[Bug 204049] vmtotal() loading is high when memory utilization is high
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Tue Oct 27 02:05:21 UTC 2015
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204049
Bug ID: 204049
Summary: vmtotal() loading is high when memory utilization is
high
Product: Base System
Version: 11.0-CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: freebsd-bugs at FreeBSD.org
Reporter: jiashiun at gmail.com
Tested on a Xeon-E5 v3 with 64GB memory and 11-current #289783
when memory utilization is high, the command 'systat -vmstat 1' will also
consumes more cpu cycles.
% top
last pid: 40272; load averages: 0.32, 4.74, 8.01 up 3+01:19:54 17:23:59
58 processes: 1 running, 57 sleeping
CPU: 0.1% user, 0.0% nice, 1.6% system, 0.1% interrupt, 98.3% idle
Mem: 4509M Active, 52G Inact, 2819M Wired, 1572M Buf, 2930M Free
Swap: 3598M Total, 3598M Free
PID USERNAME THR PRI NICE SIZE RES STATE C TIME CPU COMMAND
46841 root 30 20 0 9248M 7930M kqread 9 20.8H 11.88% bhyve
49914 jsli 1 23 0 19320K 3884K select 5 134:08 4.79% systat
the cause is supposed to be getting sysctl variable vm.vmtotal, which in turn
calls vmtotal(). This can be reproduced with sysctl command:
% time repeat 100 sysctl vm.vmtotal > /dev/null
0.055u 8.102s 0:08.19 99.5% 31+175k 0+0io 0pf+0w
It does not seem to mitigate loading by freeing memory:
% top
last pid: 14037; load averages: 0.15, 3.09, 6.45 up 3+17:45:01 09:49:06
57 processes: 1 running, 56 sleeping
CPU: 0.0% user, 0.0% nice, 1.2% system, 0.0% interrupt, 98.8% idle
Mem: 2060M Active, 45M Inact, 3004M Wired, 1572M Buf, 57G Free
Swap: 3598M Total, 623M Used, 2975M Free, 17% Inuse
PID USERNAME THR PRI NICE SIZE RES STATE C TIME CPU COMMAND
49914 jsli 1 27 0 19320K 2780K select 8 199:48 12.56% systat
1026 jsli 1 29 0 28116K 8372K select 7 45:39 0.86% tmux
% time repeat 100 sysctl vm.vmtotal > /dev/null
0.070u 25.400s 0:26.35 96.6% 28+174k 0+0io 0pf+0w
On contrast the status shortly after reboot:
% top
last pid: 1083; load averages: 0.15, 0.24, 0.12 up 0+00:02:45 09:56:59
42 processes: 3 running, 39 sleeping
CPU: 0.0% user, 0.0% nice, 0.1% system, 0.0% interrupt, 99.9% idle
Mem: 72M Active, 39M Inact, 451M Wired, 11M Buf, 62G Free
Swap: 3598M Total, 3598M Free
PID USERNAME THR PRI NICE SIZE RES STATE C TIME CPU COMMAND
1004 jsli 1 38 0 21972K 4176K CPU6 6 0:00 0.52% tmux
814 root 1 20 0 213M 14128K select 3 0:00 0.37% nmbd
1031 jsli 1 20 0 17272K 4628K select 1 0:00 0.16% systat
1083 jsli 1 38 0 9008K 2464K CPU11 11 0:00 0.05% sh
% time repeat 100 sysctl vm.vmtotal > /dev/null
0.055u 0.160s 0:00.20 105.0% 172+238k 0+0io 0pf+0w
Originally discussed in
http://lists.freebsd.org/pipermail/freebsd-hackers/2015-October/048483.html
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