We can see at-a-glance memory usage during the run with dstat but we
have no way to break that down into an overview of where memory is
going.
This adds a peer-service to dstat that records snapshots of the system
during peak memory usage. It checks periodically if there is less
memory available than before and, if so, records the running processes
and vm overview.
The intent is to add logic into the verify-pipeline jobs to use this
report and send statistics on peak memory usage to statsd [1]. We can
then build a picture of memory-usage growth over time. This type of
report would have allowed better insight into issues such as
introduced by Idf3a3a914b54779172776822710b3e52e751b1d1 where
memory-usage jumped dramatically after switching to pip versions of
libraries. Tracking details of memory usage is going to be an
important part of future development.
[1] http://graphite.openstack.org/
Change-Id: I4b0a8f382dcaa09331987ab84a68546ec29cbc18
