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

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Date: Mon, 26 Feb 2024 13:56:42 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Haitao Huang <haitao.huang@...ux.intel.com>,
 "Huang, Kai" <kai.huang@...el.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 13:48, Haitao Huang wrote:
> In case of overcomitting, i.e., sum of limits greater than the EPC
> capacity, if one group has a fault, and its usage is not above its own
> limit (try_charge() passes), yet total usage of the system has exceeded
> the capacity, whether we do global reclaim or just reclaim pages in the
> current faulting group.

I don't see _any_ reason to limit reclaim to the current faulting cgroup.

>> Last, what is the simplest (least amount of code) thing that the SGX
>> cgroup controller could implement here?
> 
> I still think the current approach of doing global reclaim is reasonable
> and simple: try_charge() checks cgroup limit and reclaim within the
> group if needed, then do EPC page allocation, reclaim globally if
> allocation fails due to global usage reaches the capacity.
> 
> I'm not sure how not doing global reclaiming in this case would bring
> any benefit.
I tend to agree.

Kai, I think your examples sound a little bit contrived.  Have actual
users expressed a strong intent for doing anything with this series
other than limiting bad actors from eating all the EPC?