dpkg-deb slow when building large packages

[Dan Kegel]

Building a 100 megabyte -dbg package (don't laugh, debugging symbols can get quite large)
takes an extra five to ten minutes in dpkg-deb. ps shows e.g.

USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
dank 6207 99.6 0.7 114984 95736 pts/31 R+ 11:11 5:00 dpkg-deb --build debian/foo-dbg ..

This is nothing new, but it is always irritating.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: dpkg 1.17.5ubuntu5.4
ProcVersionSignature: Ubuntu 3.13.0-53.89-generic 3.13.11-ckt19
Uname: Linux 3.13.0-53-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Jun 3 11:19:12 2015
SourcePackage: dpkg
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dan Kegel (dank)]

When I backtrace it, it's spending a lot of time in

lzma_code () from /lib/x86_64-linux-gnu/liblzma.so.5

and children. strace shows lots of I/O going on. So it
appears to be compression overhead.

[Dan Kegel (dank)]

Oh, and then when lintian starts running, the whole machine stops because lintian
loads a lot of stuff into RAM (6GB in this case). Tracebacks show it's spending a
lot of time in Perl's RE code.