5.15-stable review patch. If anyone has any objections, please let me know.
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From: Mel Gorman mgorman@techsingularity.net
[ Upstream commit c988dcbecf3fd5430921eaa3fe9054754f76d185 ]
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.
Note that in a future kernel release that the RT special casing will be removed. Hard realtime tasks should be locking down resources in advance and ensuring enough memory is available. Even a soft-realtime task like audio or video live decoding which cannot jitter should be allocating both memory and any disk space required up-front before the recording starts instead of relying on reserves. At best, reserve access will only delay the problem by a very short interval.
Link: https://lkml.kernel.org/r/20230113111217.14134-3-mgorman@techsingularity.net Signed-off-by: Mel Gorman mgorman@techsingularity.net Acked-by: Vlastimil Babka vbabka@suse.cz Acked-by: Michal Hocko mhocko@suse.com Cc: Matthew Wilcox willy@infradead.org Cc: NeilBrown neilb@suse.de Cc: Thierry Reding thierry.reding@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Stable-dep-of: 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves") Signed-off-by: Sasha Levin sashal@kernel.org --- 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 4e9e9cb98f336..72835cf4034bc 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4725,7 +4725,7 @@ 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);