Re: [patch -mm] oom: avoid divide by zero

[Greg Thelen <gthelen@google.com>]

David Rientjes <rientjes@google.com> writes:

> It's evidently possible for a memory controller to have a limit of 0
> bytes, so it's possible for the oom killer to have a divide by zero error
> in such circumstances.
>
> When this is the case, each candidate task's rss and swap is divided by
> one so they are essentially ranked according to whichever task attached
> to the cgroup has the most resident RAM and swap.
>
> Reported-by: Greg Thelen <gthelen@google.com>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/oom_kill.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -189,6 +189,14 @@ unsigned int oom_badness(struct task_struct *p, unsigned long totalpages)
>  	p = find_lock_task_mm(p);
>  	if (!p)
>  		return 0;
> +
> +	/*
> +	 * The memory controller can have a limit of 0 bytes, so avoid a divide
> +	 * by zero if necessary.
> +	 */
> +	if (!totalpages)
> +		totalpages = 1;
> +
>  	/*
>  	 * The baseline for the badness score is the proportion of RAM that each
>  	 * task's rss and swap space use.

I tested 2.6.34-rc5 + mmotm-2010-04-22-16-38 and the provided patch
fixes the reported problem.

Thanks David.

Tested-by: Greg Thelen <gthelen@google.com>

--
Greg

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