From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Byungchul Park <max.byungchul.park@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Rao Shoaib <rao.shoaib@oracle.com>,
kernel-team@android.com, kernel-team <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 <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: Tue, 13 Aug 2019 19:53:49 -0700 [thread overview]
Message-ID: <20190814025349.GM28441@linux.ibm.com> (raw)
In-Reply-To: <20190814001103.GA31884@X58A-UD3R>
On Wed, Aug 14, 2019 at 09:11:03AM +0900, Byungchul Park wrote:
> On Tue, Aug 13, 2019 at 08:41:45AM -0700, Paul E. McKenney wrote:
> > On Tue, Aug 13, 2019 at 02:29:54PM +0900, Byungchul Park wrote:
> > > On Mon, Aug 12, 2019 at 09:12:34AM -0400, Joel Fernandes wrote:
> > > > On Mon, Aug 12, 2019 at 07:10:52PM +0900, Byungchul Park wrote:
> > > > > On Sun, Aug 11, 2019 at 04:49:39PM -0700, Paul E. McKenney wrote:
> > > > > > Maybe. Note well that I said "potential issue". When I checked a few
> > > > > > years ago, none of the uses of rcu_barrier() cared about kfree_rcu().
> > > > > > They cared instead about call_rcu() callbacks that accessed code or data
> > > > > > that was going to disappear soon, for example, due to module unload or
> > > > > > filesystem unmount.
> > > > > >
> > > > > > So it -might- be that rcu_barrier() can stay as it is, but with changes
> > > > > > as needed to documentation.
> > > >
> > > > Right, we should update the docs. Byungchul, do you mind sending a patch that
> > > > documents the rcu_barrier() behavior?
> > >
> > > Are you trying to give me the chance? I feel thankful. It doens't matter
> > > to try it at the moment though, I can't follow-up until September. I'd
> > > better do that in Septamber or give it up this time.
> >
> > Which reminds me... I recall your asking if the kfree_rcu() patch
> > might be sensitive to the exact hardware, but I cannot locate that
> > email right off-hand. This is an excellent question! When faced with
> > floods of kfree_rcu() calls, I would expect some hardware, compiler,
> > and kernel-configuration sensitivity. Which is why it will likely be
>
> Yes.
>
> > necessary to do a few more improvements over time -- for but one example,
> > accumulating callbacks into vectors in order to reduce the number of
> > kfree()-time cache misses.
>
> Yes. That would be a pretty good way to mitigate the problem. I hope
> the simple way we've done works well enough so it would never happen
> though.
>
> Or I would check the condition of all system resourses e.g. CPU and
> memory and control the bandwith of them, of course only if that actually
> happens.
>
> Thanks a lot for sharing your opinion on it!
Didn't you say earlier that you were getting OOM on your system even
with the patches? Or did I miss the resolution of that issue?
Thanx, Paul
> Thanks,
> Byungchul
>
> > Thanx, Paul
> >
> > > Thanks,
> > > Byungchul
> > >
> > > > > > It also -might- be, maybe now or maybe some time in the future, that
> > > > > > there will need to be a kfree_rcu_barrier() or some such. But if so,
> > > > > > let's not create it until it is needed. For one thing, it is reasonably
> > > > > > likely that something other than a kfree_rcu_barrier() would really
> > > > > > be what was needed. After all, the main point would be to make sure
> > > > > > that the old memory really was freed before allocating new memory.
> > > > >
> > > > > Now I fully understand what you meant thanks to you. Thank you for
> > > > > explaining it in detail.
> > > > >
> > > > > > But if the system had ample memory, why wait? In that case you don't
> > > > > > really need to wait for all the old memory to be freed, but rather for
> > > > > > sufficient memory to be available for allocation.
> > > > >
> > > > > Agree. Totally make sense.
> > > >
> > > > Agreed, all makes sense.
> > > >
> > > > thanks,
> > > >
> > > > - Joel
> > > >
> > > > [snip]
> > >
>
next prev parent reply other threads:[~2019-08-14 2:59 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-06 21:20 [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching Joel Fernandes (Google)
2019-08-06 21:20 ` [PATCH RFC v1 2/2] rcuperf: Add kfree_rcu performance Tests Joel Fernandes (Google)
2019-08-07 0:29 ` Paul E. McKenney
2019-08-07 10:22 ` Joel Fernandes
2019-08-07 17:56 ` Paul E. McKenney
2019-08-09 16:01 ` Joel Fernandes
2019-08-11 2:01 ` Joel Fernandes
2019-08-11 23:42 ` Paul E. McKenney
2019-08-06 23:56 ` [PATCH RFC v1 1/2] rcu/tree: Add basic support for kfree_rcu batching Paul E. McKenney
2019-08-07 9:45 ` Joel Fernandes
2019-08-07 17:52 ` Paul E. McKenney
2019-08-08 9:52 ` Byungchul Park
2019-08-08 12:56 ` Joel Fernandes
2019-08-08 14:23 ` Byungchul Park
2019-08-08 18:09 ` Paul E. McKenney
2019-08-11 8:36 ` Byungchul Park
2019-08-11 8:49 ` Byungchul Park
2019-08-11 23:49 ` Paul E. McKenney
2019-08-12 10:10 ` Byungchul Park
2019-08-12 13:12 ` Joel Fernandes
2019-08-13 5:29 ` Byungchul Park
2019-08-13 15:41 ` Paul E. McKenney
2019-08-14 0:11 ` Byungchul Park
2019-08-14 2:53 ` Paul E. McKenney [this message]
2019-08-14 3:43 ` Byungchul Park
2019-08-14 16:59 ` Paul E. McKenney
2019-08-11 10:37 ` Byungchul Park
2019-08-08 23:30 ` Joel Fernandes
2019-08-09 15:16 ` Paul E. McKenney
2019-08-09 15:39 ` Joel Fernandes
2019-08-09 16:33 ` Paul E. McKenney
2019-08-09 20:22 ` Joel Fernandes
2019-08-09 20:26 ` Joel Fernandes
2019-08-09 21:25 ` Joel Fernandes
2019-08-10 3:38 ` Paul E. McKenney
2019-08-09 20:29 ` Joel Fernandes
2019-08-09 20:42 ` Paul E. McKenney
2019-08-09 21:36 ` Joel Fernandes
2019-08-10 3:40 ` Paul E. McKenney
2019-08-10 3:52 ` Joel Fernandes
2019-08-10 2:42 ` Joel Fernandes
2019-08-10 3:38 ` Paul E. McKenney
2019-08-10 4:20 ` Joel Fernandes
2019-08-10 18:24 ` Paul E. McKenney
2019-08-11 2:26 ` Joel Fernandes
2019-08-11 23:35 ` Paul E. McKenney
2019-08-12 13:13 ` Joel Fernandes
2019-08-12 14:44 ` Paul E. McKenney
2019-08-08 10:26 ` Byungchul Park
2019-08-08 18:11 ` Paul E. McKenney
2019-08-08 20:13 ` Joel Fernandes
2019-08-08 20:51 ` Paul E. McKenney
2019-08-08 22:34 ` Joel Fernandes
2019-08-08 22:37 ` Paul E. McKenney
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