LVM installer: select percentage of VG to use

[Brian Candler <b.candler@pobox.com>]

In the current Debian installer[1], if you select Guided Partitioning 
with LVM, the entire volume group is allocated for filesystems and swap.

This means you lose much of the flexibility of LVM (e.g. being able to 
choose which filesystems to extend later, or being able to create new 
logical volumes).  You could reclaim space later by shrinking one of the 
filesystems/LVs, but this is relatively painful as it must be done off-line.

This pretty much forces you to do a long-winded manual install if you 
want to leave space in your volume group, e.g. see[2]
https://nsrc.org/workshops/2014/wacren-virtualization/raw-attachment/wiki/Agenda/ex-debian-kvm-libvirt.htm#partitioning

The Ubuntu installer fixed this by asking the user what percentage of 
the volume group to use. This simple feature is a huge improvement.

Is there any chance this feature could be ported into Debian? Has this 
been discussed before?

Thanks,

Brian Candler.

[1] I've just re-tested this with Jessie Beta 1, and the behaviour is 
unchanged

[2] This is from a virtualization workshop using Debian as the base 
platform. We need to leave space in the volume group for creating 
logical volumes for virtual machines, with Ganeti. Today we have to make 
students do the whole long-winded process of creating logical volumes 
for root, swap and /var by hand.