linux-kernel - Re: [PATCH v2 1/4] mm/mremap: Optimize the start addresses in move_page

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Message-ID: <CAEXW_YRbekxrn4iUvWGzJBfwMButjT=srHZS2H9P910K8YmH=g@mail.gmail.com>
Date:   Sat, 20 May 2023 00:22:38 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Kirill A Shutemov <kirill@...temov.name>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v2 1/4] mm/mremap: Optimize the start addresses in move_page_tables()

On Sat, May 20, 2023 at 12:14 AM Joel Fernandes <joel@...lfernandes.org> wrote:
>
> On Sat, May 20, 2023 at 12:01 AM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > On Fri, May 19, 2023 at 8:57 PM Joel Fernandes <joel@...lfernandes.org> 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