linux-kernel - Re: [RFC 0/3] Implementation of cgroup isolation

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Date:	Tue, 29 Mar 2011 09:53:55 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Ying Han <yinghan@...gle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [RFC 0/3] Implementation of cgroup isolation

Hi,

On Mon 28-03-11 11:01:18, Ying Han wrote:
> On Mon, Mar 28, 2011 at 2:39 AM, Michal Hocko <mhocko@...e.cz> wrote:
> > Hi all,
> >
> > Memory cgroups can be currently used to throttle memory usage of a group of
> > processes. It, however, cannot be used for an isolation of processes from
> > the rest of the system because all the pages that belong to the group are
> > also placed on the global LRU lists and so they are eligible for the global
> > memory reclaim.
> >
> > This patchset aims at providing an opt-in memory cgroup isolation. This
> > means that a cgroup can be configured to be isolated from the rest of the
> > system by means of cgroup virtual filesystem (/dev/memctl/group/memory.isolated).
> 
> Thank you Hugh pointing me to the thread. We are working on similar
> problem in memcg currently
> 
> Here is the problem we see:
> 1. In memcg, a page is both on per-memcg-per-zone lru and global-lru.
> 2. Global memory reclaim will throw page away regardless of cgroup.
> 3. The zone->lru_lock is shared between per-memcg-per-zone lru and global-lru.

This is the primary motivation for the patchset. Except that I do not
insist on the strict isolation because I found opt-in approach less
invasive because you have to know what you are doing while you are
setting up a group. If the thing is enabled by default we can see many
side-effects during the reclaim, I am afraid.

> And we know:
> 1. We shouldn't do global reclaim since it breaks memory isolation.
> 2. There is no need for a page to be on both LRU list, especially
> after having per-memcg background reclaim.
> 
> So our approach is to take off page from global lru after it is
> charged to a memcg. Only pages allocated at root cgroup remains in
> global LRU, and each memcg reclaims pages on its isolated LRU.

This sounds like an instance where all cgroups are isolated by default
(this can be set by mem_cgroup->isolated = 1).

Thanks
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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