linux-kernel - Re: [PATCH v6 1/8] Basic kernel memory functionality for the Memory Controller

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Message-ID: <4E969F19.4010802@parallels.com>
Date:	Thu, 13 Oct 2011 12:19:37 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Greg Thelen <gthelen@...gle.com>
CC:	<linux-kernel@...r.kernel.org>, <paul@...lmenage.org>,
	<lizf@...fujitsu.com>, <kamezawa.hiroyu@...fujitsu.com>,
	<ebiederm@...ssion.com>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>, <linux-mm@...ck.org>,
	<kirill@...temov.name>, <avagin@...allels.com>, <devel@...nvz.org>
Subject: Re: [PATCH v6 1/8] Basic kernel memory functionality for the Memory
 Controller

On 10/13/2011 11:18 AM, Greg Thelen wrote:
> On Mon, Oct 10, 2011 at 3:24 AM, Glauber Costa<glommer@...allels.com>  wrote:
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index 06eb6d9..bf00cd2 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
> ...
>> @@ -255,6 +262,31 @@ When oom event notifier is registered, event will be delivered.
>>    per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
>>    zone->lru_lock, it has no lock of its own.
>>
>> +2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
>> +
>> + With the Kernel memory extension, the Memory Controller is able to limit
>
> Extra leading space before 'With'.
>
>> +the amount of kernel memory used by the system. Kernel memory is fundamentally
>> +different than user memory, since it can't be swapped out, which makes it
>> +possible to DoS the system by consuming too much of this precious resource.
>> +Kernel memory limits are not imposed for the root cgroup.
>> +
>> +Memory limits as specified by the standard Memory Controller may or may not
>> +take kernel memory into consideration. This is achieved through the file
>> +memory.independent_kmem_limit. A Value different than 0 will allow for kernel
>
> s/Value/value/
>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 3508777..d25c5cb 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
> ...
>> +static int kmem_limit_independent_write(struct cgroup *cont, struct cftype *cft,
>> +                                       u64 val)
>> +{
>> +       cgroup_lock();
>> +       mem_cgroup_from_cont(cont)->kmem_independent_accounting = !!val;
>> +       cgroup_unlock();
>
> I do not think cgroup_lock,unlock are needed here.  The cont and
> associated cgroup should be guaranteed by the caller to be valid.
> Does this lock provide some other synchronization?
Yeah, I think I was being overcautious.

With the following comments addressed, can I add your Reviewed-by to 
this one ?

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