shared memory is over-counted N times when calculating badness()

[Jeff Davis <linux@j-davis.com>]

In oom_kill.c, badness() counts half the total_vm of all the children
against the parent.

The problem with this calculation is that, if the parent and children
share memory, the shared memory is over-counted N/2 times where N is the
number of children.

There's already a hard limit on the amount of shared memory, so it's
unlikely that process is runaway due to shared memory consumption, and
shouldn't add to a process's badness() score.

Shouldn't it just use (total_vm - shared_vm) instead, and never even
count shared memory?

Regards,
	Jeff Davis

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