linux-kernel - Re: Re: [PATCH v10 12/14] x86/sgx: Turn on per-cgroup EPC reclamation

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Date: Wed, 10 Apr 2024 13:28:06 -0500
From: "Haitao Huang" <haitao.huang@...ux.intel.com>
To: Michal Koutný <mkoutny@...e.com>, "Haitao Huang"
 <haitao.huang@...ux.intel.com>
Cc: "hpa@...or.com" <hpa@...or.com>, "tim.c.chen@...ux.intel.com"
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 <linux-sgx@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
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Subject: Re: Re: [PATCH v10 12/14] x86/sgx: Turn on per-cgroup EPC reclamation

On Tue, 09 Apr 2024 10:34:06 -0500, Haitao Huang  
<haitao.huang@...ux.intel.com> wrote:

> On Tue, 09 Apr 2024 04:03:22 -0500, Michal Koutný <mkoutny@...e.com>  
> wrote:
>
>> On Mon, Apr 08, 2024 at 11:23:21PM -0500, Haitao Huang  
>> <haitao.huang@...ux.intel.com> wrote:
>>> It's always non-NULL based on testing.
>>>
>>> It's hard for me to say definitely by reading the code. But IIUC
>>> cgroup_disable command-line only blocks operations in /sys/fs/cgroup  
>>> so user
>>> space can't set up controllers and config limits, etc., for the  
>>> diasabled
>>> ones. Each task->cgroups would still have a non-NULL pointer to the  
>>> static
>>> root object for each cgroup that is enabled by KConfig, so
>>> get_current_misc_cg() thus  sgx_get_current_cg() should not return NULL
>>> regardless 'cgroup_disable=misc'.
>>>
>>> Maybe @Michal or @tj can confirm?
>>
>> The current implementation creates root css object (see cgroup_init(),
>> cgroup_ssid_enabled() check is after cgroup_init_subsys()).
>> I.e. it will look like all tasks are members of root cgroup wrt given
>> controller permanently and controller attribute files won't exist.
>>
>> (It is up to the controller implementation to do further optimization
>> based on the boot-time disablement (e.g. see uses of
>> mem_cgroup_disabled()). Not sure if this is useful for misc controller.)
>>
>> As for the WARN_ON(1), taking example from memcg -- NULL is best
>> synonymous with root. It's a judgement call which of the values to store
>> and when to intepret it.
>>
>> HTH,
>> Michal
> Thanks for the info.
>
> The way I see it, misc does not have special handling like memcg so  
> every task at least belong to the root(default) group even if it's  
> disabled by command line parameter. So we would not get NULL from  
> get_current_misc_cg(). I think I'll keep the WARN_ON_ONCE for now as a  
> reminder in case misc do have custom support for disabling in future.
>
Actually I think it makes more sense just add some comments instead of  
WARN.
That's what I did in v11 now.

Thanks
Haitao