linux-kernel - Re: [PATCH v6 09/12] x86/sgx: Restructure top-level EPC reclaim function

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Message-ID: <ZYCCFXZiMpaaYPKv@himmelriiki>
Date: Mon, 18 Dec 2023 19:32:05 +0200
From: Mikko Ylinen <mikko.ylinen@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "Mehta, Sohil" <sohil.mehta@...el.com>,
	"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>,
	"tj@...nel.org" <tj@...nel.org>,
	"mkoutny@...e.com" <mkoutny@...e.com>,
	"haitao.huang@...ux.intel.com" <haitao.huang@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bp@...en8.de" <bp@...en8.de>,
	"seanjc@...gle.com" <seanjc@...gle.com>,
	"Zhang, Bo" <zhanb@...rosoft.com>,
	"kristen@...ux.intel.com" <kristen@...ux.intel.com>,
	"anakrish@...rosoft.com" <anakrish@...rosoft.com>,
	"sean.j.christopherson@...el.com" <sean.j.christopherson@...el.com>,
	"Li, Zhiquan1" <zhiquan1.li@...el.com>,
	"yangjie@...rosoft.com" <yangjie@...rosoft.com>
Subject: Re: [PATCH v6 09/12] x86/sgx: Restructure top-level EPC reclaim
 function

On Mon, Dec 18, 2023 at 01:44:56AM +0000, Huang, Kai wrote:
> 
> Let's focus on enabling functionality first.  When you have some real
> performance issue that is related to this, we can come back then.
> 
> Btw, I think you need to step back even further.  IIUC the whole multiple LRU
> thing isn't mandatory in this initial support.
> 
> Please (again) take a look at the comments from Dave and Michal:
> 
> https://lore.kernel.org/lkml/7a1a5125-9da2-47b6-ba0f-cf24d84df16b@intel.com/#t
> https://lore.kernel.org/lkml/yz44wukoic3syy6s4fcrngagurkjhe2hzka6kvxbajdtro3fwu@zd2ilht7wcw3/

I don't think setting a hard limit without any reclaiming is preferred.

I'd rather see this similar to what the "sgx_epc.high" was in the RFC
patchset: misc.max for sgx_epc becomes the max value for EPC usage but
enclaves larger than the limit would still run OK. Per-cgroup reclaiming
allows additional controls via memory.high/max in the same cgroup.

If this reclaim flexibily was not there, the sgx_epc limit would always
have to be set based on some "peak" EPC consumption which may not even
be known at the time the limit is set.

>From a container runtime perspective (which is what I'm working for Kubernetes)
the current proposal seems best to me: a container is guaranteed at most
the amount of EPC set as the limit and no other container gets to use it.
Also, each container gets charged for reclaiming independently if a low
max value is used (which might be desirable to get more containers to run on the
same node/system). In this model, the sum of containers' max values would be
the capacity.

-- Mikko