Re: Re: Re: Re: Re: [PATCH v1] sched/numa: add per-process numa_balancing

[Gang Li]

On 11/9/21 8:12 PM, Mel Gorman wrote:
> That would be a policy decision on how existing tasks should be tuned
> if NUMA balancing is enabled at runtime after being disabled at boot
> (or some arbitrary time in the past). Introducing the prctl does mean
> that there is a semantic change for the runtime enabling/disabling
> of NUMA balancing because previously, enabling global balancing affects
> existing tasks and with prctl, it affects only future tasks. It could
> be handled in the sysctl to some exist
>
> 0. Disable for all but prctl specifications
> 1. Enable for all tasks unless disabled by prctl
> 2. Ignore all existing tasks, enable for future tasks
>
> While this is more legwork, it makes more sense as an interface than
> prctl(PR_NUMA_BALANCING,PR_SET_NUMA_BALANCING,1) failing if global
> NUMA balancing is disabled.

Why prctl(PR_NUMA_BALANCING,PR_SET_NUMA_BALANCING,1) must work while 
global numa_balancing is disabled? No offense, I think that is a bit 
redundant. And it's complicated to implement.

It's hard for me to understand the whole vision of your idea. I'm very 
sorry. Can you explain your full thoughts more specifically?

----------------------------------------------------

Also in case of misunderstanding, let me re-explain my patch using 
circuit diagram.

Before my patch, there is only one switch to control numa_balancing.

            ______process1_
...____/ __|______process2_|__...
           |______process3_|

       |
    global numa_balancing

After my patch, we can selectively disable numa_balancing for processes.
And global switch has a high priority.

            __/ __process1_
...____/ __|__/ __process2_|__...
           |__/ __process3_|

       |       |
    global  per-process

Why global numa_balancing has high priority? There are two reasons:
1. numa_balancing is useful to most processes, so there is no need to 
consider how to enable numa_balancing for a few processes while 
disabling it globally.
2. It is easy to implement. The more we think, the more complex the code 
becomes.