Re: [PATCH -mm 1/5] quick lookup memcg by ID

[KAMEZAWA Hiroyuki]

On Tue, 3 Aug 2010 08:52:16 +0530
Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:

> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-08-02 19:13:04]:
> 
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> > 
> > Now, memory cgroup has an ID per cgroup and make use of it at
> >  - hierarchy walk,
> >  - swap recording.
> > 
> > This patch is for making more use of it. The final purpose is
> > to replace page_cgroup->mem_cgroup's pointer to an unsigned short.
> > 
> > This patch caches a pointer of memcg in an array. By this, we
> > don't have to call css_lookup() which requires radix-hash walk.
> > This saves some amount of memory footprint at lookup memcg via id.
> >
> 
> It is a memory versus speed tradeoff, but if the number of created
> cgroups is low, it might not be all that slow, besides we do that for
> swap_cgroup anyway - no?
>  

In following patch, pc->page_cgroup is changed from pointer to ID.
Then, this lookup happens in lru_add/del, for example.
And, by this, we can place all lookup related things to __read_mostly.
With css_lookup(), we can't do it and have to be afraid of cache
behavior.

I hear there are a users who create 2000+ cgroups and considering
about "low number" user here is not important.
This patch is a help for getting _stable_ performance even when there are
many cgroups.

Thanks,
-Kame

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/