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

On Wed, Nov 18, 2020 at 11:10 AM Michal Hocko [off-list ref] wrote:

On Fri 13-11-20 18:16:32, Andrew Morton wrote:
[...]

quoted

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