Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process

On Fri, 13 Nov 2020 17:09:37 -0800 Suren Baghdasaryan [off-list ref] wrote:

quoted

quoted

quoted

Seems to me that the ability to reap another process's memory is a
generally useful one, and that it should not be tied to delivering a
signal in this fashion.

And we do have the new process_madvise(MADV_PAGEOUT).  It may need a
few changes and tweaks, but can't that be used to solve this problem?

Thank you for the feedback, Andrew. process_madvise(MADV_DONTNEED) was
one of the options recently discussed in
https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@mail.gmail.com (local)
. The thread describes some of the issues with that approach but if we
limit it to processes with pending SIGKILL only then I think that
would be doable.

Why would it be necessary to read /proc/pid/maps?  I'd have thought
that a starting effort would be

        madvise((void *)0, (void *)-1, MADV_PAGEOUT)

(after translation into process_madvise() speak).  Which is equivalent
to the proposed process_madvise(MADV_DONTNEED_MM)?

Yep, this is very similar to option #3 in
https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@mail.gmail.com (local)
and I actually have a tested prototype for that.

Why is the `vector=NULL' needed?  Can't `vector' point at a single iovec
which spans the whole address range?

If that's the
preferred method then I can post it quite quickly.

I assume you've tested that prototype.  How did its usefulness compare
with this SIGKILL-based approach?