On Thu 09-12-21 08:24:04, Suren Baghdasaryan wrote:

On Thu, Dec 9, 2021 at 1:12 AM Michal Hocko [off-list ref] wrote:

quoted

Do we want this on top?

As we discussed in this thread
https://lore.kernel.org/all/YY4snVzZZZYhbigV@dhcp22.suse.cz (local),
__oom_reap_task_mm in exit_mmap allows oom-reaper/process_mrelease to
unmap pages in parallel with exit_mmap without blocking each other.
Removal of __oom_reap_task_mm from exit_mmap prevents this parallelism
and has a negative impact on performance. So the conclusion of that
thread I thought was to keep that part. My understanding is that we
also wanted to remove MMF_OOM_SKIP as a follow-up patch but
__oom_reap_task_mm would stay.

OK, then we were talking past each other, I am afraid. I really wanted
to get rid of this oom specific stuff from exit_mmap. It was there out
of necessity. With a proper locking we can finally get rid of the crud.
As I've said previously oom reaping has never been a hot path.

If we really want to optimize this path then I would much rather see a
generic solution which would allow to move the write lock down after
unmap_vmas. That would require oom reaper to be able to handle mlocked
memory.
-- 
Michal Hocko
SUSE Labs