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

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Message-ID: <1460205278.6473.486.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Sat, 09 Apr 2016 05:34:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Tom Herbert <tom@...bertland.com>,
	Brenden Blanco <bblanco@...mgrid.com>,
	lsf@...ts.linux-foundation.org, 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>
Subject: Re: [Lsf] [LSF/MM TOPIC] Generic page-pool recycle facility?

On Sat, 2016-04-09 at 11:11 +0200, Jesper Dangaard Brouer wrote:
> Hi Eric,


> 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