Re: [PATCH 4/5] arch/kmap_atomic: Consolidate duplicate code

[Christoph Hellwig]

> diff --git a/arch/arc/mm/highmem.c b/arch/arc/mm/highmem.c
> index 4db13a6b9f3b..1cae4b911a33 100644
> --- a/arch/arc/mm/highmem.c
> +++ b/arch/arc/mm/highmem.c
> @@ -53,11 +53,10 @@ void *kmap_atomic(struct page *page)
>  {
>  	int idx, cpu_idx;
>  	unsigned long vaddr;
> +	void *addr = kmap_atomic_fast(page);
>  
> -	preempt_disable();
> -	pagefault_disable();
> -	if (!PageHighMem(page))
> -		return page_address(page);
> +	if (addr)
> +		return addr;

Wouldn't it make sense to just move kmap_atomic itelf to common code,
and call out to a kmap_atomic_high for the highmem case, following the
scheme in kmap?  Same for the unmap side.  That might require to support
kmap_atomic_prot everywhere first, which sounds like a really good
idea anyway, and would avoid the need for strange workaround in drm.