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.
