Re: [PATCH 3/3] memcg: simplify mem_cgroup_reclaim_iter

[Tejun Heo <tj@kernel.org>]

On Wed, Jun 05, 2013 at 03:20:21PM -0700, Tejun Heo wrote:
> Yo,
> 
> On Wed, Jun 05, 2013 at 05:17:04PM -0400, Johannes Weiner wrote:
> > That could be an advantage, yes.  But keep in mind that every
> > destruction has to perform this invalidation operation against the
> > global root_mem_cgroup's nr_node * nr_zone * nr_priority_levels
> > iterators, so you can't muck around forever, while possibly holding a
> > lock at this level.  It's not a hot path, but you don't want to turn
> > it into one, either.
> 
> nr_node tends to be pretty low in most cases, so it shouldn't be a
> problem there but yeah with high enough nodes and high enough rate of

Also, do we need to hold a lock?  It doesn't have to be completely
strict, so we might as well get away with something like,

	for_each_cached_pos() {
		if (hint == me) {
			/* simple clearing implementation, we prolly wanna push it forward */
			cached = xchg(hint, NULL);
			if (cached)
				css_put(cached);
		}
	}

It still scans the memory but wouldn't create any contention.

Thanks.

-- 
tejun

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