Re: [PATCH v2 2/2] mm, oom: remove 'prefer children over parent' heuristic

[Roman Gushchin <guro@fb.com>]

On Mon, Jan 21, 2019 at 10:50:32AM -0800, Shakeel Butt wrote:
> From the start of the git history of Linux, the kernel after selecting
> the worst process to be oom-killed, prefer to kill its child (if the
> child does not share mm with the parent). Later it was changed to prefer
> to kill a child who is worst. If the parent is still the worst then the
> parent will be killed.
> 
> This heuristic assumes that the children did less work than their parent
> and by killing one of them, the work lost will be less. However this is
> very workload dependent. If there is a workload which can benefit from
> this heuristic, can use oom_score_adj to prefer children to be killed
> before the parent.
> 
> The select_bad_process() has already selected the worst process in the
> system/memcg. There is no need to recheck the badness of its children
> and hoping to find a worse candidate. That's a lot of unneeded racy
> work. Also the heuristic is dangerous because it make fork bomb like
> workloads to recover much later because we constantly pick and kill
> processes which are not memory hogs. So, let's remove this whole
> heuristic.

This is a great cleanup, thanks!

Acked-by: Roman Gushchin <guro@fb.com>