linux-kernel - Re: [PATCH 2/6] mm/page_alloc: Treat RT tasks similar to GFP

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Date:   Thu, 8 Dec 2022 17:16:05 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux-MM <linux-mm@...ck.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, NeilBrown <neilb@...e.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] mm/page_alloc: Treat RT tasks similar to GFP_HIGH

Subject should say __GFP_HIGH as there's no GFP_HIGH?

On 11/29/22 16:16, Mel Gorman wrote:
> RT tasks are allowed to dip below the min reserve but ALLOC_HARDER is
> typically combined with ALLOC_MIN_RESERVE so RT tasks are a little
> unusual. While there is some justification for allowing RT tasks
> access to memory reserves, there is a strong chance that a RT task
> that is also under memory pressure is at risk of missing deadlines
> anyway. Relax how much reserves an RT task can access by treating
> it the same as __GFP_HIGH allocations.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3b37909617bc..da746e9eb2cf 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4852,7 +4852,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
>  		 */
>  		alloc_flags &= ~ALLOC_CPUSET;
>  	} else if (unlikely(rt_task(current)) && in_task())
> -		alloc_flags |= ALLOC_HARDER;
> +		alloc_flags |= ALLOC_MIN_RESERVE;
>  
>  	alloc_flags = gfp_to_alloc_flags_cma(gfp_mask, alloc_flags);
>