Re: [discuss][memcg] oom-kill extension

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 28 Oct 2008 22:35:21 -0700
"Paul Menage" <menage@google.com> wrote:

> On Tue, Oct 28, 2008 at 7:38 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > Under memory resource controller(memcg), oom-killer can be invoked when it
> > reaches limit and no memory can be reclaimed.
> >
> > In general, not under memcg, oom-kill(or panic) is an only chance to recover
> > the system because there is no available memory. But when oom occurs under
> > memcg, it just reaches limit and it seems we can do something else.
> >
> > Does anyone have plan to enhance oom-kill ?
> 
> We have an in-house implementation of a per-cgroup OOM handler that
> we've just ported from cpusets to cgroups. We were considering sending
> the patch in as a starting point for discussions - it's a bit of a
> kludge as it is.
> 
Sounds interesting. (but I don't ask details now.)

> It's a standalone subsystem that can work with either the memory
> cgroup or with cpusets (where memory is constrained by numa nodes).
> The features are:
> 
> - an oom.delay file that controls how long a thread will pause in the
> OOM killer waiting for a response from userspace (in milliseconds)
> 
> - an oom.await file that a userspace handler can write a timeout value
> to, and be awoken either when a process in that cgroup enters the OOM
> killer, or the timeout expires.
> 
> If a userspace thread catches and handles the OOM, the OOMing thread
> doesn't trigger a kill, but returns to alloc_pages to try again;
> alternatively userspace can cause the OOM killer to go ahead as
> normal.
> 
the userland can know "bad process" under group ?

> We've found it works pretty successfully as a last-ditch notification
> to a daemon waiting in a system cgroup which can then expand the
> memory limits of the failing cgroup if necessary (potentially killing
> off processes from some other cgroup first if necessary to free up
> more memory).
> 
This is a good news :)

> I'll try to get someone to send in the patch.
> 
O.K. looking forward to see that.

Regards,
-Kame

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