Hi all,
I would like to share a my experience about a slowness of systemd when used on
BTRFS.
My boot time was very high (about ~50 seconds); most of time it was due to
NetworkManager which took about 30-40 seconds to start (this data came from
"systemd-analyze plot").
I make several attempts to address this issue. Also I noticed that sometime
this problem disappeared; but I was never able to understand why.
However this link
https://bugzilla.redhat.com/show_bug.cgi?id=1006386
suggested me that the problem could be due to a bad interaction between systemd
and btrfs. NetworkManager was innocent.
It seems that systemd-journal create a very hight fragmented files when it
stores its log. And BTRFS it is know to behave slowly when a file is highly
fragmented.
This had caused a slow startup of systemd-journal, which in turn had blocked
the services which depend by the loggin system.
In fact after I de-fragmented the files under /var/log/journal [*], my boot
time decreased of about 20second (from 50s to 30s).
Unfortunately I don't have any data to show. The next time I will try to
collect more information. But I am quite sure that when the log are highly
fragmented systemd-journal becomes very slow on BTRFS.
I don't know if the problem is more on the systemd side or btrfs side. What I
know is that both the projects likely will be important in the near futures,
and both must work well together.
I know that I can "chattr +C" to avoid COW for some files; but I don't want to
lost also the checksum protection.
If someone is able to suggest me how FRAGMENT the log file, I can try to
collect more scientific data.
BR
G.Baroncelli
[*]
# btrfs fi defrag /var/log/journal/*/*
--
gpg @keyserver.linux.it: Goffredo Baroncelli (kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
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