Re: [patch 09/18] oom: select task from tasklist for mempolicy ooms

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 6 Jun 2010 15:34:31 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> The oom killer presently kills current whenever there is no more memory
> free or reclaimable on its mempolicy's nodes.  There is no guarantee that
> current is a memory-hogging task or that killing it will free any
> substantial amount of memory, however.

Well OK.  But we don't necesarily *want* to "free a substantial amount
of memory".  We want to resolve the oom within `current'.  That's the
sole responsibility of the oom-killer.  It doesn't have to free up
large amounts of additional memory in the expectation that sometime in
the future some other task will get an oom as well.  if the oom-killer
is working well, we can defer those actions until the problem actually
occurs.

Plus: if `current' isn't using much memory then it's probably a
short-lived or not-very-important process anyway.

> In such situations, it is better to scan the tasklist for nodes that are
> allowed to allocate on current's set of nodes and kill the task with the
> highest badness() score.  This ensures that the most memory-hogging task,
> or the one configured by the user with /proc/pid/oom_adj, is always
> selected in such scenarios.

Well... *why* is it better?  Needs more justification/explanation IMO.

A long time ago Andrea changed the oom-killer so that it basically
always killed `current', iirc.  I think that shipped in the Suse
kernel.  Maybe it was only in the case where `current' got an oom when
satisfying a pagefault, I forget the details.  But according to Andrea,
this design provided a simple and practical solution to ooms.

So I think this policy change would benefit from a more convincing
justification.


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