Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching

From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Byungchul Park <byungchul.park@lge.com>,
	linux-kernel@vger.kernel.org, Rao Shoaib <rao.shoaib@oracle.com>,
	max.byungchul.park@gmail.com, kernel-team@android.com,
	kernel-team@lge.com, Davidlohr Bueso <dave@stgolabs.net>,
	Josh Triplett <josh@joshtriplett.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	rcu@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching
Date: Thu, 8 Aug 2019 18:34:15 -0400	[thread overview]
Message-ID: <20190808223415.GG261256@google.com> (raw)
In-Reply-To: <20190808205129.GU28441@linux.ibm.com>

On Thu, Aug 08, 2019 at 01:51:29PM -0700, Paul E. McKenney wrote:
[snip]
> > Also, I am thinking that whenever we do per-slab optimization, then the
> > kmem_cache_free_bulk() can be optimized further. If all pointers are on the
> > same slab, then we can just do virt_to_cache on the first pointer and avoid
> > repeated virt_to_cache() calls. That might also give a benefit -- but I could
> > be missing something.
> 
> A sort might be required to make that work nicely, which would add some
> overhead.  Probably not that much, though, the increased locality would
> have a fighting chance of overcoming the sort's overhead.
> 
> > Right now kmem_cache_free_bulk() just looks like a kmem_cache_free() in a
> > loop except the small benefit of not disabling/enabling IRQs across each
> > __cache_free, and the reduced cache miss benefit of using the array.
> 
> C'mon!  Show some respect for the awesome power of temporal locality!!!  ;-)

Good point. I will try to respect it more in the future ;-) After all, it is
quite a useful concept.

thanks,

 - Joel