Re: [RFC]: userspace memory reaping

[Suren Baghdasaryan]

On Tue, Nov 3, 2020 at 1:35 AM Michal Hocko <mhocko@xxxxxxxx> 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...

Hmm. Adding a new SIGKILL_SYNC seems to require quite a surgery...
That will cause a change to SIGRTMIN which is used by glib and also
would affect RTSIG_MAX which I think is also used by the userspace.
I'm not sure such a change would be acceptable...

IIUC, Minchan's alternative suggestion was to do mm reaping from
inside fsync() in cases like these:

pidfd_send_signal(pidfd, SIGKILL); // send SIGKILL as usual
fsync(pidfd); // causes mm reaping in the context of the caller

I can prototype this approach quite easily and quickly and post an RFC
to energize the discussion. Any objections?

> --
> Michal Hocko
> SUSE Labs