Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG

[Michal Hocko <mhocko@kernel.org>]

On Mon 23-04-18 20:06:16, Mikulas Patocka wrote:
[...]
> @@ -404,6 +405,12 @@ void *kvmalloc_node(size_t size, gfp_t f
>  	 */
>  	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
>  
> +#ifdef CONFIG_DEBUG_SG
> +	/* Catch bugs when the caller uses DMA API on the result of kvmalloc. */
> +	if (!(prandom_u32_max(2) & 1))
> +		goto do_vmalloc;
> +#endif

I really do not think there is anything DEBUG_SG specific here. Why you
simply do not follow should_failslab path or even reuse the function?

> +
>  	/*
>  	 * We want to attempt a large physically contiguous block first because
>  	 * it is less likely to fragment multiple larger blocks and therefore
> @@ -427,6 +434,9 @@ void *kvmalloc_node(size_t size, gfp_t f
>  	if (ret || size <= PAGE_SIZE)
>  		return ret;
>  
> +#ifdef CONFIG_DEBUG_SG
> +do_vmalloc:
> +#endif
>  	return __vmalloc_node_flags_caller(size, node, flags,
>  			__builtin_return_address(0));
>  }

-- 
Michal Hocko
SUSE Labs