Re: [PATCH 3/4] Memory controller soft limit organize cgroups (v5)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Andrew Morton <akpm@linux-foundation.org> [2009-03-12 16:04:24]:

> On Thu, 12 Mar 2009 23:26:25 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> 
> > Feature: Organize cgroups over soft limit in a RB-Tree
> > 
> > From: Balbir Singh <balbir@linux.vnet.ibm.com>
> > 
> > Changelog v5...v4
> > 1. res_counter_uncharge has an additional parameter to indicate if the
> >    counter was over its soft limit, before uncharge.
> > 
> > Changelog v4...v3
> > 1. Optimizations to ensure we don't uncessarily get res_counter values
> > 2. Fixed a bug in usage of time_after()
> > 
> > Changelog v3...v2
> > 1. Add only the ancestor to the RB-Tree
> > 2. Use css_tryget/css_put instead of mem_cgroup_get/mem_cgroup_put
> > 
> > Changelog v2...v1
> > 1. Add support for hierarchies
> > 2. The res_counter that is highest in the hierarchy is returned on soft
> >    limit being exceeded. Since we do hierarchical reclaim and add all
> >    groups exceeding their soft limits, this approach seems to work well
> >    in practice.
> > 
> > This patch introduces a RB-Tree for storing memory cgroups that are over their
> > soft limit. The overall goal is to
> > 
> > 1. Add a memory cgroup to the RB-Tree when the soft limit is exceeded.
> >    We are careful about updates, updates take place only after a particular
> >    time interval has passed
> > 2. We remove the node from the RB-Tree when the usage goes below the soft
> >    limit
> > 
> > The next set of patches will exploit the RB-Tree to get the group that is
> > over its soft limit by the largest amount and reclaim from it, when we
> > face memory contention.
> > 
> >
> > ...
> >
> > +#define	MEM_CGROUP_TREE_UPDATE_INTERVAL		(HZ/4)
> 
> Wall-clock time is a quite poor way of tracking system activity. 
> There's little correlation between the two things.
> 
> >From a general design point of view it would be better to pace this
> polling activity in a manner which correlates with the amount of system
> activity.  For example, "once per 100,000 pages scanned" is much more
> adaptive than "once per 250 milliseconds".
>

Good suggestion, I want to keep the tree up-to-date before we hit
scanning for reclaim. I can experiment with the idea and try.
 
> >
> > ...
> >> @@ -2459,6 +2561,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
> >  	if (cont->parent == NULL) {
> >  		enable_swap_cgroup();
> >  		parent = NULL;
> > +		mem_cgroup_soft_limit_tree = RB_ROOT;
> 
> This can be done at compile time?
>

As in declaring using RB_ROOT, sure can be done. I'll send a series of
fixes with review comments incorporated. 

-- 
	Balbir

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>