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SubjectRe: [RFC][PATCH 3/4] Memory controller soft limit organize cgroups
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-01-08 10:11:48]:

> On Thu, 08 Jan 2009 00:11:28 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>
> > From: Balbir Singh <balbir@linux.vnet.ibm.com>
> >
> > 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.
> >
>
> Hmm, Could you clarify following ?
>
> - Usage of memory at insertsion and usage of memory at reclaim is different.
> So, this *sorted* order by RB-tree isn't the best order in general.

True, but we frequently update the tree at an interval of HZ/4.
Updating at every page fault sounded like an overkill and building the
entire tree at reclaim is an overkill too.

> Why don't you sort this at memory-reclaim dynamically ?
> - Considering above, the look of RB tree can be
>
> +30M (an amount over soft limit is 30M)
> / \
> -15M +60M

We don't have elements below their soft limit in the tree

> ?
>
> At least, pleease remove the node at uncharge() when the usage goes down.
>

We do remove the tree if it goes under its soft limit at commit_charge,
I thought I had the same code in uncharge(), but clearly that is
missing. Thanks, I'll add it there.


> Thanks,
> -Kame

--
Balbir


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