linux-kernel - Re: [PATCH -V3 2/2 UPDATE] NUMA balancing: avoid to migrate task to CPU-less node

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Date:   Tue, 08 Mar 2022 10:11:11 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     <linux-kernel@...r.kernel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH -V3 2/2 UPDATE] NUMA balancing: avoid to migrate task to
 CPU-less node

Hi, Peter,

"Huang, Ying" <ying.huang@...el.com> writes:

> In a typical memory tiering system, there's no CPU in slow (PMEM) NUMA
> nodes.  But if the number of the hint page faults on a PMEM node is
> the max for a task, The current NUMA balancing policy may try to place
> the task on the PMEM node instead of DRAM node.  This is unreasonable,
> because there's no CPU in PMEM NUMA nodes.  To fix this, CPU-less
> nodes are ignored when searching the migration target node for a task
> in this patch.
>
> To test the patch, we run a workload that accesses more memory in PMEM
> node than memory in DRAM node.  Without the patch, the PMEM node will
> be chosen as preferred node in task_numa_placement().  While the DRAM
> node will be chosen instead with the patch.
>
> Known issue: I don't have systems to test complex NUMA topology type,
> for example, NUMA_BACKPLANE or NUMA_GLUELESS_MESH.
>
> v3:
>
> - Fix a boot crash for some uncovered marginal condition.  Thanks Qian
>   Cai for reporting and testing the bug!
>
> - Fix several missing places to use CPU-less nodes as migrating
>   target.
>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Reported-and-tested-by: Qian Cai <quic_qiancai@...cinc.com> # boot crash
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Valentin Schneider <valentin.schneider@....com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

Can you update the patch to fix the bug?  Or you prefer the incremental
patch?

Best Regards,
Huang, Ying