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

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Date: Wed, 21 Feb 2024 11:06:02 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "hpa@...or.com" <hpa@...or.com>, "tim.c.chen@...ux.intel.com"
	<tim.c.chen@...ux.intel.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"jarkko@...nel.org" <jarkko@...nel.org>, "cgroups@...r.kernel.org"
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	"tglx@...utronix.de" <tglx@...utronix.de>, "haitao.huang@...ux.intel.com"
	<haitao.huang@...ux.intel.com>, "Mehta, Sohil" <sohil.mehta@...el.com>,
	"tj@...nel.org" <tj@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>,
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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()


> -int sgx_epc_cgroup_try_charge(struct sgx_epc_cgroup *epc_cg)
> +int sgx_epc_cgroup_try_charge(struct sgx_epc_cgroup *epc_cg, bool reclaim)
>  {
> -	return misc_cg_try_charge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE);
> +	for (;;) {
> +		if (!misc_cg_try_charge(MISC_CG_RES_SGX_EPC, epc_cg->cg,
> +					PAGE_SIZE))
> +			break;
> +
> +		if (sgx_epc_cgroup_lru_empty(epc_cg->cg))
> +			return -ENOMEM;
> +
> +		if (signal_pending(current))
> +			return -ERESTARTSYS;
> +
> +		if (!reclaim) {
> +			queue_work(sgx_epc_cg_wq, &epc_cg->reclaim_work);
> +			return -EBUSY;
> +		}
> +
> +		if (!sgx_epc_cgroup_reclaim_pages(epc_cg->cg, false))
> +			/* All pages were too young to reclaim, try again a little later */
> +			schedule();
> +	}
> +
> +	return 0;
>  }
>  

Seems this code change is 90% similar to the existing code in the
sgx_alloc_epc_page():

	...
	for ( ; ; ) {
                page = __sgx_alloc_epc_page();
                if (!IS_ERR(page)) {
                        page->owner = owner;
                        break;
                }

                if (list_empty(&sgx_active_page_list))
                        return ERR_PTR(-ENOMEM);

                if (!reclaim) {
                        page = ERR_PTR(-EBUSY);
                        break;
                }

                if (signal_pending(current)) {
                        page = ERR_PTR(-ERESTARTSYS);
                        break;
                }

                sgx_reclaim_pages();
                cond_resched();
        }
	...

Is it better to move the logic/code change in try_charge() out to
sgx_alloc_epc_page() to unify them?

IIUC, the logic is quite similar: When you either failed to allocate one page,
or failed to charge one page, you try to reclaim EPC page(s) from the current
EPC cgroup, either directly or indirectly.

No?