Re: [PATCH 16/17] mem/memcg: cache rightmost node

[Michal Hocko]

On Wed 26-07-17 14:09:27, Andrew Morton wrote:
> On Wed, 19 Jul 2017 09:50:36 +0200 Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> 
> > [CC Johannes and Vladimir - the whole series is
> > http://lkml.kernel.org/r/20170719014603.19029-1-dave@xxxxxxxxxxxx]
> > 
> > On Tue 18-07-17 18:46:02, Davidlohr Bueso wrote:
> > > Such that we can optimize __mem_cgroup_largest_soft_limit_node().
> > > The only overhead is the extra footprint for the cached pointer,
> > > but this should not be an issue for mem_cgroup_tree_per_node.
> > 
> > The soft limit reclaim and the associated tree manipulation is not worth
> > touching/optimizing IMHO. We strongly discourage anybody configuring
> > soft limit because of the way how it is implemented and disruptive.
> 
> I'm inclined to merge this.  Unless we plan to actually remove the code
> "soon",

this is not going to happen. It is a user visible interface so we will
have to maintain it as long as cgroup v1 interface is available

> I think it's best to continue to improve it.  Improving
> performance may never matter to anyone, but there is benefit in keeping
> up to date with the current interfaces and best practices.
 
 Well, I am not opposing the change I just think it is not worth
 bothering. Soft limit reclaim tends to be so expensive (direct limit
 down to the soft limit) that a tiny otimization has hard times to help.

-- 
Michal Hocko
SUSE Labs