[MESOS-8418] mesos-agent high cpu usage because of numerous /proc/mounts reads

• Type: Improvement
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.4.1, 1.5.1, 1.6.1
• Fix Version/s: 1.4.2, 1.5.2, 1.6.2, 1.7.0
• Component/s: agent, containerization
• Labels: containerizer performance
• Assignee: Benjamin Mahler
• Reporter: Stéphane Cottin
• Created: 09/Jan/18 09:30
• Updated: 20/Aug/18 04:35
• Resolved: 17/Jul/18 00:35

Description

/proc/mounts is read many, many times from src/(linux/fs|linux/cgroups|slave/slave).cpp.

When using overlayfs, the /proc/mounts contents can become quite large.
As an example, one of our Q/A single node running ~150 tasks, have a 361 lines/ 201299 chars /proc/mounts file.

This 200kB file is read on this node about 25 to 150 times per second. This is a (huge) waste of cpu and I/O time.

Most of these calls are related to cgroups.

Please consider these proposals :

1/ Is /proc/mounts mandatory for cgroups ?
We already have cgroup subsystems list from /proc/cgroups.
The only compelling information from /proc/mounts seems to be the root mount point,
/sys/fs/cgroup/, which could be obtained by a unique read on agent start.

2/ use /proc/self/mountstats

wc /proc/self/mounts /proc/self/mountstats
361 2166 201299 /proc/self/mounts
361 2888 50200 /proc/self/mountstats

grep cgroup /proc/self/mounts
cgroup /sys/fs/cgroup tmpfs rw,relatime,mode=755 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/cpu cgroup rw,relatime,cpu 0 0
cgroup /sys/fs/cgroup/cpuacct cgroup rw,relatime,cpuacct 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,relatime,blkio 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,relatime,memory 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,relatime,devices 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,relatime,freezer 0 0
cgroup /sys/fs/cgroup/net_cls cgroup rw,relatime,net_cls 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,relatime,perf_event 0 0
cgroup /sys/fs/cgroup/net_prio cgroup rw,relatime,net_prio 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,relatime,pids 0 0

grep cgroup /proc/self/mountstats
device cgroup mounted on /sys/fs/cgroup with fstype tmpfs
device cgroup mounted on /sys/fs/cgroup/cpuset with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/cpu with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/cpuacct with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/blkio with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/memory with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/devices with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/freezer with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/net_cls with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/perf_event with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/net_prio with fstype cgroup
device cgroup mounted on /sys/fs/cgroup/pids with fstype cgroup

This file contains all the required information, and is 4x smaller

3/ microcaching
Caching cgroups data for just 1 second would be a huge perfomance improvement, but i'm not aware of the possible side effects.

Issue Links

• relates to: MESOS-9081 cgroups::verify is expensive and is done implicitly during cgroups operations.