linux-kernel - Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to memoryless nodes

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Message-ID: <87o7ccrghz.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date: Mon, 19 Feb 2024 16:43:36 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: Byungchul Park <byungchul@...com>
Cc: mingo@...hat.com,  peterz@...radead.org,  juri.lelli@...hat.com,
  vincent.guittot@...aro.org,  dietmar.eggemann@....com,
  rostedt@...dmis.org,  bsegall@...gle.com,  mgorman@...e.de,
  bristot@...hat.com,  vschneid@...hat.com,  linux-kernel@...r.kernel.org,
  linux-mm@...ck.org,  kernel_team@...ynix.com,  akpm@...ux-foundation.org
Subject: Re: [PATCH v4] sched/numa, mm: do not try to migrate memory to
 memoryless nodes

Hi, Byungchul,

Byungchul Park <byungchul@...com> writes:

> Changes from v3:
> 	1. Rewrite the comment in code and the commit message to make it
> 	   more clear. (feedbacked by Oscar Salvador)
> 	2. Add "Reviewed-by: Oscar Salvador <osalvador@...e.de>"
>
> 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 98f5d472c08e3ed5b9b6543290d392a2e50fcf3c Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul@...com>
> Date: Mon, 19 Feb 2024 13:10:47 +0900
> Subject: [PATCH v4] sched/numa, mm: do not try to migrate memory to memoryless nodes
>
> Memoryless nodes do not have any memory to migrate to, so stop trying
> it.
>
> Signed-off-by: Byungchul Park <byungchul@...com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> ---
>  kernel/sched/fair.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d7a3c63a2171..3e3b44ae72d1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1828,6 +1828,12 @@ 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;
>  
> +	/*
> +	 * Cannot migrate to memoryless nodes.
> +	 */
> +	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.

Good catch!

IIUC, you will use patch as fix to the issue in

https://lore.kernel.org/lkml/20240216111502.79759-1-byungchul@sk.com/

If so, we need the Fixes: tag to make it land in -stable properly.

Feel free to add

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>