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SubjectRe: [PATCH v3] sched/numa, mm: do not promote folios to nodes not set N_MEMORY
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On 16.02.24 12:40, Byungchul Park wrote:
> Changes from v2:
> 1. Rewrite the comment in code and the commit message becasue it
> turns out that this patch is not the real fix for the oops
> descriped. The real fix goes in another patch below:
>
> https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/
>
> Changes from v1:
> 1. Trim the verbose oops in the commit message. (feedbacked by
> Phil Auld)
> 2. Rewrite a comment in code. (feedbacked by Phil Auld)
>
> --->8---
> From 150af2f78e19217a1d03e47e3ee5279684590fb4 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul@sk.com>
> Date: Fri, 16 Feb 2024 20:18:10 +0900
> Subject: [PATCH v3] sched/numa, mm: do not promote folios to nodes not set N_MEMORY
>
> A numa node might not have its local memory but CPUs. Promoting a folio
> to the node's local memory is nonsense. So avoid nodes not set N_MEMORY
> from getting promoted.

So there is no bug/panic that can be triggered and this is not a "fix"
but an optimization?

>
> Signed-off-by: Byungchul Park <byungchul@sk.com>
> ---
> kernel/sched/fair.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d7a3c63a2171..7ed9ef3c0134 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1828,6 +1828,13 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio,
> int dst_nid = cpu_to_node(dst_cpu);
> int last_cpupid, this_cpupid;
>
> + /*
> + * A node of dst_nid might not have its local memory. Promoting
> + * a folio to the node is meaningless.
> + */
> + if (!node_state(dst_nid, N_MEMORY))
> + return false;
> +
> /*
> * The pages in slow memory node should be migrated according
> * to hot/cold instead of private/shared.

Acked-by: David Hildenbrand <david@redhat.com>

--
Cheers,

David / dhildenb

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