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

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Message-ID: <54C27E07.6000908@roeck-us.net>
Date:	Fri, 23 Jan 2015 08:59:51 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>
CC:	akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-next@...r.kernel.org,
	Stephen Rothwell <sfr@...b.auug.org.au>, mhocko@...e.cz
Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol:
 remove unnecessary soft limit tree node test'

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

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