Messages in this thread | | | Date | Thu, 22 Feb 2018 15:55:32 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() |
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On Wed, Feb 07, 2018 at 10:10:55AM -0800, Matthew Wilcox wrote: > 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 <rostedt@goodmis.org> wrote: > > > 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.
This seems to have fallen by the wayside.
To get things going again, I suggest starting out by simply replacing the kfree() in __rcu_reclaim() with kvfree(). If desired, a kvfree_rcu() can also be defined as a synonym for kfree_rcu().
This gets us a very simple and small patch which provides the ability to dispose of kvmalloc() memory after a grace period.
Thanx, Paul
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