netdev - Re: [PATCH v6 10/10] Disable task moving when using kernel memory accounting

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Date:	Mon, 28 Nov 2011 13:32:03 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, lizf@...fujitsu.com,
	ebiederm@...ssion.com, davem@...emloft.net, paul@...lmenage.org,
	gthelen@...gle.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	kirill@...temov.name, avagin@...allels.com, devel@...nvz.org,
	eric.dumazet@...il.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v6 10/10] Disable task moving when using kernel memory
 accounting

On Fri, 25 Nov 2011 15:38:16 -0200
Glauber Costa <glommer@...allels.com> wrote:

> Since this code is still experimental, we are leaving the exact
> details of how to move tasks between cgroups when kernel memory
> accounting is used as future work.
> 
> For now, we simply disallow movement if there are any pending
> accounted memory.
> 
> Signed-off-by: Glauber Costa <glommer@...allels.com>
> CC: Hiroyouki Kamezawa <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/memcontrol.c |   23 ++++++++++++++++++++++-
>  1 files changed, 22 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 2df5d3c..ab7e57b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5451,10 +5451,19 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
>  {
>  	int ret = 0;
>  	struct mem_cgroup *mem = mem_cgroup_from_cont(cgroup);
> +	struct mem_cgroup *from = mem_cgroup_from_task(p);
> +
> +#if defined(CONFIG_CGROUP_MEM_RES_CTLR_KMEM) && defined(CONFIG_INET)
> +	if (from != mem && !mem_cgroup_is_root(from) &&
> +	    res_counter_read_u64(&from->tcp_mem.tcp_memory_allocated, RES_USAGE)) {
> +		printk(KERN_WARNING "Can't move tasks between cgroups: "
> +			"Kernel memory held. task: %s\n", p->comm);
> +		return 1;
> +	}
> +#endif

Hmm, the kernel memory is not guaranteed as being held by the 'task' ?

How about
"Now, moving task between cgroup is disallowed while the source cgroup 
 containes kmem reference." ?

Hmm.. we need to fix this task-move/rmdir issue before production use.


Thanks,
-Kame

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