Re: [RFC v2] prctl: prctl(PR_SET_IDLE, PR_IDLE_MODE_KILLME), for stateless idle loops

On Mon 20-11-17 20:48:10, Shawn Landden wrote:

On Mon, Nov 20, 2017 at 12:35 AM, Michal Hocko [off-list ref] wrote:

quoted

On Fri 17-11-17 20:45:03, Shawn Landden wrote:

quoted

On Fri, Nov 3, 2017 at 2:09 AM, Michal Hocko [off-list ref] wrote:

quoted

On Thu 02-11-17 23:35:44, Shawn Landden wrote:

quoted

It is common for services to be stateless around their main event loop.
If a process sets PR_SET_IDLE to PR_IDLE_MODE_KILLME then it
signals to the kernel that epoll_wait() and friends may not complete,
and the kernel may send SIGKILL if resources get tight.

See my systemd patch: https://github.com/shawnl/systemd/tree/prctl

Android uses this memory model for all programs, and having it in the
kernel will enable integration with the page cache (not in this
series).

16 bytes per process is kinda spendy, but I want to keep
lru behavior, which mem_score_adj does not allow. When a supervisor,
like Android's user input is keeping track this can be done in

user-space.

quoted

It could be pulled out of task_struct if an cross-indexing additional
red-black tree is added to support pid-based lookup.

This is still an abuse and the patch is wrong. We really do have an API
to use I fail to see why you do not use it.

When I looked at wait_queue_head_t it was 20 byes.

I do not understand. What I meant to say is that we do have a proper
user api to hint OOM killer decisions.

This is a FIFO queue, rather than a heuristic, which is all you get
with the current API.

Yes I can read the code. All I am saing is that we already have an API
to achieve what you want or at least very similar.

Let me be explicit.
Nacked-by: Michal Hocko [off-list ref]
until it is sufficiently explained that the oom_score_adj is not
suitable and there are no other means to achieve what you need.
-- 
Michal Hocko
SUSE Labs

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