Re: [PATCH RFC tip/core/rcu 14/41] rcu: Limit lazy-callback duration

From: Josh Triplett
Date: Wed Feb 01 2012 - 21:04:17 EST

On Wed, Feb 01, 2012 at 11:41:32AM -0800, Paul E. McKenney wrote:
> Currently, a given CPU is permitted to remain in dyntick-idle mode
> indefinitely if it has only lazy RCU callbacks queued. This is vulnerable
> to corner cases in NUMA systems, so limit the time to six seconds by
> default. (Currently controlled by a cpp macro.)

I wonder: should this scale with the number of callbacks, or do we not
want to make estimates about memory usage based on that?

Interestingly, with kfree_rcu, we actually know at callback queuing time
*exactly* how much memory we'll get back by calling the callback, and we
could sum up those numbers.

- Josh Triplett
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