Re: [PATCH 3/4] Memory controller soft limit organize cgroups (v6)

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

On Mon, 16 Mar 2009 14:17:35 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-16 09:21:26]:

> > Maybe code like this is good.
> > ==
> >  if (need_softlimit_check(mem)) {
> >      softlimit_res = res_counter_check_under_softlimit(&mem->res);
> >      if (softlimit_res) {
> >         struct mem_cgroup *mem = mem_cgroup_from_cont(softlimit_res);
> >         update_tree()....      
> >      }
> >  }
> > ==
> 
> An additional if is the problem?
My point is "check condition but the result is not used always" is ugly.

> We do all the checks under a lock we
> already hold. I ran aim9, new_dbase, dbase, compute and shared tests
> to make sure that there is no degradation. I've not seen anything
> noticable so far.
> 
ya, maybe. How about unix-bench exec test ?
(it's one of the worst application for memcg ;)

> > 
> > *And* what is important here is "need_softlimit_check(mem)".
> > As Andrew said, there may be something reasonable rather than using tick.
> > So, adding "mem_cgroup_need_softlimit_check(mem)" and improving what it checks
> > makes sense for development.
> > 
> 
> OK, that is a good abstraction, but scanning as a metric does not guarantee
> anything. It is harder to come up with better heuristics with scan
> rate than to come up with something time based. I am open to
> suggestions for something reliable though.
> 
I think making this easy-to-be-modified will help people other than us.
The memory-management algorithm is very difficult but people tend to try
their own new logic to improve overall performance.

Refactoring to make "modification of algorithm" easy makes sense for Linux, OSS.
We're not only people to modify memcontrol.c

So, I think some abstraction is good.

Thanks,
-Kame

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