Re: memcg: slab control

[Ying Han <yinghan@google.com>]

On Wed, Nov 25, 2009 at 6:35 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi
>
>> Hi,
>>
>> I wanted to see what the current ideas are concerning kernel memory
>> accounting as it relates to the memory controller.  Eventually we'll want
>> the ability to restrict cgroups to a hard slab limit.  That'll require
>> accounting to map slab allocations back to user tasks so that we can
>> enforce a policy based on the cgroup's aggregated slab usage similiar to
>> how the memory controller currently does for user memory.
>>
>> Is this currently being thought about within the memcg community?  We'd
>> like to start a discussion and get everybody's requirements and interests
>> on the table and then become actively involved in the development of such
>> a feature.
>
> I don't think memory hard isolation is bad idea. however, slab restriction
> is too strange. some device use slab frequently, another someone use get_free_pages()
> directly. only slab restriction will not make expected result from admin view.
>
> Probably, we need to implement generic memory reservation framework. it mihgt help
> implemnt rt-task memory reservation and userland oom manager.
>
> It is only my personal opinion...

Looks like the beancounters implementation counts both the kernel slab
objects as well as the
pages from get_free_pages(). But It relies the caller to pass down a
GFP flag indicating the page
or slab to be accountable or not. I am looking at the beancounters v5 at:

http://lkml.indiana.edu/hypermail/linux/kernel/0610.0/1719.html

I kind of like the idea to have a kernel memory controller instead of
kernel slab controller.
If we only count kernel slabs, do we need another mechanism to count
kernel allocations
directly from get_free_pages() ?

--Ying
>
>
> Thanks.
>
>

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