Messages in this thread | | | Date | Tue, 24 May 2011 11:03:32 +0900 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 4/5] oom: don't kill random process |
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(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 >>>>> 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. >> > > 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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