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

[Suren Baghdasaryan]

On Wed, Nov 18, 2020 at 11:10 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Fri 13-11-20 18:16:32, Andrew Morton wrote:
> [...]
> > It's all sounding a bit painful (but not *too* painful).  But to
> > reiterate, I do think that adding the ability for a process to shoot
> > down a large amount of another process's memory is a lot more generally
> > useful than tying it to SIGKILL, agree?
>
> I am not sure TBH. Is there any reasonable usecase where uncoordinated
> memory tear down is OK and a target process which is able to see the
> unmapped memory?

I think uncoordinated memory tear down is a special case which makes
sense only when the target process is being killed (and we can enforce
that by allowing MADV_DONTNEED to be used only if the target process
has pending SIGKILL). However, the ability to apply other flavors of
process_madvise() to large memory areas spanning multiple VMAs can be
useful in more cases. For example in Android we will use
process_madvise(MADV_PAGEOUT) to "shrink" an inactive background
process. Today we have to read /proc/maps and construct the vector of
VMAs even when applying this advice to the entire process. With such a
special mode we could achieve this more efficiently and with less
hussle.

> --
> Michal Hocko
> SUSE Labs