netdev - Re: [Lsf] [LSF/MM TOPIC] Generic page-pool recycle facility?

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Date:	Mon, 11 Apr 2016 22:23:09 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	lsf@...ts.linux-foundation.org, Tom Herbert <tom@...bertland.com>,
	Brenden Blanco <bblanco@...mgrid.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-mm <linux-mm@...ck.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	lsf-pc@...ts.linux-foundation.org,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	brouer@...hat.com
Subject: Re: [Lsf] [LSF/MM TOPIC] Generic page-pool recycle facility?


On Sat, 09 Apr 2016 05:34:38 -0700 Eric Dumazet <eric.dumazet@...il.com> wrote:

> On Sat, 2016-04-09 at 11:11 +0200, Jesper Dangaard Brouer wrote:
> 
> > Above code is okay.  But do you think we also can get away with the same
> > trick we do with the SKB refcnf?  Where we avoid an atomic operation if
> > refcnt==1.
> > 
> > void kfree_skb(struct sk_buff *skb)
> > {
> > 	if (unlikely(!skb))
> > 		return;
> > 	if (likely(atomic_read(&skb->users) == 1))
> > 		smp_rmb();
> > 	else if (likely(!atomic_dec_and_test(&skb->users)))
> > 		return;
> > 	trace_kfree_skb(skb, __builtin_return_address(0));
> > 	__kfree_skb(skb);
> > }
> > EXPORT_SYMBOL(kfree_skb);  
> 
> No we can not use this trick this for pages :
> 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ec91698360b3818ff426488a1529811f7a7ab87f
> 

If we have a page-pool recycle facility, then we could use the trick,
right? (As we know that get_page_unless_zero() cannot happen for pages
in the pool).

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer