linux-kernel - Re: [PATCH V3 19/30] x86/sgx: Free up EPC pages directly to support large page ranges

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Message-ID: <573970eb-f466-aad4-3808-fde5f3374e7c@intel.com>
Date:   Wed, 6 Apr 2022 10:50:23 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>
CC:     <dave.hansen@...ux.intel.com>, <tglx@...utronix.de>,
        <bp@...en8.de>, <luto@...nel.org>, <mingo@...hat.com>,
        <linux-sgx@...r.kernel.org>, <x86@...nel.org>, <seanjc@...gle.com>,
        <kai.huang@...el.com>, <cathy.zhang@...el.com>,
        <cedric.xing@...el.com>, <haitao.huang@...el.com>,
        <mark.shanahan@...el.com>, <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 19/30] x86/sgx: Free up EPC pages directly to support
 large page ranges

Hi Jarkko,

On 4/5/2022 11:35 PM, Jarkko Sakkinen wrote:
> On Tue, 2022-04-05 at 10:25 -0700, Dave Hansen wrote:
>> On 4/5/22 10:13, Reinette Chatre wrote:
>>>>> +void sgx_direct_reclaim(void)
>>>>> +{
>>>>> +       if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
>>>>> +               sgx_reclaim_pages();
>>>>> +}
>>>> Please, instead open code this to both locations - not enough redundancy
>>>> to be worth of new function. Causes only unnecessary cross-referencing
>>>> when maintaining. Otherwise, I agree with the idea.
>>>>
>>> hmmm, that means the heart of the reclaimer (sgx_reclaim_pages()) would be
>>> made available for direct use from everywhere in the driver. I will look into this.
>>
>> I like the change.  It's not about reducing code redundancy, it's about
>> *describing* what the code does.  Each location could have:
>>
>>         /* Enter direct SGX reclaim: */
>>         if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
>>                 sgx_reclaim_pages();
>>
>> Or, it could just be:
>>
>>         sgx_direct_reclaim();
>>
>> Which also provides a logical choke point to add comments, like:
>>
>> /*
>>  * sgx_direct_reclaim() should be called in locations where SGX
>>  * memory resources might be low and might be needed in order
>>  * to make forward progress.
>>  */
>> void sgx_direct_reclaim(void)
>> {
>>         ...
> 
> Maybe cutting hairs but could it be "sgx_reclaim_direct"? Rationale
> is easier grepping of reclaimer functions, e.g. when tracing.

Sure, will do.

This may not help grepping all reclaimer functions though since
the code is not consistent in this regard.

Reinette