[Devel] Re: [PATCH v3 00/28] kmem limitation for memcg

[Glauber Costa]

On 06/07/2012 02:26 PM, Frederic Weisbecker wrote:
> On Fri, May 25, 2012 at 05:03:20PM +0400, Glauber Costa wrote:
>> Hello All,
>>
>> This is my new take for the memcg kmem accounting. This should merge
>> all of the previous comments from you, plus fix a bunch of bugs.
>>
>> At this point, I consider the series pretty mature. Since last submission
>> 2 weeks ago, I focused on broadening the testing coverage. Some bugs were
>> fixed, but that of course doesn't mean no bugs exist.
>>
>> I believe some of the early patches here are already in some trees around.
>> I don't know who should pick this, so if everyone agrees with what's in here,
>> please just ack them and tell me which tree I should aim for (-mm? Hocko's?)
>> and I'll rebase it.
>>
>> I should point out again that most, if not all, of the code in the caches
>> are wrapped in static_key areas, meaning they will be completely patched out
>> until the first limit is set. Enabling and disabling of static_keys incorporate
>> the last fixes for sock memcg, and should be pretty robust.
>>
>> I also put a lot of effort, as you will all see, in the proper separation
>> of the patches, so the review process is made as easy as the complexity of
>> the work allows to.
>
> So I believe that if I want to implement a per kernel stack accounting/limitation,
> I need to work on top of your patchset.
>
> What do you think about having some sub kmem accounting based on the caches?
> For example there could be a specific accounting per kmem cache.
>
> Like if we use a specific kmem cache to allocate the kernel stack
> (as is done by some archs but I can generalize that for those who want
> kernel stack accounting), allocations are accounted globally in the memcg as
> done in your patchset but also on a seperate counter only for this kmem cache
> on the memcg, resulting in a kmem.stack.usage somewhere.
>
> The concept of per kmem cache accounting can be expanded more for any
> kind of finegrained kmem accounting.
>
> Thoughts?

I believe a general separation is too much, and will lead to knob 
explosion. So I don't think it is a good idea.

Now, for the stack itself, it can be justified. The question that 
remains to be answered is:

Why do you need to set the stack value separately? Isn't accounting the 
stack value, and limiting against the global kmem limit enough?