[systemd-devel] Slow startup of systemd-journal on BTRFS

[Chris Murphy]

On Jun 16, 2014, at 7:13 PM, cwillu <cwillu at cwillu.com> wrote:

> It's not a mmap problem, it's a small writes with an msync or fsync
> after each one problem.
> 
> For the case of sequential writes (via write or mmap), padding writes
> to page boundaries would help, if the wasted space isn't an issue.
> Another approach, again assuming all other writes are appends, would
> be to periodically (but frequently enough that the pages are still in
> cache) read a chunk of the file and write it back in-place, with or
> without an fsync. On the other hand, if you can afford to lose some
> logs on a crash, not fsyncing/msyncing after each write will also
> eliminate the fragmentation.

Normally I'd be willing to give up ~30 seconds of journal to not have fragmented journals. But then if I use systemd.log_level=debug I'd like that to trigger more frequent flushing to make sure as little of the journaling is lost as possible. Does that make sense?


Chris Murphy