linux-kernel - Re: [PATCH v12 12/14] x86/sgx: Turn on per-cgroup EPC reclamation

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Date: Tue, 30 Apr 2024 10:18:05 +1200
From: "Huang, Kai" <kai.huang@...el.com>
To: Haitao Huang <haitao.huang@...ux.intel.com>, "hpa@...or.com"
	<hpa@...or.com>, "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
	"linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>, "x86@...nel.org"
	<x86@...nel.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "jarkko@...nel.org" <jarkko@...nel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mkoutny@...e.com" <mkoutny@...e.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "Mehta, Sohil" <sohil.mehta@...el.com>, "tj@...nel.org"
	<tj@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de"
	<bp@...en8.de>
CC: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "anakrish@...rosoft.com"
	<anakrish@...rosoft.com>, "Zhang, Bo" <zhanb@...rosoft.com>,
	"kristen@...ux.intel.com" <kristen@...ux.intel.com>, "yangjie@...rosoft.com"
	<yangjie@...rosoft.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>,
	"chrisyan@...rosoft.com" <chrisyan@...rosoft.com>
Subject: Re: [PATCH v12 12/14] x86/sgx: Turn on per-cgroup EPC reclamation


>>>  /*
>>> @@ -42,7 +63,8 @@ static inline struct sgx_epc_lru_list 
>>> *sgx_lru_list(struct sgx_epc_page *epc_pag
>>>   */
>>>  static inline bool sgx_can_reclaim(void)
>>>  {
>>> -    return !list_empty(&sgx_global_lru.reclaimable);
>>> +    return !sgx_cgroup_lru_empty(misc_cg_root()) ||
>>> +           !list_empty(&sgx_global_lru.reclaimable);
>>>  }
>>
>> Shouldn't this be:
>>
>>     if (IS_ENABLED(CONFIG_CGROUP_MISC))
>>         return !sgx_cgroup_lru_empty(misc_cg_root());
>>     else
>>         return !list_empty(&sgx_global_lru.reclaimable);
>> ?
>>
>> In this way, it is consistent with the sgx_reclaim_pages_global() below.
>>
> 
> I changed to this way because sgx_cgroup_lru_empty() is now defined in 
> both KConfig cases.
> And it seems better to minimize use of the KConfig variables based on 
> earlier feedback (some are yours).
> Don't really have strong preference here. So let me know one way of the 
> other.
> 

But IMHO your code could be confusing, e.g., it can be interpreted as:

   The EPC pages can be managed by both the cgroup LRUs and the
   sgx_global_lru simultaneously at runtime when CONFIG_CGROUP_MISC
   is on.

Which is not true.

So we should make the code clearly reflect the true behaviour.