[systemd-devel] journal: How to limit the file size of runtime system.journal

[Zbigniew Jędrzejewski-Szmek]

On Mon, Dec 16, 2013 at 08:31:46AM +0100, Holger Winkelmann [TP] wrote:
> Hi,
> 
> > > > Is there any particular reason? I think thresold for runtime journal
> > > > size can lower much because in initramfs it's not supposed to have much
> > > > logs.
> > > First, there are some data strcutures which are allocated when the file
> > > is created, and if the file was very small, relatively more space would
> > > wasted. Second, repeated fields are not stored, just referenced, so things
> > > become more efficient when the file is not too small. But neither is
> > > fundamental reason, and with some tweaking the journal could be made
> > > to work much smaller files.
> > 
> > I understand. These are really good points when logs are relatively
> > large, ie. the journal is stored on a real disk.
> > 
> > However when it's in initramfs context, journal is stored in tmpfs which
> > is using the real memory resource as it's backend. 4 MB seems a little
> > bit overkill especially when memory is quite limited case, like kdump.
> > To be more specific, I think 512 KB or 1 MB is a fairly large enough
> > nubmer when journal is stored to a volatile backend.
> 
> We totally agree that a minimum size must be below 1MB either on flash or
> ramfs for embedded devices. otherwise you end up with two solutions for smaller
> and bigger devices. Is there any reference about the overhead if you use smaller
> file size? Is there technical limitation for a minimum size?
No, there's no real technical limitation. Except some hero should go through
src/jounal/journal-file.c and adjust all the constants that they also work
with very small files.

Zbyszek