On Thu, 26 Jul 2007 12:27:30 +0200 Ingo Molnar <[email protected]> wrote:
>
> * Andrew Morton <[email protected]> wrote:
>
> > > > > ( we _do_ want to baloon the dentry cache otherwise - for things like
> > > > > "find" - having a fast VFS is important. But known-use-once things
> > > > > like the daily updatedb job can clearly be annotated properly. )
> > > >
> > > > Mutter. /proc/sys/vm/vfs_cache_pressure has been there for what,
> > > > three years? Are any distros raising it during the updatedb run yet?
> > >
> > > but ... that's system-wide, and the 'dont baloon the dcache' is only a
> > > property of updatedb.
> >
> > Sure, but it's practical, isn't it? Who runs (and cares about)
> > vfs-intensive workloads during their wee-small-hours updatedb run?
>
> there's another side-effect: it likely results in the zapping of
> thousands of dentries that were cached nicely before. So we might
> exchange 'all my apps are swapped out' experience with 'all file access
> is slow'. The latter is _probably_ still an improvement over the
> balooning, but i'm not sure.
Yup. Nobody has begun to think about preserving dcache/icache across load
shifts yet, afaik. Hard.
> What we _really_ want is an updatedb that
> does not disturb the dcache.
Well. Hopefully this time next year you can prep a 16MB container and toss
your updatedb inside that. Maybe set its peak disk bandwidth utilisation
too. However that won't work ;) because I don't think anyone is looking
at containerisation of vfs cache memory yet. Perhaps full-on openvz has it,
dunno.
But updatedb is a special case, because it is so vfs-intensive. For lots
of other workloads (those which use heaps of pagecache), resource
management via containerisation will work nicely.
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