kde is compiled with --enable-fast-malloc. You can use the fast malloc routine instead of the libc routine if enviroment-variable KDE_MALLOC is set to 1. Hereby I would like to make a request to add KDE_MALLOC="1" to /etc/env.d/99kde-env if kde is compiled with --enable-fast-malloc (the default). Also for people who don't read the documentation very carefully it might be an idea to add a commented out line KDE_IS_PRELINKED=true to /etc/env.d/99kde-env. Maybe more possible kde environment variables can be added to /etc/env.d/99kde-env (commented out). For more kde environment variables see http://wiki.kdenews.org/tiki-pagehistory.php?page=Environment+Variables&diff=2
probably will put this into kde-base/kde-env as a new version.
now in kde-env-3 thanks for the report.
Putting here just for reference: probably the environment variable is not needed, and the use of fast malloc is discouraged in certain cases. http://lists.kde.org/?l=kde-optimize&m=109570191906104&w=2 http://lists.kde.org/?l=kde-devel&m=109665200700272&w=2