Re: [PATCH 5/5] mm/thp: Split huge pmds/puds if they're pinned when fork()

Yang Shi
2020-09-24T17:29:43Z

On Thu, Sep 24, 2020 at 8:47 AM Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Sep 23, 2020 at 09:07:49AM -0700, Yang Shi wrote:
> > For tmpfs map, the pmd split just clears the pmd entry without
> > reinstalling ptes (oppositely anonymous map would reinstall ptes). It
> > looks this patch intends to copy at pte level by splitting pmd. But
> > I'm afraid this may not work for tmpfs mappings.
>
> IIUC that's exactly what we want.
>
> We only want to make sure the pinned tmpfs shared pages will be kept there in
> the parent. It's not a must to copy the pages to the child, as long as they
> can be faulted in later correctly.

Aha, got your point. Yes, they can be refaulted in later. This is how
the file THP pmd split was designed.

>
> --
> Peter Xu
>