Re: [PATCH v2 1/2] x86/sgx: Add accounting for tracking overcommit

[Dave Hansen]

On 1/11/22 08:33, Haitao Huang wrote:
> On Tue, 11 Jan 2022 09:43:35 -0600, Dave Hansen <dave.hansen@xxxxxxxxx> 
> wrote:
> > On 1/11/22 06:20, Haitao Huang wrote:
> > > If the system has a ton of RAM but limited EPC, I think it makes 
> > > sense to allow more EPC swapping, can we do min(0.5*RAM, 2*EPC)?
> > > I suppose if the system is used for heavy enclave load, user would be 
> > > willing to at least use half of RAM.
> >
> > If I have 100GB of RAM and 100MB of EPC, can I really *meaningfully* 
> > run 50GB of enclaves?  In that case, if everything was swapped out 
> > evenly, I would only have a 499/500 chance that a given page reference 
> > would fault.
>
> The formula will cap swapping at 2*EPC so only 200MB swapped out.  So 
> the miss is at most 1/3.
> The original hard coded cap 1.5*EPC may still consume too much RAM if 
> RAM<1.5*EPC.

Oh, sorry, I read that backwards.

Basing it on the amount of RAM is a bit nasty.  You might either really 
overly restrict the amount of allowed EPC, or you have to handle hotplug.