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Re: [PATCH v5 14/14] Add documentation about the kmem controller [message #48418 is a reply to message #48416]

Tue, 16 October 2012 19:02

Glauber Costa
Messages: 916
Registered: October 2011

Senior Member

On 10/16/2012 10:25 PM, Christoph Lameter wrote:
> On Tue, 16 Oct 2012, Glauber Costa wrote:
>
>>
>> + memory.kmem.limit_in_bytes # set/show hard limit for kernel memory
>> + memory.kmem.usage_in_bytes # show current kernel memory allocation
>> + memory.kmem.failcnt # show the number of kernel memory usage hits limits
>> + memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded
>
> Does it actually make sense to limit kernel memory?

Yes.

> The user generally has
> no idea how much kernel memory a process is using and kernel changes can
> change the memory footprint. Given the fuzzy accounting in the kernel a
> large cache refill (if someone configures the slab batch count to be
> really big f.e.) can account a lot of memory to the wrong cgroup. The
> allocation could fail.
>

It heavily depends on the type of the user. The user may not know how
much kernel memory precisely will be used, but he/she usually knows
quite well that it shouldn't be all cgroups together shouldn't use more
than available in the system.

IOW: It is usually safe to overcommit user memory, but not kernel
memory. This is absolutely crucial in any high-density container host,
and we've been doing this in OpenVZ for ages (in an uglier form than this)

> Limiting the total memory use of a process (U+K) would make more sense I
> guess. Only U is probably sufficient? In what way would a limitation on
> kernel memory in use be good?
>

The kmem counter is also fed into the u counter. If the limit value of
"u" is equal or greater than "k", this is actually what you are doing.

For a lot of application yes, only U is sufficient. This is the default,
btw, since "k" is only even accounted if you set the limit.

All those use cases are detailed a bit below in this file.

A limitation of kernel memory use would be good, for example, to prevent
abuse from non-trusted containers in a high density, shared, container
environment.

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[Message index]

		[PATCH v5 00/14] kmem controller for memcg. By: Glauber Costa on Tue, 16 October 2012 10:16
		[PATCH v5 03/14] memcg: change defines to an enum By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 03/14] memcg: change defines to an enum By: David Rientjes on Wed, 17 October 2012 21:50
		[PATCH v5 01/14] memcg: Make it possible to use the stock for more than one page. By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 01/14] memcg: Make it possible to use the stock for more than one page. By: akpm on Wed, 17 October 2012 22:11
		Re: [PATCH v5 01/14] memcg: Make it possible to use the stock for more than one page. By: Glauber Costa on Thu, 18 October 2012 08:55
		[PATCH v5 04/14] kmem accounting basic infrastructure By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: Michal Hocko on Tue, 16 October 2012 12:14
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: David Rientjes on Wed, 17 October 2012 22:08
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: Glauber Costa on Thu, 18 October 2012 09:02
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: Tejun Heo on Thu, 18 October 2012 19:47
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: Tejun Heo on Thu, 18 October 2012 19:37
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 04/14] kmem accounting basic infrastructure By: Glauber Costa on Thu, 18 October 2012 09:04
		[PATCH v5 11/14] memcg: allow a memcg with kmem charges to be destructed. By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 11/14] memcg: allow a memcg with kmem charges to be destructed. By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 11/14] memcg: allow a memcg with kmem charges to be destructed. By: Glauber Costa on Thu, 18 October 2012 09:33
		[PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: KAMEZAWA Hiroyuki on Wed, 17 October 2012 06:40
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Thu, 18 October 2012 09:16
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: David Rientjes on Thu, 18 October 2012 22:06
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Fri, 19 October 2012 09:10
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: David Rientjes on Fri, 19 October 2012 09:31
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Fri, 19 October 2012 10:00
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: David Rientjes on Wed, 17 October 2012 22:37
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Thu, 18 October 2012 09:23
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: David Rientjes on Thu, 18 October 2012 21:59
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Fri, 19 October 2012 10:08
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: David Rientjes on Fri, 19 October 2012 20:34
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Mon, 22 October 2012 12:34
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Michal Hocko on Mon, 22 October 2012 12:51
		Re: [PATCH v5 06/14] memcg: kmem controller infrastructure By: Glauber Costa on Mon, 22 October 2012 12:52
		[PATCH v5 05/14] Add a __GFP_KMEMCG flag By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 05/14] Add a __GFP_KMEMCG flag By: Michal Hocko on Tue, 16 October 2012 12:15
		Re: [PATCH v5 05/14] Add a __GFP_KMEMCG flag By: David Rientjes on Wed, 17 October 2012 22:09
		[PATCH v5 09/14] memcg: kmem accounting lifecycle management By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 09/14] memcg: kmem accounting lifecycle management By: David Rientjes on Wed, 17 October 2012 23:28
		Re: [PATCH v5 09/14] memcg: kmem accounting lifecycle management By: Michal Hocko on Thu, 18 October 2012 06:14
		Re: [PATCH v5 09/14] memcg: kmem accounting lifecycle management By: Glauber Costa on Thu, 18 October 2012 09:42
		[PATCH v5 10/14] memcg: use static branches when code not in use By: Glauber Costa on Tue, 16 October 2012 10:16
		[PATCH v5 14/14] Add documentation about the kmem controller By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: Michal Hocko on Tue, 16 October 2012 12:23
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: Christoph Lameter on Tue, 16 October 2012 18:25
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: Glauber Costa on Tue, 16 October 2012 19:02
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: Christoph Lameter on Tue, 16 October 2012 19:30
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 14/14] Add documentation about the kmem controller By: Glauber Costa on Thu, 18 October 2012 09:38
		[PATCH v5 13/14] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 13/14] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 13/14] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs By: Glauber Costa on Thu, 18 October 2012 09:37
		[PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: Glauber Costa on Tue, 16 October 2012 10:16
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: Christoph Lameter on Tue, 16 October 2012 15:31
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: Glauber Costa on Tue, 16 October 2012 18:55
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: akpm on Wed, 17 October 2012 22:12
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: Glauber Costa on Thu, 18 October 2012 09:24
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: akpm on Thu, 18 October 2012 20:44
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: Glauber Costa on Thu, 18 October 2012 11:53
		Re: [PATCH v5 07/14] mm: Allocate kernel pages to the right memcg By: David Rientjes on Wed, 17 October 2012 22:43
		Re: [PATCH v5 00/14] kmem controller for memcg. By: akpm on Wed, 17 October 2012 22:11
		Re: [PATCH v5 00/14] kmem controller for memcg. By: Glauber Costa on Thu, 18 October 2012 08:52
		Re: [PATCH v5 00/14] kmem controller for memcg. By: akpm on Thu, 18 October 2012 19:21
		Re: [PATCH v5 00/14] kmem controller for memcg. By: Glauber Costa on Fri, 19 October 2012 09:55

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