[linux-lvm] is it right to specify '-l' with all the free PE in VG when creating a thin pool?

[Eric Ren]

Hello,

I find that it will fail to create a thin pool with all the free PE in VG as follows:

# pvs
   PV         VG   Fmt  Attr PSize   PFree
   /dev/sdb        lvm2 ---  200.00g 200.00g
# vgcreate vgtest /dev/sdb
   Volume group "vgtest" successfully created
# pvdisplay
   --- Physical volume ---
   PV Name               /dev/sdb
   VG Name               vgtest
   PV Size               200.00 GiB / not usable 32.00 MiB
   Allocatable           yes
   PE Size               4.00 MiB
   Total PE              51192
   Free PE               51192
   Allocated PE          0
   PV UUID               JD74c2-R4zZ-cgs5-c5Ty-1abQ-cf7l-gdSxzz
# lvcreate -l 51192 --thinpool thinpool0 vgtest
   Volume group "vgtest" has insufficient free space (51167 extents): 51192 required.

while it works when specifying '-l' this way:

# lvcreate -l 100%FREE --thinpool thinpool0 vgtest
   Logical volume "thinpool0" created.

Is this something by design? or something may be wrong?
I can replicate this on both:

CentOS Linux release 7.3.1611 (Core)
lvm2-2.02.166-1.el7.x86_64

and
SUSE Linux Enterprise Server 12 SP2
lvm2-2.02.120-72.8.x86_64

Thanks,
Eric