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

[Goffredo Baroncelli]

Hi Kai,


I investigate a bit why readahead doesn't defrag the journal.
I put in CC also the mailing list for "the record".

On 06/17/2014 03:33 AM, Kai Krakow wrote:
[...]
> Instead, for me, the readahead collector catches access to my system
> journal and thus defragments it. That's not the case for your system
> which explains why it won't be defragmented for you when enabling
> readahead.

The readahead program skips file greater than 10M. If you look at its man page, it documents the switch --file-size-max. The default value is READAHEAD_FILE_SIZE_MAX which is equal to 10M.
So only when the system.journal is smaller than this value, the readahead defrags it.
But this happens only few times. 

This behavior seems to me reasonable to avoid blocking a system when a big file is touched during the boot.

BR
G.Baroncelli

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