Is there a way to trigger numa_balancing instantly?

Is there a way to trigger numa_balancing instantly?

[Andreas Hollmann]

Hi,

is there a way to trigger numa_balancing instantly?

For applications that consist of several phases it
would be very useful to trigger numa_balancing
instantly instead of waiting until it will be triggered
automatically after a certain delay.

The application could trigger a balancing operation
when it comes from one phase to next phase and
these two phases have completely different memory
access patterns.

Would it be possible to integrate a new sysctl
that triggers the balancing for a certain pid?

Something like

echo $PID > /proc/sys/kernel/numa_balancing_now_pid

or

echo 1 > /proc/$PID/numa_balancing_now

numa_balancing could be disabled globally and only triggerd
in certain conditions. Additionally it would be nice to
enable periodic numa_balancing only for certain processes and
not globally.

echo 1 > /proc/$PID/numa_balancing

What do you think?

--

Following sysctls are provided by numa_balancing
in /proc/sys/kernel

numa_balancing                                  0
numa_balancing_migrate_deferred       16
numa_balancing_scan_delay_ms          1000
numa_balancing_scan_period_max_ms 60000
numa_balancing_scan_period_min_ms 1000
numa_balancing_scan_size_mb            256

In https://www.kernel.org/doc/Documentation/sysctl/kernel.txt

numa_balancing_settle_count is mentioned, but it seems that it
disappeared, at least in on my kernel version (3.14).

Best regards,
Andreas Hollmann