linux-kernel - Re: [PATCH] memcg: implement low limits

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Message-ID: <20130228143052.GE6573@dhcp22.suse.cz>
Date:	Thu, 28 Feb 2013 15:30:52 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Roman Gushchin <klamm@...dex-team.ru>
Cc:	Johannes Weiner-Arquette <hannes@...xchg.org>,
	"bsingharora@...il.com" <bsingharora@...il.com>,
	"kamezawa.hiroyu@...fujitsu.com" <kamezawa.hiroyu@...fujitsu.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	"mel@....ul.ie" <mel@....ul.ie>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH] memcg: implement low limits

On Wed 27-02-13 18:57:32, Roman Gushchin wrote:
[...]
> >>  + *
> >>  + */
> >>  +unsigned int mem_cgroup_low_limit_scale(struct lruvec *lruvec)
> >>  +{
> >>  + struct mem_cgroup_per_zone *mz;
> >>  + struct mem_cgroup *memcg;
> >>  + unsigned long long low_limit;
> >>  + unsigned long long usage;
> >>  + unsigned int i;
> >>  +
> >>  + mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
> >>  + memcg = mz->memcg;
> >>  + if (!memcg)
> >>  + return 0;
> >>  +
> >>  + low_limit = res_counter_read_u64(&memcg->res, RES_LOW_LIMIT);
> >>  + if (!low_limit)
> >>  + return 0;
> >>  +
> >>  + usage = res_counter_read_u64(&memcg->res, RES_USAGE);
> >>  +
> >>  + if (usage < low_limit)
> >>  + return DEF_PRIORITY - 2;
> >>  +
> >>  + for (i = 0; i < DEF_PRIORITY - 2; i++)
> >>  + if (usage - low_limit > (usage >> (i + 3)))
> >>  + break;
> >
> > why this doesn't depend in the current reclaim priority?
> 
> How do you want to use reclaim priority here?

But then you can get up to 2*DEF_PRIORITY-2 priority (in
get_scan_count) in the end and we are back to my original and more
fundamental objection that the low_limit depends on the group size
because small groups basically do not get scanned when under/close_to
limit while big groups do get scanned and reclaimed.

> I don't like an idea to start ignoring low limit on some priorities.

Well, but you are doing that already. If you are reclaiming for prio 0 then
you add up just DEF_PRIORITY-2 which means you reclaim for all groups with
more than 1024 pages on the LRUs.
[...]
-- 
Michal Hocko
SUSE Labs
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