Subject: Re: [RFC PATCH 5/5] powerpc/mm/hash: Increase VA range to 256TB

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 07 Feb 2017 15:46:00 +1100

On Tue, 2017-02-07 at 09:47 +0530, Aneesh Kumar K.V wrote:
> > Benjamin Herrenschmidt <[email-masked]> writes:
> 
> > That's 48 bits. I would keep the limit at 47 without some explicit
> > opt-in by applications. That's what users get on x86 and we know
> > some GPUs have limits there.
> 
> The idea is to have linux personality values that will limit the
> effective address to different memory range. By default max effective
> address will be limited to 64TB. Applications can then extend this to
> 128TB or 512TB. So we will have two personality values PER_LINUX_128TB
> and PER_LINUX_512TB ?

No. I think we can go up to 47-bits without any personality
requirement. For above, a single personality indicating that the
application has no limit.

Check what Intel is doing for 5-level trees

Cheers,
Ben.