Re: [PATCHv7 02/14] mm: Add support for unaccepted memory

Mike Rapoport
2022-07-25T13:00:42Z

On Mon, Jul 25, 2022 at 02:23:20PM +0200, Borislav Petkov wrote:
> On Fri, Jul 22, 2022 at 12:30:36PM -0700, Dave Hansen wrote:
> > Sure does... *Something* has to manage the cache coherency so that old
> > physical aliases of the converted memory don't write back and clobber
> > new data. But, maybe the hardware is doing that now.
>
> Let's hope.
>
> > Yeah, that two-tier system is the way it's happening today from what
> > I understand. This whole conversation is about how to handle the >4GB
> > memory.
>
> Would it be possible to pre-accept a bunch of mem - think "pre-fault" -
> from userspace?
>
> I.e., I'm thinking some huge process is going to start in the VM, VM
> userspace goes and causes a chunk of memory to be pre-accepted and then
> the process starts and runs more-or-less smoothly as the majority of its
> memory has already been "prepared".

An application in the VM can do mlock() or mmap(..., MAP_POPULATE, ...) and
this will essentially force acceptance of that memory.

But there's no sysctl or something for that.

> Or does that not make any sense from mm perspective?
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette

--
Sincerely yours,
Mike.