Re: [PATCH 1/1] mm: introduce process_reap system call

Andy Lutomirski
2021-06-30T18:26:35Z

On Wed, Jun 23, 2021 at 12:28 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> In modern systems it's not unusual to have a system component monitoring
> memory conditions of the system and tasked with keeping system memory
> pressure under control. One way to accomplish that is to kill
> non-essential processes to free up memory for more important ones.
> Examples of this are Facebook's OOM killer daemon called oomd and
> Android's low memory killer daemon called lmkd.
> For such system component it's important to be able to free memory
> quickly and efficiently. Unfortunately the time process takes to free
> up its memory after receiving a SIGKILL might vary based on the state
> of the process (uninterruptible sleep), size and OPP level of the core
> the process is running. A mechanism to free resources of the target
> process in a more predictable way would improve system's ability to
> control its memory pressure.
> Introduce process_reap system call that reclaims memory of a dying process
> from the context of the caller. This way the memory in freed in a more
> controllable way with CPU affinity and priority of the caller. The workload
> of freeing the memory will also be charged to the caller.
> The operation is allowed only on a dying process.

At the risk of asking a potentially silly question, should this just
be a file in procfs?

Also, please consider removing all mention of the word "reap" from the
user API. For better or for worse, "reap" in UNIX refers to what
happens when a dead task gets wait()ed. I sincerely wish I could go
back in time and gently encourage whomever invented that particular
abomination to change their mind, but my time machine doesn't work.

--Andy