Re: [patch 2/2] fix file counting

[Andrew Morton]

"Paul E. McKenney" <paulmck@xxxxxxxxxx> 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.

Dipankar's patch risks worsening large-SMP scalability, doesn't it? 
Putting an atomic op into the file_free path?

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?

(And it forgot to initialise the atomic_t)

(And has a couple of suspicious-looking module exports.  We don't support
CONFIG_PROC_FS=m).

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