@gapan: however "depfinder bind-9.18.37-x86_64-1_slack15.0" does not list jemalloc as dependency, which is weird as "ldd /usr/sbin/named" lists libjemalloc.so.2 as dependency (as "not found" if jemalloc is not installed). Could it be an issue of depfinder?
Well... the issue is not with depfinder. The issue is that while the bind-9.16.25 package that came with slackware 15.0 originally did not actually depend on jemalloc, the upgraded bind-9.18.37 package does. You can confirm this yourself if you downgrade to the 9.16.25 package and run ldd on /usr/bin/named-*, upgrade and then run it again.
I have just added jemalloc (and nghttp2) to the dependencies list of bind. Next time bind will be upgraded (or reinstalled) it should pull them as dependencies (as soon as mirrors sync). But for now, you'll have to fix it manually by installing jemalloc.