Re: JITs and 52-bit VA

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Wed, Jun 22, 2016 at 12:56:56PM -0700, Dave Hansen wrote:
> >> > +1. Also it might be (not sure though, just guessing) suitable to do such
> >> > thing via memory cgroup controller, instead of carrying this limit per
> >> > each process (or task structure/vma or mm).
> > I think we'll want this per mm.  After all, a high-VA-limit-aware bash
> > should be able run high-VA-unaware programs without fiddling with
> > cgroups.
> 
> Yeah, cgroups don't make a lot of sense.

cgroups make sense in terms of shriking data: we only need to
setup the limit once and every process lives in the cgroup
get the limit, no need to carry it per every mm. So I guessed
it might be usefull.

> On x86, the 48-bit virtual address is even hard-coded in the ABI[1].  So
> we can't change *any* program's layout without either breaking the ABI
> or having it opt in.
> 
> But, we're also lucky to only have one VA layout since day one.
> 
> 1. www.x86-64.org/documentation/abi.pdf - a??... Therefore, conforming
> processes may only use addresses from 0x00000000 00000000 to 0x00007fff
> ffffffff .a??

	Cyrill

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