This is unnecessary and just makes the oom killer egregiously long. We
are already diagnosing problems here at Google where the oom killer holds
tasklist_lock on the readside for far too long, causing other cpus waiting
for a write_lock_irq(&tasklist_lock) to encounter issues when irqs are
disabled and it is spinning. A second tasklist scan is simply a
non-starter.
[ This is also one of the reasons why we needed to introduce
mm->oom_disable_count to prevent a second, expensive tasklist scan. ]
You misunderstand the code. Both select_bad_process() and oom_kill_process()
are under tasklist_lock(). IOW, no change lock holding time.
A second iteration through the tasklist in select_bad_process() will
extend the time that tasklist_lock is held, which is what your patch does.
It never happen usual case. Plz think when happen all process score = 1.
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