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

[Haitao Huang]

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.

> This isn't about a "heavy enclave load".  If there is *that* much  
> swapped-out enclave memory, will an enclave even make meaningful forward  
> progress?