Re: [RFC PATCH 3/3] ovl: implement stacked mmap for shared map

[Miklos Szeredi <miklos@szeredi.hu>]

On Mon, Aug 31, 2020 at 5:52 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Aug 31, 2020 at 4:47 PM cgxu <cgxu519@mykernel.net> wrote:
> >
> > On 8/30/20 7:33 PM, Amir Goldstein wrote:

> > > Interesting direction, not sure if this is workable.
> > > I don't know enough about mm to say.
> > >
> > > But what about the rest of the operations?
> > > Did you go over them and decide that overlay doesn't need to implement them?
> > > I doubt it, but if you did, please document that.
> >
> > I did some check for rest of them, IIUC ->fault will be enough for this
> > special case (shared read-only mmap with no upper), I will remove
> > ->page_mkwrite in v2.

Hmm, so this is just for that specific corner case?  Not a generic
shared mmap implementation?

>
> Ok I suppose you checked that ->map_pages is not relevant?
>
> >
> > # I do not consider support ->huge_fault in current stage due to many fs
> > cannot support DAX properly.
> >
> > BTW, do you know who should I add to CC list for further deep review of
> > this code? fadevel-list?
> >
>
> fsdevel would be good, but I would wait for initial feedback from Miklos
> before you post v2...

I could dig into the details of page fault handling, but that's not an
area that I'm intimately familiar with.    So yeah, a high level
description of what happens on mmap, page fault, write fault, etc...
would be really appreciated.

Thanks,
Miklos