btrfs filesystem show takes a long time

btrfs filesystem show takes a long time

[Stefan K]

Dear Maintainer,

the command btrfs fi show takes too much time:

time btrfs fi show              
Label: none  uuid: 513dc574-e8bc-4336-b181-00d1e9782c1c
Total devices 2 FS bytes used 2.34GiB
devid    1 size 927.79GiB used 4.03GiB path /dev/sdv2
devid    2 size 927.79GiB used 4.03GiB path /dev/sdar2

real    12m59.763s
user    0m0.008s
sys     0m0.044s


time btrfs fi show
Label: none  uuid: 513dc574-e8bc-4336-b181-00d1e9782c1c
Total devices 2 FS bytes used 2.34GiB
devid    1 size 927.79GiB used 4.03GiB path /dev/sdv2
devid    2 size 927.79GiB used 4.03GiB path /dev/sdar2

real    6m22.498s
user    0m0.012s
sys     0m0.024s


time btrfs fi show
Label: none  uuid: 513dc574-e8bc-4336-b181-00d1e9782c1c
Total devices 2 FS bytes used 2.34GiB
devid    1 size 927.79GiB used 4.03GiB path /dev/sdv2
devid    2 size 927.79GiB used 4.03GiB path /dev/sdar2

real    6m19.796s
user    0m0.012s
sys     0m0.024s


Maybe its related to that I've some harddisk in my system:
ls /dev/disk/by-path/ |grep -v part |wc -l
44

This is also a known Debian Bug #891717

-- System Information:
Debian Release: 9.3
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-5-amd64 (SMP w/20 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages btrfs-progs depends on:
ii  e2fslibs    1.43.4-2
ii  libblkid1   2.29.2-1
ii  libc6       2.24-11+deb9u1
ii  libcomerr2  1.43.4-2
ii  liblzo2-2   2.08-1.2+b2
ii  libuuid1    2.29.2-1
ii  zlib1g      1:1.2.8.dfsg-5

Re: btrfs filesystem show takes a long time

[David Sterba]

Hi,

thanks for the report, I've forwarded it to the issue tracker
https://github.com/kdave/btrfs-progs/issues/148

The show command uses the information provided by blkid, that presumably
caches that. The default behaviour of 'fi show' is to skip mount checks,
so the delays are likely caused by blkid, but that's not the only
possible reason.

You may try to run the show command under strace to see where it blocks.

Re: btrfs filesystem show takes a long time

[Stefan K]

Hi,

> You may try to run the show command under strace to see where it blocks.
any recommendations for strace options?


On Friday, September 14, 2018 1:25:30 PM CEST David Sterba wrote:
> Hi,
> 
> thanks for the report, I've forwarded it to the issue tracker
> https://github.com/kdave/btrfs-progs/issues/148
> 
> The show command uses the information provided by blkid, that presumably
> caches that. The default behaviour of 'fi show' is to skip mount checks,
> so the delays are likely caused by blkid, but that's not the only
> possible reason.
> 
> You may try to run the show command under strace to see where it blocks.
>