Re: [patch 4/7 -mm] oom: badness heuristic rewrite

Andrew Morton
2010-02-11T21:44:24Z

On Thu, 11 Feb 2010 01:14:43 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> On Wed, 10 Feb 2010, Rik van Riel wrote:
>
> > > OOM_ADJUST_MIN and OOM_ADJUST_MAX have been exported to userspace since
> > > 2006 via include/linux/oom.h. This alters their values from -16 to -1000
> > > and from +15 to +1000, respectively.
> >
> > That seems like a bad idea. Google may have the luxury of
> > being able to recompile all its in-house applications, but
> > this will not be true for many other users of /proc/<pid>/oom_adj
> >
>
> Changing any value that may have a tendency to be hardcoded elsewhere is
> always controversial, but I think the nature of /proc/pid/oom_adj allows
> us to do so for two specific reasons:
>
> - hardcoded values tend not the fall within a range, they tend to either
> always prefer a certain task for oom kill first or disable oom killing
> entirely. The current implementation uses this as a bitshift on a
> seemingly unpredictable and unscientific heuristic that is very
> difficult to predict at runtime. This means that fewer and fewer
> applications would hardcode a value of '8', for example, because its
> semantics depends entirely on RAM capacity of the system to begin with
> since badness() scores are only useful when used in comparison with
> other tasks.

You'd be amazed what dumb things applications do. Get thee to
http://google.com/codesearch?hl=en&lr=&q=[^a-z]oom_adj[^a-z]&sbtn=Search
and start reading. All 641 matches ;)

Here's one which which writes -16:
http://google.com/codesearch/p?hl=en#eN5TNOm7KtI/trunk/wlan/vendor/asus/eeepc/init.rc&q=[^a-z]oom_adj[^a-z]&sa=N&cd=70&ct=rc

Let's not change the ABI please.