linux-kernel - Re: [PATCH v16 10/16] x86/sgx: Implement async reclamation for cgroup

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Message-Id: <D3QWE0Z23AVM.1ZWNVW0C9NWMR@kernel.org>
Date: Tue, 27 Aug 2024 21:15:58 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Haitao Huang" <haitao.huang@...ux.intel.com>,
 <dave.hansen@...ux.intel.com>, <kai.huang@...el.com>, <tj@...nel.org>,
 <mkoutny@...e.com>, <chenridong@...wei.com>,
 <linux-kernel@...r.kernel.org>, <linux-sgx@...r.kernel.org>,
 <x86@...nel.org>, <cgroups@...r.kernel.org>, <tglx@...utronix.de>,
 <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
 <sohil.mehta@...el.com>, <tim.c.chen@...ux.intel.com>
Cc: <zhiquan1.li@...el.com>, <kristen@...ux.intel.com>, <seanjc@...gle.com>,
 <zhanb@...rosoft.com>, <anakrish@...rosoft.com>,
 <mikko.ylinen@...ux.intel.com>, <yangjie@...rosoft.com>,
 <chrisyan@...rosoft.com>
Subject: Re: [PATCH v16 10/16] x86/sgx: Implement async reclamation for
 cgroup

On Wed Aug 21, 2024 at 4:53 AM EEST, Haitao Huang wrote:
> From: Kristen Carlson Accardi <kristen@...ux.intel.com>
>
> In cases EPC pages need be allocated during a page fault and the cgroup
> usage is near its limit, an asynchronous reclamation needs to be
> triggered to avoid blocking the page fault handling.
>
> To keep implementation simple, use a workqueue instead of kthread to
> schedule the asynchronous reclamation work. Add corresponding work item and
> function definitions for EPC cgroup.
>
> In sgx_cgroup_try_charge(), if caller does not allow synchronous
> reclamation, queue an asynchronous work into the workqueue.
>
> The current global reclaimer, ksgxd, maintains a threshold for the
> minimal free EPC pages to avoid thrashing when allocating EPC pages.
> Similarly, only reclaiming EPC pages from the current cgroup when its
> usage actually reaches limit could also cause thrashing.  To avoid that,
> define a similar "per-cgroup usage threshold" and actively trigger
> asynchronous per-cgroup EPC reclamation when the usage reaches the
> threshold after try_charge() is successful.
>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
> Co-developed-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
> Tested-by: Jarkko Sakkinen <jarkko@...nel.org>

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko