From: Thomas Huth <1912224@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1912224] Re: qemu may freeze during drive-mirroring on fragmented FS
Date: Fri, 14 May 2021 19:29:19 -0000 [thread overview]
Message-ID: <162102055919.2052.8116041793882558126.malone@wampee.canonical.com> (raw)
In-Reply-To: 161098039664.6686.1246044899603761821.malonedeb@wampee.canonical.com
This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:
https://gitlab.com/qemu-project/qemu/-/issues/307
** Changed in: qemu
Status: New => Expired
** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #307
https://gitlab.com/qemu-project/qemu/-/issues/307
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https://bugs.launchpad.net/bugs/1912224
Title:
qemu may freeze during drive-mirroring on fragmented FS
Status in QEMU:
Expired
Bug description:
We have odd behavior in operation where qemu freeze during long
seconds, We started an thread about that issue here:
https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05623.html
It happens at least during openstack nova snapshot (qemu blockdev-mirror)
or live block migration(which include network copy of disk).
After further troubleshoots, it seems related to FS fragmentation on
host.
reproducible at least on:
Ubuntu 18.04.3/4.18.0-25-generic/qemu-4.0
Ubuntu 16.04.6/5.10.6/qemu-5.2.0-rc2
# Lets create a dedicated file system on a SSD/Nvme 60GB disk in my case:
$sudo mkfs.ext4 /dev/sda3
$sudo mount /dev/sda3 /mnt
$df -h /mnt
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 59G 53M 56G 1% /mnt
#Create a fragmented disk on it using 2MB Chunks (about 30min):
$sudo python3 create_fragged_disk.py /mnt 2
Filling up FS by Creating chunks files in: /mnt/chunks
We are probably full as expected!!: [Errno 28] No space left on device
Creating fragged disk file: /mnt/disk
$ls -lhs
59G -rw-r--r-- 1 root root 59G Jan 15 14:08 /mnt/disk
$ sudo e4defrag -c /mnt/disk
Total/best extents 41971/30
Average size per extent 1466 KB
Fragmentation score 2
[0-30 no problem: 31-55 a little bit fragmented: 56- needs defrag]
This file (/mnt/disk) does not need defragmentation.
Done.
# the tool^^^ says it is not enough fragmented to be able to defrag.
#Inject an image on fragmented disk
sudo chown ubuntu /mnt/disk
wget https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img
qemu-img convert -O raw bionic-server-cloudimg-amd64.img \
bionic-server-cloudimg-amd64.img.raw
dd conv=notrunc iflag=fullblock if=bionic-server-cloudimg-amd64.img.raw \
of=/mnt/disk bs=1M
virt-customize -a /mnt/disk --root-password password:xxxx
# logon run console activity ex: ping -i 0.3 127.0.0.1
$qemu-system-x86_64 -m 2G -enable-kvm -nographic \
-chardev socket,id=test,path=/tmp/qmp-monitor,server,nowait \
-mon chardev=test,mode=control \
-drive file=/mnt/disk,format=raw,if=none,id=drive-virtio-disk0,cache=none,discard\
-device virtio-blk-pci,scsi=off,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,write-cache=on
$sync
$echo 3 | sudo tee -a /proc/sys/vm/drop_caches
#start drive-mirror via qmp on another SSD/nvme partition
nc -U /tmp/qmp-monitor
{"execute":"qmp_capabilities"}
{"execute":"drive-mirror","arguments":{"device":"drive-virtio-disk0","target":"/home/ubuntu/mirror","sync":"full","format":"qcow2"}}
^^^ qemu console may start to freeze at this step.
NOTE:
- smaller chunk sz and bigger disk size the worst it is.
In operation we also have issue on 400GB disk size with average 13MB/extent
- Reproducible also on xfs
Expected behavior:
-------------------
QEMU should remain steady, eventually only have decrease storage Performance
or mirroring, because of fragmented fs.
Observed behavior:
-------------------
Perf of mirroring is still quite good even on fragmented FS,
but it breaks qemu.
###################### create_fragged_disk.py ############
import sys
import os
import tempfile
import glob
import errno
MNT_DIR = sys.argv[1]
CHUNK_SZ_MB = int(sys.argv[2])
CHUNKS_DIR = MNT_DIR + '/chunks'
DISK_FILE = MNT_DIR + '/disk'
if not os.path.exists(CHUNKS_DIR):
os.makedirs(CHUNKS_DIR)
with open("/dev/urandom", "rb") as f_rand:
mb_rand=f_rand.read(1024 * 1024)
print("Filling up FS by Creating chunks files in: ",CHUNKS_DIR)
try:
while True:
tp = tempfile.NamedTemporaryFile(dir=CHUNKS_DIR,delete=False)
for x in range(CHUNK_SZ_MB):
tp.write(mb_rand)
os.fsync(tp)
tp.close()
except Exception as ex:
print("We are probably full as expected!!: ",ex)
chunks = glob.glob(CHUNKS_DIR + '/*')
print("Creating fragged disk file: ",DISK_FILE)
with open(DISK_FILE, "w+b") as f_disk:
for chunk in chunks:
try:
os.unlink(chunk)
for x in range(CHUNK_SZ_MB):
f_disk.write(mb_rand)
os.fsync(f_disk)
except IOError as ex:
if ex.errno != errno.ENOSPC:
raise
###########################################################3
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prev parent reply other threads:[~2021-05-14 19:41 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-18 14:33 [Bug 1912224] [NEW] qemu may freeze during drive-mirroring on fragmented FS Alexandre arents
2021-01-22 13:19 ` [Bug 1912224] " Alexandre arents
2021-01-25 9:34 ` Alexandre arents
2021-02-02 8:36 ` Alexandre arents
2021-02-03 10:02 ` Max Reitz
2021-02-03 12:24 ` Max Reitz
2021-02-03 14:21 ` Alexandre arents
2021-02-03 16:51 ` Max Reitz
2021-02-04 9:11 ` Alexandre arents
2021-02-10 13:36 ` Alexandre arents
2021-05-12 18:13 ` Thomas Huth
2021-05-14 19:29 ` Thomas Huth [this message]
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