linux-kernel - Re: [PATCH v6 18/29] Allocate memory for memcg caches whenever a new memcg appears

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Date:	Wed, 7 Nov 2012 08:05:10 +0100
From:	Glauber Costa <glommer@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v6 18/29] Allocate memory for memcg caches whenever a
 new memcg appears

On 11/06/2012 01:23 AM, Andrew Morton wrote:
> On Thu,  1 Nov 2012 16:07:34 +0400
> Glauber Costa <glommer@...allels.com> wrote:
> 
>> Every cache that is considered a root cache (basically the "original" caches,
>> tied to the root memcg/no-memcg) will have an array that should be large enough
>> to store a cache pointer per each memcg in the system.
>>
>> Theoreticaly, this is as high as 1 << sizeof(css_id), which is currently in the
>> 64k pointers range. Most of the time, we won't be using that much.
>>
>> What goes in this patch, is a simple scheme to dynamically allocate such an
>> array, in order to minimize memory usage for memcg caches. Because we would
>> also like to avoid allocations all the time, at least for now, the array will
>> only grow. It will tend to be big enough to hold the maximum number of
>> kmem-limited memcgs ever achieved.
>>
>> We'll allocate it to be a minimum of 64 kmem-limited memcgs. When we have more
>> than that, we'll start doubling the size of this array every time the limit is
>> reached.
>>
>> Because we are only considering kmem limited memcgs, a natural point for this
>> to happen is when we write to the limit. At that point, we already have
>> set_limit_mutex held, so that will become our natural synchronization
>> mechanism.
>>
>> ...
>>
>> +static struct ida kmem_limited_groups;
> 
> Could use DEFINE_IDA() here
> 
>>
>> ...
>>
>>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>>  {
>> +	int ret;
>> +
>>  	memcg->kmemcg_id = -1;
>> -	memcg_propagate_kmem(memcg);
>> +	ret = memcg_propagate_kmem(memcg);
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (mem_cgroup_is_root(memcg))
>> +		ida_init(&kmem_limited_groups);
> 
> and zap this?
> 

Ok.

I am starting to go over your replies now, and general question:
Since you have already included this in mm, would you like me to
resubmit the series changing things according to your feedback, or
should I send incremental patches?


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