Re: [RFC]: userspace memory reaping

[Minchan Kim <minchan@kernel.org>]

On Tue, Nov 03, 2020 at 01:40:41PM -0800, Suren Baghdasaryan wrote:
> On Tue, Nov 3, 2020 at 1:32 PM Minchan Kim <minchan@kernel.org> wrote:
> >
> > On Tue, Nov 03, 2020 at 10:35:50AM +0100, Michal Hocko wrote:
> > > On Mon 02-11-20 12:29:24, Suren Baghdasaryan wrote:
> > > [...]
> > > > To follow up on this. Should I post an RFC implementing SIGKILL_SYNC
> > > > which in addition to sending a kill signal would also reap the
> > > > victim's mm in the context of the caller? Maybe having some code will
> > > > get the discussion moving forward?
> > >
> > > Yeah, having a code, even preliminary, might help here. This definitely
> > > needs a good to go from process management people as that proper is land
> > > full of surprises...
> >
> > Just to remind a idea I suggested to reuse existing concept
> >
> >     fd = pidfd_open(victim process)
> >     fdatasync(fd);
> >     close(fd);
> >
> 
> Yep, I just posted a comment about that. I think though your above
> sequence is missing a pidfd_send_signal(fd, SIGKILL) before the
> fdatasync(fd)...
> Not sure if fdatasync(pidfd) or fsync(pidfd) would be more appropriate
> for this but will use one and we can discuss details in the RFC with
> the code.

IMO, fdatasync would be better symantic since fsync invovles metadata
(i.e., task_struct, mm_struct and so on). I think what you need is
just pages attached to address_space, which sounds like data, not
metadata.