linux-kernel - Re: memcg: save 20% of per-page memcg memory overhead

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Date:	Thu, 3 Feb 2011 20:32:47 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: memcg: save 20% of per-page memcg memory overhead

* Johannes Weiner <hannes@...xchg.org> [2011-02-03 15:26:01]:

> This patch series removes the direct page pointer from struct
> page_cgroup, which saves 20% of per-page memcg memory overhead (Fedora
> and Ubuntu enable memcg per default, openSUSE apparently too).
> 
> The node id or section number is encoded in the remaining free bits of
> pc->flags which allows calculating the corresponding page without the
> extra pointer.
> 
> I ran, what I think is, a worst-case microbenchmark that just cats a
> large sparse file to /dev/null, because it means that walking the LRU
> list on behalf of per-cgroup reclaim and looking up pages from
> page_cgroups is happening constantly and at a high rate.  But it made
> no measurable difference.  A profile reported a 0.11% share of the new
> lookup_cgroup_page() function in this benchmark.

Wow! defintely worth a deeper look.

> 
> 	Hannes

-- 
	Three Cheers,
	Balbir
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