Re: [PATCH v2 1/4] mm/mremap: Optimize the start addresses in move_page_tables()

[Joel Fernandes]

On Sat, May 20, 2023 at 12:14 AM Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:
>
> On Sat, May 20, 2023 at 12:01 AM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, May 19, 2023 at 8:57 PM Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:
> > >
> > > I also realize that I don't really need to check whether the masked
> > > source address falls under a VMA neighboring to that of the source's.
> >
> > I don't think that's true.
> >
> > You can't start randomly moving other source vma's that may have other contents.
>
> If the beginning part of the PMD is not mapped at the destination, I
> thought maybe a whole PMD could be moved to it. But I guess not
> because we don't want those contents to be accessible. So then in that
> case we have to forbid the optimization for all intra-VMA moves except
> those involving the stack. I will think more about it.

Duh, we can't move crap from the source like that also because it has
real data. I think I got confused between "moving" and "copying". I
feel silly, maybe it is time to go to sleep and live to fight another
day.

 - Joel