growfiles in ubunt_ltp test will eat up all the disk space

There are 4 different KVM node, all deployed with Bionic + 8G disk space:

A: 18.04
Disk space:
/dev/vda1 7.3G 4.7G 2.3G 68% /

B: 18.04 + proposed packages
Disk space:
/dev/vda1 7.3G 5.2G 1.7G 76% /

C: 18.04 + linux-kvm kernel
Disk space:
/dev/vda1 7.3G 4.9G 2.1G 71% /

D: 18.04 + linux-kvm kernel + proposed packages:
Disk space:
/dev/vda1 7.3G 5.5G 1.5G 79% /

For node A, C (2.3, 2.1G free space), only the gf18 test will fail:
<<<test_start>>>
tag=gf18 stime=1535959767
cmdline="growfiles -W gf18 -b -e 1 -i 0 -L 120 -w -u -r 10-5000 -I r -l -S 2 -f Lgf04_ -d $TMPDIR"
contacts=""
analysis=exit
<<<test_output>>>
growfiles(gf18): 1218 growfiles.c/2037: 523098 tlibio.c/735 write(6, buf, 1) ret:-1, errno=28 No space left on device
gf18 1 TFAIL : growfiles.c:132: Test failed
<<<execution_status>>>
initiation_status="ok"
duration=62 termination_type=exited termination_id=1 corefile=no
cutime=1247 cstime=2400
<<<test_end>>>

For node B (1.7G free space), gf15 and gf18 will fail
The failure in gf15 is not "No space left on device":
<<<test_start>>>
tag=gf15 stime=1535960672
cmdline="growfiles -W gf15 -b -e 1 -u -r 1-49600 -I r -u -i 0 -L 120 -f Lgfile1 -d $TMPDIR"
contacts=""
analysis=exit
<<<test_output>>>
growfiles(gf15): 1140 growfiles.c/2249: 78642 tlibio.c/1002 pwrite(6, buf, 46818, 1951330224) returned=80
growfiles(gf15): 1140 growfiles.c/1752: 78642 Hit max errors value of 1
gf15 1 TFAIL : growfiles.c:132: Test failed
<<<execution_status>>>
initiation_status="ok"
duration=17 termination_type=exited termination_id=1 corefile=no
cutime=1306 cstime=302
<<<test_end>>>

For node D (1.5G free space), gf14, gf15 and gf18 will fail

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-1020-kvm 4.15.0-1020.20
ProcVersionSignature: User Name 4.15.0-1020.20-kvm 4.15.18
Uname: Linux 4.15.0-1020-kvm x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
Date: Mon Sep 3 06:15:36 2018
SourcePackage: linux-kvm
UpgradeStatus: No upgrade log present (probably fresh install)