From: Dipankar Sarma <dipankar@in.ibm.com>
To: Andrew Morton <akpm@osdl.org>
Cc: paulmck@us.ibm.com, dada1@cosmosbay.com, torvalds@osdl.org,
linux-kernel@vger.kernel.org,
viro@parcelfarce.linux.theplanet.co.uk, nickpiggin@yahoo.com.au,
hch@infradead.org
Subject: Re: [patch 2/2] fix file counting
Date: Sun, 29 Jan 2006 00:12:45 +0530 [thread overview]
Message-ID: <20060128184245.GE5633@in.ibm.com> (raw)
In-Reply-To: <20060127152857.32066a69.akpm@osdl.org>
On Fri, Jan 27, 2006 at 03:28:57PM -0800, Andrew Morton wrote:
> "Paul E. McKenney" <paulmck@us.ibm.com> wrote:
> >
> > > > I am using a patch that seems sligthly better : It removes the filp_count_lock
> > > > as yours but introduces a percpu variable, and a lazy nr_files . (Its value
> > > > can be off with a delta of +/- 16*num_possible_cpus()
> > >
> > > Yes, I think that is better.
> >
> > I agree that Eric's approach likely improves performance on large systems
> > due to decreased cache thrashing. However, the real problem is getting
> > both good throughput and good latency in RCU callback processing, given
> > Lee Revell's latency testing results. Once we get that in hand, then
> > we should consider Eric's approach.
Lee's problem now seems to be fixed with my rcu-rt-flush-list patch.
So, atleast for now we can keep that issue aside.
> Dipankar's patch risks worsening large-SMP scalability, doesn't it?
> Putting an atomic op into the file_free path?
It does. However I didn't see any degradation running kernbench
on a 4-way box a few months ago when I had originally written
this patch. It would be nice if someone from SGI can give
this a spin on a really big machine.
It is not as if we didn't have costly operations. Under memory
pressure, we would probably have been acquiring the file_count_lock
quite often. That lock is now gone. That said, I would like to
get a lazy percpu counter implementation done at some point
in time. So far, I have just kept the things simple.
> And afaict it fixes up the skew in the nr_files accounting but we're still
> exposed to the risk of large amounts of memory getting chewed up due to RCU
> latencies?
That is hopefully fixed by my rcu-batch-tuning patch. I tested it using
a program that does open()/close() of /dev/null in a tight
loop. [x86_64 3.6GHz]
> (And it forgot to initialise the atomic_t)
I declared it static. Isn't that sufficient ?
> (And has a couple of suspicious-looking module exports. We don't support
> CONFIG_PROC_FS=m).
Where ? All proc functions are wrapped in #ifdef CONFIG_PROC_FS and that
is what I have done. What am I missing here ?
Thanks
Dipankar
next prev parent reply other threads:[~2006-01-28 18:43 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-26 18:40 [patch 0/2] RCU: fix various latency/oom issues Dipankar Sarma
2006-01-26 18:41 ` [patch 1/2] rcu batch tuning Dipankar Sarma
2006-01-26 18:42 ` [patch 2/2] fix file counting Dipankar Sarma
2006-01-26 20:15 ` Eric Dumazet
2006-01-27 22:54 ` Andrew Morton
2006-01-27 23:14 ` Paul E. McKenney
2006-01-27 23:28 ` Andrew Morton
2006-01-28 18:42 ` Dipankar Sarma [this message]
2006-01-28 18:51 ` Andrew Morton
2006-01-28 19:10 ` Dipankar Sarma
2006-01-30 17:00 ` Dipankar Sarma
2006-01-31 10:33 ` Eric Dumazet
2006-01-31 20:19 ` Dipankar Sarma
2006-01-26 19:33 ` [patch 1/2] rcu batch tuning Paul E. McKenney
2006-01-26 19:42 ` Dipankar Sarma
2006-02-17 15:41 [PATCH 0/2] RCU updates Dipankar Sarma
2006-02-17 15:43 ` [PATCH 1/2] rcu batch tuning Dipankar Sarma
2006-02-17 15:46 ` [PATCH 2/2] fix file counting Dipankar Sarma
2006-02-18 9:04 ` Andrew Morton
2006-02-18 9:25 ` Dipankar Sarma
2006-02-18 9:45 ` Andrew Morton
2006-02-18 10:06 ` Dipankar Sarma
2006-02-18 10:10 ` Andrew Morton
2006-02-18 10:44 ` Dipankar Sarma
2006-02-18 12:14 ` Christoph Hellwig
2006-02-18 12:31 ` Arjan van de Ven
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