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Re: [PATCH v3 04/13] kmem accounting basic infrastructure [message #48123 is a reply to message #48112]

Thu, 27 September 2012 18:30

Glauber Costa
Messages: 916
Registered: October 2011

Senior Member

On 09/27/2012 06:58 PM, Tejun Heo wrote:
> Hello, Mel.
>
> On Thu, Sep 27, 2012 at 03:43:07PM +0100, Mel Gorman wrote:
>>> I'm not too convinced. First of all, the overhead added by kmemcg
>>> isn't big.
>>
>> Really?
>>
>> If kmemcg was globally accounted then every __GFP_KMEMCG allocation in
>> the page allocator potentially ends up down in
>> __memcg_kmem_newpage_charge which
>>
>> 1. takes RCU read lock
>> 2. looks up cgroup from task
>> 3. takes a reference count
>> 4. memcg_charge_kmem -> __mem_cgroup_try_charge
>> 5. release reference count
>>
>> That's a *LOT* of work to incur for cgroups that do not care about kernel
>> accounting. This is why I thought it was reasonable that the kmem accounting
>> not be global.
>
> But that happens only when pages enter and leave slab and if it still
> is significant, we can try to further optimize charging. Given that
> this is only for cases where memcg is already in use and we provide a
> switch to disable it globally, I really don't think this warrants
> implementing fully hierarchy configuration.
>

Not totally true. We still have to match every allocation to the right
cache, and that is actually our heaviest hit, responsible for the 2, 3 %
we're seeing when this is enabled. It is the kind of path so hot that
people frown upon branches being added, so I don't think we'll ever get
this close to being free.

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[Message index]

		[PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Tue, 18 September 2012 14:04
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Fri, 21 September 2012 16:34
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Mon, 24 September 2012 08:09
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Wed, 26 September 2012 14:03
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 14:33
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Wed, 26 September 2012 16:01
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 17:34
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 16:36
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 17:36
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 17:44
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 17:53
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 18:01
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 18:56
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 19:34
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 19:46
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 19:56
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 20:02
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 20:16
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 21:24
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 22:10
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 22:29
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 22:42
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 22:54
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 23:08
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 23:20
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 26 September 2012 23:33
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 12:15
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 12:20
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 12:40
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 12:40
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 12:54
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Mel Gorman on Thu, 27 September 2012 14:28
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Thu, 27 September 2012 14:49
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 14:57
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Thu, 27 September 2012 17:46
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 17:56
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 18:45
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sun, 30 September 2012 07:57
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sun, 30 September 2012 08:02
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: James Bottomley on Sun, 30 September 2012 08:56
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sun, 30 September 2012 10:37
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: James Bottomley on Sun, 30 September 2012 11:25
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Mon, 01 October 2012 00:57
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Mon, 01 October 2012 08:43
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Mon, 01 October 2012 08:46
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 03 October 2012 22:59
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Mon, 01 October 2012 08:36
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 12:08
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 12:11
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Thu, 27 September 2012 14:33
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Mel Gorman on Thu, 27 September 2012 14:43
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Thu, 27 September 2012 14:58
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 27 September 2012 18:30
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sun, 30 September 2012 08:23
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Mon, 01 October 2012 08:45
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 03 October 2012 22:54
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Thu, 04 October 2012 11:55
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sat, 06 October 2012 02:19
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Thu, 27 September 2012 15:09
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Sun, 30 September 2012 08:47
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Mon, 01 October 2012 09:27
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Tejun Heo on Wed, 03 October 2012 22:43
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Michal Hocko on Fri, 05 October 2012 13:47
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Johannes Weiner on Wed, 26 September 2012 22:11
		Re: [PATCH v3 04/13] kmem accounting basic infrastructure By: Glauber Costa on Wed, 26 September 2012 22:45

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