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

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Date: Thu, 22 Feb 2024 11:09:52 -0600
From: "Haitao Huang" <haitao.huang@...ux.intel.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"
 <cgroups@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "mkoutny@...e.com" <mkoutny@...e.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "Mehta, Sohil"
 <sohil.mehta@...el.com>, "tj@...nel.org" <tj@...nel.org>, "mingo@...hat.com"
 <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>, "Huang, Kai"
 <kai.huang@...el.com>
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 Wed, 21 Feb 2024 05:06:02 -0600, Huang, Kai <kai.huang@...el.com> wrote:

>
>> -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?

Only these lines are the same:
                 if (!reclaim) {
                         page = ERR_PTR(-EBUSY);
                         break;
                 }

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

In sgx_alloc_epc_page() we do global reclamation but here we do per-cgroup  
reclamation. That's why the logic of other lines is different though they  
look similar due to similar function names. For the global reclamation we  
need consider case in that cgroup is not enabled. Similarly  
list_empty(&sgx_active_page_list) would have to be changed to check root  
cgroup if cgroups enabled otherwise check global LRU.  The (!reclaim) case  
is also different.  So I don't see an obvious good way to abstract those  
to get meaningful savings.

Thanks
Haitao