Re: [RFC 06/13] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations

[Vlastimil Babka]

On 05/18/2016 05:24 PM, Michal Hocko wrote:
>>   
>> So the following patch attempts what you suggest, if I understand you
>> correctly. GFP_TRANSHUGE includes all possible flag, and then they are
>> removed as needed. I don't really think it helps code readability
>> though.
> 
> yeah it is ugly has _hell_. I do not think this deserves too much time
> to discuss as the flag is mostly internal but one last proposal would be
> to define different THP allocations context explicitly. Some callers
> would still need some additional meddling but maybe it would be slightly
> better to read. Dunno. Anyway if you think this is not really an
> improvement then I won't insist on any change to your original patch.
> ---
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 570383a41853..e7926b466107 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -255,9 +255,14 @@ struct vm_area_struct;
>   #define GFP_DMA32	__GFP_DMA32
>   #define GFP_HIGHUSER	(GFP_USER | __GFP_HIGHMEM)
>   #define GFP_HIGHUSER_MOVABLE	(GFP_HIGHUSER | __GFP_MOVABLE)
> -#define GFP_TRANSHUGE	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
> +
> +/* Optimistic or latency sensitive THP allocation - page fault path */
> +#define GFP_TRANSHUGE_LIGHT	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
>   			 __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN) & \
>   			 ~__GFP_RECLAIM)
> +/* More serious THP allocation request - kcompactd */
> +#define GFP_TRANSHUGE (GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM) & \
> +			~__GFP_NORETRY

[...]

OK I took the core idea and arrived at the following. I think it could
work and the amount of further per-site modifications to GFP_TRANSHUGE*
is reduced, but if anyone think it's overkill to have two
GFP_TRANSHUGE*, I will just return to the original patch.