linux-kernel - Re: RFC [Patch] Remove "please try 'cgroup_disable=memory' option if you don't want memory cgroups" printk at boot time.

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Message-ID: <20100401045310.GB6337@balbir.in.ibm.com>
Date:	Thu, 1 Apr 2010 10:23:10 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: RFC [Patch] Remove "please try 'cgroup_disable=memory' option if
 you don't want memory cgroups" printk at boot time.

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-04-01 10:48:59]:

> On Wed, 31 Mar 2010 13:57:46 -0400
> Rik van Riel <riel@...hat.com> wrote:
> 
> > On 03/31/2010 11:54 AM, Larry Woodman wrote:
> > > On Wed, 2010-03-31 at 11:28 -0400, Larry Woodman wrote:
> > >> We are considering removing this printk at boot time from RHEL because
> > >> it will confuse customers, encourage them to change the boot parameters
> > >> and generate extraneous support calls.  Its documented in
> > >> Documentation/kernel-parameters.txt anyway.  Any thoughts???
> > 
> > Yeah, that is a strange boot message...
> > 
> > Acked-by: Rik van Riel <riel@...hat.com>
> > 
> please CC linux-mm and maintainers.
> 
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> It have been there for a year and I think memory usage by page_cgroup
> will not surprise linux kernel users, more.
> 
> Assume x86-32.
> 
> RHEL allows amount of memory up to 16G, right?
> 
> without memcg: memmap uses 32bytes * 16G/4k = 128M.
> with memcg:    memmap+page_cgroup uses (32+20) bytes * 16G/4k = 208M.
> 
> I thought this may cause OOM in ZONE_NORMAL. Then, I added it when I wrote
> original patch. This kind of memory eater can cause trouble when it pops
> up suddenly. But I think 'one year' can be an excuse.
>

I've seen this issue come up on multiple machines, I think the printk
is useful. However, we might need to change the panic() to a big fat
warning and disable the memcg controller if we fail to allocate memory
in page_cgroup_init_flatmem(). 

-- 
	Three Cheers,
	Balbir
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