Re: [PATCH 4/5] oom: don't kill random process

From: KOSAKI Motohiro
Date: Mon May 23 2011 - 22:03:48 EST

(2011/05/24 10:58), David Rientjes wrote:
On Tue, 24 May 2011, KOSAKI Motohiro wrote:

This is unnecessary and just makes the oom killer egregiously long. We
are already diagnosing problems here at Google where the oom killer
tasklist_lock on the readside for far too long, causing other cpus
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

[ 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
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.

I don't care if it happens in the usual case or extremely rare case. It
significantly increases the amount of time that tasklist_lock is held
which causes writelock starvation on other cpus and causes issues,
especially if the cpu being starved is updating the timer because it has
irqs disabled, i.e. write_lock_irq(&tasklist_lock) usually in the clone or
exit path. We can do better than that, and that's why I proposed my patch
to CAI that increases the resolution of the scoring and makes the root
process bonus proportional to the amount of used memory.

Do I need to say the same word? Please read the code at first.

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