Add new pgscan_khugepaged vmstat counter metric

[myllynen]

Recent kernels provide the following statistics:

root@f39-server:~# uname -r
6.7.11-200.fc39.x86_64
root@f39-server:~# grep pgscan /proc/vmstat | cut -d' ' -f1
pgscan_kswapd
pgscan_direct
pgscan_khugepaged
pgscan_direct_throttle
pgscan_anon
pgscan_file

Currently there is no metric corresponding to pgscan_khugepaged:

root@f39-server:~# pminfo mem.vmstat | grep -e pgscan_anon -e pgscan_file -e pgscan_khugepaged
mem.vmstat.pgscan_anon
mem.vmstat.pgscan_file

Please add new pgscan_khugepaged counter metric. Thanks.