Re: [PATCH v3 1/5] mm: pagewalk: add the ability to install PTEs

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Fri, Oct 25, 2024 at 09:08:24PM +0200, David Hildenbrand wrote:
> > >
> > > We already discussed in the past that we need a better and more efficient
> > > way to walk page tables. I have part of that on my TODO list, but I'm
> > > getting distracted.
> >
> > Yes I remember an LSF session on this, it's a really obvious area of improvement
> > that stands out at the moment for sure.
> >
> > Having worked several 12+ hour days in a row though recently I can relate to
> > workload making this difficult though :)
>
> Yes :)
>
> >
> > >
> > > *Inserting* (not walking/modifying existing things as most users to) as done
> > > in this patch is slightly different though, likely "on thing that fits all"
> > > will not apply to all page table walker user cases.
> >
> > Yeah, there's also replace scenarios which then have to do egregious amounts of
> > work to make sure we do everything right, in fact there's duplicates of this in
> > mm/madvise.c *grumble grumble*.
> >
> > >
> > > --
> > > Cheers,
> > >
> > > David / dhildenb
> > >
> >
> > OK so I guess I'll hold off my TODOs on this as you are looking in this area and
> > I trust you :)
>
> It will probably take me a while until I get to it, though. I'd focus on
> walking (and batching what we can) first, then on top modifying existing
> entries.

Yeah entirely understandable and that's the right order I think, the
modifying path is the trickier one especially with all the special cases
all over the place...

>
> The "install something where there is nothing yet" (incl. populating fresh
> page tables etc.) case probably deserves a separate "walker".

Yes this would avoid all the heavy handling a replace handler needs.

>
> If you end up having spare cycles and want to sync on a possible design for
> some part of that bigger task -- removing the old pagewalk logic -- please
> do reach out! :)

Thanks, I may have a play when I have a brief moment, as I feel quite
strongly we need to attack this (as do you I feel! :) will send some RFC or
some thoughts or whatever should I do so!

>
> --
> Cheers,
>
> David / dhildenb
>

Cheers!