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From:   Mel Gorman <mgorman@techsingularity.net>
To:     Linux-MM <linux-mm@kvack.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, NeilBrown <neilb@suse.de>,
        Thierry Reding <thierry.reding@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 2/6] mm/page_alloc: Treat RT tasks similar to GFP_HIGH
Date:   Tue, 29 Nov 2022 15:16:57 +0000
Message-Id: <20221129151701.23261-3-mgorman@techsingularity.net>
In-Reply-To: <20221129151701.23261-1-mgorman@techsingularity.net>
References: <20221129151701.23261-1-mgorman@techsingularity.net>
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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@techsingularity.net>
---
 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);
 
-- 
2.35.3