Re: [PATCH] mm/debug: optimize once judgment with clang

[vbabka@kernel.org]

On 3/9/26 16:34, Xie Yuanbin wrote:
> commit 242b872239f6a7deacbc ("include/linux/once_lite.h: fix judgment in
> WARN_ONCE with clang") helps optimize performance and size under the
> clang compiler, but the modification is not complete.
> 
> Port the modification to VM_WARN_ON_ONCE_PAGE(), VM_WARN_ON_ONCE_FOLIO(),
> VM_WARN_ON_ONCE_MM() and VM_WARN_ON_ONCE_VMA().
> 
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: David Laight <david.laight.linux@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Xie Yuanbin <qq570070308@gmail.com>

We don't need to make debug code (hence perf doesn't matter there) more ugly
just for clang's sake, I think.

> ---
>  include/linux/mmdebug.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index ab60ffba08f5..a167c5aa525e 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -60,7 +60,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>  	static bool __section(".data..once") __warned;			\
>  	int __ret_warn_once = !!(cond);					\
>  									\
> -	if (unlikely(__ret_warn_once && !__warned)) {			\
> +	if (unlikely(__ret_warn_once) && unlikely(!__warned)) {		\
>  		dump_page(page, "VM_WARN_ON_ONCE_PAGE(" __stringify(cond)")");\
>  		__warned = true;					\
>  		WARN_ON(1);						\
> @@ -80,7 +80,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>  	static bool __section(".data..once") __warned;			\
>  	int __ret_warn_once = !!(cond);					\
>  									\
> -	if (unlikely(__ret_warn_once && !__warned)) {			\
> +	if (unlikely(__ret_warn_once) && unlikely(!__warned)) {		\
>  		dump_page(&folio->page, "VM_WARN_ON_ONCE_FOLIO(" __stringify(cond)")");\
>  		__warned = true;					\
>  		WARN_ON(1);						\
> @@ -91,7 +91,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>  	static bool __section(".data..once") __warned;			\
>  	int __ret_warn_once = !!(cond);					\
>  									\
> -	if (unlikely(__ret_warn_once && !__warned)) {			\
> +	if (unlikely(__ret_warn_once) && unlikely(!__warned)) {		\
>  		dump_mm(mm);						\
>  		__warned = true;					\
>  		WARN_ON(1);						\
> @@ -102,7 +102,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>  	static bool __section(".data..once") __warned;			\
>  	int __ret_warn_once = !!(cond);					\
>  									\
> -	if (unlikely(__ret_warn_once && !__warned)) {			\
> +	if (unlikely(__ret_warn_once) && unlikely(!__warned)) {		\
>  		dump_vma(vma);						\
>  		__warned = true;					\
>  		WARN_ON(1);						\