[Devel] Re: [PATCH v4 00/25] kmem limitation for memcg

[Kamezawa Hiroyuki]

(2012/06/18 19:27), 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 guys, specially concerning the big churn
> inside the allocators themselves.
> 
> My focus in this new round was to keep the changes in the cache internals to
> a minimum. To do that, I relied upon two main pillars:
> 
>   * Cristoph's unification series, that allowed me to put must of the changes
>     in a common file. Even then, the changes are not too many, since the overal
>     level of invasiveness was decreased.
>   * Accounting is done directly from the page allocator. This means some pages
>     can fail to be accounted, but that can only happen when the task calling
>     kmem_cache_alloc or kmalloc is not the same task allocating a new page.
>     This never happens in steady state operation if the tasks are kept in the
>     same memcg. Naturally, if the page ends up being accounted to a memcg that
>     is not limited (such as root memcg), that particular page will simply not
>     be accounted.
> 
> The dispatcher code stays (mem_cgroup_get_kmem_cache), being the mechanism who
> guarantees that, during steady state operation, all objects allocated in a page
> will belong to the same memcg. I consider this a good compromise point between
> strict and loose accounting here.
> 

2 questions.

  - Do you have performance numbers ?

  - Do you think user-memory memcg should be switched to page-allocator level accounting ?
    (it will require some study for modifying current bached-freeing and per-cpu-stock
     logics...)

Thanks,
-Kame