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

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Message-ID: <afa2dc80-16a3-d3d1-5090-9430eaafc841@alibaba-inc.com>
Date:   Wed, 15 Nov 2017 01:32:16 +0800
From:   "Yang Shi" <yang.s@...baba-inc.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, 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 11/14/17 1:39 AM, Michal Hocko wrote:
> On Tue 14-11-17 03:10:22, Yang Shi wrote:
>>
>>
>> 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?
> 
> Maybe I have misunderstood, but you are using slab allocator. So you
> would need to force it to use a different charging context than current.

Yes.

> I haven't checked deeply but this doesn't look trivial to me.

I agree. This is also what I explained to Jan and Amir in earlier 
discussion.

Yang

>