Intermittent resource usage problem

For the last few days I've been getting these messages emailed to me from the server.  Yesterday I doubled the server RAM.. still getting the messages.  How can I troubleshoot this accurately?  PHP 7, latest wordpress, NGINX, Plesk Onyx.  VPS ram is 2GB now, up from 1 GB improvement.

Subject: lfd on Excessive resource usage: xyzsite (24659 (Parent PID:7656))

Time:         Tue Oct 31 08:42:51 2017 -0300
Account:      xyzsite
Resource:     Virtual Memory Size
Exceeded:     417 > 400 (MB)
Executable:   /opt/plesk/php/7.0/sbin/php-fpm
Command Line: php-fpm: pool
PID:          24659 (Parent PID:7656)
Killed:       No
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JohnBusiness Consultant (Owner)Commented:
Start with Admin Tools, Resource Monitor and let is run for a couple of hours. This will show you short term trends in CPU, Disk Usage, Network Usage and Memory Usage. This is probably the easiest tool to work with.

You can also use Admin Tools, Performance Monitor. This is more advanced but you need to set up the data collection sets you want.
David FavorLinux/LXD/WordPress/Hosting SavantCommented:
2G for any site is very low, to begin with.

The message relates to FPM, which tells you the likely place to start pruning code is WordPress .php files.

You can resolve this at the cost of slowing down your site considerably by looking at the average RSS size (from ps) of your FPM processes + then reducing the number of max instances to some value low enough to reduce your memory usage.

And likely this will cause many visitor pages to be served slow or blank.

I'm looking at RSS values across many client sites I host + I find this...

Well tooled sites fpm RSS run 10M-50M + sites which slap on any old theme + plugins run 100M-300M+, so you can see how choosing your theme + plugins well makes a huge difference.

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