linux-kernel - Re: [-mm patch] Show memcg information during OOM (v2)

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Message-ID: <20090203101921.GY918@balbir.in.ibm.com>
Date:	Tue, 3 Feb 2009 15:49:21 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	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 (v2)

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-02-03 17:04:27]:

> On Tue, 3 Feb 2009 12:57:01 +0530
> Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
> > Checkpatch caught an additional space, so here is the patch again
> > 
> > 
> > Description: Add RSS and swap to OOM output from memcg
> > 
> > From: Balbir Singh <balbir@...ux.vnet.ibm.com>
> > 
> > Changelog v2..v1:
> > 
> > 1. Add more information about task's memcg and the memcg
> >    over it's limit
> > 2. Print data in KB
> > 3. Move the print routine outside task_lock()
> > 4. Use rcu_read_lock() around cgroup_path, strictly speaking it
> >    is not required, but relying on the current memcg implementation
> >    is not a good idea.
> > 
> > 
> > This patch displays memcg values like failcnt, usage and limit
> > when an OOM occurs due to memcg.
> > 
> > Thanks go out to Johannes Weiner, Li Zefan, David Rientjes,
> > Kamezawa Hiroyuki, Daisuke Nishimura and KOSAKI Motohiro for
> > review.
> > 
> 
> IIUC, this oom_kill is serialized by memcg_tasklist mutex.
> Then, you don't have to allocate buffer on stack.
> 
> 
> > +void mem_cgroup_print_mem_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.
> > +	 */
> > +	char task_memcg_name[MEM_CGROUP_OOM_BUF_SIZE];
> > +	char memcg_name[MEM_CGROUP_OOM_BUF_SIZE];
> > +	int ret;
> > +
> 
> making this as
> 
> static char task_memcg_name[PATH_MAX];
> static char memcg_name[PATH_MAX];
> 
> is ok, I think. and the patch will be more simple.
>

I am having second thoughts about this one. It introduces a standard
overhead of 2 pages on x86*, while the first one will work for most
cases and all the overhead is on stack, which disappears quickly.
That is the reason I did not do it in the first place and put it as a
NOTE.
 
-- 
	Balbir
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