Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'

From: Guenter Roeck <linux@roeck-us.net>
To: Johannes Weiner <hannes@cmpxchg.org>, Christoph Lameter <cl@linux.com>
Cc: akpm@linux-foundation.org, mm-commits@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-next@vger.kernel.org,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	mhocko@suse.cz
Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test'
Date: Fri, 23 Jan 2015 08:59:51 -0800	[thread overview]
Message-ID: <54C27E07.6000908@roeck-us.net> (raw)
In-Reply-To: <20150123160204.GA32592@phnom.home.cmpxchg.org>

On 01/23/2015 08:02 AM, Johannes Weiner wrote:
> On Fri, Jan 23, 2015 at 09:17:44AM -0600, Christoph Lameter wrote:
>> On Fri, 23 Jan 2015, Johannes Weiner wrote:
>>
>>> Is the assumption of this patch wrong?  Does the specified node have
>>> to be online for the fallback to work?
>>
>> Nodes that are offline have no control structures allocated and thus
>> allocations will likely segfault when the address of the controls
>> structure for the node is accessed.
>>
>> If we wanted to prevent that then every allocation would have to add a
>> check to see if the nodes are online which would impact performance.
>
> Okay, that makes sense, thank you.
>
> Andrew, can you please drop this patch?
>
Problem is that there are three patches.

2537ffb mm: memcontrol: consolidate swap controller code
2f9b346 mm: memcontrol: consolidate memory controller initialization
a40d0d2 mm: memcontrol: remove unnecessary soft limit tree node test

Reverting (or dropping) a40d0d2 alone is not possible since it modifies
mem_cgroup_soft_limit_tree_init which is removed by 2f9b346.

Guenter