linux-kernel - Re: [PATCH 08/11] sched/numa: Bias swapping tasks based on their preferred node

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Date:   Thu, 13 Feb 2020 11:31:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Phil Auld <pauld@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/11] sched/numa: Bias swapping tasks based on their
 preferred node

On Wed, Feb 12, 2020 at 09:36:51AM +0000, Mel Gorman wrote:
> When swapping tasks for NUMA balancing, it is preferred that tasks move
> to or remain on their preferred node. When considering an imbalance,
> encourage tasks to move to their preferred node and discourage tasks from
> moving away from their preferred node.

Wasn't there an issue for workloads that span multiple nodes?

Say a 4 node system with 2 warehouses? Then each JVM will want 2 nodes,
instead of a single node, and strong preferred node stuff makes it
difficult to achieve this.

I forgot how we dealt with these cases, just something I worry about
when reading this.