Re: [PATCH v2] mm: process_mrelease: introduce PROCESS_MRELEASE_REAP_KILL flag

[Michal Hocko]

On Wed 29-04-26 14:13:59, Minchan Kim wrote:
> This policy differs from the global OOM killer, which kills all processes
> sharing the same mm to guarantee memory reclamation at all costs (preventing
> system hangs).

Incorrect, we do the same for memcg OOM killer as well. This is not
about preventing system hands. But rather to 

> However, process_mrelease() is invoked by userspace policy.
> If it fails due to sharing, userspace can simply adapt and select another
> victim process (such as another background app in Android case) to release
> memory. We do not need to force success or affect processes that were not
> targeted.

This is a wrong justification for the proposed semantic. You seem to be
assuming this is just fine rather than this would be problematic for
reasons a), b) and c). If there are no strong reasons _against_
following the global policy then we should stick with it. There are very
good reasons why we are doing that on the global level.

If for no other reasons then the proposed semantic severly criples the
shared MM case. You are left with a racy kill and call process_mrelease
approach. You certainly do not want to allow a simple way for tasks to
evade your LMK, do you? So just choose something else is a very bad
approach.

So unless you are aware of a specific reason(s) where collective kill is a
clearly an incorrect behavior then I believe the proper way is to kill
all processes sharing the mm (unless you are crossing any security
boundary when doing that).
-- 
Michal Hocko
SUSE Labs