linux-kernel - Re: [RFC] EPOLL_KILLME: New flag to epoll_wait() that subscribes process to death row (new syscall)

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Date:   Fri, 3 Nov 2017 10:22:49 +0100
From:   peter enderborg <peter.enderborg@...ymobile.com>
To:     Colin Walters <walters@...bum.org>,
        Shawn Landden <slandden@...il.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [RFC] EPOLL_KILLME: New flag to epoll_wait() that subscribes
 process to death row (new syscall)

On 11/01/2017 04:22 PM, Colin Walters wrote:
>
> On Wed, Nov 1, 2017, at 11:16 AM, Colin Walters wrote:
>> as the maintainer of glib2 which is used by a *lot* of things; I'm not
> (I meant to say "a" maintainer)
>
> Also, while I'm not an expert in Android, I think the "what to kill" logic
> there lives in userspace, right?   So it feels like we should expose this
> state in e.g. /proc and allow userspace daemons (e.g. systemd, kubelet) to perform
> idle collection too, even if the system isn't actually low on resources
> from the kernel's perspective.
>
> And doing that requires some sort of kill(pid, SIGKILL_IF_IDLE) or so?
>
You are right, in android it is the activity manager that performs this tasks. And if services
dies without talking to the activity manager the service is restarted, unless it is
on highest oom score. A other problem is that a lot communication in android is binder not epoll.

And a signal that can not be caught not that good. But a "warn" signal of the userspace choice in
something in a context similar to ulimit. SIGXFSZ/SIGXCPU that you can pickup and notify activity manager might work.

However, in android this is already solved with OnTrimMemory that is message sent from activitymanager to
application, services etc when system need memory back.