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Date: Tue, 9 Apr 2024 11:03:22 +0200
From: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
To: Haitao Huang <haitao.huang@linux.intel.com>
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Subject: Re: Re: [PATCH v10 12/14] x86/sgx: Turn on per-cgroup EPC reclamation
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On Mon, Apr 08, 2024 at 11:23:21PM -0500, Haitao Huang <haitao.huang@linux.=
intel.com> wrote:
> It's always non-NULL based on testing.
>=20
> 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 u=
ser
> 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=3Dmisc'.
>=20
> 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

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