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Date: Tue, 27 Feb 2024 11:38:44 +1300
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Subject: Re: [PATCH v9 10/15] x86/sgx: Add EPC reclamation in cgroup
 try_charge()
Content-Language: en-US
To: Dave Hansen <dave.hansen@intel.com>, Haitao Huang
	<haitao.huang@linux.intel.com>, "tj@kernel.org" <tj@kernel.org>,
	"jarkko@kernel.org" <jarkko@kernel.org>, "x86@kernel.org" <x86@kernel.org>,
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	<hpa@zytor.com>, "mingo@redhat.com" <mingo@redhat.com>,
	"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>, "mkoutny@suse.com"
	<mkoutny@suse.com>, "Mehta, Sohil" <sohil.mehta@intel.com>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>, "bp@alien8.de" <bp@alien8.de>
CC: "mikko.ylinen@linux.intel.com" <mikko.ylinen@linux.intel.com>,
	"seanjc@google.com" <seanjc@google.com>, "anakrish@microsoft.com"
	<anakrish@microsoft.com>, "Zhang, Bo" <zhanb@microsoft.com>,
	"kristen@linux.intel.com" <kristen@linux.intel.com>, "yangjie@microsoft.com"
	<yangjie@microsoft.com>, "Li, Zhiquan1" <zhiquan1.li@intel.com>,
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References: <20240205210638.157741-1-haitao.huang@linux.intel.com>
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From: "Huang, Kai" <kai.huang@intel.com>
In-Reply-To: <a2d633da-6ab8-49d0-bca5-1e9eb7c3fc9a@intel.com>
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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.