Re: [PATCH 1/2] mm: fix missing handler for __GFP_NOWARN

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

On Tue, 10 May 2022 19:38:08 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote:

> We expect no warnings to be issued when we specify __GFP_NOWARN, but
> currently in paths like alloc_pages() and kmalloc(), there are still
> some warnings printed, fix it.

Looks sane to me.

> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -35,6 +35,17 @@ struct folio_batch;
>  /* Do not use these with a slab allocator */
>  #define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK)
>  
> +#define WARN_ON_ONCE_GFP(cond, gfp)	({				\
> +	static bool __section(".data.once") __warned;			\
> +	int __ret_warn_once = !!(cond);					\
> +									\
> +	if (unlikely(!(gfp & __GFP_NOWARN) && __ret_warn_once && !__warned)) { \
> +		__warned = true;					\
> +		WARN_ON(1);						\
> +	}								\
> +	unlikely(__ret_warn_once);					\
> +})

I don't think WARN_ON_ONCE_GFP is a good name for this.  But
WARN_ON_ONCE_IF_NOT_GFP_NOWARN is too long :(

WARN_ON_ONCE_NOWARN might be better.  No strong opinion here, really.

> @@ -4902,8 +4906,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	 * We also sanity check to catch abuse of atomic reserves being used by
>  	 * callers that are not in atomic context.
>  	 */
> -	if (WARN_ON_ONCE((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
> -				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)))
> +	if (WARN_ON_ONCE_GFP((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) ==
> +				(__GFP_ATOMIC|__GFP_DIRECT_RECLAIM), gfp_mask))
>  		gfp_mask &= ~__GFP_ATOMIC;
>  
>  retry_cpuset:

I dropped this hunk - Neil's "mm: discard __GFP_ATOMIC"
(https://lkml.kernel.org/r/163712397076.13692.4727608274002939094@noble.neil.brown.name)
deleted this code.