linux-kernel - Re: [PATCH v2] fs: fsnotify: account fsnotify metadata to kmemcg

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Date:   Tue, 14 Nov 2017 03:10:22 +0800
From:   "Yang Shi" <yang.s@...baba-inc.com>
To:     Michal Hocko <mhocko@...nel.org>, Jan Kara <jack@...e.cz>
Cc:     amir73il@...il.com, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs: fsnotify: account fsnotify metadata to kmemcg



On 11/9/17 5:54 AM, Michal Hocko wrote:
> [Sorry for the late reply]
> 
> On Tue 31-10-17 11:12:38, Jan Kara wrote:
>> On Tue 31-10-17 00:39:58, Yang Shi wrote:
> [...]
>>> I do agree it is not fair and not neat to account to producer rather than
>>> misbehaving consumer, but current memcg design looks not support such use
>>> case. And, the other question is do we know who is the listener if it
>>> doesn't read the events?
>>
>> So you never know who will read from the notification file descriptor but
>> you can simply account that to the process that created the notification
>> group and that is IMO the right process to account to.
> 
> Yes, if the creator is de-facto owner which defines the lifetime of
> those objects then this should be a target of the charge.
> 
>> I agree that current SLAB memcg accounting does not allow to account to a
>> different memcg than the one of the running process. However I *think* it
>> should be possible to add such interface. Michal?
> 
> We do have memcg_kmem_charge_memcg but that would require some plumbing
> to hook it into the specific allocation path. I suspect it uses kmalloc,
> right?

Yes.

I took a look at the implementation and the callsites of 
memcg_kmem_charge_memcg(). It looks it is called by:

* charge kmem to memcg, but it is charged to the allocator's memcg
* allocate new slab page, charge to memcg_params.memcg

I think this is the plumbing you mentioned, right?

Thanks,
Yang

>