Date: Tue, 14 Jul 2009 12:46:17 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Paul Menage <menage@google.com>
Cc: lizf@cn.fujitzu.com, containers@lists.linux-foundation.org,
       linux-kernel@vger.kernel.org,
       libcg-devel <libcg-devel@lists.sourceforge.net>,
       akpm@linux-foundation.org, bblum@google.com
Subject: Re: [PATCH 0/2] CGroups: cgroup member list enhancement/fix
Message-ID: <20090714071617.GK5051@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
References: <20090702231814.3969.44308.stgit@menage.mtv.corp.google.com> <20090705063850.GX11273@balbir.in.ibm.com> <6599ad830907101658i13e4046br70377a487dd6b49b@mail.gmail.com> <20090713121138.GC5051@balbir.in.ibm.com> <6599ad830907130926v7788af12hdcd76e4ccb3ab6de@mail.gmail.com> <20090714055638.GI5051@balbir.in.ibm.com> <6599ad830907132349u6cf52060t4fafb6637cbe4ed1@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
In-Reply-To: <6599ad830907132349u6cf52060t4fafb6637cbe4ed1@mail.gmail.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1768
Lines: 44

* menage@google.com <menage@google.com> [2009-07-13 23:49:16]:

> On Mon, Jul 13, 2009 at 10:56 PM, Balbir Singh<balbir@linux.vnet.ibm.com> wrote:
> >>
> >> Waiting for the next scheduling point might be too long, since a
> >> thread can block for arbitrary amounts of time and keeping the marker
> >> around for arbitrary time (unless we add a new task_struct field)
> >> would be tricky. Marking the cgroup or tgid as being migrated which
> >> then triggers the extra synchronization in the fork path (but which
> >> isn't needed at other times) is probably where we'll end up.
> >
> >
> > Hmm... but we would not need that information till we schedule the
> > tasks, adding a field to task_struct is what I had in mind.
> 
> Waiting until schedule to move the threads would result in them still
> showing up in the old "tasks" file until they next ran, which would be
> confusing and misleading.
>

Yes, agreed, even first access to the data struture based lazy
migration might not be too helpful, since it can be very context
dependent.
 
> As a first cut, we were planning to add an rwsem that gets taken for
> read in cgroup_fork(), released in cgroup_post_fork(), and taken for
> write when moving an entire process to a new cgroup; not ideal
> performance-wise, but safe.
> 
> If adding a field to task_struct is an option, then the rwsem could be
> per thread-group leader, which would reduce contention.
>

We should also document that moving large processes with several
threads can be expensive.
 

-- 
	Balbir
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/