linux-kernel - Re: [PATCH v9 10/15] x86/sgx: Add EPC reclamation in cgroup try

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Message-ID: <420b53a7-90fd-48fb-9f08-d28fc936e0f8@intel.com>
Date: Tue, 27 Feb 2024 11:38:44 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, Haitao Huang
	<haitao.huang@...ux.intel.com>, "tj@...nel.org" <tj@...nel.org>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "x86@...nel.org" <x86@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>, "hpa@...or.com"
	<hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>,
	"tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>, "mkoutny@...e.com"
	<mkoutny@...e.com>, "Mehta, Sohil" <sohil.mehta@...el.com>,
	"linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "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 v9 10/15] x86/sgx: Add EPC reclamation in cgroup
 try_charge()



On 27/02/2024 11:31 am, Dave Hansen wrote:
> On 2/26/24 14:24, Huang, Kai wrote:
>> What is the downside of doing per-group reclaim when try_charge()
>> succeeds for the enclave but failed to allocate EPC page?
>>
>> Could you give an complete answer why you choose to use global reclaim
>> for the above case?
> 
> There are literally two different limits at play.  There's the limit
> that the cgroup imposes and then the actual physical limit.
> 
> Hitting the cgroup limit induces cgroup reclaim.
> 
> Hitting the physical limit induces global reclaim.
> 
> Maybe I'm just being dense, but I fail to understand why you would want
> to entangle those two different concepts more than absolutely necessary.

OK.  Yes I agree doing per-cgroup reclaim when hitting physical limit 
would bring another layer of consideration of when to do global reclaim, 
which is not necessary now.