https://access.redhat.com/solutions/3031521

Heartbaat failureでslow requestの要因になる。

recommend real memory / 64
Real Memory の64分の1をvm.min_free_kbytesに割り当てておく。

# free  -m
              total        used        free      shared  buff/cache   available
Mem:          15841       13244        1000         813        1596         973
Swap:          8063          88        7975

# sysctl vm.min_free_kbytes
vm.min_free_kbytes = 90112

echo 'vm.min_free_kbytes = 524288' >> /etc/sysctl.conf
sysctl -p

 
[37618448.777187] rocksdb:low0: page allocation failure: order:2, mode:0x4020
[37618448.777189] CPU: 5 PID: 2598581 Comm: rocksdb:low0 Kdump: loaded Tainted: G           OE  ------------   3.10.0-1062.18.1.el7.x86_64 #1

[37618448.778300] swapper/12: page allocation failure: order:2, mode:0x4020
[37618448.778307] CPU: 12 PID: 0 Comm: swapper/12 Kdump: loaded Tainted: G           OE  ------------   3.10.0-1062.18.1.el7.x86_64 #1