linux-kernel - Re: [-mm patch] Show memcg information during OOM (v3)

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Message-Id: <20090205135503.f89049e9.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 5 Feb 2009 13:55:03 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	balbir@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [-mm patch] Show memcg information during OOM (v3)

On Thu, 05 Feb 2009 12:00:05 +0800
Lai Jiangshan <laijs@...fujitsu.com> wrote:

>
> > +void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
> > +{
> > +	struct cgroup *task_cgrp;
> > +	struct cgroup *mem_cgrp;
> > +	/*
> > +	 * Need a buffer on stack, can't rely on allocations. The code relies
> > +	 * on the assumption that OOM is serialized for memory controller.
> > +	 * If this assumption is broken, revisit this code.
> > +	 */
> > +	static char task_memcg_name[PATH_MAX];
> > +	static char memcg_name[PATH_MAX];
> 
> Is there any lock which protects this static data?
> 

As commented, seriealized by memory cgroup. see memcg_taslist mutex.


> > +	int ret;
> > +
> > +	if (!memcg)
> > +		return;
> > +
> > +	mem_cgrp = memcg->css.cgroup;
> > +	task_cgrp = mem_cgroup_from_task(p)->css.cgroup;
> > +
> > +	rcu_read_lock();
> > +	ret = cgroup_path(task_cgrp, task_memcg_name, PATH_MAX);
> > +	if (ret < 0) {
> > +		/*
> > +		 * Unfortunately, we are unable to convert to a useful name
> > +		 * But we'll still print out the usage information
> > +		 */
> > +		rcu_read_unlock();
> > +		goto done;
> > +	}
> > +	ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
> > +	 if (ret < 0) {
> > +		rcu_read_unlock();
> > +		goto done;
> > +	}
> > +
> > +	rcu_read_unlock();
> 
> IIRC, a preempt_enable() will add about 50 bytes to kernel size.
> 
I think compliler does good job here....


> I think these lines are also good for readability:
> 
> 	rcu_read_lock();
> 	ret = cgroup_path(task_cgrp, task_memcg_name, PATH_MAX);
> 	if (ret >= 0)
> 		ret = cgroup_path(mem_cgrp, memcg_name, PATH_MAX);
> 	rcu_read_unlock();
> 

In mmotm set, there is no 2 buffers. just one.
Sorry, if you have comments, patch against mmotm is welcome.

Thanks,
-Kame

> 	if (ret < 0) {
> 		/*
> 		 * Unfortunately, we are unable to convert to a useful name
> 		 * But we'll still print out the usage information
> 		 */
> 		goto done;
> 	}
> 
> Lai
> 
> > +
> > +	printk(KERN_INFO "Task in %s killed as a result of limit of %s\n",
> > +			task_memcg_name, memcg_name);
> > +done:
> > +
> > +	printk(KERN_INFO "memory: usage %llukB, limit %llukB, failcnt %llu\n",
> > +		res_counter_read_u64(&memcg->res, RES_USAGE) >> 10,
> > +		res_counter_read_u64(&memcg->res, RES_LIMIT) >> 10,
> > +		res_counter_read_u64(&memcg->res, RES_FAILCNT));
> > +	printk(KERN_INFO "memory+swap: usage %llukB, limit %llukB, "
> > +		"failcnt %llu\n",
> > +		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
> > +		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
> > +		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
> > +}
> > +
> >  /*
> >   * Unlike exported interface, "oom" parameter is added. if oom==true,
> >   * oom-killer can be invoked.
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index d3b9bac..2f3166e 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -394,6 +394,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> >  		cpuset_print_task_mems_allowed(current);
> >  		task_unlock(current);
> >  		dump_stack();
> > +		mem_cgroup_print_oom_info(mem, current);
> >  		show_mem();
> >  		if (sysctl_oom_dump_tasks)
> >  			dump_tasks(mem);
> > 
> 
> 
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