On Wed, Jun 11, 2014 at 11:28:54PM +0200, Goffredo Baroncelli wrote: > 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.
systemd has a very stupid journal write pattern. It checks if there is space in the file for the write, and if not it fallocates the small amount of space it needs (it does *4 byte* fallocate calls!) and then does the write to it. All this does is fragment the crap out of the log files because the filesystems cannot optimise the allocation patterns. Yup, it fragments journal files on XFS, too. http://oss.sgi.com/archives/xfs/2014-03/msg00322.html IIRC, the systemd developers consider this a filesystem problem and so refused to change the systemd code to be nice to the filesystem allocators, even though they don't actually need to use fallocate... Cheers, Dave. -- Dave Chinner da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
