Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu()

On Wed, Feb 07, 2018 at 05:45:13PM +0100, Jesper Dangaard Brouer wrote:

On Wed, 7 Feb 2018 08:57:00 -0500
Steven Rostedt [off-list ref] wrote:

quoted

To me kvfree() is a special case and should not be used by RCU as a
generic function. That would make RCU and MM much more coupled than
necessary.

For the record, I fully agree with Steve here. 

And being a performance "fanatic" I don't like to have the extra branch
(and compares) in the free code path... but it's a MM-decision (and
sometimes you should not listen to "fanatics" ;-))

While free_rcu() is not withut its performance requirements, I think it's
currently dominated by cache misses and not by branches.  By the time RCU
gets to run callbacks, memory is certainly L1/L2 cache-cold and probably
L3 cache-cold.  Also calling the callback functions is utterly impossible
for the branch predictor.

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