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Date: Wed, 18 Jan 2012 10:25:09 +0100 From: Johannes Weiner <hannes@...xchg.org> To: Sha <handai.szj@...il.com> Cc: Ying Han <yinghan@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Michal Hocko <mhocko@...e.cz>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [patch 2/2] mm: memcg: hierarchical soft limit reclaim On Wed, Jan 18, 2012 at 03:17:25PM +0800, Sha wrote: > > > I don't think it solve the root of the problem, example: > > > root > > > -> A (hard limit 20G, soft limit 12G, usage 20G) > > > -> A1 ( soft limit 2G, usage 1G) > > > -> A2 ( soft limit 10G, usage 19G) > > > ->B1 (soft limit 5G, usage 4G) > > > ->B2 (soft limit 5G, usage 15G) > > > > > > Now A is hitting its hard limit and start hierarchical reclaim under A. > > > If we choose B1 to go through mem_cgroup_over_soft_limit, it will > > > return true because its parent A2 has a large usage and will lead to > > > priority=0 reclaiming. But in fact it should be B2 to be punished. > > > Because A2 is over its soft limit, the whole hierarchy below it should > > be preferred over A1, so both B1 and B2 should be soft limit reclaimed > > to be consistent with behaviour at the root level. > > Well it is just the behavior that I'm expecting actually. But with my > humble comprehension, I can't catch the soft-limit-based hierarchical > reclaiming under the target cgroup (A2) in the current implementation > or after the patch. Both the current mem_cgroup_soft_reclaim or > shrink_zone select victim sub-cgroup by mem_cgroup_iter, but it > doesn't take soft limit into consideration, do I left anything ? No, currently soft limits are ignored if pressure originates from below root_mem_cgroup. But iff soft limits are applied right now, they are applied hierarchically, see mem_cgroup_soft_limit_reclaim(). In my opinion, the fact that soft limits are ignored when pressure is triggered sub-root_mem_cgroup is an artifact of the per-zone tree, so I allowed soft limits to be taken into account below root_mem_cgroup. But IMO, this is something different from how soft limit reclaim is applied once triggered: currently, soft limit reclaim applies to a whole hierarchy, including all children. And this I left unchanged. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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