Re: [PATCH v9 0/7] Make cpuid <-> nodeid mapping persistent

Andrew Morton
2016-07-25T23:20:22Z

On Mon, 25 Jul 2016 16:35:42 +0800 Dou Liyang <douly.fnst@cn.fujitsu.com> wrote:

> [Problem]
>
> cpuid <-> nodeid mapping is firstly established at boot time. And workqueue caches
> the mapping in wq_numa_possible_cpumask in wq_numa_init() at boot time.
>
> When doing node online/offline, cpuid <-> nodeid mapping is established/destroyed,
> which means, cpuid <-> nodeid mapping will change if node hotplug happens. But
> workqueue does not update wq_numa_possible_cpumask.
>
> So here is the problem:
>
> Assume we have the following cpuid <-> nodeid in the beginning:
>
> Node | CPU
> ------------------------
> node 0 | 0-14, 60-74
> node 1 | 15-29, 75-89
> node 2 | 30-44, 90-104
> node 3 | 45-59, 105-119
>
> and we hot-remove node2 and node3, it becomes:
>
> Node | CPU
> ------------------------
> node 0 | 0-14, 60-74
> node 1 | 15-29, 75-89
>
> and we hot-add node4 and node5, it becomes:
>
> Node | CPU
> ------------------------
> node 0 | 0-14, 60-74
> node 1 | 15-29, 75-89
> node 4 | 30-59
> node 5 | 90-119
>
> But in wq_numa_possible_cpumask, cpu30 is still mapped to node2, and the like.
>
> When a pool workqueue is initialized, if its cpumask belongs to a node, its
> pool->node will be mapped to that node. And memory used by this workqueue will
> also be allocated on that node.

Plan B is to hunt down and fix up all the workqueue structures at
hotplug-time. Has that option been evaluated?

Your fix is x86-only and this bug presumably affects other
architectures, yes? I think a "Plan B" would fix all architectures?

Thirdly, what is the merge path for these patches? Is an x86
or ACPI maintainer working with you on them?