Re: [PATCHv4] memcg: reclaim memory from node in round-robin

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 26 May 2011 12:52:07 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 6 May 2011 15:13:02 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> 
> > > It would be much better to work out the optimum time at which to rotate
> > > the index via some deterministic means.
> > > 
> > > If we can't think of a way of doing that then we should at least pace
> > > the rotation frequency via something saner than wall-time.  Such as
> > > number-of-pages-scanned.
> > > 
> > 
> > 
> > What I think now is using reclaim_stat or usigng some fairness based on
> > the ratio of inactive file caches. We can calculate the total sum of
> > recalaim_stat which gives us a scan_ratio for a whole memcg. And we can
> > calculate LRU rotate/scan ratio per node. If rotate/scan ratio is small,
> > it will be a good candidate of reclaim target. Hmm,
> > 
> >   - check which memory(anon or file) should be scanned.
> >     (If file is too small, rotate/scan ratio of file is meaningless.)
> >   - check rotate/scan ratio of each nodes.
> >   - calculate weights for each nodes (by some logic ?)
> >   - give a fair scan w.r.t node's weight.
> > 
> > Hmm, I'll have a study on this.
> 
> How's the study coming along ;)
> 
> I'll send this in to Linus today, but I'll feel grumpy while doing so. 
> We really should do something smarter here - the magic constant will
> basically always be suboptimal for everyone and we end up tweaking its
> value (if we don't, then the feature just wasn't valuable in the first
> place) and then we add a tunable and then people try to tweak the
> default setting of the tunable and then I deride them for not setting
> the tunable in initscripts and then we have to maintain the stupid
> tunable after we've changed the internal implementation and it's all
> basically screwed up.
> 
> How to we automatically determine the optimum time at which to rotate,
> at runtime?
> 

Ah, I think I should check it after dirty page accounting comes...because
ratio of dirty pages is an important information..

Ok, what I think now is just comparing the number of INACTIVE_FILE or the number
of FILE CACHES per node. 

I think we can periodically update per-node and total amount of file caches
and we can record per-node 
   node-file-cache * 100/ total-file cache
information into memcg's per-node structure.

Then, I think we can do some scheduling like lottery scheduling, a scan proportional
to the ratio of file caches in the memcg. If it's better to check INACTIVE_ANON, 
I think swappiness can be used in above calcuration.

But yes, I or someone may be able to think of something much better.

Thanks,
-Kame





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