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

[WANG Chao]

On 12/13/13 at 02:18pm, Zbigniew Jędrzejewski-Szmek wrote:
> On Fri, Dec 13, 2013 at 01:49:51PM +0800, WANG Chao wrote:
> > On 12/13/13 at 06:42am, Zbigniew Jędrzejewski-Szmek wrote:
> > > On Fri, Dec 13, 2013 at 01:33:17PM +0800, WANG Chao wrote:
> > > > Hi,
> > > > 
> > > > In kdump environment, memory resource is quite limited. I find that the
> > > > runtime journal file (/run/log/journal/$id/system.journal) is 4 MB and I
> > > > think that is too much for a initramfs context.
> > > > 
> > > > After tuning both RuntimeMaxUse=1% or RuntimeMaxFileSiz=100K, I find
> > > > system.journal is still 4 MB in size. So here comes my questions:
> > > > 
> > > > 1. Did miss use of these two config options? Because regarding the
> > > > journald.conf(5), it seems I was totally doing it right.
> > > 4MB is the minimum. Those settings are ignored if you set anything
> > > lower.
> > 
> > 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.

Thanks
WANG Chao