Hi,

I've hit a memory issue a few times.  It appears to be related to nxml-mode.

I start by adding a custom schema locating file to find a compact relax NG schema for
DocBook version 5.0.

--------------------
(add-to-list 'rng-schema-locating-files "~/.emacs.d/schema/schemas.xml")

% cat 
<locatingRules xmlns="http://thaiopensource.com/ns/locating-rules/1.0">
  <documentElement localName="section" typeId="DocBook"/> 
  <documentElement localName="chapter" typeId="DocBook"/>
  <documentElement localName="article" typeId="DocBook"/>
  <documentElement localName="book" typeId="DocBook"/>
  <typeId id="DocBook" uri="/usr/local/share/xml/docbook/5.0/rng/docbook.rnc"/>
</locatingRules>
--------------------

Everything will be fine, then while editing text the problem will be triggered.
Within about one minute Emacs's memory usage will go from something like 150 MB
to several GB, then all swap will be exhausted and the Emacs process will die.

% cat /var/log/messages | grep emacs
Jul 14 16:46:59 phe kernel: Jul 14 16:46:59 phe kernel: pid 63738 (emacs-25.0.95), uid 1001, was killed: out of swap space
Jul 14 17:12:03 phe kernel: Jul 14 17:12:03 phe kernel: pid 98492 (emacs-25.0.95), uid 1001, was killed: out of swap space
Jul 14 19:35:39 phe kernel: Jul 14 19:35:39 phe kernel: pid 1411 (emacs-25.0.95), uid 1001, was killed: out of swap space
Jul 15 14:36:40 phe kernel: Jul 15 14:36:40 phe kernel: pid 44880 (emacs-25.0.95), uid 1001, was killed: out of swap space
Jul 15 21:44:14 phe kernel: Jul 15 21:44:14 phe kernel: pid 77392 (emacs-25.0.95), uid 1001, was killed: out of swap space

This was occurring before I made the change to the indentation code I posted
about earlier.  I haven't filed a bug report yet, because I haven't been able to
figure out an explicit action to trigger it, nor have I been able to trigger it
with Emacs -Q.

Joseph