Re: [patch -mm 2/9 v2] oom: sacrifice child with highest badness score for parent

[Nick Piggin <npiggin@suse.de>]

On Mon, Feb 15, 2010 at 02:20:03PM -0800, David Rientjes wrote:
> When a task is chosen for oom kill, the oom killer first attempts to
> sacrifice a child not sharing its parent's memory instead.
> Unfortunately, this often kills in a seemingly random fashion based on
> the ordering of the selected task's child list.  Additionally, it is not
> guaranteed at all to free a large amount of memory that we need to
> prevent additional oom killing in the very near future.
> 
> Instead, we now only attempt to sacrifice the worst child not sharing its
> parent's memory, if one exists.  The worst child is indicated with the
> highest badness() score.  This serves two advantages: we kill a
> memory-hogging task more often, and we allow the configurable
> /proc/pid/oom_adj value to be considered as a factor in which child to
> kill.
> 
> Reviewers may observe that the previous implementation would iterate
> through the children and attempt to kill each until one was successful
> and then the parent if none were found while the new code simply kills
> the most memory-hogging task or the parent.  Note that the only time
> oom_kill_task() fails, however, is when a child does not have an mm or
> has a /proc/pid/oom_adj of OOM_DISABLE.  badness() returns 0 for both
> cases, so the final oom_kill_task() will always succeed.
> 
> Acked-by: Rik van Riel <riel@redhat.com>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Nick Piggin <npiggin@suse.de>