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

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Date:   Wed, 06 Apr 2022 09:35:39 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>,
        Reinette Chatre <reinette.chatre@...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

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.

BR, Jarkko