Re: [PATCH] thp: reduce khugepaged freezing latency

[Tejun Heo]

Hello,

On Wed, Nov 09, 2011 at 08:59:25AM -0800, Tejun Heo wrote:
> Freezer depends on the usual "set_current_state(INTERRUPTIBLE); check
> freezing; schedule(); check freezing" construct and sends
> INTERRUPTIBLE wake up after setting freezing state.  The
> synchronization hasn't been completely clear but recently been cleaned
> up, so as long as freezing condition is tested after INTERRUPTIBLE is
> set before going to sleep, the event won't go missing.
> 
> Maybe we need a helper here, which would be named horribly -
> schedule_timeout_interruptible_freezable().  (cc'ing Oleg) Oleg, maybe
> we need schedule_timeout(@sleep_type) too?

Ah, crap, still waking up.  Sorry about that.  So, yes, there's a race
condition above.  You need to set TASK_INTERRUPTIBLE before testing
freezing and use schedule_timeout() instead of
schedule_timeout_interruptible().  Was getting confused with
prepare_to_wait().  That said, why not use prepare_to_wait() instead?

Thanks.

-- 
tejun
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