Re: OOM notifications

[Rene Herman <rene.herman@keyaccess.nl>]

On 10/19/2007 12:01 AM, Rene Herman wrote:
> On 10/18/2007 11:18 PM, Rik van Riel wrote:
>
> > On Thu, 18 Oct 2007 23:06:52 +0200
> > Rene Herman <rene.herman@keyaccess.nl> wrote:
> >
> > > They don't -- that's why I asked if you need both scenario's active
> > > at the same time. SIGDANGER would just be SIGPLEASEFREEALLYOUCAN with
> > > the operator deciding through setting the level at which point
> > > applications get it.
> > >
> > > Or put differently; what's the additional value of notifying an
> > > application that the system is about to go balistic when you've
> > > already asked it to free all it could earlier? SIGSEEDAMNITITOLDYOUSO?
> >
> > The first threshold - "we are about to swap" - means the application
> > frees memory that it can.  Eg. free()d memory that glibc has not yet
> > given back to the kernel, or JVM running the garbage collector, or ...
> >
> > The second threshold - "we are out of memory" - means that the first
> > approach has failed and the system needs to do something else. On an
> > embedded system, I would expect some application to exit or maybe
> > restart itself.
>
> That first threshold sounds fine yes. To me, the second mostly sounds 
> like a job for SIGTERM though.
>
> The OOM killer could after it selected the task for killing first try a 
> TERM on it to give a chance to exit gracefully and only when that 
> doesn't help make it eligible for killing on a second round through the 
> badness calculation.
>
> You could moreover _never_ make a task eligible for killing before it 
> received a SIGTERM, thereby guaranteeing that everyone got the SIGTERM 
> before killing anything, and it seems SIGTERM would be a more focussed 
> version of SIGDANGER2 then.

Well, no, that "guarantee" is fairly badly formulated but I mean "before 
everyone got a SIGTERM" ofcourse. That is, first do the same selection as 
now but don't send KILL but TERM and mark the task as having received a TERM 
already and make it not eligible anymore. Only when there are no TERM 
eligible tasks anymore, start sending KILL.

> Would at least forego any need for multiplexing the DANGER signal.

Rene.
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