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

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Date: Mon, 26 Feb 2024 14:31:28 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Huang, Kai" <kai.huang@...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 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.