linux-kernel - Re: [PATCH v5 04/14] kmem accounting basic infrastructure

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Date:	Thu, 18 Oct 2012 21:03:23 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>, <devel@...nvz.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 04/14] kmem accounting basic infrastructure

On 10/18/2012 02:12 AM, Andrew Morton wrote:
> On Tue, 16 Oct 2012 14:16:41 +0400
> Glauber Costa <glommer@...allels.com> wrote:
> 
>> This patch adds the basic infrastructure for the accounting of kernel
>> memory. To control that, the following files are created:
>>
>>  * memory.kmem.usage_in_bytes
>>  * memory.kmem.limit_in_bytes
>>  * memory.kmem.failcnt
> 
> gargh.  "failcnt" is not a word.  Who was it who first thought that
> omitting voewls from words improves anything?
> 
> Sigh.  That pooch is already screwed and there's nothing we can do
> about it now.
> 

Dunno =(


>>  * memory.kmem.max_usage_in_bytes
>>
>> They have the same meaning of their user memory counterparts. They
>> reflect the state of the "kmem" res_counter.
>>
>> Per cgroup kmem memory accounting is not enabled until a limit is set
>> for the group. Once the limit is set the accounting cannot be disabled
>> for that group.  This means that after the patch is applied, no
>> behavioral changes exists for whoever is still using memcg to control
>> their memory usage, until memory.kmem.limit_in_bytes is set for the
>> first time.
>>
>> We always account to both user and kernel resource_counters. This
>> effectively means that an independent kernel limit is in place when the
>> limit is set to a lower value than the user memory. A equal or higher
>> value means that the user limit will always hit first, meaning that kmem
>> is effectively unlimited.
>>
>> People who want to track kernel memory but not limit it, can set this
>> limit to a very high number (like RESOURCE_MAX - 1page - that no one
>> will ever hit, or equal to the user memory)
>>
>>
>> ...
>>
>> +/* internal only representation about the status of kmem accounting. */
>> +enum {
>> +	KMEM_ACCOUNTED_ACTIVE = 0, /* accounted by this cgroup itself */
>> +};
>> +
>> +#define KMEM_ACCOUNTED_MASK (1 << KMEM_ACCOUNTED_ACTIVE)
>> +
>> +#ifdef CONFIG_MEMCG_KMEM
>> +static void memcg_kmem_set_active(struct mem_cgroup *memcg)
>> +{
>> +	set_bit(KMEM_ACCOUNTED_ACTIVE, &memcg->kmem_accounted);
>> +}
>> +#endif
> 
> I don't think memcg_kmem_set_active() really needs to exist.  It has a
> single caller and is unlikely to get any additional callers, so just
> open-code it there?
> 

Actually they exist as a way to make everything fit in closer to
80-columns without writing the function spanning 10 lines.

I can open code them if you guys prefer.
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