Messages in this thread | | | Date | Thu, 18 Sep 2008 18:56:11 +0200 | From | Manfred Spraul <> | Subject | Re: [RFC PATCH] rcu: introduce kfree_rcu() |
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Paul E. McKenney wrote: > On Thu, Sep 18, 2008 at 12:18:28PM +0800, Lai Jiangshan wrote: > >> sometimes a rcu callback is just calling kfree() to free a struct's memory >> (we say this callback is a trivial callback.). >> this patch introduce kfree_rcu() to do these things directly, easily. >> > > Interesting! Please see questions and comments below. > > >> There are 4 reasons that we need kfree_rcu(): >> >> 1) unloadable modules: >> a module(rcu callback is defined in this module) using rcu must >> call rcu_barrier() when unload. rcu_barrier() will increase >> the system's overhead(the more cpus the worse) and >> rcu_barrier() is very time-consuming. if all rcu callback defined >> in this module are trivial callback, we can just call kfree_rcu() >> instead, save a rcu_barrier() when unload. >> Hmm: why is rcu_barrier() sufficient to prevent races? Offlining a cpu reorders rcu callbacks - rcu_barrier() can return before all previous call_rcu() callbacks were called.
-- Manfred
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