From: Tejun Heo <tj@kernel.org>
To: Glauber Costa <glommer@parallels.com>
Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
Michal Hocko <mhocko@suse.cz>,
Peter Zijlstra <peterz@infradead.org>,
Paul Turner <pjt@google.com>,
Johannes Weiner <hannes@cmpxchg.org>, Thomas Graf <tgraf@suug.ch>,
"Serge E. Hallyn" <serue@us.ibm.com>,
Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
Neil Horman <nhorman@tuxdriver.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
"Daniel P. Berrange" <berrange@redhat.com>,
Lennart Poettering <lennart@poettering.net>,
Kay Sievers <kay.sievers@vrfy.org>
Subject: Re: [RFC] cgroup TODOs
Date: Mon, 17 Sep 2012 10:21:23 -0700 [thread overview]
Message-ID: <20120917172123.GB18677@google.com> (raw)
In-Reply-To: <5056E467.2090108@parallels.com>
Hello, Glauber.
On Mon, Sep 17, 2012 at 12:50:47PM +0400, Glauber Costa wrote:
> > Can you be a bit more specific?
>
> What I mean is that if some operation needs to operate locked, they will
> have to lock. Whether or not the locking is called from cgroup core or
> not. If the lock is not available outside, people will end up calling a
> core function that locks.
I was asking whether you have certain specific operations on mind.
> >> And the problem is that people need to lock. cgroup_lock is needed
> >> because the data you are accessing is protected by it. The way I see it,
> >> it is incredible how we were able to revive the BKL in the form of
> >> cgroup_lock after we finally manage to successfully get rid of it!
> >
> > I wouldn't go as far as comparing it to BKL.
>
> Of course not, since it is not system-wide. But I think the comparison
> still holds in spirit...
Subsystem-wide locks covering non-hot paths aren't evil things. We
have a lot of them and they work fine. BKL was a completely different
beast initially with implicit locking on kernel entry and unlocking on
sleeping and then got morphed into some chimera inbetween afterwards.
Simple locking is a good thing. If finer-grained locking is
necessary, we sure do that but please stop throwing over-generalized
half-arguments at it. It doesn't help anything.
> you seem to hear "comount", and think of unified vision, and that is the
> reason for this discussion to still be going on. Mounting is all about
> the root. And if you comount, hierarchies have the same root.
>
> In your example, the different controllers are comounted. They have not
> the same view, but the possible views are restricted to be a subset of
> the underlying tree - because they are mounted in the same place, forced
> or not.
Heh, I can't really tell whether you understand it or not. Here and
in the previous thread too. You seem to understand that there are
different views upto this point.
> In a situation like this, it makes all the sense in the world to use the
> css_id as a primary identifier, because it will be guaranteed to be the
And then you say something like this (or that this would remove
walking different hierarchies in the previous thread - yes, to a
certain point but not completely). css_id is a per-css attribute.
How can that be the "primariy" identifier when there can be multiple
views? For each userland-visible cgroup, there must be a css_set
which points to the css's belonging to it, which may not be at the
same level - multiple nodes in the userland visible tree may point to
the same css.
If you mean that css_id would be the primary identifier for that
specific controller's css, why even say that? That's true now and
won't ever change.
> same. What makes the tree overly flexible, is that you can have multiple
> roots, starting in multiple places, with arbitrary topologies downwards.
And now you seem to be on the same page again. But then again, you're
asserting that incorporating forced co-mounts *now* is a gradual step
towards the goal, which is utterly bonkers. I don't know. I just
can't understand what you're thinking at all.
Thanks.
--
tejun
next prev parent reply other threads:[~2012-09-17 17:21 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-13 20:58 [RFC] cgroup TODOs Tejun Heo
2012-09-14 9:04 ` Mike Galbraith
2012-09-14 17:17 ` Tejun Heo
2012-09-14 9:10 ` Daniel P. Berrange
2012-09-14 13:58 ` Vivek Goyal
2012-09-14 19:29 ` Tejun Heo
2012-09-14 21:51 ` Kay Sievers
[not found] ` <5052E7DF.7040000@parallels.com>
2012-09-14 9:12 ` Li Zefan
2012-09-14 11:22 ` Peter Zijlstra
2012-09-14 17:59 ` Tejun Heo
2012-09-14 18:23 ` Peter Zijlstra
2012-09-14 18:33 ` Tejun Heo
2012-09-14 17:43 ` Tejun Heo
2012-09-17 8:50 ` Glauber Costa
2012-09-17 17:21 ` Tejun Heo [this message]
2012-09-14 11:15 ` Peter Zijlstra
2012-09-14 12:54 ` Daniel P. Berrange
2012-09-14 17:53 ` Tejun Heo
2012-09-14 14:25 ` Vivek Goyal
2012-09-14 14:53 ` Peter Zijlstra
2012-09-14 15:14 ` Vivek Goyal
2012-09-14 21:57 ` Tejun Heo
2012-09-17 15:27 ` Vivek Goyal
2012-09-18 18:08 ` Vivek Goyal
2012-09-14 21:39 ` Tejun Heo
2012-09-17 15:05 ` Vivek Goyal
2012-09-17 16:40 ` Tejun Heo
2012-09-14 15:03 ` Michal Hocko
2012-09-19 14:02 ` Michal Hocko
2012-09-19 14:03 ` [PATCH 2.6.32] memcg: warn on deeper hierarchies with use_hierarchy==0 Michal Hocko
2012-09-19 19:38 ` David Rientjes
2012-09-20 13:24 ` Michal Hocko
2012-09-20 22:33 ` David Rientjes
2012-09-21 7:16 ` Michal Hocko
2012-09-19 14:03 ` [PATCH 3.0] " Michal Hocko
2012-09-19 14:05 ` [PATCH 3.2+] " Michal Hocko
2012-09-14 18:07 ` [RFC] cgroup TODOs Vivek Goyal
2012-09-14 18:53 ` Tejun Heo
2012-09-14 19:28 ` Vivek Goyal
2012-09-14 19:44 ` Tejun Heo
2012-09-14 19:49 ` Tejun Heo
2012-09-14 20:39 ` Tejun Heo
2012-09-17 8:40 ` Glauber Costa
2012-09-17 17:30 ` Tejun Heo
2012-09-17 14:37 ` Vivek Goyal
2012-09-14 18:36 ` Aristeu Rozanski
2012-09-14 18:54 ` Tejun Heo
2012-09-15 2:20 ` Serge E. Hallyn
2012-09-15 9:27 ` Controlling devices and device namespaces Eric W. Biederman
2012-09-15 22:05 ` Serge E. Hallyn
2012-09-16 0:24 ` Eric W. Biederman
2012-09-16 3:31 ` Serge E. Hallyn
2012-09-16 11:21 ` Alan Cox
2012-09-16 11:56 ` Eric W. Biederman
2012-09-16 12:17 ` Eric W. Biederman
2012-09-16 13:32 ` Serge Hallyn
2012-09-16 14:23 ` Eric W. Biederman
2012-09-16 16:13 ` Alan Cox
2012-09-16 17:49 ` Eric W. Biederman
2012-09-16 16:15 ` Serge Hallyn
2012-09-16 16:53 ` Eric W. Biederman
2012-09-16 8:19 ` [RFC] cgroup TODOs James Bottomley
2012-09-16 14:41 ` Eric W. Biederman
2012-09-17 13:21 ` Aristeu Rozanski
2012-09-14 22:03 ` Dhaval Giani
2012-09-14 22:06 ` Tejun Heo
2012-09-20 1:33 ` Andy Lutomirski
2012-09-20 18:26 ` Tejun Heo
2012-09-20 18:39 ` Andy Lutomirski
2012-09-21 21:40 ` Tejun Heo
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