert().

My MUA (sylpheed) is unable to generate a plain-text version of the
patch for me, so much hand-editing will be needed.  It would be nice
if the patch could be demangled at the sending end, please.

I agree that linux-kernel should have been cc'ed on a change of this
nature.